UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): August 8, 2025

Assembly Biosciences, Inc.

(Exact name of Registrant as Specified in Its Charter)

Delaware

001-35005

20-8729264

(State or Other Jurisdiction

of Incorporation)

(Commission

File Number)

(IRS Employer

Identification No.)

Two Tower Place, 7th Floor,

South San Francisco, California

94080

(Address of Principal Executive Offices)

(Zip Code)

Registrant’s Telephone Number, Including Area Code: (833) 509-4583

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading

Symbol(s)

Name of each exchange

on which registered

Common Stock, par value $0.001

ASMB

The Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 7.01 Regulation FD Disclosure.

On August 8, 2025, Assembly Biosciences, Inc. (the “Company”) issued a press release announcing interim results from the Phase 1b portion of its ongoing Phase 1a/b clinical study evaluating ABI-5366, an investigational long-acting herpes simplex virus (“HSV”) helicase-primase inhibitor candidate for recurrent genital herpes (the “ABI-5366 Study”). A copy of the press release is attached as Exhibit 99.1 and is incorporated herein by reference.

The information in this Item 7.01 is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section, nor shall it be deemed incorporated by reference into any registration statement or other filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Item 8.01 Other Events.

The Company announced interim results from the ABI-5366 Study. For the powered antiviral endpoint, HSV type 2 (“HSV-2”) shedding rate, highly potent antiviral activity was observed with a 94% reduction compared to placebo (p<0.01) over the 29-day evaluation period in the cohort evaluating a 350 mg weekly dose. This reduction exceeds our target for the study of an 80%-85% reduction in the rate of HSV-2 shedding.

For a secondary clinical endpoint of genital lesion rate, a 94% reduction compared to placebo (p<0.01) was observed with the 350 mg weekly dose. The rate of samples with high viral load (i.e., >10⁴ copies/mL HSV DNA), a potential surrogate for HSV-2 transmission and a secondary endpoint, was reduced by 98% compared to placebo (p<0.05) in this cohort.

ABI-5366 was observed to be well-tolerated at oral doses up to 350 mg weekly in participants seropositive for HSV-2 with recurrent genital herpes. The observed pharmacokinetic profile continues to support once-weekly dosing and the potential for once-monthly oral dosing regimens. With these data, the Company expects to move directly into Phase 2 clinical study preparation in parallel with completion of this Phase 1b study, which includes an ongoing cohort evaluating a monthly oral dosing regimen. The in-life portions of chronic toxicology studies of ABI-5366 are now complete and these studies are expected to support longer-term dosing in Phase 2.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.


Exhibit Number		Description

99.1		Press Release dated August 8, 2025.

104		Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

Assembly Biosciences, Inc.

Date: August 8, 2025

/s/ John O. Gunderson

John O. Gunderson

VP, General Counsel and Corporate Secretary

ASSEMBLY BIOSCIENCES, INC. 8-K