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424B5 1 tm2618395-1_424b5.htm 424B5 tm2618395-1_424b5 - none - 7.0041183s

The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to these securities has been filed with the Securities and Exchange Commission and is effective. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities and they are not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Filed Pursuant to Rule 424(b)(5)

Registration No. 333-280548

SUBJECT TO COMPLETION, DATED JUNE 22, 2026

PRELIMINARY PROSPECTUS SUPPLEMENT
(to Prospectus dated June 28, 2024)

$500,000,000

Common Shares

Pre-Funded Warrants to Purchase Common Shares

Definium Therapeutics, Inc.

We are offering $500,000,000 of our common shares, without par value, at a public offering price of $ per share and, to certain investors, pre-funded warrants to purchase common shares. The purchase price of each pre-funded warrant will equal the price per share at which the common shares are being sold to the public in this offering, minus $ , which is the exercise price of each pre-funded warrant. This prospectus supplement also relates to the offering of the common shares issuable upon exercise of the pre-funded warrants.

Our common shares are listed on the Nasdaq Global Select Market (“Nasdaq”) under the symbol “DFTX”. The last reported sale price of our common shares on Nasdaq on June 18, 2026 was $24.48 per share. We do not intend to list the pre-funded warrants on Nasdaq, any other national securities exchange or any other nationally recognized trading system.

Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page S-10 of this prospectus supplement, page 8 of the accompanying prospectus and under similar headings in the documents incorporated by reference into this prospectus supplement and the accompanying prospectus.

We are an “emerging growth company” under applicable Securities and Exchange Commission rules and are subject to reduced public company reporting requirements. See “Prospectus Supplement Summary—Implications of Being an Emerging Growth Company.”

Neither the Securities and Exchange Commission nor any state or other securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Per share

Per pre-funded
warrant

Total

Public Offering Price

Underwriting Discounts and Commissions(1)

Proceeds to Definium Therapeutics, Inc. before expenses

(1)

We have agreed to reimburse the underwriters for certain expenses. See “Underwriting” beginning on page S-33 of this prospectus supplement for additional information regarding underwriter compensation.

We have granted the underwriters an option to purchase up to an additional $75,000,000 of common shares from us at the public offering price, less the underwriting discounts and commissions payable by us. This option is exercisable, in whole or in part, for a period of 30 days following the date of this prospectus supplement. If the underwriters exercise the option in full, the total underwriting discounts and commissions payable by us will be approximately $ , and the total proceeds to us, before expenses, will be approximately $ .

Delivery of the common shares and the pre-funded warrants is expected to be made on or about June , 2026.

J.P. Morgan	Jefferies	Leerink Partners	BofA Securities
Evercore ISI		Stifel
Oppenheimer & Co.		LifeSci Capital

Prospectus Supplement dated June , 2026

	ABOUT THIS PROSPECTUS SUPPLEMENT					S-ii
	PROSPECTUS SUPPLEMENT SUMMARY					S-1
	THE OFFERING					S-7
	RISK FACTORS					S-10
	SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS					S-13
	USE OF PROCEEDS					S-16
	DIVIDEND POLICY					S-17
	DILUTION					S-18
	DESCRIPTION OF THE SECURITIES WE ARE OFFERING					S-20
	CERTAIN CANADIAN FEDERAL INCOME TAX CONSIDERATIONS					S-23
	CERTAIN U.S. FEDERAL INCOME TAX CONSIDERATIONS					S-25
	UNDERWRITING					S-33
	LEGAL MATTERS					S-39
	EXPERTS					S-39
	WHERE YOU CAN FIND MORE INFORMATION					S-39
	INCORPORATION OF CERTAIN INFORMATION BY REFERENCE					S-40
	ENFORCEABILITY OF CIVIL LIABILITIES					S-41

	ABOUT THIS PROSPECTUS					ii
	SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS					1
	MARKET, INDUSTRY AND OTHER DATA					3
	THE COMPANY					4
	RISK FACTORS					8
	USE OF PROCEEDS					9
	SELLING SECURITYHOLDERS					10
	PLAN OF DISTRIBUTION					11
	GENERAL DESCRIPTION OF OUR SECURITIES					14
	DESCRIPTION OF OUR COMMON SHARES					15
	DESCRIPTION OF OUR WARRANTS					16
	DESCRIPTION OF OUR DEBT SECURITIES					18
	DESCRIPTION OF OUR UNITS					23
	WHERE YOU CAN FIND MORE INFORMATION					24
	INCORPORATION BY REFERENCE					24
	LEGAL MATTERS					24
	EXPERTS					25

Endpoint	DT120 ODT 100 µg	Placebo ODT	Placebo-Adjusted Difference
MADRS: LS mean change at Week 6*	-13.3	-5.2	-8.1 (p<0.0001)
MADRS: LS mean change at Week 12**	-11.0	-3.6	-7.3 (p<0.0001)
MADRS: LS mean change at Week 1**	-17.6	-3.4	-14.2 (p<0.0001)
CGI-S: LS mean change at Week 6**	-1.2	-0.3	-0.9 (p<0.0001)

Public offering price per common share			$
Net tangible book value per common share as of March 31, 2026	$	2.49
Increase per common share attributable to sale of common shares in this offering
As adjusted net tangible book value per common share after this offering
Dilution per common share to new investors in this offering			$

Name	Number of common shares	Number of pre-funded warrants
J.P. Morgan Securities LLC
Jefferies LLC
Leerink Partners LLC
BofA Securities, Inc.
Evercore Group L.L.C.
Stifel, Nicolaus & Company, Incorporated
Oppenheimer & Co. Inc.
LifeSci Capital LLC
Total

SEC Form 424B5 filed by Definium Therapeutics Inc.