Parabilis Medicines, Inc.

S-11 ck0001657677-20260519.htm S-1

As filed with the Securities and Exchange Commission on May 19, 2026.

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

d

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

(Exact name of registrant as specified in its charter)

Cambridge, MA 02140

(617) 945-9510

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Mathai Mammen, M.D., Ph.D.

Chief Executive Officer

Cambridge, MA 02140

(617) 945-9510

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public: As soon as practicable after this registration statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box:☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

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 7(a)(2)(B) of the Securities Act.☐

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state or other jurisdiction where the offer or sale is not permitted.

Subject to Completion, Dated May 19, 2026

PRELIMINARY PROSPECTUS

Shares

This is an initial public offering of shares of common stock of Parabilis Medicines, Inc. We are offering shares of our common stock.

Following this offering, we will have two classes of common stock: the voting common stock offered hereby and non-voting common stock. For a description of the rights of the voting common stock and non-voting common stock, see the section titled “Description of Capital Stock” beginning on page 201 of this prospectus. We are offering voting common stock in this offering, and unless otherwise noted, all references in this prospectus to our “common stock,” “common shares” or “shares” refer to our voting common stock.

Prior to this offering, there has been no public market for our common stock. It is currently estimated that the initial public offering price per share will be between $ and $ . We have applied to list our common stock on The Nasdaq Global Market under the symbol “PBLS”. We believe that upon the completion of this offering, we will meet the standards for listing on The Nasdaq Global Market, and the completion of this offering is contingent upon such listing.

We are an “emerging growth company” and “smaller reporting company” as defined under the U.S. federal securities laws and, as such, we have elected to comply with certain reduced public company reporting requirements in this prospectus and future filings.

Investing in our common stock involves a high degree of risk. See the section titled “Risk Factors” beginning on page 15 to read about factors you should carefully consider before deciding to invest in shares of our common stock.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

(1)

See the section titled “Underwriting” for additional information regarding compensation payable to the underwriters.

We have granted the underwriters the option to purchase up to an additional shares of common stock from us, at the initial public offering price, less the underwriting discounts and commissions.

In connection with our strategic research collaboration, Regeneron Pharmaceuticals, Inc. ("Regeneron") has agreed to purchase approximately $75.0 million of shares of our common stock in a concurrent private placement exempt from the registration requirements of the Securities Act of 1933, as amended, at a per share price equal to 90% of the initial public offering price (or shares based on the assumed initial public offering price of $ per share, which is the midpoint of the price range set forth above). The private placement would close concurrently with, and be contingent and conditioned upon consummation of, this offering; however, this offering is not contingent on the consummation of the concurrent private placement. In connection with the concurrent private placement, we expect to enter into a stock purchase agreement with Regeneron. The underwriters of this offering will not receive any fee in connection with the concurrent private placement.

The underwriters expect to deliver the shares against payment on or about , 2026.

Prospectus dated , 2026