Compass Therapeutics to Present Phase 1 Data for CTX-471, A Novel CD137 Agonist Antibody, Demonstrating Anti-Tumor Activity in Patients Who Have Progressed on Approved PD-1 or PD-L1 Inhibitors at the American Society of Clinical Oncology (ASCO) Annual Meeting 2024

• CTX-471, a novel anti-CD137 agonist antibody, demonstrated anti-tumor activity in the Company’s Phase 1 Dose Escalation and Dose Expansion, first-in-human monotherapy study in patients with metastatic or locally advanced malignancies who had progressed on approved PD-1 or PD-L1 inhibitors.
• Five clinical responses were observed, all in patients who previously received checkpoint inhibitors. A durable partial response (PR) in a patient with small-cell lung cancer (SCLC) converted to a complete response, as confirmed by PET scan. Four additional PRs were also observed, 3 of 11 (27.3%) patients with melanoma (2 confirmed, one unconfirmed) and one of four (25%) patients with mesothelioma (PR confirmed).
• CTX-471 was well tolerated. The dose-limiting toxicity in the dose-escalation portion of the study was thrombocytopenia (decreased platelet count). These two episodes both resolved to normal. There was a low incidence of liver toxicity (6.3%), and the majority (80%) of adverse events were low grade (Grade 1 or Grade 2).

BOSTON, May 23, 2024 (GLOBE NEWSWIRE) — Compass Therapeutics, Inc. (Nasdaq: CMPX), a clinical-stage, oncology-focused biopharmaceutical company developing proprietary antibody-based therapeutics to treat multiple human diseases, today announced an upcoming poster presentation of its novel anti-CD137 agonist antibody, CTX-471, in patients with progressive disease following PD-1/PD-L1 inhibitors in metastatic or locally advanced malignancies.

The Company’s Phase 1 open-label, first-in-human study evaluated CTX-471 as a monotherapy in patients with metastatic or locally advanced malignancies that have progressed while receiving an approved PD-1 or PD-L1 inhibitor. The monotherapy portion of this study had two parts: a Dose Escalation phase and a Dose Expansion phase. Monotherapy dose escalation ranged from 0.1–1.2mg/kg intravenous (IV) biweekly, while Dose Expansion explored two dose levels: 0.3 and 0.6 mg/kg. The primary objective was to evaluate the safety and tolerability of CTX-471, with secondary objectives including pharmacokinetics (PK), immunogenicity, and clinical activity.

“We continue to make great strides with our CTX-471 clinical program, and we are excited to report data from the monotherapy arm of our Phase 1 trial,” said Thomas Schuetz, M.D., Ph.D., Co-founder, President of R&D, and Vice Chairman of the board at Compass. “CTX-471 was well tolerated with a low level of liver toxicity, suggesting a differentiated safety profile compared with other CD137-targeted agents. Importantly, a patient with refractory small-cell lung cancer, who had a durable partial response for 3 years, converted to a PET-negative complete response. We observed four additional partial responses, 3 patients with melanoma and one patient with mesothelioma. The clinical responses observed to date demonstrate the potential of our novel anti-CD137 antibody in patients with advanced malignancies who have limited treatment options.”

Data highlights from the poster presentation include:

• 19 patients were treated in the dose escalation and 60 patients were treated in the expansion portion of the monotherapy arm of the study (62% were male, median age of 66 years).
• A complete response (CR) was confirmed by PET scan in 1 of 3 patients with small-cell lung cancer. This patient, treated in the third-line setting, had a durable Partial Response (PR) for approximately 3 years prior to converting to a CR. Four additional PRs were also observed: 3 of 11 (27.3%) patients with melanoma and 1 of 4 (25%) patients with mesothelioma.
• CTX-471 monotherapy was observed to be generally well-tolerated, with the majority of adverse events (AEs) being Grade 1-2.

A copy of the presentation materials can be accessed on the News & Events section under “Presentations” of the Company’s website at www.compasstherapeutics.com once the presentation has concluded.

About CTX-471

CTX-471 is a fully human monoclonal antibody that binds and activates a novel epitope of the co-stimulatory receptor CD137, also known as 4-1BB, a member of the tumor necrosis factor receptor superfamily. The antibody is currently being evaluated in a Phase 1b clinical trial in patients with solid tumors that have progressed after at least three months on an approved PD-1 or PD-L1 inhibitor. Initial results reported from a monotherapy cohort of the study included partial responses in melanoma, small cell lung cancer, and mesothelioma, and CTX-471 has been observed to be generally well tolerated. In preclinical studies, CTX-471 has demonstrated potent monotherapy activity against multiple syngeneic tumor models, including the generation of long-term functional immunological memory.

About Compass Therapeutics

Compass Therapeutics, Inc. is a clinical-stage oncology-focused biopharmaceutical company developing proprietary antibody-based therapeutics to treat multiple human diseases. Compass’s scientific focus is on the relationship between angiogenesis, the immune system, and tumor growth. The company pipeline of novel product candidates is designed to target multiple critical biological pathways required for an effective anti-tumor response. These include modulation of the microvasculature via angiogenesis-targeted agents, induction of a potent immune response via activators on effector cells in the tumor microenvironment, and alleviation of immunosuppressive mechanisms used by tumors to evade immune surveillance. Compass plans to advance its product candidates through clinical development as both standalone therapies and in combination with proprietary pipeline antibodies based on supportive clinical and nonclinical data. The company was founded in 2014 and is headquartered in Boston, Massachusetts. For more information, visit the Compass Therapeutics website at https://www.compasstherapeutics.com.

Forward-Looking Statements

This press release contains forward-looking statements. Statements in this press release that are not purely historical are forward-looking statements. Such forward-looking statements include, among other things, references to Compass’s financial position to continue advancing its product candidates, expectations about cash runway, business and development plans, and statements regarding Compass’s product candidates, including their development and clinical trial milestones such as the expected trial design, timing of enrollment, patient dosing and data readouts, regulatory plans with respect to Compass’s product candidates and the therapeutic potential thereof. Actual results could differ from those projected in any forward-looking statements due to numerous factors. Such factors include, among others, Compass’s ability to raise the additional funding it will need to continue to pursue its business and product development plans, the inherent uncertainties associated with developing product candidates and operating as a development stage company, Compass’s ability to identify additional product candidates for development, Compass’s ability to develop, complete clinical trials for, obtain approvals for and commercialize any of its product candidates, competition in the industry in which Compass operates and market conditions. These forward-looking statements are made as of the date of this press release, and Compass assumes no obligation to update the forward-looking statements, or to update the reasons why actual results could differ from those projected in the forward-looking statements, except as required by law. Investors should consult all of the information set forth herein and should also refer to the risk factor disclosure set forth in the reports and other documents Compass files with the U.S. Securities and Exchange Commission (SEC) available at www.sec.gov, including without limitation Compass’s latest Annual Report on Form 10-K, Quarterly Report on Form 10-Q and subsequent filings with the SEC.

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