KRRO 10-K & 10-Q changes, risk factors and insider trading

Since inception, we have incurred significant operating losses. Our net loss was $83.6$117.3 million and $81.2$83.6 million for the years ended December 31, 20242025 and 2023,2024, respectively. As of December 31, 2024,2025, we had an accumulated deficit of $266.6$383.8 million. We have financed our operations primarily through private placements of our convertible preferred stock and more recently, common stock in the private placement that closed immediately prior to theour November 2023 business combination and our2023, April 2024 and March 2026 private placement.placements, and sales under our at-the-market offering program. Substantially all of our losses have resulted from expenses incurred in connection with our research and development and from general and administrative costs associated with our operations.operations, and most recently, a $30.9 million impairment charge in the fourth quarter of 2025 related to our operating lease right-of-use asset and fixed assets. We expect to continue to incur significant expenses, increasing operating losses, and negative operating cash flows for the foreseeable future. The net losses we incur may fluctuate significantly from quarter to quarter. We anticipate that our expenses will increase substantially if and as we:

progress KRRO-110our development candidates, including KRRO-121, through clinical development;

continue current research programs and preclinical and clinical development of any productlead candidates or development candidates we may identify;

seek to identify additional research programs and productlead candidates and nominate development candidates;

further develop Oligonucleotide Promoted Editing of RNA, or OPERA, our RNA editing platform;

seek marketing approvals for any productdevelopment candidates that successfully complete clinical trials;

develop, maintain and enhance a sustainable, scalable, reproducible and transferable manufacturing process for the product candidates we may develop;

acquire or in-license productlead candidates, development candidates, intellectual property and technologies;

should we decide to do so, build and maintain a commercial-scale cGMPcurrent good manufacturing practices, or cGMP, manufacturing facility; and operate as a public company.

We expect that it will be many years, if ever, before we have a RNA editing product ready for commercialization. To become and remain profitable, we must develop and, either directly or through collaborators, eventually commercialize a product or products with market potential. This will require us to be successful in a range of challenging activities, including identifying productlead candidates, completing preclinical studies and clinical trials of productdevelopment candidates, obtaining marketing approval for these productdevelopment candidates, manufacturing, marketing and selling those products for which we may obtain marketing approval and satisfying any post-marketing requirements. We may never succeed in these activities and, even if we do,are, may never generate revenues that are significant or large enough to achieve profitability.

WeIn have transitioned from discovery, research and development to clinical stage for our product candidate, KRRO-110, and in JanuaryNovember 2025, we announced thethat dosingwe did not reach projected levels of theprotein firstin participantspatients in our Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD.AATD and our other programs are in early stages of development. In addition, we undertook workforce reductions in May 2025 and November 2025, and in the fourth quarter of 2025, as result of identified indicators of impairment for our long-lived assets, primarily including our operating lease right-of-use, or ROU, asset, and property and equipment, we recognized a non-cash, long-lived asset impairment charge of $30.9 million. Because of the numerous risks and uncertainties associated with developing oligonucleotide productlead candidates and development candidates, and the risks associated with conducting preclinical studies and clinical trials, we are unable to predict the extent of any future losses or when we will become profitable, if at all. If we do achieve profitability, we may not be able to sustain or increase profitability on a quarterly or annual basis. Our failure to become and remain profitable would decrease the value of our company and could impair our ability to raise capital, maintain our research and development efforts, expand business or continue our operations. A decline in our value could also cause you to lose all or part of your investment. Further, we may not even experience the expected benefits of our May 2025 and November 2025 workforce reductions or our decision to discontinue clinical development of KRRO-110. Further, the long-lived asset impairment charges recognized may affect how investors, analysts, and counterparties assess our financial position and prospects, potentially making it more difficult or expensive to raise capital or enter into collaborations on favorable terms.

Our ability to generate revenue from product sales and achieve profitability depends on our ability, alone or with collaborative partners, to successfully complete the development of, and obtain the regulatory approvals necessary to commercialize, product candidates we may identify for development. We do not anticipate generating revenues from product sales for many years, if ever. Our ability to generate future revenues from product sales depends heavily on our, or our collaborators’, ability to successfully:

identify productlead candidates and successfully complete research and development of such productlead candidates;

seek and obtain regulatory and marketing approvals for any productdevelopment candidates for which we complete clinical trials;

launch and commercialize any productdevelopment candidates for which we may obtain regulatory and marketing approval by establishing a sales force, marketing and distribution infrastructure, or alternatively, collaborating with a commercialization partner;

qualify for adequate coverage and reimbursement by government and third-party payors for any productdevelopment candidates for which we may obtain regulatory and marketing approval;

establish and maintain supply and manufacturing relationships with third parties that can provide adequate, in both amount and quality, products and services to support clinical development and the market demand for any productdevelopment candidates for which we obtain regulatory and marketing approval;

develop, maintain and enhance a sustainable, scalable, reproducible and transferable manufacturing process for the productdevelopment candidates we may develop;

Our expenses could increase beyond expectations if we are required by the FDA, the EMA, HREC, or TGA, or other regulatory authorities to perform clinical and other studies in addition to those that we currently anticipate. Even if one or more of the product candidates we may develop are approved for commercial sale, we anticipate incurring significant costs associated with commercializing any approved productdevelopment candidate. Additionally, such products may become subject to unfavorable pricing regulations, third-party reimbursement practices or healthcare reform initiatives. Even if we are able to generate revenues from the sale of any approved productdevelopment candidates, we may not become profitable and may need to obtain additional funding to continue operations.

We expect our expenses to continue to increase in connection with our ongoing activities, particularly as we identify, continue the research and development of, initiate preclinical studies and clinical trials of, and seek marketing approval for, productour lead candidates and development candidates. Because we have limited financial and managerial resources, we have prioritized our research programs and leadoligonucleotide optimization efforts in specific indications among many potential options. Specifically, our initial development programs target liver and central nervous systems indications, amongst others. As a result of this prioritization, we may forego or delay pursuit of opportunities with other productlead candidates or development candidates or for other indications that later prove to have greater clinical or commercial potential and we may need to reprioritize our focus in the future. Our resource allocation decisions may cause us to fail to capitalize on viable commercial products or profitable market opportunities. For example, KRRO-110, which used an LNP delivery system, did not reach projected levels of protein in patients in our Phase 1/2a REWRITE clinical trial for AATD and we have since transitioned to a GalNAc-conjugated delivery system for our AATD program. Our spending on current and future research and development programsprograms, lead candidates and productdevelopment candidates for specific indications may not yield any commercially viable products.

In addition, if we obtain marketing approval for any product candidates we may develop, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing and distribution to the extent that such sales, marketing, manufacturing and distribution are not the responsibility of a collaborator. Furthermore, we expect to continue to incur additional costs associated with operating as a public company. Accordingly, we will need to obtain substantial additional funding in connection with our continuing operations. If we are unable to raise capital when needed or on attractive terms, we would be forced to delay, reduce or eliminate our research and product development programs or future commercialization efforts.

As of December 31, 2024,2025, our cash, cash equivalents and marketable securities were $163.1$85.2 million, excluding restricted cash, or $166.5$88.6 million, including restricted cash. We believe our existing cash, cash equivalents and marketable securitiessecurities, together with the net proceeds raised under sales under our at-the-market offering program and March 2026 private placement, will be sufficient to fund our operating expenses and capital expenditure requirements through several value-creating milestones (including completion of the Phase 1/2a REWRITE clinical trial of KRRO-110) and into the second half of 2026.2028. However, our operating plan may change as a result of factors currently unknown, and expectations regarding our cash runway and ability to reach data inflection points are based on numerous assumptions that may prove to be untrue. As a result, we may be required to raise capital sooner than anticipated and our exposure to certain contingent liabilities and contractual obligations may be greater than anticipated. Our future capital requirements will depend on many other factors, including those discussed in the risk factor entitled “We have incurred significant losses since inception. We expect to incur losses for the foreseeable future and may never achieve or maintain profitability.”

Any additional fundraising efforts may divert our management from their day-to-day activities, which may adversely affect our ability to develop and commercialize any productdevelopment candidates we may develop. We cannot be certain that additional funding will be available on acceptable terms or at all. Although we have an effective shelf registration statement and an at-the-market offering program, we have not sold any shares under the program and we have no committed source of additional capital. If we are unable to raise additional capital in sufficient amounts or on terms acceptable to us, we may have to significantly delay, scale back or discontinue the development or commercialization of any productdevelopment candidates or other research and development initiatives. We could be required to seek collaborators for potential productlead candidates earlier than we would otherwise plan or on terms that are less favorable than might otherwise be available. We could also be required to relinquish or license our rights to productlead candidates on unfavorable terms in certain markets where we otherwise would seek to pursue development or commercialization ourselves.

We havedid dosednot veryreach fewprojected participantslevels of protein in patients in our Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD and have transitioned to GalNAc-conjugated delivery for our AATD program, and may experience delays in developing a potential treatment for AATD. We have not receivedcompleted any clinical trials nor reported any clinical trial results for any of our proposed delivery methods or RNA editing approachesapproaches. in clinical trials and anyAny favorable results we may have from our earlier preclinical studies may not be predictive of results that may be observed in later preclinical studies or clinical trials.

The scientific evidence to support the feasibility of developing productdevelopment candidates using our proprietary RNA editing technology is both preliminary and limited. We have dosed very few participants in our Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD. Although we observed functional protein in AATD andpatients following a single administration of KRRO-110, we did not reach projected levels of protein in patients as of the data cut off date. We have not yet receivedcompleted any clinical trialtrials results.for Forany example,of KRRO-110our usesproposed LNPsdelivery asmethods or RNA editing approaches, and we have transitioned from LNP to GalNAc-conjugated delivery for our AATD program. Accordingly, we may experience delays in developing a deliverypotential modalitytreatment andfor AATD. In the future, we may use other delivery modalities to deliver our other productlead candidates. While LNPs have been validated clinically to deliver oligonucleotides, such as siRNA, they havewere not been clinically proven to deliver oligonucleotides for RNA editing, such as KRRO-110 and our other productlead candidates. Similarly, while GalNAc-conjugated delivery has been validated in multiple FDA-approved oligonucleotide therapeutics, there are no FDA-approved GalNAc-conjugated RNA editing oligonucleotide therapeutics. Both of our most advanced programs, KRRO-121 and our AATD program, utilize GalNAc-conjugated delivery. If GalNAc-conjugated delivery fails to effectively deliver our RNA editing oligonucleotides, multiple programs in our pipeline could be adversely affected.

In addition, our proprietary RNA editing technology itself may lead to other issues, such as inability to deliver the desired efficacy or safety-related consequences as it is tested in clinical trials. We have not generated any clinical trial results to date. The design of a clinical trial can determine whether its results will support approval of a productdevelopment candidate and flaws in the design of a clinical trial may not become apparent until the clinical trial is well advanced. Furthermore, preclinical and clinical data are often susceptible to varying interpretations and analyses, and many companies that have believed their productdevelopment candidates performed satisfactorily in preclinical studies and clinical trials have nonetheless failed to obtain marketing approval of their productdevelopment candidates. Many productlead candidates that initially showed promise in early stage testing for treating a variety of diseases have later been found to lack efficacy or to cause side effects that prevented further clinical development of the product candidates.development. Accordingly, any favorable results we may have from our earlier preclinical studies may not be predictive of results that may be observed in further preclinical studies or clinical trials.

If preclinical studies or clinical trials of any productlead candidatescandidate or development candidate we may identify and develop fail to demonstrate safety and efficacy to the satisfaction of regulatory authorities or do not otherwise produce positive results, we may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and commercialization of such productdevelopment candidates.candidate.

Before obtaining marketing approval from regulatory authorities for the sale of any productdevelopment candidates we may identify and develop, we must complete preclinical development and then conduct extensive clinical trials to demonstrate the safety and efficacy in humans. Clinical testing is expensive, difficult to design and implement, can take many years to complete, and the outcome is uncertain as to outcome.uncertain. A failure of one or more clinical trials can occur at any stage of testing.development. The outcome of preclinical testing and early clinical trials may not be predictive of the success of later clinical trials, and interim results of a clinical trial do not necessarily predict final results.

Moreover, preclinical and clinical data are often susceptible to varying interpretations and analyses. Many companies that have believed their productlead candidates or development candidates performed satisfactorily in preclinical studies and clinical trials have nonetheless failedfailed, to obtainpreventing marketing approval of their productdevelopment candidates. For example, despite our preclinical data, we did not reach projected levels of protein in AATD patients in our REWRITE Phase 1/2a clinical trial.

We and our collaborators, if any, may experience numerous unforeseen events during, or as a result of, clinical trials that could delay or prevent our ability to receive marketing approval or commercialize any productdevelopment candidates we may identify and develop, including:

regulators, institutional review boards, or IRBs, or independent ethics committees may not authorize us or our investigators to commence a clinical trial or conduct a clinical trial at a prospective trial site;

clinical trials of any productdevelopment candidates we may develop may produce negative or inconclusive results, and we may decide, or regulators may require us, to conduct additional clinical trials or abandon product development or research programs;

the number of patients required for clinical trials of any product candidates we may develop may be larger than we anticipate; enrollment of suitable participants in these clinical trials, which may be particularly challenging for some of the rare genetically defined diseases wesuch areas targeting in our most advanced programs,UCD, may be delayed or slower than we anticipate; or patients may drop out of these clinical trials at a higher rate than we anticipate;

regulators, IRBs, or independent ethics committees may require that we or our investigators suspend or terminate clinical research or clinical trials of any productdevelopment candidates we may develop for various reasons, including noncompliance with regulatory requirements, a finding of undesirable side effects or other unexpected characteristics, or that the participants are being exposed to unacceptable health risks or after an inspection of our clinical trial operations or trial sites;

the cost of clinical trials of any productdevelopment candidates we may develop may be greater than we anticipate;

the supply or quality of any productdevelopment candidates we may develop or other materials necessary to conduct clinical trials of any productdevelopment candidates we may develop may be insufficient or inadequate, including as a result of delays in the testing, validation, manufacturing, and delivery of any productdevelopment candidates we may develop to the clinical sites by us or by third parties with whom we have contracted to perform certain of those functions;

occurrence of serious adverse events associated with any productdevelopment candidates we may develop that are viewed to outweigh their potential benefits;

If we or our collaborators are required to conduct additional clinical trials or other testing of any productdevelopment candidates we may develop beyond those that we currently contemplate, if we or our collaborators are unable to successfully complete clinical trials or other testing of any productdevelopment candidates we may develop,candidates, or if the results of these trials or tests are not positive or are only modestly positive or if there are safety concerns, we or our collaborators may:

be delayed in obtaining marketing approval for any such productdevelopment candidates we may develop or not obtain marketing approval at all;

Product development costs will also increase if we or our collaborators experience delays in clinical trials or other testing or in obtaining marketing approvals. We do not know whether any clinical trials will begin as planned, will need to be restructured, or will be completed on schedule, or at all. Significant clinical trial delays also could shorten any periods during which we may have the exclusive right to commercialize any productdevelopment candidates we may develop, could allow our competitors to bring products to market before we do, and could impair our ability to successfully commercialize any productdevelopment candidates we may develop, any of which may harm our business, financial condition, results of operations, and prospects.

Clinical trials of a new productdevelopment candidate require the enrollment of a sufficient number of patients, including patients who are suffering from the disease the productdevelopment candidate is intended to treat and who meet other eligibility criteria. Rates of patient enrollment are affected by many factors, including the stage and severity of disease, the nature and requirements of the protocol, the proximity of patients to clinical sites, the availability of effective treatments for the relevant disease, and the eligibility criteria for the clinical trial, possible adverse effects from treatments, the existence of competing clinical trials, the involvement of patient advocacy groups, the availability of new or alternative treatments, lack of efficacy, personnel issues and ease of participation in our clinical trials, among others. Clinical trials can also be impacted by other events unrelated to our business, such as the Russian invasion of Ukraine, recent turmoil in the Middle East or other geopolitical events orand unrest, such as recent hostilities involving Iran, global pandemics (such as what occurred duringe.g., COVID-19), or economic uncertainty, including imposition of tariffs that impact the supply chain.chain, or disruptions due to government shutdowns, which can impact regulatory reviews. In April 2025, the United States imposed tariffs on imports on its trading partners and tariff policy (and trading partners subject to such tariffs) has continued to evolve. Historically, tariffs have led to increased costs, political and trade tensions, which negatively affect global supply chains. These types of events can disrupt clinical trial sites and delay patient enrollment, all of which would have a negative impact on our business and ability to obtain regulatory approval. Delays or difficulties in patient enrollment or difficulties retaining trial participants, including as a result of the availability of existing or other investigational treatments, can result in increased costs, longer development times or termination of a clinical trial.

The gene editing field and RNA editing in particular is relatively new and is evolving rapidly. We are very early in our development efforts and may not be successful in identifying and developing productany candidates. It will be many years before we or our collaborators commercialize a productdevelopment candidate or generate any revenues, if ever. Additionally, other genegenetic editingmedicine technologies may be discovered that provide significant advantages over RNA editing, which could materially harm our business.

The success of our business depends primarily upon our ability to identify, develop and commercialize productdevelopment candidates. We are very early in our development efforts and have focused our research and development efforts to date on developing OPERA, our RNA editing platform, and identifying our initial targeted disease indications. We currently only recentlyhave commencedone dosingnominated development candidate in our first-in-humanpipeline, trialKRRO-121 as terminated further development of KRRO-110 forafter AATD.it failed to reach projected levels of protein in our first in-human clinical trial. Although we believe we can demonstrate many of the key advantages of RNA editing, because we are very early in our development efforts, we are not yet certain of the results we may achieve, which may be important for registration and commercialization of ourany products.candidates we successfully develop. Such uncertainties include, but are not limited to, the level of editing efficiency needed in a target tissue type to achieve a clinical benefit, and associated safety of our edits in humans. We have also not yet shown that preclinical editing activity can result in clinically important effects, nor that the data generated by our preclinical studies can translate into positive results in clinical trials.

We only have one product candidate, KRRO-110, in a Phase 1/2a clinical trial. All of our other product development programs are still in the research or preclinical stage of development. Our research methodology may be unsuccessful in identifying productlead candidates, our productdevelopment candidates may be shown to have harmful side effects in preclinical in vitro experiments or animal model studies, they may not show promising signals of therapeutic effect in such experiments or studies or they may have other characteristics that may make the productdevelopment candidates impractical to manufacture, unmarketable, or unlikely to receive marketing approval.

The pharmacological properties ascribed to the productlead candidates we are testing in preclinical studies may not be positively demonstrated in clinical trials in patients, and they may interact with human biological systems in unforeseen, ineffective or harmful ways.ways (such as we experienced in our REWRITE Phase 1/2a clinical trial). If our productdevelopment candidates prove to be ineffective, unsafe or commercially unviable, OPERA and our pipeline would have little, if any, value, which would substantially harm our business, financial condition, results of operations and prospects. In addition, our approach, which focuses on using oligonucleotides for drug development, as opposed to multiple or other, more advanced proven technologies, and new products and technologies that may enter the market, may expose us to additional financial risks and make it more difficult to raise additional capital if we are not successful in developing one or more productdevelopment candidates that receive regulatory approval. Our ability to generate product revenue, which we do not expect will occur for many years, if ever, will depend heavily on the successful development and eventual commercialization of any productdevelopment candidates we may discover, which may never occur. We currently generate no revenue from sales of any product, and we may never be able to develop or commercialize a marketable product.

In addition, although we believe OPERA, our RNA editing platform, will position us to expand our portfolio of productdevelopment candidates beyond the initial product candidates we may develop, we have not yet successfully developed any product candidate and our ability to expand our portfolio may never materialize.

We are focused on developing products based on RNA editing. Although there have been significant advances in the field of gene editing in recent years, RNA editing technologies are new and largely unproven. The technologies that we have developed have not yet been clinically tested, nor are we aware of anycompleted clinical trials for safety or efficacy having been completed by third parties using RNA editing or similar technologies.development. The scientific evidence to support the feasibility of developing productdevelopment candidates based on these technologies is both preliminary and limited. Successful development of productdevelopment candidates by us will require solving a number of issues, including optimizing the efficiency and specificity of such productdevelopment candidates, and ensuring the therapeutic selectivity of such productdevelopment candidates. There can be no assurance we will be successful in solving any or all of these issues.

We have concentrated our research efforts to date on preclinical work to bring therapeutics to the clinic for our initial indications, and our future success is highly dependent on the successful development of OPERA, our RNA editing platform, as well as cellular delivery methods and therapeutic applications of that technology. While some of the existing, non-RNA editing, gene editing technologies developed by third parties have progressed to clinical trials, they continue to suffer from various limitations, and such limitations may affect our future success. While a number of clinical trials for oligonucleotide products conducted by other companies have not been successful, some have received regulatory approval. The pharmacological properties ascribed to the productdevelopment candidates we are testing or will test in the future may not be positively demonstrated in clinical trials in patients, and they may interact with human biological systems in unforeseen, ineffective or harmful ways. If our productdevelopment candidates prove to be ineffective, unsafe or commercially unviable, our OPERA platform and our pipeline would have little, if any, value, which would substantially harm our business, financial condition, results of operations and prospects. We may decide to alter or abandon our initial programs as new data becomes available and we gain experience in developing base editing therapeutics. We cannot be sure that our technologies will yield satisfactory products that are safe and effective, scalable or profitable in our initial indications or any other indication we pursue.

We are very early in our development efforts, and our preclinical studies and clinical trials may not be successful. If we are unable to commercialize our productdevelopment candidates or experiencesexperience significant delays in doing so, our business will be materially harmed.

We are very early in our development of productdevelopment candidates and have focused our efforts to date primarily on platform development, discovery, research, and preclinical development.development Weand havehad only recently dosed thea firstsmall number of participants in our terminated Phase 1/2a REWRITE clinical trial of KRRO-110 for AATDAATD. andOur alldevelopment candidate, KRRO-121, is advancing toward a regulatory filing anticipated in the second half of 2026. All of our other programs are still in the research or preclinical stage of development. Our ability to generate product revenues, which we do not expect will occur for many years, if ever, will depend heavily on the successful development, marketing approval and eventual commercialization of our productdevelopment candidates, which may never occur. We have not yet generated revenue from product sales or otherwise, and we may never be able to develop or commercialize a marketable product.

Commencing clinical trials in the United States is subject to acceptance by the FDA of an IND and finalizing the trial design based on discussions with the FDA and other regulatory authorities. In the event that the FDA requires us to complete additional preclinical studies or we are required to satisfy other FDA requests prior to commencing clinical trials, the start of our first clinical trials may be delayed or we may be unsuccessful obtaining clearance to proceed into clinical development. Even after we receive and incorporate guidance from these regulatory authorities, the FDA or other regulatory authorities could disagree that we have satisfied their requirements to commence any clinical trial or change their position on the acceptability of our trial designs or the clinical endpoints selected, which may require us to complete additional preclinical studies or clinical trials, delay the enrollment of our clinical trials, abandon our clinical development plans or meet stricter approval conditions than we currently expect. There are equivalent processes and risks applicable to CTAsclinical trial applications, or CTAs, in other countries, including countries in the European Union, orUnited EU,Kingdom and Australia, where we recently dosed the first participants in our Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD.Australia.

Commercialization of any productdevelopment candidates we may develop will require preclinical and clinical development; regulatory and marketing approval in multiple jurisdictions, including by the FDA, the EMA, HREC and TGA; manufacturing supply, capacity and expertise; a commercial organization; and significant marketing efforts. The success of our productdevelopment candidates will depend on many factors, including the following:

effective INDs or comparable foreign applications that allow commencement of our planned clinical trials or future clinical trials for any productdevelopment candidates we may develop;

We are a clinical-stage biopharmaceutical company with a mission to discover, develop and commercialize a new class of genetic medicines based on editing RNA, enabling the treatment of both rare and highly prevalent diseases.

We are generating a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process to effect a precise yet transient change to a single basenucleoside edit.(adenosine to an inosine edit). By editing RNA instead of DNA, we are expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. UsingWe use an oligonucleotide-based approach,approach weand expect to bring our medicines to patients by leveraging our proprietary platform with precedented delivery modalities, including N-acetylgalactosamine, or GalNAc, -conjugated delivery for subcutaneous administration, manufacturing know-how, and established regulatory pathways of approved oligonucleotide medicines. However, the scientific evidence to support the feasibility of developing productour development candidates using our RNA editing technology is both preliminary and limited. Moreover, regulators have not yet established any definitive guidelines related to overall development considerations for RNA editing therapies and limited clinical data has been generated to date.

Since inception, we have focused primarily on organizing and staffing our company, business planning, raising capital, securing related intellectual property, and conducting research and development activities for our potential programs and productdevelopment candidates. Since inception, we have funded our operations primarily through the private placement of our equity securities. To date, we have raised approximately $223.6 million of aggregate gross proceeds from the sale of our convertible preferred stock, and $117.3 million from the sale of shares of common stock issued in a private placement that closed immediately prior to the November 2023 business combination andcombination, $70.0 million from the April 2024 private placement of shares of our common stock.stock, $5.1 million from sales under our at-the-market offering program, and $85.0 million from the March 2026 private placement.

We have incurred significant operating losses since inception. Our net losses were $83.6$117.3 million and $81.2$83.6 million for the years ended December 31, 20242025 and 2023,2024, respectively. We had an accumulated deficit of $266.6$383.8 million as of December 31, 2024.2025. We expect to continue to incur significant and increasing expenses and operating losses and negative operating cash flows for the foreseeable future as we continue our research and development efforts, advance productdevelopment candidates into and through clinical development, and seek regulatory approvals for our pipelinedevelopment candidates. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending on the timing of our preclinical studies, initiation and conduct of any clinical trials, and our expenditures on other research and development activities, including the expansion of our pipeline.

We do not have any productdevelopment candidates approved for sale and have not generated any revenue from product sales. We will not generate revenue from product sales unless and until we successfully obtain regulatory approval for our productdevelopment candidates, if ever, and as appropriate, move pipeline candidates into the clinic and complete clinical development. If we obtain regulatory approval for our productdevelopment candidates and do not enter into third-party commercialization partnerships, we expect to incur significant expenses related to developing commercialization capabilities to support product sales, marketing, manufacturing and distribution activities. As a result, we will need substantial additional funding to support our continuing operations and pursue our development and growth strategy. Until we can generate significant revenue from product sales, if ever, we expect to finance our operations through a combination of public or private offerings of securities, debt financings or other sources, such as potential collaboration agreements, strategic alliances and licensing arrangements. We may be unable to raise additional funds or enter into such other agreements or arrangements when needed on acceptable terms, or at all. Our failure to raise capital or enter into such agreements as, and when needed, could have a negative effect on our business, results of operations and financial condition.

We have not generated any revenue from product sales, and do not expect to generate any revenue from the sale of products in the near future. During the year ended December 31, 2025 and 2024, we recognized $6.4 million and $2.3 million of collaboration revenue, respectively, which is related to our research collaboration and license agreement with Novo Nordisk. DuringIn November 2025, we agreed to a 12 month pause on such collaboration with Novo Nordisk, and accordingly, we do not expect to recognize any material collaboration revenue under such agreement during the year12-month endedhold December 31, 2023, we recognized no collaboration revenue.period.

For additional information about our revenue recognition policy, see Note 2 and Note 1312 into theour audited consolidated financial statements included in this Annual Report on Form 10-K.

Research and development expenses consist primarily of costs incurred for our research and development activities, including our discovery of novel genetic medicines and the development of our productdevelopment candidates, salaries and benefits, and third-party license fees. We expense research and development costs as incurred, which include:

A large portion of our research and development expenses have been external expenses, which we track on a program-by-program basis following nomination as a development candidate. Our internal research and development expenses are primarily personnel-related expenses, including stock-based compensation expense and facility expenses, mainly including office rent expenses and depreciation expenses. We do not allocate our internal research and development expenses to specific drugdevelopment candidate programs as they are deployed across multiple projects under research and development.

The successful development of our productdevelopment candidates is highly uncertain. We plan to substantially increase our research and development expenses for the foreseeable future as we continue the development of our product candidates, conduct discovery and research activities for our preclinical programs, and expandsexpand our pipeline. We cannot determine with certainty the timing of initiation, the duration or the completion costs of current or future preclinical studies and clinical trials of our productdevelopment candidates due to the inherently unpredictable nature of preclinical and clinical development. Clinical and preclinical development timelines, the probability of success and development costs can differ materially from expectations. We anticipate that we will make determinations as to which productlead candidates and development candidates to pursue and how much funding to direct to each product candidate on an ongoing basis in response to the results of ongoing and future preclinical studies and clinical trials, regulatory developments and our ongoing assessments as to each productdevelopment candidate’s commercial potential. Our clinical development costs are expected to increase significantly as we commence clinical trials. We anticipate that our expenses will increase substantially, particularly due to the numerous risks and uncertainties associated with developing productdevelopment candidates, including the uncertainty of:

whether our productdevelopment candidates show safety and efficacy in our clinical trials;

obtaining and maintaining patent and trade secret protection and regulatory exclusivity for our productdevelopment candidates;

commercializing productdevelopment candidates, if and when approved, whether alone or in collaboration with others; and continued acceptable safety profile of products following any regulatory approval.

Any changes in the outcome of any of these variables with respect to the development of our productdevelopment candidates in preclinical and clinical development could mean a significant change in the costs and timing associated with the development of these productdevelopment candidates. We may never succeed in achieving regulatory approval for any of our productdevelopment candidates. We may obtain unexpected results from our clinical trials. We may elect to discontinue, delay or modify clinical trials of some productdevelopment candidates or focus on other productdevelopment candidates. For example, if the FDA, EMA, HREC, TGA or another regulatory authority were to delay the planned start of clinical trials or require us to conduct clinical trials or other testing beyond those that we currently expect or if we experience significant delays in enrollment in any planned clinical trial, we could be required to expend significant additional financial resources and time on the completion of clinical development of that productdevelopment candidate.

We anticipate that our general and administrative expenses will increasedecrease or remain flat in the near future as we increase our headcount to support our continuedcurrent planned research activities and development of our productlead candidates.candidates and development candidates at current personnel levels. However, should we grow our operations, we anticipate that such personnel-related expenses would increase. We also expect to continue to incur costs associated with being a public company and maintaining controls over financial reporting, including costs of accounting, audit, legal, regulatory, compliance and director and officer insurance costs as well as investor and public relations expenses.

During the year ended December 31, 2025 and 2024, we recognized $6.4 million and $2.3 million of collaboration revenuerevenue, respectively, from our research collaboration and license agreement with Novo Nordisk. DuringIn November 2025, we agreed to a 12 month pause on our collaboration with Novo Nordisk. Accordingly, we do not expect to recognize any material collaboration revenue under such agreement during the year12-month endedhold December 31, 2023, we recognized no collaboration revenue.period.

Total other income, net was $5.2 million for the year ended December 31, 2025, compared to $8.5 million for the year ended December 31, 2024, compared to $3.4 million for the year ended December 31, 2023.2024. The increasedecrease of $5.1$3.3 million was primarily due to an increase of $5.1 million inlower interest income earnedgenerated from oura lower cash, cash equivalentsequivalent and marketable securities drivenbalance byin interest2025 ratescompared andto higher marketable securities balance.2024.

Since our inception, we have generated recurring net losses. We have not yet commercialized any productproducts and we do not expect to generate revenue from sales of any products for several years, if at all. Since inception, we have funded our operations primarily through proceeds from the issuance of convertible preferred stock and common stock. To date, we have raised approximately $223.6 million of aggregate gross proceeds from the sale of convertible preferred stock, $117.3 million from the sale of shares of common stock issued in a private placement that closed immediately prior to the November 2023 business combination andcombination, $70.0 million from the April 2024 private placement of shares of our common stock.stock, $5.1 million from the January 2026 sales under our at-the-market offering program, and $85.0 million from the March 2026 private placement. As of December 31, 2024,2025, we had cash, cash equivalents and marketable securities of $163.1$85.2 million.

In December 2024, we entered into a sales agreement with TD Securities (USA) LLC, or TD Cowen, under which we may, from time to time, issue and sell shares of our common stock having aggregate sales proceeds of up to $100.0 million, in a series of one or more at-the-market equity offerings. As of December 31, 2024,2025, we havehad not sold any shares of common stock under our at-the-market equity offering program. In January 2026, we issued 501,861 shares of common stock under the at-the-market offering program for gross proceeds of $5.1 million.

As of December 31, 2024,2025, we had cash, cash equivalents and marketable securities of $163.1$85.2 million. We expect that our cash, cash equivalents and marketable securities outstanding as of December 31, 2024,2025, together with the net proceeds raised under the January at-the-market offering program sales and March 2026 private placement, will be sufficient to fund our operating expenses and capital expenditure requirements into the second half of 2026 (including completion of the Phase 1/2a REWRITE clinical trial of KRRO-110 and progress additional product candidates).2028. We have based this estimate on assumptions that may prove to be wrong, and we could expend our capital resources sooner than we expect. We may also pursue additional cash resources through public or private equity, collaborations or debt financings. There is no assurance that we will be successful in obtaining sufficient financing on acceptable terms to continue funding our operations.

We expect to continue to incur significant expenses, operating losses, and negative operating cash flows for the foreseeable future as we continue our novel genetic medicine discovery efforts, advance our pipeline candidates into the clinic and through clinical trials, seek regulatory approval of our productdevelopment candidates and pursue commercialization of any approved productdevelopment candidates. In addition, we expect to continue to incur costs associated with operating as a public company.

Because of the numerous risks and uncertainties associated with research, development and commercialization of our productdevelopment candidates, we are unable to estimate the exact amount of our working capital requirements.

the scope, progress, results, and costs of discovery, preclinical development, laboratory testing, manufacturing and clinical trials for KRRO-110KRRO-121 and other product candidates we may develop;

the extent to which we partner our programs, acquiresacquire or in-licensesin-license other productlead candidates, development candidates and technologies or entersenter into additional collaborations;

ourany future headcount growth and associated costscosts, asshould we expand our research and development efforts;

the cost of defending potential intellectual property disputes, including patent infringement actions brought by third parties against us or any of our productlead candidates or development candidates;

the costs and timing of future commercialization activities, including product manufacturing, marketing, sales and distribution, for any productdevelopment candidates for which we receive marketing approval;

Until such time, if ever, as we can generate substantial product revenues to support our cost structure, we expect to finance our cash needs through a combination of equity offerings, debt financings, collaborations and other similar arrangements. To the extent that we raise additional capital through the sale of equity or convertible securities, the ownership interest of our stockholders will be or could be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect the rights of our common stockholders. Debt financing and equity financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends. If we raise funds through collaborations, or other similar arrangements with third parties, we may have to relinquish valuable rights to our technologies, future revenue streams, research programs or productdevelopment candidates or grant licenses on terms that may not be favorable to us and/or may reduce the value of our common shares. If we are unable to raise additional funds through equity or debt financings when needed, we may be required to delay, limit, reduce or terminate our product research and development or grant rights to develop and market our productdevelopment candidates even if we would otherwise prefer to develop and market such productdevelopment candidates ourselves.

Cash Provided by (Used in) Investing Activities

Since inception, we have incurred significant operating losses. Our net loss was $19.6$38.5 million and $23.4$49.2 million for the threesix months ended MarchJune 31,30, 2026 and 2025, respectively. As of MarchJune 31,30, 2026, we had an accumulated deficit of $403.5$422.4 million. We have financed our operations primarily through private placements of our convertible preferred stock and common stock, and sales under our ATM offering program. Substantially all of our losses have resulted from expenses incurred in connection with our research and development and from general and administrative costs associated with our operations, and recently, a $30.9 million impairment charge in the fourth quarter of 2025 related to our operating lease right-of-use asset and fixed assets. We expect to continue to incur significant expenses, increasing operating losses, and negative operating cash flows for the foreseeable future. The net losses we incur may fluctuate significantly from quarter to quarter. We anticipate that our expenses will increase substantially if and as we:

progress our development candidates, including KRRO-121,KRRO-121 and KRRO-111, through clinical development;

We expect our expenses to continue to increase in connection with our ongoing activities, particularly as we identify, continue the research and development of, initiate preclinical studies and clinical trials of, and seek marketing approval for, our lead candidates and development candidates. Because we have limited financial and managerial resources, we have prioritized our research programs and oligonucleotideREO optimization efforts in specific indications among many potential options. Specifically, our initial development programs target liver and central nervous systems indications, amongst others. As a result of this prioritization, we may forego or delay pursuit of opportunities with other lead candidates or development candidates or for other indications that later prove to have greater clinical or commercial potential and we may need to reprioritize our focus in the future. Our resource allocation decisions may cause us to fail to capitalize on viable commercial products or profitable market opportunities. For example, KRRO-110, which used an LNP delivery system, did not reach projected levels of protein in patients in our now terminated Phase 1/2a REWRITE clinical trial for AATD and we have since transitioned to a GalNAc-conjugated delivery system for our AATD program.program and are now developing KRRO-111, a GalNAc-conjugated REO for AATD. Our spending on current and future research and development programs, lead candidates, and development candidates for specific indications may not yield any commercially viable products.

As of MarchJune 31,30, 2026, our cash, cash equivalents and marketable securities were $157.1$137.9 million, excluding restricted cash, or $160.5$140.3 million, including restricted cash. We believe our existing cash, cash equivalents and marketable securities will be sufficient to fund our operating expenses and capital expenditure requirements through several value-creating milestones and into the second half of 2028. However, our operating plan may change as a result of factors currently unknown, and expectations regarding our cash runway and ability to reach data inflection points are based on numerous assumptions that may prove to be untrue. As a result, we may be required to raise capital sooner than anticipated and our exposure to certain contingent liabilities and contractual obligations may be greater than anticipated. Our future capital requirements will depend on many other factors, including those discussed in the risk factor entitled “We have incurred significant losses since inception. We expect to incur losses for the foreseeable future and may never achieve or maintain profitability.”

We did not reach projected levels of protein in patients in our now terminated Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD and have transitioned to KRRO-111, a GalNAc-conjugated delivery for our AATD program, and may experience delays in developing a potential treatment for AATD. We have not completed any clinical trials nor reported any clinical trial results for any of our proposed delivery methods or RNA editing approaches. Any favorable results we may have from our earlier preclinical studies may not be predictive of results that may be observed in later preclinical studies or clinical trials.

The scientific evidence to support the feasibility of developing development candidates using our proprietary RNA editing technology is both preliminary and limited. We dosed very few participants in our now terminated Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD. Although we observed functional protein in AATD patients following a single administration of KRRO-110, we did not reach projected levels of protein in patients as of the data cut off date. We have not completed any clinical trials for any of our proposed delivery methods or RNA editing approaches, and we have transitioned from LNP to GalNAc-conjugated delivery for KRRO-111, our REO for our AATD program. Accordingly, we may experience delays in developing a potential treatment for AATD. In the future, we may use other delivery modalities to deliver our other lead candidates. While LNPs have been validated clinically to deliver oligonucleotides, such as siRNA, they were not clinically proven to deliver oligonucleotides for RNA editing, such as KRRO-110 and our other lead candidates. Similarly, while GalNAc-conjugated delivery has been validated in multiple FDA-approved oligonucleotide therapeutics, there are no FDA-approved GalNAc-conjugated RNA editing oligonucleotideREO therapeutics. Both of our most advanced programs, KRRO-121 and our AATD program,KRRO-111, utilize GalNAc-conjugated delivery. If GalNAc-conjugated delivery fails to effectively deliver our RNA editing oligonucleotides,REOs, multiple programs in our pipeline could be adversely affected.

We have concentrated a significant portion of our current resources and efforts on the advancement of KRRO-121, our lead development candidate for the treatment of hyperammonemia, including UCD and HE. KRRO-121 is in preclinical development and has not been tested in humans. KRRO-121 utilizes GalNAc-conjugated delivery and is designed to generate a stabilized, de novo variant of GS with enhanced ammonia clearance capacity. We anticipate submitting a regulatory filing to enable commencement of a first-in-human clinical trial in the second half of 2026. However, there can be no assurance that KRRO-121 will demonstrate safety or efficacy in humans, that our regulatory filing will be accepted, or that we will be able to initiate or complete clinical trials on our anticipated timeline. If KRRO-121 fails to demonstrate safety or efficacy, or if we experience significant delays in its regulatory filing or clinical development, our business, financial condition, results of operations and prospects would be materially and adversely affected. Following the termination of our REWRITE clinical program investigating KRRO-110 for AATD, KRRO-121we only recently nominated KRRO-111, our GalNac-conjugated REO for AATD and it is ourin onlyearly nominated development candidate, which increases the concentrationstages of riskclinical in a single program.development. Our other programs, including our AATD GalNAc-conjugated program, our longevity and liver health program targeting AMPKγ1, and our ALS program targeting TDP-43, are in earlier stages of preclinical development and may not advance to clinical development on a timely basis, or at all.

The success of our business depends primarily upon our ability to identify, develop and commercialize development candidates. We are very early in our development efforts and have focused our research and development efforts to date on developing OPERA, our RNA editing platform, and identifying our initial targeted disease indications. We currently only have onetwo nominated development candidatecandidates in our pipeline, KRRO-121, and more recently, KRRO-111, as we terminated further development of KRRO-110 after it failed to reach projected levels of protein in our first in-human clinical trial. Although we believe we can demonstrate many of the key advantages of RNA editing, because we are very early in our development efforts, we are not yet certain of the results we may achieve, which may be important for registration and commercialization of any candidates we successfully develop. Such uncertainties include, but are not limited to, the level of editing efficiency needed in a target tissue type to achieve a clinical benefit, and associated safety of our edits in humans. We have also not yet shown that preclinical editing activity can result in clinically important effects, nor that the data generated by our preclinical studies can translate into positive results in clinical trials.

We are very early in our development of development candidates and have focused our efforts to date primarily on platform development, discovery, research, and preclinical development and had only dosed a small number of participants in our now terminated Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD. Our development candidate, KRRO-121, is advancing toward a regulatory filing anticipated in the second half of 2026.2026 and we only recently nominated KRRO-111 as our GalNac-conjugated REO for AATD. All of our other programs are still in the research or preclinical stage of development. Our ability to generate product revenues, which we do not expect will occur for many years, if ever, will depend heavily on the successful development, marketing approval and eventual commercialization of our development candidates, which may never occur. We have not yet generated revenue from product sales or otherwise, and we may never be able to develop or commercialize a marketable product.

Our development candidates are based upon new discoveries, technologies and therapeutic approaches. Key participants in pharmaceutical marketplaces, such as physicians, third-party payors and consumers, may not adopt a product intended to improve therapeutic results that is based on the technology employed by oligonucleotides.REOs. As a result, it may be more difficult for us to convince the medical community and third-party payors to accept and use our product, or to provide favorable reimbursement.

Because we are developing oligonucleotides,REOs, which are considered a relatively new class of drugs, there is increased risk that the outcome of our clinical trials will not be sufficient to obtain regulatory approval.

The FDA and comparable ex-U.S. regulatory agencies have relatively limited experience with oligonucleotides, which may increase the complexity, uncertainty and length of the regulatory review process for any development candidates. Even though the FDA issued two draft guidance documents in December 2021 relating to IND submissions for individualized antisense oligonucleotide drugs for severely debilitating or life-threatening genetic diseases, one with clinical focus, the other with chemistry manufacturing and controls focus, and in June 2024 final guidance on clinical pharmacology considerations for the development of oligonucleotide therapeutics, the FDA and its foreign counterparts have not yet established any definitive policies, practices or guidelines in relation to overall development considerations for RNA editing oligonucleotideREO therapies. The general lack of policies, practices or guidelines specific to oligonucleotides may hinder or slow review by the FDA or other foreign regulatory agencies of any regulatory filings that we may submit. Moreover, the FDA or other foreign regulatory agencies may respond to these submissions by defining requirements we may not have anticipated. Addressing such requirements could lead to significant delays in the development of our development candidates. In addition, because there may be approved treatments for some of the diseases for which we may seek approval, in order to receive regulatory approval, we may need to demonstrate through clinical trials that the development candidates we develop to treat these diseases, if any, are not only safe and effective, but safer or more effective than existing products. Furthermore, in recent years, there has been increased public and political pressure on the FDA with respect to the approval process for new drugs. As a result of the foregoing factors, we may never receive regulatory approval to market and commercialize any development candidate. Even if we obtain regulatory approval, the approval may be for disease indications or patient populations that are not as broad as we intended or desired or may require labeling that includes significant use or distribution restrictions or safety warnings. We may be required to perform additional or unanticipated clinical trials to obtain regulatory approval or be subject to additional post-marketing studies or other requirements to maintain such approval. As a result, we may never succeed in developing a marketable product, we may not become profitable and the value of our common stock could decline.

We and the third parties upon which we rely face a variety of evolving threats, which could cause cybersecurity incidents or data breaches. Cybersecurity incidents and data breaches are increasing in their frequency, sophistication and intensity, and have become increasingly difficult to detect. Cybersecurity incidents and data breaches could include wrongful conduct by hostile foreign governments, industrial espionage, wrongful conduct by employees or vendors, human error, wire fraud and other forms of cyber fraud, the deployment of harmful malware or ransomware, denial-of-service attacks, social engineering fraud (including successful phishing attacks) or other means to threaten data confidentiality, integrity and availability. A cybersecurity incident or data breach could cause serious negative consequences for us, including, without limitation, the disruption of operations, the misappropriation of confidential business information, including financial information, trade secrets, financial loss and the disclosure of corporate strategic plans.

Like other companies in our industry, we and our third party vendors, have experienced, or may experience, threats and cybersecurity incidents relating to our and our third-party vendors’ information systems and infrastructure. Although we devote resources to protect our information systems, there can be no assurance that our efforts will prevent cybersecurity incidents or data breaches that could result in business, legal, financial or reputational harm to us, or would have a material adverse effect on our results of operations and financial condition. Attempts to disrupt or gain unauthorized access to our and our third-party vendors’ information systems from malicious third parties or insider threats may incorporate widely varying and frequently changing tactics, which may be enhanced or facilitated by artificial intelligence. Further, our contracts may not contain limitations of liability, and even where they do, there can be no assurance that limitations of liability in our contracts are sufficient to protect us from liabilities, damages, or claims related to our privacy and data security obligations. Although we maintain cyber liability insurance, this insurance may not provide adequate coverage against potential liabilities related to any experienced cybersecurity incident or breach. For additional information on our cybersecurity obligations as well as our cybersecurity program, see Item 1 “Business—Government Regulation—Privacy and Cybersecurity” and Item 1C “Cybersecurity” in the 2025 10-K.

We have not yet manufactured our development candidates on a commercial scale, and may not be able to do so for any of our development candidates. We currently rely on third parties in the supply and manufacture of materials for our research, preclinical and clinical activities and may continue to do so for the foreseeable future, including if we received regulatory approval for any development candidate. We may do the same for the commercial supply of our drug product. We use third parties to perform additional steps in the manufacturing process, such as the filling, finishing and labeling of vials and storage of our development candidates and we expect to do so for the foreseeable future. There can be no assurance that our supply of research, preclinical and clinical development drug candidates and other materials will not be limited, interrupted or restricted or will be of satisfactory quality or continue to be available at acceptable prices. Replacement of any of the third parties we may engage could require significant effort and expertise because there may be a limited number of qualified replacements. In addition, raw materials, reagents, and components used in the manufacturing process, particularly those for which we have no other source or supplier, may not be available, may not be suitable or acceptable for use due to material or component defects, or may introduce variability into the supply of our development candidates. Furthermore, with the increase of companies developing nucleic acid therapeutics, there may be increased competition for the supply of the raw materials that are necessary to make our oligonucleotides,REOs, which could severely impact the manufacturing of our development candidates.

As of MarchJune 31,30, 2026, we had 4957 full-time employees, including 3742 who hold Ph.D. degrees or other advanced degrees; 3340 employees are engaged in research and development and 1617 employees are engaged in management or general and administrative activities. In May 2025, we announced a workforce reduction and organizational streamlining and in November 2025, we announced a further workforce reduction to extend our cash runway. In connection with the growth and advancement of our pipeline, we expect that we will need to increase the number of our employees and the scope of our operations, particularly in the areas of drug development, regulatory affairs, and as any development candidates near later stage clinical trials and potential commercialization by us, and sales and marketing. To manage our anticipated future growth, we must continue to implement and improve our managerial, operational and financial systems, expand our facilities, and continue to recruit and train additional qualified personnel. Our workforce reduction may make these efforts more challenging. Due to our limited financial resources and the limited experience of our management team in managing a company with such anticipated growth, we may not be able to effectively manage the expected future expansion of our operations or recruit and train additional qualified personnel. Any inability to manage growth could delay the execution of our business plans or disrupt our operations.

The future growth of our business may depend in part on our ability to in-license or otherwise acquire the rights to additional development candidates and technologies. There has been extensive patenting activity in the field of gene editing. Pharmaceutical companies, biotechnology companies and academic institutions are competing with us or are expected to compete with us in the in the field of gene editing technology and filing patent applications potentially relevant to our business. In order to market our development candidates, we may find it necessary or prudent to obtain licenses from third-party intellectual property holders. However, we may be unable to secure such licenses or otherwise acquire or in-license any compositions, methods of use, processes, or other intellectual property rights from third parties that we identify as necessary to develop or commercialize our development candidates or other key technologies. We may also require licenses from third parties for certain additional technologies, including technologies relating to RNA editing, such as guide RNA modification, or target sequences as well as delivery technologies for development candidates we may develop. We may not be able to obtain such a license on an exclusive basis, on commercially reasonable terms, or at all, which could prevent us from commercializing our development candidates or allow our competitors or other third parties the chance to access technology that is important to our business.

Our business may be impacted by macroeconomic conditions, including inflation, rising interest rates and volatile market conditions, and other uncertainties beyond our control, including geopolitical events, such as recentongoing U.S. and Israeli military action in Iran, and effects thereof.

Our ability to effectively run our business could be adversely affected by general conditions in the global economy and in the financial services industry. Various macroeconomic factors could adversely affect our business, including fears concerning the banking sector (such as what occurred in 2023), changes in inflation, interest rates and overall economic conditions and uncertainties (including as a result of announced tariffs or other policy changes by the current U.S. administration). Actual events involving limited liquidity, defaults, non-performance or other adverse developments that affect financial institutions, transactional counterparties or other companies in the financial services industry or the financial services industry generally, or concerns or rumors about any events of these kinds or other similar risks, have in the past and may in the future lead to market-wide liquidity problems. A severe or prolonged economic downturn could result in a variety of risks, including our ability to raise additional funding on a timely basis or on acceptable terms. A weak or declining economy could also impact third parties upon whom we depend to run our business. Although we assess our banking relationships as we believe necessary or appropriate, our access to funding sources in amounts adequate to finance or capitalize our current and projected future business operations could be significantly impaired by factors that affect us, the financial institutions with which we have arrangements directly, or the financial services industry or economy in general. Moreover, significant political, trade, regulatory developments, and other circumstances beyond our control, such as geopolitical events, like the recentongoing U.S. and Israeli military action in Iran and effects thereof, could have a material adverse effect on our financial condition or results of operations.

We are a biopharmaceutical company leveraging a novel oligonucleotide promoted editing of RNA, or OPERA, platform to develop a new class of genetic medicines for rare and highly prevalent diseases. OPERA provides precise, tissue-directed delivery of oligonucleotidesRNA-editing oligonucleotides, or REOs, that modify the targeted native mRNA transcript to repair or form a de-novo protein with enhanced functionality. The platform combines a suite of capabilities consisting of sophisticated knowledge of transcription biology through ADAR proteins (Adenosine Deaminases Acting on RNA), machine learning optimization of oligonucleotides,REOs, linker chemistry expertise, along with use of a highly targeted tissue-specific delivery methodology. As such, the OPERA platform has enabled us to generate and advance a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, providing precise yet transient single base edits to produce therapeutic proteins with augmented activity versus its endogenous counterpart. By editing RNA instead of DNA, we are expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an oligonucleotide-basedREO-based approach, we expect to bring our medicines to patients by leveraging our proprietary OPERA platform with precedented delivery modalities, including N-acetylgalactosamine, or GalNAc, conjugated for delivery for subcutaneous administration, manufacturing know-how, and established regulatory pathways of approved oligonucleotide medicines. However, the scientific evidence to support the feasibility of developing our development candidates using our RNA editing technology is both preliminary and limited. Moreover, regulators have not yet established any definitive guidelines related to overall development considerations for RNA editing therapies and limited clinical data has been generated to date.

The versatility of RNA editing combined with our OPERA platform broadens the therapeutic target space significantly. The advent of large-scale genome sequencing has progressively revealed causal genetic variation underlying several human diseases, both rare and highly prevalent. Genetic mutations, including single nucleotide variants, or SNVs, implicated in disease have been found to be diverse in nature and can affect the function of genes and their associated downstream biochemical pathways. Data correlating DNA to RNA to disease phenotype have demonstrated that SNVs lead to a loss-of-function or a gain-of-function of the gene. In addition, the majority of SNVs implicated in complex diseases are due to modulation of gene function. By editing RNA to mimic aan SNV, we believe we will be able to address unmet patient need by transiently modifying gene expression and the resultant protein function.

We continue to make meaningful advancements across our programs, including KRRO-121 as a potential first-in-class treatment for hyperammonemia that has the potential to address substantial unmet need in patients with poor ammonia control, including those with urea cycle disorders, or UCD, and hepatic encephalopathy, or HE. KRRO-121 is a GalNAc-conjugated RNA editing oligonucleotideREO for the potential treatment of hyperammonemia in patients with UCDs of any mutational background as well as patients with HE. Utilizing our proprietary OPERA platform, KRRO-121 is designed to obviate the need for a functional urea cycle and instead generate a stabilized, de novo glutamine synthetase, or GS, protein, a critical enzyme in an alternate pathway involved in ammonia clearance. This synthetic rescue approach is designed to augment ammonia clearance in hyperammonemia-driven diseases such as UCDs and HE. Our preclinical data support the potential for KRRO-121 to be a pan-UCD treatment that may control ammonia levels, along with the potential to enable diet liberalization, reduce dependence on nitrogen scavengers, and lower the risk of hyperammonemic crises. KRRO-121 also has the potential to enhance ammonia control in HE patients, which may reduce the risk of recurrent HE episodes. KRRO-121 may offer infrequent subcutaneous dosing, which, if confirmed in clinical studies, could offer significant improvement over current treatments that require multiple daily doses. KRRO-121 has the potential to be a differentiated, first-in-class, disease-modifying therapy for both UCD and HE. In August 2026, we announced the European Medicines Agency, or EMA, granted orphan drug designation for KRRO-121 for patients with UCDs. We anticipateremain aon regulatory filingtrack to enable commencement ofcommence a first-in-human trial for KRRO-121 in the second half of 2026.

We have incurred significant operating losses since inception. Our net losses were $19.6$38.5 million and $23.4$49.2 million for the threesix months ended MarchJune 31,30, 2026 and 2025, respectively. We had an accumulated deficit of $403.5$422.4 million as of MarchJune 31,30, 2026. We expect to continue to incur significant and increasing expenses and operating losses and negative operating cash flows for the foreseeable future as we continue our research and development efforts, advance development candidates through clinical development, and seek regulatory approvals for our development candidates. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending on the timing of our preclinical studies, initiation and conduct of any clinical trials, and our expenditures on other research and development activities, including the expansion of our pipeline.

We have not generated any revenue from product sales, and do not expect to generate any revenue from the sale of products in the near future. During the threesix months ended MarchJune 31,30, 2026 and 2025, we recognized $0.0 million and $2.6$4.0 million of collaboration revenue, respectively, which is related to our research collaboration and license agreement with Novo Nordisk. In November 2025, we agreed to a 12-month pause on such collaboration with Novo Nordisk, accordingly, we do not expect to recognize any material collaboration revenue under such agreement during the 12-month hold period.

Comparison of the Three and Six Months Ended MarchJune 31,30, 2026 and 2025

The following table summarizes our results of operations for the three and six months ended MarchJune 31,30, 2026 and 2025:

During the three months ended MarchJune 31,30, 2026 and 2025, we recognized $0.0 million and $2.6$1.5 million, respectively, of collaboration revenue from our research collaboration and license agreement with Novo Nordisk. During the six months ended June 30, 2026 and 2025, we recognized $0.0 million and $4.0 million, respectively, of collaboration revenue from our research collaboration and license agreement with Novo Nordisk. In November 2025, we agreed to a 12-month pause on our collaboration with Novo Nordisk. Accordingly, we do not expect to recognize any material collaboration revenue under such agreement during the 12-month hold period.

The following table summarizes our research and development expenses for the three and six months ended MarchJune 31,30, 2026 and 2025:

Research and development expenses were $12.9$13.6 million for the three months ended MarchJune 31,30, 2026, compared to $19.7$20.1 million for the three months ended MarchJune 31,30, 2025. The decrease was primarily due to the following:

a $5.4$6.1 million decrease in KRRO-110 external expenses primarily due to the termination of the Phase 1/2a REWRITE clinical trial during the first quarter of 2026; and a $2.5$1.7 million decrease in other research and pre-development candidate expenses primarily due to a decrease in lab supplies and consumables; and a $1.3 million decrease in personnel-related expenses, primarily due to a decrease in headcount resulting from the May and November 2025 workforce reductionsreductions, partially offset by an increase in stock-based compensation costs; and a $1.3 million decrease in other research and pre-development candidate expenses; and a $0.9$0.7 million decrease in facilities expenses primarily due to a decrease in depreciation expense attributable to the impairment charge recorded during the fourth quarter of 2025;

offset by a $3.3$1.7 million increase in KRRO-111 external expenses, primarily due to an increase in preclinical and manufacturing costs; and a $1.6 million increase in KRRO-121 external expenses, primarily due to an increase in preclinical and manufacturing costs.

The following table summarizes our general and administrative expenses for the three and six months ended MarchJune 31,30, 2026 and 2025:

General and administrative expenses were $7.5$6.5 million for the three months ended MarchJune 31,30, 2026, compared to $7.8$7.3 million for the three months ended MarchJune 31,30, 2025. The decrease was primarily due to athe decrease in facilities expenses and information technology expenses, partially offset by an increase in personnel expenses mainly due to increased stock-based compensation costs.following:

Total other income, net was $0.9$1.3 million for the three months ended MarchJune 31,30, 2026, compared to $1.6$1.4 million for the three months ended MarchJune 31,30, 2025. The decrease of $0.7$0.1 million was primarily due to lowerfluctuations interestin incomeforeign generatedcurrency fromexchange a lower cash, cash equivalent and marketable securities balance during the quarter prior to the March 2026 PIPE.rates.

Since our inception, we have generated recurring net losses. We have not yet commercialized any product and we do not expect to generate revenue from sales of any products for several years, if at all. Since inception, we have funded our operations primarily through proceeds from the issuance of convertible preferred stock and common stock. To date, we have raised approximately $501.0 million of aggregate gross proceeds from sales of our equity securities. As of MarchJune 31,30, 2026, we had cash, cash equivalents and marketable securities of $157.1$137.9 million.

Since inception, we have incurred significant operating losses and, as of MarchJune 31,30, 2026, had an accumulated deficit of $403.5$422.4 million. We expect to continue to incur significant expenses, operating losses, and negative operating cash flows for the foreseeable future. In addition, we have not yet commercialized any product and we do not expect to generate revenue from sales of any products for several years, if at all.

In December 2024, we entered into a sales agreement with TD Cowen Securities (USA) LLC, or TD Cowen, under which we may, from time to time, issue and sell shares of our common stock having aggregate sales proceeds of up to $100.0 million, in a series of one or more at-the-market equity, or ATM, offerings. In January 2026, we issued 501,861 shares of common stock under the ATM offering program for gross proceeds of $5.1 million, before deducting offering expenses of approximately $0.1 million.

In March 2026, we closed athe March 2026 PIPE selling (i) an aggregate of 4,501,928 shares of our common stock at a purchase price of $11.11 per share and (ii) pre-funded warrants to acquire an aggregate 3,148,836 shares of our common stock (at an exercise price of $0.001 per share) at a purchase price of $11.109 per pre-funded warrant, which resulted in gross cash proceeds of approximately $85.0 million, before deducting placement agent fees and offering expenses of approximately $4.7 million.

As of MarchJune 31,30, 2026, we had cash, cash equivalents and marketable securities of $157.1$137.9 million. We expect that our cash, cash equivalents and marketable securities outstanding as of MarchJune 31,30, 2026 will be sufficient to fund our operating expenses and capital expenditure requirements into the second half of 2028. We have based this estimate on assumptions that may prove to be wrong, and we could expend our capital resources sooner than we expect. We may also pursue additional cash resources through public or private equity, collaborations or debt financings. There is no assurance that we will be successful in obtaining sufficient financing on acceptable terms to continue funding our operations.

the scope, progress, results, and costs of discovery, preclinical development, laboratory testing, manufacturing and clinical trials for KRRO-121, a GalNAc-conjugated candidate for AATD,KRRO-111, and other development candidates we may develop;

the extent to which we partner our programs, acquiresacquire or in-licensesin-license other lead candidates, development candidates and technologies or enters into additional collaborations;

Comparison of the ThreeSix Months Ended MarchJune 31,30, 2026 and 2025

The following table summarizes our cash flows for the threesix months ended MarchJune 31,30, 2026 and 2025:

Net cash used in operating activities was $24.5$33.1 million for the threesix months ended MarchJune 31,30, 2025,2026, primarily resulted from our net loss of $23.4$38.5 million, which was primarily attributable to our research and development activities and our general and administrative expenses,expenses along withand changes in our operating assets and liabilities of $3.9$1.2 million, offset by $2.8$6.6 million of non-cash items.

Net cash used in investing activities was $32.2$50.1 million for the threesix months ended MarchJune 31,30, 2026 and consisted primarily of the purchase of marketable securities and the purchase of property and equipment, offset by proceeds from maturities of marketable securities.

Net cash provided by investing activities was $32.8$21.5 million for the threesix months ended MarchJune 31,30, 2025 and consisted primarily of the proceeds from maturities of marketable securities, offset by the purchase of marketable securities and the purchase of property and equipment.

Net cash provided by financing activities was $88.2$85.3 million for the threesix months ended MarchJune 31,30, 2026 and consisted of net proceeds from the March 2026 PIPE, sales of shares under our ATM program, and exercises of stock options.

Net cash provided by financing activities was $0.1$0.2 million for the threesix months ended MarchJune 31,30, 2025 and consisted primarily of proceeds from exercises of stock options.