Phase II study of zolbetuximab plus pembrolizumab in claudin 18.2: Positive locally advanced or metastatic gastric or gastroesophageal junction adenocarcinoma (G/GEJ)—ILUSTRO Cohort 3.
Authors: Samuel J Klempner, Jaffer A. Ajani, Salah-Eddin Al-Batran, Yung-Jue Bang, Daniel V.T. Catenacci, Peter C. Enzinger, David H. Ilson, Sunnie Kim, Florian Lordick, Manish A. Shah, Kohei Shitara, Ahsan Arozullah, Jung Wook Park, Jeffrey J. Raizer, Eric Van Cutsem, Rui-hua Xu
Journal: Journal of Clinical Oncology (2021)

TPS260 Background: Five-year survival with advanced G/GEJ is poor, and limited biomarkers exist to inform optimal treatment selection. Pembrolizumab, an anti–programmed death-1 receptor (PD-1) antibody, is approved for advanced/metastatic PD-ligand 1–positive (PD-L1 + ) G/GEJ that progressed after ≥2 lines of therapy. The transmembrane tight junction protein claudin 18.2 (CLDN18.2) is normally confined to gastric mucosa but is often overexpressed in G/GEJ with roughly one-third of patients (pts) having high expression (≥75%). Zolbetuximab, a chimeric IgG1 monoclonal antibody, binds to CLDN18.2 and mediates cancer cell death through antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity. Phase 2 (NCT01630083) results showed prolonged survival with zolbetuximab + epirubicin, oxaliplatin, and capecitabine (EOX) vs EOX alone in G/GEJ. Results of nonclinical studies showed enhanced antitumor activity with zolbetuximab + anti-murine PD-1 antibody, and it was hypothesized that a combination with pembrolizumab (new Cohort 3) might augment ADCC and antitumor immune response in CLDN18.2 overexpressing G/GEJ. Methods: This phase 2 open-label study (NCT03505320) will enroll ~112 adult pts from 22 sites in 5 countries into 3 cohorts; this abstract describes Cohort 3 (~62 pts). Key eligibility criteria are advanced/metastatic G/GEJ, measurable disease (RECIST v1.1), adequate organ function and performance status, and high/intermediate (Cohort 3A) or high (Cohort 3B) expression of CLDN18.2. Central testing of tumor tissue will determine CLDN18.2 expression; pts are considered CLDN18.2 positive (CLDN18.2 + ) if ≥75% (high) or ≥50% to &lt; 75% (intermediate) of tumor cells demonstrate moderate-to-strong membranous IHC staining. Patients in Cohort 3B are required to be PD-L1 + , defined as a combined positive score ≥1 (IHC staining per the Dako 22C3 PD-L1 assay). Patients will receive zolbetuximab + pembrolizumab in the third/later line in Cohort 3A and third line in Cohort 3B. In Cohort 3A (safety cohort), zolbetuximab will be administered at a loading dose of 800 mg/m 2 IV on Day 1 Cycle 1 followed by 600 mg/m 2 IV every 3 weeks; a reduction from 600 mg/m 2 every 3 weeks is permitted. Pembrolizumab 200 mg IV will be administered on Day 1 of each 21-day cycle. Cohort 3B (expansion cohort) zolbetuximab dose is determined from results of Cohort 3A. Imaging will occur every 6 weeks for 24 weeks and every 12 weeks thereafter. The primary endpoint is objective response rate; additional endpoints include duration of response, disease control rate, and progression-free survival by independent review committee and investigator assessment. Pharmacokinetics, safety/tolerability, quality of life, and immunogenicity will be assessed. The study is currently recruiting pts. Clinical trial information: NCT03505320.