Abstract CT035: Proof-of-concept and preliminary efficacy of triple IAP blockade to maximize immunogenic cell death and induce efficient adaptive immune response: First report on the ASTEROID phase 1 trial

Abstract Background: Dying cells play an important role in CD8+ T cell-mediated immunity. While apoptosis is mainly immunologically silent, necroptosis is immunogenic and can more efficiently initiate an adaptive immune response that could be augmented by immune checkpoint inhibition (ICI). Inhibitor of Apoptosis (IAP) proteins are key gatekeepers of how a cell dies, and frequently overexpressed in cancer. ASTX660 (tolinapant) is a triple blocker of cIAP1/2 and XIAP, sensitizing cancer cells to death ligands through ripoptosome formation, activating ‘danger’ co-stimulatory signals and dendritic cell (DC) maturation required to prime a potent antitumor response. Methods: We assessed the safety, pharmacodynamic (PD), and clinical activity of 7 days of oral ASTX660 given prior to pembrolizumab 200 mg (Q3W), in patients (pts) refractory to standard therapy. TITE-CRM was used to explore ASTX660 doses 90-180 mg. Serial paired blood and tumor samples were analyzed to interrogate the effect of ASTX660 on cell death, tumor microenvironment and host immune system. Results: 22 pts have been enrolled; median age 55 years (range 38-81); male:female 5:17; all ECOG PS ≤1; median 4.5 prior therapies. Tumor types included breast, head and neck (HN), hepatocellular, cervical, pancreatic and cholangiocarcinoma. Combination ASTX660-pembrolizumab is currently recruiting at highest dose 180 mg without any dose limiting toxicities (DLT) seen within the 6-week DLT observation period. Most common adverse events (AE) were G1-2 rash, nausea, and asymptomatic increases in amylase, lipase and transaminases; all reversible and easily manageable. Four iRECIST confirmed partial responses were seen in 10 efficacy evaluable pts treated at biologically active dose levels 120 and 150 mg (Overall response rate 40%), including 2 pts with ER+ HER2- breast cancer, 1 cervical adenocarcinoma pt (exceptional response following initial pseudoprogression) and a HN cancer pt refractory to ICI monotherapy. 3/4 responders are ongoing. Efficacy data from pts treated at highest dose level 180 mg is pending. FACS of paired blood samples from responders shows a significant rise in %CD57+/CD3+ cytotoxic effector T cells [mean 11.90% (pre-) vs 14.25% (post-ASTX660); p=.0176]. These changes were not seen in the non-responders group. Full PD from paired blood and tumour sampling will be shared at the meeting. Conclusion: ASTX660-pembrolizumab is is well-tolerated with durable antitumor responses in pts with immunologically cold tumors, providing the first clinical proof-of-concept of immunogenic cell death induction leading to effective adaptive immune response when combined with ICI. Recommended Phase 2 dose optimization and expansion cohorts in immunologically cold cancers are ongoing. Citation Format: Crescens Tiu, Wing Yau, Victoria Sanchez-Perez, Giovanni Codacci-Pisanelli, Ching Leung, Eden S. Andrews, Bristi Basu, Anna Zachariou, Toby Prout, Mona Parmar, Alison Turner, Xiaoran Lai, Zhulin Yin, Karen E. Swales, Syed Haider, Thomas Lund, Diego C. Dos Reis, Tatiany L. Silveira, Alan S. Dunlop, Ann-Marie Baker, Bora Gurel, Ana Ferreira, Claudia Bertan, Nina Tunariu, Edward W. Johnston, Alistair Ring, Tencho Tenev, Tomoko Smyth, Simone Jueliger, Udai Banerji, Johann S. de Bono, Alec Paschalis, Adam Sharp, Anna Minchom, Christina Yap, Pascal Meier, Juanita S. Lopez. Proof-of-concept and preliminary efficacy of triple IAP blockade to maximize immunogenic cell death and induce efficient adaptive immune response: First report on the ASTEROID phase 1 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT035.