A phase II clinical trial of the phosphatidylserine targeting antibody, bavituximab, in combination with pembrolizumab in patients with advanced hepatocellular carcinoma.

Abstract

TPS599 Background: Phosphatidylserine (PS) is an immunosuppressive lipid segregated to the inner leaflet of the plasma membrane of normal cells. PS is externalized to the outer leaflet of the plasma membrane on cells that line tumor blood vessels, tumor cells and exosomes in the tumor microenvironment creating a specific target for anticancer treatments. Bavituximab is a PS targeting antibody that binds to PS via β2 glycoprotein-1 (β2GP1), an abundant serum glycoprotein. Bavituximab can modulate the tumor immune microenvironment to promote anti-tumor immune activity. This clinical trial is evaluating the effect of combining bavituxumab and the checkpoint inhibitor pembrolizumab in patients with advanced hepatocellular carcinoma (HCC). Methods: This is a single arm phase 2 clinical trial for patients with histologically confirmed HCC which is not eligible for curative and/or loco-regional therapy. No prior systemic therapy for HCC is allowed. Patients should be > 18 years, have Child-Pugh Score A, ECOG 0-1 and meet the following laboratory criteria: total bilirubin ≤ 2.0, INR ≤ 1.7; Hgb ≥ 8.5 g/dl; AST, ALT ≤5 times ULN; platelet ≥ 50,000/mm3; and albumin ≥ 2.5 g/dl. Major exclusion criteria include thromboembolic event within the last 6 months, clinically evident ascites, GI bleeding within 2 months, uncontrolled hypertension, HIV and autoimmune disease (except DM1, childhood allergies and thyroid abnormalities if adequately controlled. Dosing is as follows: Bavituximab: 3 mg/kg IV weekly, pembrolizumab: 200 mg IV every 3 weeks. The primary objective is to determine the overall response rate (ORR) of therapy. Secondary objectives are to determine the safety, tolerability and other measures of clinical efficacy (overall survival, 6 month PFS, and duration of response). Tumor and blood samples are being collected to assess for pharmacodynamic biomarkers. A minimax two-stage method will be used to analyze ORR after the first 15 patients are accrued. If 3 or more of the first 15 patients have either a complete or partial response, 13 additional patients will be enrolled. ORR will be analyzed by RECIST 1.1 criteria. Clinical trial information: NCT03519997.