Preliminary safety and efficacy data of BGB-A333, an anti-PD-L1 monoclonal antibody, alone and in combination with tislelizumab in patients with advanced solid tumors.

Background: Programmed cell death protein-1 (PD-1) and its ligand, programmed death-ligand 1 (PD-L1), play critical roles in the immune modulation of tumor progression. Although both pathways have overlapping elements, each has a distinct mechanism of action. Nonclinical studies have demonstrated that potential synergistic antitumor effects can result from blocking both PD-1 and PD-L1. BGB-A333 is an investigational humanized IgG1 monoclonal antibody against PD-L1 that has antitumor activity in xenograft models. Tislelizumab, a clinical-stage anti-PD-1 antibody engineered to minimize binding to FcgammaR on macrophages in order to abrogate antibody-dependent phagocytosis, has demonstrated clinical activity in patients with advanced solid tumors. Here we report preliminary results from the phase 1 component of an open-label phase 1/2 study (NCT03379259) of BGB-A333 alone and in combination with tislelizumab in patients with advanced solid tumors. Method(s): Phase 1 of this study consisted of two parts. In Part A, patients received single-agent BGB-A333 IV Q3W at increasing doses; in Part B patients received BGB-A333 1350 mg IV Q3W + tislelizumab 200 mg IV Q3W. Eligible patients had unresectable advanced or metastatic cancer and an ECOG performance status of <=1. Safety/tolerability profile (primary endpoint) was examined by monitoring adverse events (AEs); secondary endpoints included antitumor activity, assessed by RECIST v1.1, and the pharmacokinetic (PK) parameters of each antibody. Result(s): As of Oct 30, 2019, 15 patients were enrolled in Part A (450 mg, n=3; 900 mg, n=3; 1350 mg, n=6; 1800 mg, n=3) and 12 in Part B. Across both parts, patients were female (n=17/29; 63%); squamous cell carcinoma of either skin or head and neck (n=5) and ovarian cancer (n=4) were the most common tumor types. Thirteen patients (48%) had >=2 lines of prior systemic therapy. The most common treatment-related AEs (TRAEs) were fatigue (N=5; Part A, n=3; Part B, n=2) and nausea (N=4; n