Korro Bio, Inc.

Previous wording

Our clinical-stage development program is investigating KRRO-110 as a treatment for AATD where, using our proprietary RNA editing approach, we are repairing a pathogenic variant on RNA. KRRO-110 has the potential to be disease-modifying and provide a differentiated therapeutic option. In January 2025, we announced dosing of the first participants in our REWRITE clinical program investigating KRRO-110 as a treatment for AATD. REWRITE is a two-part single and multiple dose-escalating Phase 1/2a clinical trial that will evaluate the safety and tolerability of KRRO-110 in up to 64 participants, including healthy adults and clinically stable AATD patients with the PiZZ genotype. Secondary and exploratory endpoints include pharmacokinetic and pharmacodynamic parameters that will guide optimal dose selection for later stage studies. In May 2025, we announced approval to expand our Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD into New Zealand, and we continue to progress enrollment, site activation and expansion into other geographies beyond Australia and New Zealand, including the United States. In March 2025, we announced that the U.S. Food and Drug Administration, or FDA, has granted orphan drug designation to KRRO-110 for the treatment of AATD. Interim data from single ascending doses in healthy volunteers and AATD patients is expected in the second half of 2025, and completion of the REWRITE Phase 1/2a trial is anticipated in 2026. Based on the preclinical data, we believe KRRO-110 has best-in-class potential for the treatment of AATD. However, KRRO-110 is in early clinical development and there is no guarantee that it will be successful.

Current wording

Our clinical-stage development program is investigating KRRO-110 as a treatment for AATD where, using our proprietary RNA editing approach, we are repairing a pathogenic variant on RNA. KRRO-110 has the potential to be disease-modifying and provide a differentiated therapeutic option. In January 2025, we announced dosing of the first participants in our REWRITE clinical program investigating KRRO-110 as a treatment for AATD. REWRITE is a two-part single and multiple dose-escalating Phase 1/2a clinical trial that will evaluate the safety and tolerability of KRRO-110 in up to 64 participants, including healthy adults and clinically stable AATD patients with the PiZZ genotype. Secondary and exploratory endpoints include pharmacokinetic and pharmacodynamic parameters that will guide optimal dose selection for later stage studies. We have completed dosing of over 80% of planned healthy volunteers across multiple single ascending dose cohorts, including dose levels that are expected to be pharmacologically relevant in PiZZ patients. We have not observed any treatment emergent serious adverse events or dose limiting toxicities as of the date of this Quarterly Report on Form 10-Q. In May 2025, we announced approval to expand our Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD into New Zealand, and we continue to progress enrollment, site activation and expansion into other geographies beyond Australia and New Zealand, including the United States. In March 2025 and July 2025, we announced that the U.S. Food and Drug Administration, or FDA, and the European Medicines Agency, or EMA, respectively, granted orphan drug designation to KRRO-110 for the treatment of AATD. Interim data from single ascending doses in healthy volunteers and AATD patients is expected in the second half of 2025, and completion of the REWRITE Phase 1/2a trial, including Part 2 (multiple ascending doses in individuals with AATD), is anticipated in 2026. Based on the preclinical data, we believe KRRO-110 has best-in-class potential for the treatment of AATD. However, KRRO-110 is in early clinical development and there is no guarantee that it will be successful.

Previous wording

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 product 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, $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 and $70.0 million from the April 2024 private placement of shares of our common stock.

Current wording

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, $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 and $70.0 million from the April 2024 private placement of shares of our common stock.

Previous wording

We have incurred significant operating losses since inception. Our net losses were $23.4 million and $19.6 million for the three months ended March 31, 2025 and 2024, respectively. We had an accumulated deficit of $290.0 million as of March 31, 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 product candidates through clinical development, and seek regulatory approvals for our pipeline 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.

Current wording

We have incurred significant operating losses since inception. Our net losses were $49.2 million and $41.4 million for the six months ended June 30, 2025 and 2024, respectively. We had an accumulated deficit of $315.7 million as of June 30, 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 product candidates through clinical development, and seek regulatory approvals for our pipeline 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.

Previous wording

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 three months ended March 31, 2025, we recognized $2.6 million of collaboration revenue, which is related to our September 2024 research collaboration and license agreement with Novo Nordisk A/S, or Novo Nordisk. During the three months ended March 31, 2024, we recognized no collaboration revenue.

Current wording

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 six months ended June 30, 2025, we recognized $4.0 million of collaboration revenue, which is related to our September 2024 research collaboration and license agreement with Novo Nordisk. During the six months ended June 30, 2024, we recognized no collaboration revenue.

Previous wording

Any changes in the outcome of any of these variables with respect to the development of our product candidates in preclinical and clinical development could mean a significant change in the costs and timing associated with the development of these product candidates. We may never succeed in achieving regulatory approval for any of our product candidates. We may obtain unexpected results from our clinical trials. We may elect to discontinue, delay or modify clinical trials of some product candidates or focus on other product candidates. For example, if the FDA, European Medicines Agency, or EMA, HREC, Therapeutic Goods Administration, or TGA, the Health and Disability Ethics Committees, or HDEC, 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 product candidate.

Current wording

Any changes in the outcome of any of these variables with respect to the development of our product candidates in preclinical and clinical development could mean a significant change in the costs and timing associated with the development of these product candidates. We may never succeed in achieving regulatory approval for any of our product candidates. We may obtain unexpected results from our clinical trials. We may elect to discontinue, delay or modify clinical trials of some product candidates or focus on other product candidates. For example, if the FDA, EMA, HREC, Therapeutic Goods Administration, or TGA, the Health and Disability Ethics Committees, or HDEC, 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 product candidate.

Previous wording

Comparison of the Three Months Ended March 31, 2025 and 2024

Current wording

Comparison of the Three and Six Months Ended June 30, 2025 and 2024

Previous wording

The following table summarizes our results of operations for the three months ended March 31, 2025 and 2024:

Current wording

The following table summarizes our results of operations for the three and six months ended June 30, 2025 and 2024:

Previous wording

During the three months ended March 31, 2025, we recognized $2.6 million of collaboration revenue from our research collaboration and license agreement with Novo Nordisk. During the three months ended March 31, 2024, we recognized no collaboration revenue.

Current wording

During the three and six months ended June 30, 2025, we recognized $1.5 million and $4.0 million, respectively, of collaboration revenue from our research collaboration and license agreement with Novo Nordisk. During the three and six months ended June 30, 2024, we recognized no collaboration revenue.

Previous wording

The following table summarizes our research and development expenses for the for the three months ended March 31, 2025 and 2024:

Current wording

The following table summarizes our research and development expenses for the three and six months ended June 30, 2025 and 2024:

Previous wording

Research and development expenses were $19.7 million for the three months ended March 31, 2025, compared to $13.6 million for the three months ended March 31, 2024. The increase was primarily due to a $3.9 million increase in KRRO-110 external expenses, which was attributable to a $2.4 million increase in clinical trial activities in 2025 for the Phase 1/2a REWRITE clinical trial and achievement of a $1.5 million development milestone under our collaboration and license agreement with Genevant Sciences GmbH. A portion of the increase was also due to a $1.2 million increase in personnel-related expenses driven by an increase in headcount to support the expansion of our research and clinical development function, and a $1.1 million increase in other research and pre-development candidate expenses.

Current wording

Research and development expenses were $40.8 million for the six months ended June 30, 2025, compared to $30.7 million for the six months ended June 30, 2024. The increase was primarily due to a $3.3 million increase in KRRO-110 external expenses, which was attributable to a $2.8 million increase in clinical trial expenses in 2025 for the Phase 1/2a REWRITE clinical trial and a $0.5 million net increase in development milestone under our collaboration and license agreement with Genevant Sciences GmbH. A portion of the increase was also due to a $3.5 million increase in personnel-related expenses mainly driven by an increase in headcount prior to the May 2025 workforce reduction, increased average payroll costs per headcount to support our research and clinical development function and one-time severance charges related to the workforce reduction, and a $3.4 million increase in other research and pre-development candidate expenses as we furthered development of our rare metabolic disorders program.

Previous wording

The following table summarizes our general and administrative expenses for the three months ended March 31, 2025 and 2024:

Current wording

The following table summarizes our general and administrative expenses for the three and six months ended June 30, 2025 and 2024:

Previous wording

Total other income, net was $1.6 million for the three months ended March 31, 2025, compared to $1.9 million for the three months ended March 31, 2024. The decrease of $0.3 million was primarily due to a lower cash, cash equivalent and marketable securities balance as of March 31, 2025.

Current wording

Total other income, net was $1.4 million for the three months ended June 30, 2025, compared to $2.3 million for the three months ended June 30, 2024. The decrease of $0.9 million was primarily due to lower interest income generated from a lower cash, cash equivalent and marketable securities balance as of June 30, 2025.

Previous wording

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 $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 and $70.0 million from the April 2024 private placement of shares of our common stock. As of March 31, 2025, we had cash, cash equivalents and marketable securities of $139.0 million.

Current wording

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 $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 and $70.0 million from the April 2024 private placement of shares of our common stock. As of June 30, 2025, we had cash, cash equivalents and marketable securities of $119.6 million.

Previous wording

Since inception, we have incurred significant operating losses and, as of March 31, 2025, had an accumulated deficit of $290.0 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.

Current wording

Since inception, we have incurred significant operating losses and, as of June 30, 2025, had an accumulated deficit of $315.7 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.

Previous wording

As of March 31, 2025, we had cash, cash equivalents and marketable securities of $139.0 million. We expect that our cash, cash equivalents and marketable securities outstanding as of March 31, 2025 will be sufficient to fund our operating expenses and capital expenditure requirements into 2027. 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.

Current wording

As of June 30, 2025, we had cash, cash equivalents and marketable securities of $119.6 million. We expect that our cash, cash equivalents and marketable securities outstanding as of June 30, 2025 will be sufficient to fund our operating expenses and capital expenditure requirements into 2027. 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.

Previous wording

The following table summarizes our cash flows for the three months ended March 31, 2025 and 2024:

Current wording

The following table summarizes our cash flows for the six months ended June 30, 2025 and 2024:

Previous wording

Net cash used in operating activities was $24.5 million for the three months ended March 31, 2025, which consisted of $23.4 million of net loss, $2.8 million of non-cash adjustments to net loss and a decrease of $3.9 million in the net change in operating assets and liabilities. Non-cash adjustments primarily consisted of $1.8 million of stock-based compensation expenses and $1.2 million of depreciation expenses, partially offset by $0.3 million of net amortization of premiums and discounts on marketable securities. The decrease in net assets consisted primarily of a $2.5 million decrease in accrued expenses and other liabilities, a $0.6 million decrease in deferred revenue, a $0.6 million decrease in prepaid expenses and other current assets, a $0.4 million decrease in other non-current assets and a $0.2 million decrease in accounts receivable, partially offset by a $0.4 million increase in operating lease liabilities and a $0.1 million increase in accounts payable.

Current wording

Net cash used in operating activities was $43.7 million for the six months ended June 30, 2025, which consisted of $49.2 million of net loss, $6.2 million of non-cash adjustments to net loss and a decrease of $0.7 million in the net change in operating assets and liabilities. Non-cash adjustments primarily consisted of $3.7 million of stock-based compensation expenses and $2.5 million of depreciation expenses. The decrease in net assets consisted primarily of a $1.0 million decrease in deferred revenue and a $0.6 million decrease in accounts receivable in connection with the collaboration arrangement with Novo Nordisk, a $0.5 million decrease in accrued expenses and other liabilities, and a $0.1 million decrease in operating lease liabilities, partially offset by a $1.1 million increase in accounts payable mainly due to the timing of vendor payment and, a $0.4 million increase in prepaid expenses and other current assets, and a $0.4 million increase in other non-current assets.

Previous wording

Net cash provided by investing activities was $32.8 million for the three months ended March 31, 2025 and consisted primarily of $32.9 million of proceeds from maturities of marketable securities, offset by $0.1 million of purchase of property and equipment.

Current wording

Net cash provided by investing activities was $21.5 million for the six months ended June 30, 2025 and consisted primarily of $32.9 million of proceeds from maturities of marketable securities, offset by $11.2 million of purchases of marketable securities and $0.2 million of purchase of property and equipment.

Previous wording

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

Current wording

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