Abstract

TPS6117 Background: Single agent pembrolizumab in relapsed / metastatic head and neck squamous cell carcinoma (R/M HNSCC) has an estimated ORR of 19% and median OS of 13.6 months. There are several factors which may influence which patients respond to antibodies targeting the PD-1 axis. Regulatory T cells (Tregs) play a significant role in an immunosuppressive tumor microenvironment. Anti-PD-1 antibodies induce Treg activation in part through AKT pathway activation, which may contribute to low response rates to checkpoint inhibitor therapy. AKT blockade selectively inhibits the proliferation of human Tregs. Additionally, inhibition of the PI3K-AKT-mTOR pathway limits myeloid-derived suppressor cells (MDSC) infiltration and differentiation, and boosts CD8+ T cell memory and effector function. Ipatasertib is an oral highly selective small-molecule inhibitor of all three isoforms of AKT. This phase 2 trial is designed to compare progression-free survival (PFS) in first line R/M, HNSCC patients treated with the combination ipatasertib and pembrolizumab versus pembrolizumab monotherapy treatment. Methods: In this open-label randomized phase 2 multicenter trial, patients with R/M HNSCC are treated with pembrolizumab 200mg on day 1 +/- ipatasertib 400mg QD days 1-14 of 21-day cycles. Patients must have PD-L1 CPS score ³ 1, have measurable disease per RECIST 1.1, and consent to on-treatment biopsy. Patients will be excluded if they have received prior systemic therapy for R/M HNSCC, cannot swallow a pill, or require insulin for diabetes. The primary objective is to compare the PFS between the two arms. We will estimate the relative hazard ratio associated with ipatasertib plus pembrolizumab compared to pembrolizumab alone using the Cox Model where randomized treatment assignment is the only variable in the model. Secondary objectives include ORR, safety and tolerability of the combination, and changes in tumor immune cell infiltration, AKT signaling, and changes in peripheral blood immune cells. Ultimately, a total of 48 patients will be enrolled, with 24 patients in each cohort. To date, a total of 22 patients have been enrolled from 15 sites. Accrual is ongoing (NCT05172258). Clinical trial information: NCT05172258 .