Definium Therapeutics officer proposes $516K share sale

The notice also lists 13,008 common shares sold on June 25, 2026, for an aggregate market value of $548,027.04.

Rhea-AI Filing Summary

A Form 144 notice concerning Definium Therapeutics, Inc. (DFTX) lists officer Mark Sullivan's proposed sale of 14,051 common shares, with an approximate sale date of September 25, 2026 and an aggregate market value of $516,093.23. Morgan Stanley Smith Barney LLC is named as broker. The securities are described as restricted stock vesting under a registered plan.

Key Figures

Shares listed for sale: 14,051 shares Aggregate market value: $516,093.23 Shares outstanding: 134,367,000 shares +2 more

5 metrics

Shares listed for sale 14,051 shares Approximate sale date: September 25, 2026

Aggregate market value $516,093.23 Shares listed for sale

Shares outstanding 134,367,000 shares Common shares outstanding

Shares sold in prior three months 13,008 shares June 25, 2026

Aggregate market value of prior sale $548,027.04 Sale on June 25, 2026

Key Terms

Rule 144, Restricted Stock Vesting Under a Registered Plan, Registered Plan

3 terms

Rule 144 regulatory

"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.

Restricted Stock Vesting Under a Registered Plan financial

"Restricted Stock Vesting Under a Registered Plan"

Registered Plan financial

"Vesting Under a Registered Plan"

A registered plan is a savings or investment account that a government recognizes for special tax treatment and rules, such as limits on how much you can put in and conditions for withdrawals. For investors it matters because those rules change how much of your gains are taxed, how quickly your money can be accessed and what strategies make sense — like a labeled jar that gives tax breaks but comes with rules about when and how you can take the money out.

FAQ

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

How many DFTX shares does Mark Sullivan plan to sell?

The proposed sale listed for officer Mark Sullivan is 14,051 common shares, with an approximate sale date of September 25, 2026 and an aggregate market value of $516,093.23. Morgan Stanley Smith Barney LLC is named as broker.

How many DFTX shares did Mark Sullivan sell in the prior three months?

The prior-three-months table lists 13,008 common shares sold on June 25, 2026, with an aggregate market value of $548,027.04.

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

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Available on EDGAR 09/25/2026 - 04:34 PM Accepted by SEC EDGAR 09/25/2026 - 04:19 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	0001331843
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	DEFINIUM THERAPEUTICS, INC.
SEC File Number	001-40360
Address of Issuer	ONE WORLD TRADE CENTER SUITE 8500 NEW YORK NEW YORK 10007
Phone	212-220-6633
Name of Person for Whose Account the Securities are To Be Sold	MARK SULLIVAN
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	Officer

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	Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004	14051	516093.23	134367000	09/25/2026	NASDAQ

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	09/25/2026	Restricted Stock Vesting Under a Registered Plan	Issuer			14051	09/25/2026	Services Rendered

* 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

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
MARK SULLIVAN ONE WORLD TRADE CENTER SUITE 8500 NEW YORK NY 10007	Common	06/25/2026	13008	548027.04

144: Remarks and Signature

Remarks
Date of Notice	09/25/2026
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/ Mark Sullivan
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)