# EDGAR Filing Document

**Accession Number:** 0001728117
**File Stem:** 0001728117-25-000040
**Filing Date:** 2025-6
**Character Count:** 13983
**Document Hash:** e109fee6e1d852aebdde9ffdd515c761
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001728117-25-000040.hdr.sgml**: 20250616

**ACCESSION NUMBER**: 0001728117-25-000040

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 14

**CONFORMED PERIOD OF REPORT**: 20250616

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Other Events

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20250616

**DATE AS OF CHANGE**: 20250616

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Gossamer Bio, Inc.
- **CENTRAL INDEX KEY:** 0001728117
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 475461709
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-38796
- **FILM NUMBER:** 251048535

**BUSINESS ADDRESS:**
- **STREET 1:** 3115 MERRYFIELD ROW
- **STREET 2:** SUITE 120
- **CITY:** SAN DIEGO
- **STATE:** CA
- **ZIP:** 92121
- **BUSINESS PHONE:** (858) 684-1300

**MAIL ADDRESS:**
- **STREET 1:** 3115 MERRYFIELD ROW
- **STREET 2:** SUITE 120
- **CITY:** SAN DIEGO
- **STATE:** CA
- **ZIP:** 92121

?xml version='1.0' encoding='ASCII'? goss-20250616

**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): June 16, 2025**

 

**GOSSAMER BIO, INC.**

**(Exact name of Registrant as Specified in Its Charter)**

 

---

| | | |
|:---|:---|:---|
| **Delaware** | **001-38796** | **47-5461709** |
| **(State or Other Jurisdiction<br>of Incorporation)** | **(Commission File Number)** | **(IRS Employer<br>Identification No.)** |

---

**3115 Merryfield Row, Suite 120**

**San Diego, California, 92121**

**(Address of Principal Executive Offices) (Zip Code)**

**(858) 684-1300**

**(Registrant's Telephone Number, Including Area Code)**

**N/A**

**(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 (see General Instructions A.2. below):

☐ 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:

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| | | |
|:---|:---|:---|
| **Title of each class** | **Trading<br>Symbol(s)** | **Name of each exchange on which registered** |
| Common Stock, $0.0001 par value per share | GOSS | 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. ☐

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**Item 7.01 Regulation FD Disclosure.**

On June 16, 2025, Gossamer Bio, Inc. (the "Company") issued a press release reporting the completion of enrollment for the ongoing, global registrational Phase 3 PROSERA Study evaluating seralutinib in Functional Class II and III pulmonary arterial hypertension (PAH) patients discussed in Item 8.01 below. The full text of the press release is attached as Exhibit 99.1 to this Current Report.

The information contained in this Item 7.01, including in Exhibit 99.1 hereto, is being "furnished" and shall not be deemed "filed" for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, is not subject to the liabilities of that section and is not deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended, except as shall be expressly set forth by specific reference in such a filing.

**Item 8.01 Other Events.**

On June 16, 2025, the Company announced the completion of enrollment for the ongoing, global registrational Phase 3 PROSERA Study evaluating seralutinib in Functional Class II and III PAH patients. The patient population enrolled in PROSERA aligns with the target demographic, as evidenced by the preliminary baseline characteristics. The PROSERA Study utilizes enrichment criteria, including the REVEAL Lite 2 Risk Score and other criteria, to identify patients more likely to show a greater magnitude of effect on 6MWD at week 24, as informed by the Phase 2 TORREY study.

**Seralutinib Clinical Trial Baseline Characteristics: Phase 3 PROSERA Study v. Phase 2 TORREY Study**

---

| | | |
|:---|:---|:---|
| | PROSERA Phase 3\* | TORREY Phase 2 |
| Study Participants | n = 390 | n = 86 |
| Mean 6MWD | 374 meters | 408 meters |
| Mean NT-proBNP | 987 ng/L | 628 ng/L |
| Functional Class III Patients | 289 (74%) | 36 (42%) |
| Geographic Distribution | North America: 75 (19%)<br>Rest of World: 315 (81%) | North America: 59 (69%)<br>Rest of World: 27 (31%) |
| *\*Baseline characteristics are preliminary and subject to change.* | *\*Baseline characteristics are preliminary and subject to change.* | *\*Baseline characteristics are preliminary and subject to change.* |

---

The Company expects to announce topline results from the ongoing Phase 3 PROSERA Study in February 2026.

**Item 9.01 Financial Statements and Exhibits.**

(d) Exhibits.

---

| | |
|:---|:---|
| **Exhibit<br>Number** | **Description** |
| 99.1 | <u>[Press Release](goss-20250616xexx991.htm)</u> <u>dated June 16, 2025</u>  |
| 101 | Cover Page Interactive Data File (embedded within the Inline XBRL document) |

---

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**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.

---

| | | |
|:---|:---|:---|
| | GOSSAMER BIO, INC. | GOSSAMER BIO, INC. |
| Date: June 16, 2025 | By: | /s/ Bryan Giraudo |
|  |  | Bryan Giraudo |
|  |  | Chief Financial Officer and Chief Operating Officer |

---

## Exhibit 99.1

**Exhibit 99.1**

![newgosslogoa.jpg](newgosslogoa.jpg)

**Gossamer Bio Announces Completion of Enrollment in Registrational Phase 3 PROSERA Study for the Treatment of PAH**

*- Enrollment Completed in Ongoing Registrational PROSERA Phase 3 Study in PAH -*

*- Topline Results Announcement from PROSERA Phase 3 Expected in February 2026 -*

*- Blinded Preliminary Baseline Characteristics Align with Intended Study Population -*

SAN DIEGO—(BUSINESS WIRE)— June 16<sup>th</sup>, 2025 — Gossamer Bio, Inc. (Nasdaq: GOSS), a late-stage, clinical biopharmaceutical company focused on the development and commercialization of seralutinib for the treatment of pulmonary arterial hypertension (PAH) and pulmonary hypertension associated with interstitial lung disease (PH-ILD), today announced enrollment completion for the ongoing, global registrational Phase 3 PROSERA Study evaluating seralutinib in Functional Class II and III PAH patients. Gossamer Bio and the Chiesi Group are jointly developing seralutinib under a global collaboration agreement.

"Completing enrollment for the Phase 3 PROSERA Study represents an important step forward in our mission to develop seralutinib as a potential first-in-class treatment option for PAH," said Faheem Hasnain, CEO, Chairman and Co-founder of Gossamer Bio. "We are deeply grateful to the patients, caregivers, and investigators who made this possible through their dedication and partnership."

Mr. Hasnain continued, "Building on insights from the Phase 2 TORREY Study, we focused on selecting a patient population that aligns closely with the study's objectives and is more likely to exhibit a clinically significant benefit in 24 weeks. Given the preliminary baseline characteristics of PROSERA, we firmly believe that we have accomplished this patient selection goal. We are eager to be able to share topline results from this registrational study early next year."

Enrollment in the ongoing Phase 3 PROSERA Study was closed on June 11th. The Phase 3 PROSERA Study is a double-blind, placebo-controlled, global registrational clinical trial evaluating seralutinib in PAH patients, on top of background PAH therapy. Patients are assigned 1:1 to either the seralutinib or placebo arms. Patients receive blinded treatment for up to 48 weeks.

The primary endpoint of the PROSERA Study is change in six-minute walk distance (6MWD) from baseline as compared to placebo at week 24. Included in the key secondary endpoints is time to clinical worsening, as compared to placebo, up to week 48. In addition to other secondary and exploratory endpoints, safety and tolerability will be evaluated.

The patient population enrolled in PROSERA aligns with the target demographic, as evidenced by the preliminary baseline characteristics. The PROSERA Study utilizes enrichment criteria, including the REVEAL Lite 2 Risk Score and other criteria, to identify patients more likely to show a greater magnitude of effect on 6MWD at week 24, as informed by the Phase 2 TORREY study. We expect to announce topline results from the ongoing Phase 3 PROSERA Study in February 2026.

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**Baseline Characteristics: PROSERA Study (Phase 3) v. TORREY Study (Phase 2)**

---

| | | |
|:---|:---|:---|
| | PROSERA Phase 3\* | TORREY Phase 2 |
| Study Participants | n = 390 | n = 86 |
| Mean 6MWD | 374 meters | 408 meters |
| Mean NT-proBNP | 987 ng/L | 628 ng/L |
| Functional Class III Patients | 289 (74%) | 36 (42%) |
| Geographic Distribution | North America: 75 (19%)<br>Rest of World: 315 (81%) | North America: 59 (69%)<br>Rest of World: 27 (31%) |
| *\*Baseline characteristics are preliminary and subject to change.* | *\*Baseline characteristics are preliminary and subject to change.* | *\*Baseline characteristics are preliminary and subject to change.* |

---

**About Gossamer Bio**

Gossamer Bio is a late-stage, clinical biopharmaceutical company focused on the development and commercialization of seralutinib for the treatment of pulmonary arterial hypertension and pulmonary hypertension associated with interstitial lung disease. Its goal is to be an industry leader in, and to enhance the lives of patients living with, pulmonary hypertension.

**Forward-Looking Statements**

Gossamer cautions you that statements contained in this press release regarding matters that are not historical facts are forward-looking statements. These statements are based on the Company's current beliefs and expectations. Such forward-looking statements include, but are not limited to, statements regarding: the anticipated timing of a data readout from our Phase 3 PROSERA Study; the potential or likelihood for a meaningful data readout from our PROSERA Study; and the first-in-class commercial potential of seralutinib. The inclusion of forward-looking statements should not be regarded as a representation by Gossamer that any of its plans will be achieved. Actual results may differ from those set forth in this press release due to the risks and uncertainties inherent in Gossamer's business, including, without limitation: potential delays in the commencement, enrollment and completion of clinical trials; disruption to our operations from unexpected events, including clinical trial delays; the Company's dependence on third parties in connection with product manufacturing, research and preclinical and clinical testing; the results of preclinical studies and early clinical trials are not necessarily predictive of future results; the success of Gossamer's clinical trials and preclinical studies for seralutinib; regulatory developments in the United States and foreign countries; unexpected adverse side effects or inadequate efficacy of seralutinib that may limit its development, regulatory approval and/or commercialization, or may result in clinical holds, recalls or product liability claims; Gossamer's ability to obtain and maintain intellectual property protection for seralutinib; Gossamer's ability to comply with its obligations in collaboration agreements with third parties or the agreements under which it licenses intellectual property rights from third parties; unstable market and economic conditions and adverse developments with respect to financial institutions and associated liquidity risk may adversely affect our business and financial condition and the broader economy and biotechnology industry; Gossamer may use its capital resources sooner than it expects; and other risks described in the Company's prior press releases and the Company's filings with the Securities and Exchange Commission (SEC), including under the heading "Risk Factors" in the Company's annual report on Form 10-K and any subsequent filings with the SEC. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and Gossamer undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this

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cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.

**For Investors and Media:** 

Bryan Giraudo, Chief Financial Officer & Chief Operating Officer

Gossamer Bio Investor Relations

ir@gossamerbio.com

<br>