Item 1.01. Entry into a Material Definitive Agreement.
On July 11, 2018, Assembly Biosciences, Inc. (the “Company”)
entered into an underwriting agreement (the “Underwriting Agreement”) with Jefferies LLC, Leerink Partners LLC and
William Blair & Company, L.L.C., as representatives of the several underwriters listed in Schedule 1 thereto (the “Underwriters”),
in connection with the issuance and sale of 4,000,000 shares of the Company’s common stock, par value $0.001 per share (the
“Common Stock”), at a public offering price of $36.00 per share (the “Offering”). In addition, pursuant
to the Underwriting Agreement, the Company granted the Underwriters a 30-day option to purchase up to 600,000 additional shares
of Common Stock on the same terms, and the Underwriters exercised the option in full on July 12, 2018 (the “Option Exercise”).
The Company received net proceeds of approximately $155.4 million from the Offering and the Option Exercise, after deducting underwriting
discounts and commissions and estimated offering expenses payable by the Company.
The Underwriting Agreement contains customary representations,
warranties, covenants and conditions. In the Underwriting Agreement, the Company agreed to indemnify the Underwriters against certain
liabilities that could be incurred by them in connection with the Offering.
The Offering was made pursuant to (i) an effective Registration
Statement on Form S-3 (File No. 333-208806) filed with the Securities and Exchange Commission (the “SEC”) on December
30, 2015, including a related base prospectus dated January 19, 2016, (ii) an effective Registration Statement on Form S-3 (File
No. 333-222366) filed with the SEC on December 29, 2017, including a related base prospectus dated January 10, 2018, and (ii) a
related prospectus supplement dated July 11, 2018 and filed with the SEC pursuant to Rule 424(b)(5) under the Securities Act of
1933, as amended. The closing of the sale of the shares contemplated by the Underwriting Agreement occurred on July 16, 2018.
The foregoing summary of the Underwriting Agreement is qualified
in its entirety by reference to the Underwriting Agreement attached hereto as Exhibit 1.1 hereto and is incorporated herein by
reference.
The Company issued press releases on
July 10, 2018, July 11, 2018 and July 16, 2018 announcing the commencement of the Offering, the pricing of the Offering and the
closing of the Offering, respectively, which press releases are attached as Exhibits 99.1, 99.2 and 99.3, respectively, to this
report.