Sionna Therapeutics SEC Filings

Sionna Therapeutics (SION) reported insider activity on a Form 4 showing that RA Capital–affiliated entities, which are identified as both directors and 10% owners, sold shares of Sionna common stock over several days. On November 17, 2025, they executed multiple sales, including a sale of 17,913 shares of common stock at a weighted average price of $40.2 per share, in transactions within a price range of $40.00 to $40.85.

Additional sales took place on November 17–19, 2025 at weighted average prices described in the footnotes as ranging from $39.40 to $42.13 per share, all through various RA Capital funds and accounts. The filing notes that detailed breakdowns of the individual trade prices within each range are available upon request, and that the RA Capital entities and individuals disclaim beneficial ownership beyond their economic interest.

Sionna Therapeutics (SION) filed its Q3 2025 10‑Q, reporting a net loss of $20.3 million for the quarter and $54.8 million year-to-date as it advances cystic fibrosis programs. Cash, cash equivalents and marketable securities totaled $325.0 million as of September 30, 2025, supported by the February IPO.

Quarterly operating expenses were $23.8 million, including research and development $16.0 million and general and administrative $7.8 million. Interest income was $3.5 million. The company completed an IPO at $18.00 per share for net proceeds of approximately $199.6 million, and its preferred stock converted into 27,149,206 common shares. Shares outstanding were 44,628,788 as of October 31, 2025.

Sionna initiated a Phase 2a trial of SION‑719 as an add‑on to standard of care and a Phase 1 dual‑combination study with SION‑451, with topline data anticipated in mid‑2026. Management believes existing liquidity funds operations beyond twelve months and, based on current plans, into 2028.

Sionna Therapeutics (SION): RA Capital–affiliated reporting persons disclosed open‑market sales of common stock. Trades occurred on 10/24/2025 at $39.50 and on 10/28/2025 at a weighted average price of $39.58, with individual transactions ranging from $39.50 to $39.81.

Following the 10/28 transactions, indirect holdings reported included 6,905,625 shares (RA Capital Healthcare Fund, L.P.) and 715,988 shares (RA Capital Nexus Fund, L.P.), plus 2,240,708 shares (Nexus Fund III) and 209,391 shares (a separately managed account). The filing identifies the reporting persons as Director and 10% Owner where indicated, and notes that a partner of the adviser serves on the board.

Sionna Therapeutics (SION) President & CEO (also a Director) reported option exercises and open‑market sales on 10/21/2025 under a pre‑established Rule 10b5‑1 trading plan adopted on May 21, 2025.

The executive exercised non‑qualified stock options at $6.11 per share and sold the resulting shares at weighted average prices of $34.44, $35.63, $36.60, and $37.31 (each comprising multiple trades within stated ranges). Following these transactions, the reporting person directly owned 547,343 shares. The options exercised were from grants expiring on March 1, 2032, with vesting in forty‑eight equal monthly installments following February 2, 2022.

Sionna Therapeutics (SION): Director Form 4 discloses Rule 10b5‑1 sales. On 10/21/2025, indirect holdings associated with the reporting person sold multiple blocks of common stock via pre‑planned trades. Examples include 22,339 shares at a weighted average $32.69, 19,948 shares at $33.87, 5,763 shares at $34.91, and 25,327 shares at $35.69. Prices reflect weighted averages from disclosed ranges. Following these transactions, shares indirectly held by funds were 2,309,035 for Atlas Venture Fund XI, L.P. and 686,567 for Atlas Venture Opportunity Fund II, L.P., as reported.

Sionna Therapeutics (SION) director reported open‑market sales of common stock executed under Rule 10b5‑1 trading plans. The filings list multiple sales on 10/16/2025, 10/17/2025, and 10/20/2025 at weighted average prices disclosed for each tranche.

Examples include 73,296 shares at $32.84 and 45,117 shares at $31.69 by Atlas Venture Fund XI, L.P., and 15,384 shares at $32.84 and 9,470 shares at $31.69 by Atlas Venture Opportunity Fund II, L.P. Following the reported transactions, Atlas Venture Fund XI, L.P. held 2,382,495 shares and Atlas Venture Opportunity Fund II, L.P. held 701,985 shares, each reported as indirect holdings.

The footnotes state the plans were adopted on February 25, 2025 and that prices reflect weighted averages across ranges for each trade date.

Sionna Therapeutics (SION) — insider transaction update: The President & CEO, who also serves as a director, reported option exercises and corresponding open‑market sales under a Rule 10b5‑1 trading plan adopted on May 21, 2025.

On 10/15/2025, 14,775 shares were acquired via option exercise at $6.11 and sold the same day at a weighted average price of $31.1108. On 10/16/2025, 10,225 shares were acquired via option exercise at $6.11 and sold at a weighted average price of $31.4612, and an additional 200 shares were exercised at $6.11 and sold at $34. Following these transactions, common stock beneficially owned directly was 547,343 shares. Derivative holdings show 152,942 non‑qualified stock options beneficially owned following the reported transactions.

Sionna Therapeutics (SION) disclosed insider activity on a Form 4. A director reported open‑market sales of common stock on 10/10, 10/13, 10/14, and 10/15/2025, executed under Rule 10b5‑1 trading plans adopted on February 25, 2025 by Atlas Venture Fund XI, L.P. and Atlas Venture Opportunity Fund II, L.P.

Examples: on 10/15, Atlas Venture Fund XI, L.P. sold 65,726 shares at a weighted average price of $30.37 (range $29.95–$30.94) and 30,032 shares at $31.12 (range $30.95–$31.30). Atlas Venture Opportunity Fund II, L.P. sold 13,795 shares at $30.37 and 6,303 shares at $31.12. Following the reported transactions, indirect holdings were 2,619,185 shares (Atlas Venture Fund XI, L.P.) and 751,664 shares (Atlas Venture Opportunity Fund II, L.P.).