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”) patients by developing novel medicines that normalize the function of the cystic fibrosis transmembrane conductance regulator (“CFTR”) protein to deliver clinically meaningful benefit to CF patients. Our goal is to deliver differentiated medicines for people living 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 CF patients.

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 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.

Previous wording

We believe our robust pipeline of NBD1 stabilizers and complementary CFTR modu lators provide multiple potential pathways to achieving our goal, either in combination with each other to produce a proprietary dual combination CF therapy, or an NBD1 stabilizer in combination with the current standard of care for CF.

Current wording

We believe our robust pipeline provides multiple potential pathways to achieve our mission, either through development of an NBD1 stabilizer and a complementary modulator in combination with each other to produce a proprietary dual combination, or an NBD1 stabilizer administered in combination with the standard of care for CF. While we have prioritized development of a proprietary dual combination, we believe both development pathways offer attractive commercial opportunities.

Previous wording

In June 2025, we announced positive topline data from our two randomized, double-blinded, placebo-controlled Phase 1 clinical trials evaluating SION-719 and SION-451, our lead NBD1 stabilizer product candidates, in over 200 healthy volunteers, and our plans to advance both compounds to the next phase of clinical development. The trials assessed the safety, tolerability, and pharmacokinetics ("PK") of single and multiple ascending doses of each product candidate, as well as food effect and tablet bioequivalence.

Current wording

In June 2025, we announced positive topline data from our two randomized, double-blinded, placebo-controlled Phase 1 clinical trials evaluating SION-719 and SION-451, our lead NBD1 stabilizer product candidates, in healthy volunteers, and our plans to advance both compounds to the next phase of clinical development. The trials assessed the safety, tolerability, and pharmacokinetics ("PK") of single and multiple ascending doses of each product candidate, as well as food effect and tablet bioequivalence.

Previous wording

Both SION-719 and SION-451 were generally well tolerated in these trials, with no serious adverse events, treatment emergent adverse events that led to discontinuation of drug, or dose-limiting toxicities observed. The Phase 1 data also supported the use of a tablet formulation in future trials and indicated that both compounds could be dosed in a fed or fasted state. Both NBD1 stabilizers met target exposure thresholds. Based on the Phase 1 data and our preclinical CF human bronchial epithelial ("CFHBE") model, we believe our NBD1 stabilizers have the potential to provide clinically meaningful benefit, including the potential to restore CFTR function up to wild-type levels, when SION-719 is administered as an add-on to the standard of care or when SION-451 is used in proprietary dual combinations with one of our complementary modulators.

Current wording

Both SION-719 and SION-451 were generally well tolerated in these trials, with no serious adverse events, treatment emergent adverse events that led to discontinuation of drug, or dose-limiting toxicities observed. The Phase 1 data also supported the use of a tablet formulation in future trials and indicated that both compounds could be dosed in a fed or fasted state. Both NBD1 stabilizers met target exposure thresholds. Based on the Phase 1 data and our preclinical CF human bronchial epithelial ("CFHBE") model, we believe our NBD1 stabilizers have the potential to provide clinically meaningful benefit for people with CF when SION-719 is administered as an add-on to the standard of care or when SION-451 is used in proprietary dual combinations with one of our complementary modulators.

Previous wording

In October 2025, we announced the initiation of a Phase 2a proof-of-concept trial in CF patients evaluating SION-719 as an add-on to the standard of care. The Phase 2a trial, called PreciSION CF, is designed to evaluate the safety, tolerability, and PK of SION-719 when administered with the standard of care for CF, Vertex Pharmaceuticals, Inc.'s Trikafta, and to assess change in CFTR function as measured by sweat chloride levels. Prior to initiation, we completed a drug-drug interaction study, which confirmed SION-719 can be dosed with Trikafta according to its label. Additionally, in August 2025, we announced the initiation of a Phase 1 dual combination trial in healthy volunteers evaluating SION-451 in dual combinations with each of galicaftor (SION-2222) and SION-109, two of our complementary CFTR modulators. The trial will evaluate the safety, tolerability, and PK of varying doses of the dual combinations and will inform selection of a dual combination for further development. Topline data from both trials are anticipated in mid-2026.

Current wording

In April 2026, we announced the completion of enrollment in our Phase 2a proof-of-concept trial in CF patients evaluating SION-719 as an add-on to the standard of care. The Phase 2a trial, called PreciSION CF, is designed to evaluate the safety, tolerability, and PK of SION-719 when administered with the standard of care for CF, Vertex Pharmaceuticals, Inc.'s Trikafta, and to assess change in CFTR function as measured by sweat chloride levels. Additionally, in August 2025, we announced the initiation of a Phase 1 dual combination trial in healthy volunteers evaluating SION-451 in dual combinations with each of SION-2222 and SION-109, two of our complementary CFTR modulators. The trial will evaluate the safety, tolerability, and PK of varying doses of the dual combinations and will inform selection of a dual combination for further development. Topline data from both trials are anticipated in the summer of 2026.

Previous wording

Since our inception in 2019, we have not generated any revenue. We have historically funded our operations primarily with proceeds from the sale and issuance of our preferred stock. As of September 30, 2025, we raised aggregate net proceeds of$330.4 million from the sale and issuance of our preferred stock. In February 2025, we completed our initial public offering ("IPO") and raised aggregate net proceeds of$199.6 million from the sale of 12,176,467 shares of common stock, which included 1,588,234 shares of common stock sold pursuant to the underwriters' full exercise of their option to purchase additional shares.

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 March 31, 2026, we have not sold any shares of common stock under the sales agreement. As of March 31, 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 $54.8 million and $45.8 million for the nine months ended September 30, 2025, and 2024, respectively. As of September 30, 2025, we had an accumulated deficit of $235.9 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 $26.8 million and $16.5 million for the three months ended March 31, 2026, and 2025, respectively. As of March 31, 2026, we had an accumulated deficit of $283.1 million.

Previous wording

As of September 30, 2025, we had cash, cash equivalents and marketable securities of $325.0 million. Based upon our current operating plans, we believe that with 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. In addition, we could utilize 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 March 31, 2026, we had cash, cash equivalents and marketable securities of $289.9 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. In addition, we could utilize 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

Research and development expenses consist primarily of costs associated with the preclinical and clinical development of our current and potential future product candidates. In particular, our research and development expenses include:

Current wording

Research and development expenses consist primarily of costs associated with the preclinical and clinical development of our current and potential future product candidates. In particular, our research and development expenses may include:

Previous wording

•external expenses, including expenses incurred under arrangements with third parties, such as contract research organizations (“CROs”), contract development and manufacturing organizations (“CDMOs”), consultants and our scientific advisors;

Current wording

•external expenses, including expenses incurred under arrangements with third parties, such as contract research organizations, contract development and manufacturing organizations, consultants and our scientific advisors;

Previous wording

(1)NBD1 and combination development program costs include NBD1 stabilizer activities and development of our proprietary combination therapy. Complementary modulator program costs include manufacturing expenses for the complementary modulators.

Current wording

(1)NBD1 and combination development program costs include NBD1 stabilizer activities and development of our proprietary combination therapy.

Previous wording

Research and development expenses increased by $2.1 million to $45.1 million for the nine months ended September 30, 2025, from $43.0 million for the nine months ended September 30, 2024. The increase in research and development expenses was primarily due to:

Current wording

Research and development expenses increased by $5.3 million to $19.0 million for the three months ended March 31, 2026, from $13.7 million for the three months ended March 31, 2025. The increase in research and development expenses was primarily due to:

Previous wording

•direct research and development expenses increased by $3.1 million primarily due to an increase in clinical programs and combination development activities; and

Current wording

•direct research and development expenses increased by $2.5 million primarily due to an increase in clinical programs and combination development activities; and

Previous wording

•unallocated research and development expenses decreased by $11.6 million primarily due to IPR&D acquisition costs incurred in connection with our license agreement with AbbVie of $13.6 million in the third quarter of 2024, partially offset by a $1.5 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 $2.7 million primarily due to a $2.3 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.

Previous wording

General and administrative expenses increased by $4.4 million to $7.8 million for the three months ended September 30, 2025, from $3.4 million for the three months ended September 30, 2024. The increase in general and administrative expenses was primarily due to:

Current wording

General and administrative expenses increased by $4.6 million to $10.6 million for the three months ended March 31, 2026, from $6.0 million for the three months ended March 31, 2025. The increase in general and administrative expenses was primarily due to:

Previous wording

As of September 30, 2025, we had $325.0 million in cash, cash equivalents and marketable securities.

Current wording

As of March 31, 2026, we had $289.9 million in cash, cash equivalents and marketable securities.

Previous 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.

Current wording

For the three months ended March 31, 2026, net cash used in operating activities was $21.8 million primarily due to our net loss of $26.8 million and changes in operating assets and liabilities of $2.1 million, partially offset by $7.0 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 nine months ended September 30, 2024, net cash used in operating activities was $41.0 million primarily due to our net loss of $45.8 million and changes in operating assets and liabilities of $6.2 million, partially offset by $11.0 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense, non-cash expense related to IPR&D acquisition and amortization of discounts on marketable securities.

Current wording

For the three months ended March 31, 2025, net cash used in operating activities was $16.3 million primarily due to our net loss of $16.5 million and changes in operating assets and liabilities of $1.9 million, partially offset by $2.0 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 used in investing activities was $142.1 million during the nine months ended September 30, 2024, due to purchases of marketable securities of $175.6 million, partially offset by maturities of marketable securities of $33.5 million.

Current wording

Net cash provided by investing activities was $24.8 million during the three months ended March 31, 2026, which was primarily driven by maturities of marketable securities of $50.1 million, partially offset by purchases of marketable securities of $25.3 million.

Previous 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 and purchases of property and equipment of $0.2 million, partially offset by maturities of marketable securities of $141.0 million.

Current wording

Net cash used in investing activities was $141.2 million during the three months ended March 31, 2025, which was primarily driven by purchases of marketable securities of $171.6 million, partially offset by maturities of marketable securities of $30.5 million.

Previous wording

Net cash provided by financing activities was $180.4 million during the nine months ended September 30, 2024, during which time the Company closed its Series C Financing.

Current wording

Net cash provided by financing activities was $202.4 million during the three months ended March 31, 2025, during which time the Company closed its initial public offering.

Previous wording

As of September 30, 2025, we had cash, cash equivalents and marketable securities of $325.0 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 March 31, 2026, we had cash, cash equivalents and marketable securities of $289.9 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.

Previous wording

During the nine months ended September 30, 2025, 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

During the three months ended March 31, 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.

Previous wording

During the nine months ended September 30, 2025, 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 three months ended March 31, 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.

Previous wording

We will remain an emerging growth company until the earlier of (1) the last day of the fiscal year (a) following the fifth anniversary of the completion of our IPO, (b) in which we have total annual gross revenue of at least $1.235 billion or (c) in which we are deemed to be a “large accelerated filer” under the rules of the SEC, which means, among other things, the market value of our common stock that is held by non-affiliates exceeds

Current wording

We will remain an emerging growth company until the earlier of (1) the last day of the fiscal year (a) following the fifth anniversary of the completion of our initial public offering, (b) in which we have total annual gross revenue of at least $1.235 billion or (c) in which we are deemed to be a “large accelerated filer” under the rules of the SEC, which means, among other things, the market value of our common stock that is held by non-affiliates exceeds $700.0 million as of the last business day of our most recently completed second fiscal quarter and (2) the date on which we have issued more than $1.0 billion in non-convertible debt during the prior three-year period.