Phase Ib trial of pembrolizumab and XL888 in patients with advanced gastrointestinal malignancies.

Abstract

TPS526 Background: Heat shock protein 90 (HSP90) has a central role in modulating tumor microenvironment, inflammatory signaling pathways (NF-κB, HIF-1α and Jak-STAT), tumor antigen presentation and expression, PD-L1 expression and macrophage migration inhibitory factor (MIF) as well as cytokine production. Inhibitors of HSP90 have been shown in preclinical studies and in patient samples to exert anti-tumor effects and modulate signaling pathways. XL888 is a selective inhibitor of HSP90. Based on this preclinical rationale, we have developed a phase Ib/II trial to determine the recommended phase II dose, evaluate the safety, toxicity profile, preliminary antitumor activity, and immunogenicity of the XL888 and Pembrolizumab combination in previously treated patients with advanced gastrointestinal tumors. Methods: The phase Ib trial design is standard 3+3. XL888 is administered orally (PO) in three dose levels of 45 (DL1), 90 (DL2), 60 (only if DLT on DL2) mg twice weekly with pembrolizumab at 200 mg IV on day 1, in 21-day cycles. Eligible patients must have stage IV or locally advanced unresectable gastrointestinal adenocarcinomas who have failed at least one prior therapy (patients with colorectal adenocarcinoma must have previously received oxaliplatin, irinotecan, and fluoropyrimidine), age ≥18 years, ECOG PS 0-1, no prior anti PD-1 or anti-PD-L1 agent. After recommended phase II dose is established, an expansion phase will enroll 16 patients with pancreatic adenocarcinoma (Arm A) and 16 patients with colorectal adenocarcinoma (Arm B). Primary endpoint response rate. In the expansion phase patients will receive initial cycle (3 weeks) treatment with either pembrolizumab or pembrolizumab plus XL888 and then starting cycle 2 all patients receive the combination. Blood will be collected pre-treatment, post 1st and 2nd cycle. Eight patients in each arm will undergo pre and post treatment tumor biopsies. This design will enable us to evaluate the effects of pembrolizumab alone versus the combination. This study was activated in June 2017 and to date 4 patients were enrolled in dose escalation phase. The dose expansion phase is expected to start accrual in December 2017. Clinical trial information: NCT03095781.