Sionna Therapeutics SEC Filings

Elena Ridloff, CFO & Head of Corporate Development of Sionna Therapeutics, Inc. (SION), reported sales of common stock on August 26-28, 2025 under a Rule 10b5-1 trading plan adopted May 20, 2025. The filings show sales of 3,700 shares on 08/26 at a weighted-average price of $25.13 (prices ranged $25.00–$25.28), 3,618 shares on 08/27 at $25.10 (range $25.00–$25.32), and 16,098 shares on 08/28 at $25.97 (range $25.01–$26.41). Post-transaction beneficial ownership is reported as 67,832 shares after 08/26, 64,214 after 08/27, and 48,116 after 08/28. The Form 4 was submitted by one reporting person and signed by an attorney-in-fact on 08/28/2025.

Sionna Therapeutics (SION) Form 144 shows a proposed sale of 25,000 common shares through Morgan Stanley Smith Barney LLC with an aggregate market value of $601,500. The securities were acquired and are scheduled for sale on 08/26/2025 following an exercise of stock options paid in cash. The filing also records a prior Rule 10b5-1 sale of 25,000 shares on 08/20/2025 that generated $568,715 in gross proceeds. The filing lists total shares outstanding as 44,139,823. The notice includes the standard attestation that the seller does not possess undisclosed material adverse information and references reliance on a 10b5-1 plan where applicable.

Sionna Therapeutics (SION) Form 144 notice reports a proposed sale of 33,000 shares of common stock through Morgan Stanley Smith Barney, with an aggregate market value of $793,980 and an approximate sale date of 08/26/2025 on NASDAQ. The shares were acquired on 06/15/2023 upon exercise of stock options and paid in cash. The filer also disclosed recent Rule 10b5-1 sales by the same account: 17,500 shares sold on 08/20/2025 for $397,152 and 34,500 shares sold on 08/19/2025 for $727,112.80. The filing includes the standard representation that the seller is not aware of undisclosed material adverse information and references a possible 10b5-1 plan adoption date field (not populated in the text provided).

Michael Cloonan, President & CEO and Director of Sionna Therapeutics (SION), reported transactions on 08/20/2025 executed under a Rule 10b5-1 plan. On that date he exercised a non-qualified stock option to acquire 25,000 shares at $6.11 per share, increasing his option-derived common stock to 25,000 shares exercisable and leaving him with 572,343 shares beneficially owned immediately after the acquisition. The option vests monthly in 48 installments following 02/02/2022 and has an expiration in 2032.

Simultaneously, Mr. Cloonan sold 25,000 common shares in multiple transactions at a weighted average price of $22.75 per share (individual sale prices ranged $21.07 to $23.99). After the sale his reported beneficial ownership was 547,343 shares. The filing states these trades were made pursuant to the 10b5-1 plan adopted 05/21/2025 and was signed via attorney-in-fact on 08/21/2025.

Sionna Therapeutics CFO Elena Ridloff reported sales of common stock under a pre-established Rule 10b5-1 trading plan. On 08/19/2025 she sold 34,500 shares at a weighted average price of $21.08 (individual trade prices ranged $20.67 to $21.57), reducing her beneficial ownership to 89,032 shares. On 08/20/2025 she sold an additional 17,500 shares at a weighted average price of $22.69 (individual trade prices ranged $22.00 to $23.355), reducing her beneficial ownership to 71,532 shares. The Form 4 notes the transactions were executed automatically under a plan adopted May 20, 2025, and the report was signed by an attorney-in-fact on 08/21/2025.

Sionna Therapeutics (SION) filed a Form 144 notifying the proposed sale of 17,500 common shares through Morgan Stanley Smith Barney, with an aggregate market value of $375,900.00, and an approximate sale date of 08/20/2025 on NASDAQ. The shares were acquired on 09/20/2022 via previously exercised stock options and paid in cash. The filing shows 44,139,823 shares outstanding. The filing also discloses Rule 10b5-1 sales by Elena Ridloff totaling 34,500 common shares on 08/19/2025 for gross proceeds of $727,112.80. The notice includes the standard representation that the seller is unaware of undisclosed material adverse information.

Sionna Therapeutics (SION) reported a Form 144 notice showing a proposed sale of 25,000 common shares—about 0.057% of the 44,139,823 shares outstanding—via Morgan Stanley Smith Barney on 08/20/2025 on NASDAQ. The filer acquired the shares on 08/20/2025 by exercising stock options and paid cash for them. The aggregate market value of the proposed sale is listed as $537,000.00. The filing notes there were no reported sales in the prior three months. The filer certifies they are not aware of any undisclosed material adverse information and includes the standard Rule 144 and Rule 10b5-1 representations.

Sionna Therapeutics (SION) filing of a Form 144 notifies the proposed sale of 34,500 shares of common stock through Morgan Stanley Smith Barney LLC on 08/19/2025. The shares have an aggregate market value of $737,955.00 and the company reports 44,139,823 shares outstanding. The securities were acquired on 09/20/2022 through previously exercised stock options from the issuer and were paid for in cash. The filer reports "Nothing to Report" for securities sold during the past three months. The notice includes the filers representation that they do not possess undisclosed material adverse information.

Sionna Therapeutics is a clinical-stage biopharmaceutical company focused on NBD1 stabilizers for cystic fibrosis. For the six months ended June 30, 2025 the company reported a net loss of $34.6 million and an accumulated deficit of $215.6 million. As of June 30, 2025 it held $337.3 million in cash, cash equivalents and marketable securities and raised $199.6 million net proceeds from its IPO. Outstanding common shares were 44.139823 million as of August 1, 2025.

Clinically, Sionna announced positive topline Phase 1 data in over 200 healthy volunteers for lead NBD1 stabilizers SION-719 and SION-451: both were generally well tolerated with no serious adverse events or dose-limiting toxicities and met exposure thresholds the company believes support further development. SION-719 is planned to advance to a Phase 2a add-on trial pending a drug-drug interaction study and SION-451 will advance to a Phase 1 dual-combination trial; both initiations are anticipated in the second half of 2025. Management states existing resources are expected to fund operations into 2028.