Abstract CT107: Correlation of biomarkers and clinical benefit of intratumoral BO112 and pembrolizumab in patients with anti PD1 refractory melanoma

Abstract Background: There is a lack of predictive biomarkers for immunotherapy in melanoma. In terms of IHC, there is no strong rational to support the use of PD-L1 expression. BRAF mutations occur in 40-50% of melanomas and the MAPK pathway may also be activated by NRAS mutations. Patients harboring these mutations face usually a worse prognosis. BO-112 is a double stranded synthetic RNA formulated with polyethyleneimine (PEI) that, by mimicking the effect of a viral infection, mobilizes the immune system. Prior data from a phase I trial (NCT02828098) suggest that, when administered intratumorally, it causes an increase in CD8 infiltration and PD-L1 expression. The role of these and other biomarkers is being explored in the present phase II clinical trial. Study Design: Single arm study with BO-112 plus pembrolizumab (NCT04570332) in patients with advanced melanoma in progression to anti-PD1 therapy. Tumors were genotyped by next generation sequencing, whole exome sequencing and tumor mutation burden. Antitumor and immunological effects of the treatment in the tumor microenvironment were assessed by PDL1 and CD8 immunohistochemistry with a paired biopsy performed after 21 days of treatment. Results: A preliminary analysis has been performed, based on patients evaluable for clinical benefit (defined as response or stable disease>16 weeks). Samples from 35 patients have been analyzed, with 24 patients paired biopsies available. Patients with “cold” tumors (PD-L1 negative and CD8 low) at baseline had a trend to lack of clinical benefit. Only basal PD-L1 in the inflammatory component showed a statistically significant correlation with clinical outcome (4/20 (25%) tumors PDL1 IC negative had benefit versus 10/15 (67%) positive), p=0.0053. Fifteen patients had an increase in PD-L1 and 14 patients had increase in CD8 infiltrate after BO-112 treatment; the lack of increase in PDL1 and CD8 after treatment was also predictive of lack of response (p=0.04). BRAF/NRAS driver mutations correlated with positive outcome. Clinical benefit was observed in 4 of 17 (24%) patients not carrying activating mutations whereas 11 out of 18 (61%) patients with BRAF/NRAS activating mutations had clinical benefit (p=0.02), mainly in cutaneous histology (14% versus 65%, p=0.02). Mucosal melanoma patients (n=3) achieved an ORR 66.7% and DCR 100%. The two mucosal melanoma patients with partial response harbored SETD2 mutations and one of them showed extensive cyclic nucleotide-gated (CNGs), indicative of defects in DNA repair pathways. Regarding acral melanoma patients (n=9), no responses were observed, even in the single case with a NRAS mutation. The only patient achieving clinical benefit, with stable disease>16 weeks; had a unique mutation profile, with TP53 (inactivating) and KIT (activating) mutations. Conclusions: Patients basal mutant BRAF/NRAS could have more probability of benefit from BO-112 and pembrolizumab combination. PD-L1 and/or CD8 increase is an early marker of response. These findings could help to select patients in future clinical trials. Further investigation into predictive biomarkers is warranted. Citation Format: Ruth Roman, Philippe Saiag, Caroline Dutriaux, Luis de la Cruz Merino, Eduardo Castanon, Miguel F. Sanmamed, Caroline Robert, Juan F. Rodríguez-Moreno, Pablo Cerezuela-Fuentes, Ana M. Arance, María González Cao, Henry Montaudié, María Pilar López Criado, Julie Charles, Alfonso Berrocal, María del Carmen Álamo de la Gala, Enrique de Miguel, Elisa Funk-Brentano, Sorilla Prey, Eva Muñoz-Couselo, Delvys Rodríguez Abreu, Juan Martín-Liberal, Helena Escuin-Ordinas, Mark Branum, Sonia Macia, Marisol Quintero, Javier Sánchez López, Marya F. Chaney, Beatriz García-Peláez, Marta Vives-Usano, Miguel Ángel Molina, Stéphane Dalle, Iván Márquez-Rodas. Correlation of biomarkers and clinical benefit of intratumoral BO112 and pembrolizumab in patients with anti PD1 refractory melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT107.