Abstract 2921: Extended treatment with IAP inhibitor xevinapant post radiotherapy improves therapeutic efficacy and promotes antitumor immunity in preclinical models
Authors: Yeung Tsz-Lun , Jiang Feng , Huang Hui , Yu Huakui , Chiu Li-Ya , Bonnemaison Mathilde , Marelli Bo , Ferretti Roberta , Lindemann Ralph , Esdar Christina 
Published: March 2024

Abstract
Background: Xevinapant is a first-in-class, oral IAP (inhibitor of apoptosis protein) inhibitor designed to restore cancer cell sensitivity to apoptosis induced by radiotherapy (RT) and chemotherapy. In a randomized phase 2 study of patients with unresected locally advanced squamous cell carcinoma of the head and neck, xevinapant + chemoradiotherapy (CRT) significantly improved locoregional control at 18 months, 3-year progression-free survival and nearly doubled 5-year overall survival vs. placebo + CRT (53% vs. 28%). Two phase 3 trials, in which patients receive 6 cycles of xevinapant or placebo monotherapy (3 cycles in combination with standard-of-care (C)RT followed by 3 cycles of monotherapy), are ongoing. Based on the roles of IAPs in apoptosis and tumor immunity, continual dosing of xevinapant post RT may deliver additional therapeutic benefit through modulation of multiple tumor microenvironment (TME) compartments.
Methods: The impact on antitumor efficacy of xevinapant dosing duration was evaluated in A1419 (head and neck), LLC (lung) and MC38 (colorectal) syngeneic tumor-bearing mice treated with vehicle control, RT alone (3.6Gy, QD, 5 days), or RT + xevinapant (100 mg/kg, QD, 1, 2, or 4 weeks). To assess treatment-mediated TME modulation in MC38 tumors, RNAseq and FACS-based immune profiling was performed, followed by functional validation with ex vivo ELISpot assays, in vitro immunogenic cell death assays, T cell activation assays, and macrophage polarization and viability assays. To evaluate the effect of xevinapant on RT-induced cancer associated fibroblast (CAF) activation and CAF-modulated immune phenotype, activation assay and cytokine profiling was performed.
Results: In the tumor models tested, RT in combination with extended xevinapant dosing markedly improved efficacy and prolonged survival compared to treatment arms of RT with shorter xevinapant dosing durations, RT alone, and vehicle control. RNAseq and FACS analyses suggested a TME with enhanced antitumor immunity, while ELISpot and in vitro T cell assays confirmed that extended xevinapant dosing promoted antigen-specific T cell response and T cell activation. Furthermore, macrophage polarization and viability assays suggested that xevinapant reduced the viability of M2 macrophages which may have contributed to the increased M1:M2 macrophage ratio and the improved antitumor immune response observed in vivo. In addition, via the suppression of RT-mediated CAF activation, xevinapant may promote M1 polarization of macrophages and recruitment of T cells by upregulating GM-CSF and CXCL10 in CAFs.
Conclusions: Extended dosing of xevinapant post concurrent RT improved antitumor efficacy and prolonged survival of tumor-bearing mice. Mechanistic investigation suggested that such benefit may be, in part, modulated by xevinapant enhanced antitumor immunity.
Citation Format: Tsz-Lun Yeung, Feng Jiang, Hui Huang, Huakui Yu, Li-Ya Chiu, Mathilde Bonnemaison, Bo Marelli, Roberta Ferretti, Ralph Lindemann, Christina Esdar. Extended treatment with IAP inhibitor xevinapant post radiotherapy improves therapeutic efficacy and promotes antitumor immunity in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2921.