RA Capital plans $21.8M Sionna stock sale

Rhea-AI Filing Summary

Sionna Therapeutics, Inc. (SION) received a notice that RA Capital Healthcare Fund, L.P. intends to sell common stock under Rule 144 through Goldman Sachs & Co. The notice covers 3,448,811 shares of common stock, with an aggregate market value of $21,834,318, to be sold on or about September 17, 2026 on Nasdaq.

The fund previously acquired Sionna common shares in private transactions dated February 2, 2022 (606,502 shares) and March 4, 2024 (1,819,723 shares), and in the initial public offering dated February 7, 2025 (1,022,586 shares). Sionna reports 45,212,399 common shares outstanding in connection with this notice.

Key Figures

Shares to be sold under Rule 144: 3,448,811 shares Aggregate market value of shares to be sold: $21,834,318 Shares outstanding: 45,212,399 shares +4 more

7 metrics

Shares to be sold under Rule 144 3,448,811 shares Common stock covered by the notice for sale through Goldman Sachs & Co.

Aggregate market value of shares to be sold $21,834,318 Value of Sionna common stock covered by the Form 144 notice

Shares outstanding 45,212,399 shares Sionna Therapeutics common shares outstanding referenced in the Form 144

Planned sale date September 17, 2026 Approximate date of proposed Rule 144 sale on Nasdaq

Shares acquired on February 2, 2022 606,502 shares Common stock acquired in a private transaction from Sionna Therapeutics

Shares acquired on March 4, 2024 1,819,723 shares Common stock acquired in a private transaction from Sionna Therapeutics

Shares acquired on February 7, 2025 IPO 1,022,586 shares Common stock acquired in Sionna Therapeutics’ initial public offering

Key Terms

Rule 144, Private Transaction, Initial Public Offering, Aggregate Market Value, +1 more

5 terms

Rule 144 regulatory

"See the definition of "person" in paragraph (a) of Rule 144."

Rule 144 is a U.S. securities regulation that sets conditions under which restricted or insider-held shares can be legally resold to the public, such as required holding periods, availability of public information, limits on how much can be sold at once, and certain filing requirements. For investors it matters because it determines when previously locked-up shares can enter the market — like a release valve that can increase supply, affect share price, and signal insider intent.

Private Transaction financial

"Common Stock | 02/02/2022 | Private Transaction | Sionna Therapeutics"

A private transaction is the sale or transfer of securities, assets, or ownership stakes carried out directly between a small number of parties rather than on a public exchange. For investors it matters because these deals are less visible and often less liquid than public trades, so pricing can be harder to verify, the investment can be harder to sell quickly, and buyers or sellers may gain strategic advantages not available in open markets — like negotiated terms similar to a private garage sale versus a crowded marketplace.

Initial Public Offering financial

"Common Stock | 02/07/2025 | InitialPublic Offering | Sionna Therapeutics"

An initial public offering (IPO) is when a private company first sells its shares to the public and becomes a stock-listed company. It matters because it allows the company to raise money from a wide range of investors, helping it grow, while giving early shareholders a way to sell some of their ownership.

Aggregate Market Value financial

"Common Stock | Goldman Sachs & Co ... | 3448811 | 21834318 | 45212399"

Aggregate market value is the combined price you would pay to buy all outstanding shares of a company or all companies in a group at current market prices — essentially the sum of each stock’s market capitalization. It matters to investors because it shows the overall size and weight of an investment or sector (like the total cost to buy every piece of a puzzle), helps compare scale across companies or markets, and influences index composition and risk exposure.

Nasdaq market

"| 45212399 | 09/17/2026 | Nasdaq"

The Nasdaq is a stock exchange where many companies' shares are bought and sold, functioning much like a marketplace for investments. It matters to investors because it provides a platform to buy and sell ownership stakes in companies, helping them track the value of those companies and make informed decisions. As one of the largest and most technology-focused markets, it also reflects trends and developments in the business world.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What does the Form 144 filing mean for SION (Sionna Therapeutics, Inc.)?

It states that RA Capital Healthcare Fund, L.P. has filed a notice of proposed sale under Rule 144 for 3,448,811 shares of Sionna common stock through Goldman Sachs & Co., with an approximate sale date of September 17, 2026 on Nasdaq.

How many SION shares are covered by RA Capital’s planned Rule 144 sale?

The notice covers 3,448,811 shares of Sionna Therapeutics common stock, with an indicated aggregate market value of $21,834,318 in the Form 144 securities information section.

How many SION shares are outstanding according to this Form 144?

The Form 144 lists 45,212,399 Sionna Therapeutics common shares as outstanding in the securities information table associated with the proposed Rule 144 sale.

When were the SION shares to be sold by RA Capital originally acquired?

The securities to be sold were acquired as Sionna common stock on February 2, 2022 (606,502 shares, private transaction), March 4, 2024 (1,819,723 shares, private transaction), and February 7, 2025 (1,022,586 shares, initial public offering).

What is the role of Goldman Sachs & Co. in this SION Form 144 filing?

Goldman Sachs & Co., listed with its New York address, appears as the broker in connection with the proposed Rule 144 sale of 3,448,811 Sionna Therapeutics common shares on Nasdaq.

Who signed the Form 144 related to SION shares?

The Form 144 notice is signed “/s/ Rajeev Shah” on behalf of the selling holder’s account, in connection with the proposed Rule 144 sale of Sionna Therapeutics common stock.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 09/17/2026 - 05:10 PM Accepted by SEC EDGAR 09/17/2026 - 05:10 PM Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001315082
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	SIONNA THERAPEUTICS, INC.
SEC File Number	001-42504
Address of Issuer	21 HICKORY DRIVE, SUITE 500 WALTHAM MASSACHUSETTS 02451
Phone	617-819-2020
Name of Person for Whose Account the Securities are To Be Sold	RA Capital Healthcare Fund, L.P.
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Director
Relationship to Issuer	10% Stockholder

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common Stock	Goldman Sachs & Co 200 West St. New York NY 10282	3448811	21834318	45212399	09/17/2026	Nasdaq GM

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common Stock	02/02/2022	Private Transaction	Sionna Therapeutics			606502	02/02/2022	Wire
Common Stock	03/04/2024	Private Transaction	Sionna Therapeutics			1819723	03/04/2024	Wire
Common Stock	02/07/2025	InitialPublic Offering	Sionna Therapeutics			1022586	02/07/2025	Wire

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Nothing to Report

144: Remarks and Signature

Remarks
Date of Notice	09/17/2026
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ Rajeev Shah
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)