Sionna Therapeutics, Inc.

Previous wording

We are a clinical-stage biopharmaceutical company on a mission to revolutionize the current treatment paradigm for cystic fibrosis (“CF”) by developing novel medicines that normalize the function of the cystic fibrosis transmembrane conductance regulator (“CFTR”) protein to deliver clinically meaningful benefit to people with CF. Our goal is to deliver differentiated medicines for people with CF that can restore their CFTR function to as close to normal as possible by directly stabilizing CFTR’s nucleotide binding domain 1 (“NBD1”). We believe stabilizing NBD1 is central to unlocking dramatic improvements in clinical outcomes and quality of life for people with CF. We are also advancing a portfolio of complementary CFTR modulator candidates designed to work synergistically with our NBD1 stabilizers to improve CFTR function, as seen in preclinical models.

Current wording

We are a clinical-stage biopharmaceutical company on a mission to revolutionize the current treatment paradigm for cystic fibrosis (“CF”) by developing novel medicines that improve the function of the cystic fibrosis transmembrane conductance regulator (“CFTR”) protein to deliver clinically meaningful benefit to people with CF. Our goal is to deliver differentiated medicines for people with CF that can restore their CFTR function to as close to normal as possible by directly stabilizing CFTR’s nucleotide binding domain 1 (“NBD1”). We are advancing a pipeline of small molecules, NBD1 stabilizers, engineered to correct the defects caused by F508del, the most common CF mutation, which resides in NBD1. Our portfolio also includes multiple complementary CFTR modulators designed to work synergistically with our NBD1 stabilizers to improve CFTR function.

Previous wording

Since our inception, we have funded our operations primarily with proceeds from private placements of convertible preferred stock and through net proceeds from our initial public offering. In March 2026, we entered into a sales agreement with Leerink Partners LLC (“Leerink”), to issue and sell shares of our common stock, from time to time, for aggregate gross sale proceeds of up to $250.0 million through an "at the market" equity offering program under which Leerink is acting as sales agent. As of June 30, 2026, we have not sold any shares of common stock under the sales agreement. As of June 30, 2026, we raised aggregate net proceeds of$530.0 million from the sale and issuance of our preferred stock and our initial public offering. We have not generated any revenue from product sales or other sources.

Current wording

Since our inception, we have funded our operations primarily with proceeds from private placements of convertible preferred stock and through net proceeds from our initial public offering. In March 2026, we entered into a sales agreement with Leerink Partners LLC (“Leerink”), to issue and sell shares of our common stock, from time to time, for aggregate gross sale proceeds of up to $250.0 million through an "at the market" equity offering program under which Leerink is acting as sales agent. As of September 30, 2026, we had not sold any shares of common stock under the sales agreement. As of September 30, 2026, we raised aggregate net proceeds of$530.0 million from the sale and issuance of our preferred stock and our initial public offering. We have not generated any revenue from product sales or other sources.

Previous wording

Due to our significant research, development and manufacturing expenditures, we have accumulated substantial losses and negative cash flows since our inception, including net losses of $56.7 million and $34.6 million for the six months ended June 30, 2026, and 2025, respectively. As of June 30, 2026, we had an accumulated deficit of $313.0 million.

Current wording

Due to our significant research, development and manufacturing expenditures, we have accumulated substantial losses and negative cash flows since our inception, including net losses of $89.1 million and $54.8 million for the nine months ended September 30, 2026, and 2025, respectively. As of September 30, 2026, we had an accumulated deficit of $345.4 million.

Previous wording

•continue to advance the clinical development of our current and future product candidates;

Current wording

•continue to advance the clinical development of our current and future product candidates, including conducting our planned clinical trial(s);

Previous wording

•continue to advance our research activities and seek to discover and develop additional product candidates to expand our pipeline;

Current wording

•continue to advance our research and preclinical activities and seek to discover and develop additional product candidates;

Previous wording

•continue to utilize third parties to manufacture our product candidates;

Current wording

•continue to utilize third parties to manufacture our product candidates and ensure sufficient manufacturing capabilities to produce our drug substances and drug products;

Previous wording

•pursue regulatory approvals for any current or future product candidates that successfully complete clinical trials;

Current wording

•seek regulatory approvals for any current or future product candidates that successfully complete clinical trials;

Previous wording

•undertake pre-commercial activities, and scale-up external commercial-scale manufacturing capabilities, to commercialize any current or future product candidates which may obtain regulatory approval;

Current wording

•undertake any pre-commercial activities and scale-up external commercial-scale manufacturing capabilities;

Previous wording

•ultimately establish a sales, marketing and distribution infrastructure to commercialize any current or future product candidates which may receive regulatory approval; and

Current wording

•ultimately establish a sales, marketing and distribution infrastructure to commercialize any product candidates for which we may receive regulatory approval;

Previous wording

•add operational, financial and management information systems;

Current wording

•add additional operational, financial, clinical, quality and management information systems; and

Previous wording

In addition, we have several clinical development, regulatory, and commercial milestones, as well as royalty payment obligations under our licensing arrangements. Our net losses may fluctuate significantly from quarter to quarter and year to year, depending on the timing of our ongoing and planned clinical trials and our expenditures on other research and development activities.

Current wording

In addition, we have several clinical development, regulatory, and commercial milestones, as well as royalty payment obligations under our licensing arrangements. Our net losses may fluctuate significantly from quarter to quarter and year to year, depending on the timing of our planned clinical trial(s) and our expenditures on other research and development activities.

Previous wording

As of June 30, 2026, we had cash, cash equivalents and marketable securities of $268.3 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and marketable securities will be sufficient to fund our operations into 2028. We have based this estimate on assumptions that may prove to be wrong, and we could exhaust our available capital resources sooner than we expect. See the sections titled “—Liquidity and Capital Resources” and “Risk Factors—Risks Related to Our Limited Operating History, Financial Condition and Need for Additional Capital” included elsewhere in this Quarterly Report.

Current wording

As of September 30, 2026, we had cash, cash equivalents and marketable securities of $249.8 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and marketable securities will be sufficient to fund our operations into the second half of 2029. We have based this estimate on assumptions that may prove to be wrong, and we could exhaust our available capital resources sooner than we expect. See the sections titled “—Liquidity and Capital Resources” and “Risk Factors—Risks Related to Our Limited Operating History, Financial Condition and Need for Additional Capital” included elsewhere in this Quarterly Report.

Previous wording

•personnel-related costs, including salaries, payroll tax, bonuses, benefits and stock-based compensation for employees engaged in research and development functions;

Current wording

•personnel-related costs, including salaries, payroll tax, bonuses, benefits, severance and stock-based compensation for employees engaged in research and development functions;

Previous wording

General and administrative expenses consist primarily of personnel-related costs, including salaries, payroll tax, bonuses, benefits and stock-based compensation charges for those individuals in executive, legal, finance, human resources, information technology and other administrative functions. Other significant costs include legal fees relating to intellectual property and corporate matters, professional fees for auditing, accounting, tax and consulting services. Lastly, corporate overhead expenses such as information technology, insurance, facilities, and depreciation that are not allocated to the Company’s research and development activities are included in general and administrative expenses. We recognize general and administrative expenses in the periods in which they are incurred.

Current wording

General and administrative expenses consist primarily of personnel-related costs, including salaries, payroll tax, bonuses, benefits, severance and stock-based compensation charges for those individuals in executive, legal, finance, human resources, information technology and other administrative functions. Other significant costs include legal fees relating to intellectual property and corporate matters, professional fees for auditing, accounting, tax and consulting services. Lastly, corporate overhead expenses such as information technology, insurance, facilities, and depreciation that are not allocated to the Company’s research and development activities are included in general and administrative expenses. We recognize general and administrative expenses in the periods in which they are incurred.

Previous wording

We anticipate that our general and administrative expenses will increase in the future to support our increased research and development activities, pre-commercial preparation activities for our product candidates and any future product candidates and, if any product candidate receives marketing approval, commercialization activities. These increases will likely include increased costs related to the hiring of additional personnel and fees paid to outside consultants, among other expenses. We also anticipate increased expenses related to audit, accounting, legal and regulatory services associated with public company reporting and compliance, director and officer insurance premiums, investor and public relations costs and other administrative and professional services associated with operating as a public company.

Current wording

As a result of the reduction in our general and administrative workforce and other cost-saving measures implemented under the Restructuring, we expect our ongoing general and administrative expenses to decrease in the near term. However, certain costs associated with operating as a public company may remain significant or increase, including expenses related to audit, accounting, legal, intellectual property, director and officer insurance, and investor and public relations activities. Over the longer-term, our general and administrative expenses could increase if we expand our research and development activities, undertake pre-commercial activities for our product candidates and any future product candidates and, if any product candidate receives marketing approval, commercialization activities. These increases will likely include increased costs related to the hiring of additional personnel and fees paid to outside consultants, among other expenses.

Previous wording

•direct research and development expenses increased by $4.0 million primarily due to an increase in clinical programs and combination development activities; and

Current wording

•direct research and development expenses increased by $2.3 million primarily due to an increase in development activities and activities related to the wind-down of the SION-719 add-on program; and

Previous wording

•unallocated research and development expenses increased by $2.5 million primarily due to a $2.2 million increase in personnel-related expenses including stock-based compensation, driven by an increase in the size of our workforce to support our clinical pipeline.

Current wording

•unallocated research and development expenses increased by $3.7 million primarily due to a $3.4 million increase in personnel-related expenses including stock-based compensation, and restructuring related costs associated with the workforce reduction.

Previous wording

General and administrative expenses increased by $4.1 million to $10.6 million for the three months ended June 30, 2026, from $6.5 million for the three months ended June 30, 2025. The increase in general and administrative expenses was primarily due to:

Current wording

General and administrative expenses increased by $5.0 million to $12.8 million for the three months ended September 30, 2026, from $7.8 million for the three months ended September 30, 2025. The increase in general and administrative expenses was primarily due to:

Previous wording

Interest income decreased by $1.1 million to $2.6 million for the three months ended June 30, 2026, from $3.7 million for the three months ended June 30, 2025, primarily due to lower average balances of cash, cash equivalents and investments in marketable securities, reflecting the use of such balances to fund operating expenses.

Current wording

Interest income decreased by $1.0 million to $2.4 million for the three months ended September 30, 2026, from $3.5 million for the three months ended September 30, 2025, primarily due to lower average balances of cash, cash equivalents and investments in marketable securities, reflecting the use of such balances to fund operating expenses.

Previous wording

•direct research and development expenses increased by $6.5 million primarily due to an increase in clinical programs and combination development activities; and

Current wording

•direct research and development expenses increased by $8.8 million primarily due to an increase in development activities and activities related to the wind-down of the SION-719 add-on program; and

Previous wording

•unallocated research and development expenses increased by $5.2 million primarily due to a $4.6 million increase in personnel-related expenses including stock-based compensation, driven by an increase in the size of our workforce to support our clinical pipeline.

Current wording

•unallocated research and development expenses increased by $8.9 million primarily due to a $7.9 million increase in personnel-related expenses including stock-based compensation, and restructuring related costs associated with the workforce reduction.

Previous wording

General and administrative expenses increased by $8.7 million to $21.2 million for the six months ended June 30, 2026, from $12.5 million for the six months ended June 30, 2025. The increase in general and administrative expenses was primarily due to:

Current wording

General and administrative expenses increased by $13.8 million to $34.0 million for the nine months ended September 30, 2026, from $20.3 million for the nine months ended September 30, 2025. The increase in general and administrative expenses was primarily due to:

Previous wording

Interest income decreased by $1.3 million to $5.4 million for the six months ended June 30, 2026, from $6.7 million for the six months ended June 30, 2025, primarily due to lower average balances of cash, cash equivalents and investments in marketable securities, reflecting the use of such balances to fund operating expenses.

Current wording

Interest income decreased by $2.3 million to $7.8 million for the nine months ended September 30, 2026, from $10.1 million for the nine months ended September 30, 2025, primarily due to lower average balances of cash, cash equivalents and investments in marketable securities, reflecting the use of such balances to fund operating expenses.

Previous wording

Since our inception, we have not generated any revenue from product sales and have incurred significant operating losses and negative cash flows from operations. We expect to continue to incur significant expenses and operating losses for the foreseeable future as we advance the clinical development of our product candidates and any future product candidates. As such, we expect our research and development and general and administrative costs will continue to increase significantly, including the costs associated with operating as a public company. As a result, we will need additional capital to fund our operations, which we may obtain from additional equity or debt financings or strategic agreements.

Current wording

Since our inception, we have not generated any revenue from product sales and have incurred significant operating losses and negative cash flows from operations. Although we expect our ongoing operating expenses to decrease in the near term as a result of the Restructuring, we expect to continue to incur significant expenses and operating losses for the foreseeable future as we advance the clinical development of our product candidates and maintain the infrastructure necessary to operate as a public company. Our expenses could increase over the longer term if we advance our current or future product candidates into later stages of development or toward commercialization. As a result, we will need additional capital to fund our operations, which we may obtain from additional equity or debt financings or strategic agreements.

Previous wording

In March 2026, we entered into a sales agreement with Leerink to issue and sell shares of our common stock, from time to time, for aggregate gross sale proceeds of up to $250.0 million through an "at the market" equity offering program under which Leerink is acting as sales agent. As of June 30, 2026, we have not sold any shares of common stock under the sales agreement.

Current wording

In March 2026, we entered into a sales agreement with Leerink to issue and sell shares of our common stock, from time to time, for aggregate gross sale proceeds of up to $250.0 million through an "at the market" equity offering program under which Leerink is acting as sales agent. As of September 30, 2026, we had not sold any shares of common stock under the sales agreement.

Previous wording

As of June 30, 2026, we had $268.3 million in cash, cash equivalents and marketable securities.

Current wording

As of September 30, 2026, we had $249.8 million in cash, cash equivalents and marketable securities.

Previous wording

For the six months ended June 30, 2026, net cash used in operating activities was $44.1 million primarily due to our net loss of $56.7 million and changes in operating assets and liabilities of $1.7 million, partially offset by $14.3 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Current wording

For the nine months ended September 30, 2026, net cash used in operating activities was $62.8 million primarily due to our net loss of $89.1 million and changes in operating assets and liabilities of $4.5 million, partially offset by $21.8 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Previous wording

For the six months ended June 30, 2025, net cash used in operating activities was $34.4 million primarily due to our net loss of $34.6 million and changes in operating assets and liabilities of $4.2 million, partially offset by $4.4 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Current wording

For the nine months ended September 30, 2025, net cash used in operating activities was $49.7 million primarily due to our net loss of $54.8 million and changes in operating assets and liabilities of $2.4 million, partially offset by $7.5 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Previous wording

Net cash provided by investing activities was $46.3 million during the six months ended June 30, 2026, which was primarily driven by maturities of marketable securities of $104.6 million, partially offset by purchases of marketable securities of $58.4 million.

Current wording

Net cash provided by investing activities was $85.2 million during the nine months ended September 30, 2026, which was primarily driven by maturities of marketable securities of $154.9 million, partially offset by purchases of marketable securities of $69.7 million.

Previous wording

Net cash used in investing activities was $164.4 million during the six months ended June 30, 2025, which was primarily driven by purchases of marketable securities of $228.0 million, partially offset by maturities of marketable securities of $63.7 million.

Current wording

Net cash used in investing activities was $141.3 million during the nine months ended September 30, 2025, which was primarily driven by purchases of marketable securities of $282.1 million, partially offset by maturities of marketable securities of $141.0 million.

Previous wording

Net cash provided by financing activities was $2.6 million during the six months ended June 30, 2026, primarily due to exercise proceeds totaling $3.2 million, partially offset by payments of deferred offering costs of $0.6 million related to the sales agreement entered into in March 2026.

Current wording

Net cash provided by financing activities was $3.0 million during the nine months ended September 30, 2026, primarily due to exercise proceeds totaling $3.6 million, partially offset by payments of deferred offering costs of $0.6 million related to the sales agreement entered into in March 2026.

Previous wording

Net cash provided by financing activities was $202.1 million during the six months ended June 30, 2025, during which time the Company closed its initial public offering.

Current wording

Net cash provided by financing activities was $204.1 million during the nine months ended September 30, 2025, during which time the Company closed its initial public offering.

Previous wording

As of June 30, 2026, we had cash, cash equivalents and marketable securities of $268.3 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and investments in marketable securities, will be sufficient to fund our operations into 2028. However, our forecast for the period of time through which our financial resources will be adequate to support our operations is a forward-looking statement that involves risks and uncertainties, and actual results could vary materially. Additionally, conducting preclinical studies and clinical trials is costly, and the timing of progress and expenses in these studies and trials is uncertain. We will need to raise substantial additional capital in the future.

Current wording

As of September 30, 2026, we had cash, cash equivalents and marketable securities of $249.8 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and investments in marketable securities, will be sufficient to fund our operations into the second half of 2029. However, our forecast for the period of time through which our financial resources will be adequate to support our operations is a forward-looking statement that involves risks and uncertainties, and actual results could vary materially. Additionally, conducting preclinical studies and clinical trials is costly, and the timing of progress and expenses in these studies and trials is uncertain. We will need to raise substantial additional capital in the future.

Previous wording

During the six months ended June 30, 2026, we evaluated certain contractual arrangements with a contract manufacturing organization and recognized related costs during the period. We evaluate such arrangements on an ongoing basis. Other than this matter, there were no material changes to our contractual obligations and commitments described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.

Current wording

Other than this matter, there were no material changes to our contractual obligations and commitments described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.

Previous wording

During the six months ended June 30, 2026, there were no material changes to our critical accounting estimates described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.

Current wording

During the nine months ended September 30, 2026, there were no material changes to our critical accounting estimates described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.