Abstract CT089: Clinical and translational results of the academic ARIANES Phase 2 basket study: Longitudinal bulk and single-cell RNAseq analyses of patient tumors identify biological correlates of response to PARP inhibitors and anti-PD-L1 therapy

Abstract Background: Poly (ADP-ribose) polymerase inhibitors (PARPi) have immunomodulatory properties that may potentiate anti-PD-L1 therapy. The academic phase 2 basket trial ARIANES evaluated the PARPi rucaparib (R) and anti-PD-L1 atezolizumab (A) in selected patients (pts). We performed single-cell RNA + T-cell receptor sequencing (scRNA+TCR-Seq) and bulk RNA-Seq on sequential tumor biopsies, concomitant plasma proteomics, and whole exome sequencing in a pt subset. Methods: ARIANES included 4 molecularly selected DNA damage response deficient (DDRd), 3 platinum-sensitive, and 2 unselected cohorts of pts with non-breast non-ovarian cancers. R was administered for 3 weeks followed by R+A. Primary endpoint was overall response rate (ORR) by RECISTv1.1 at 12 weeks per cohort. Bulk and scRNA+TCR-Seq were performed on biopsies collected at baseline (B), on R, and on R + A in the same lesion. We used partial least squares discriminant analysis to integrate multi-omics and identify pathways associated with response. We tracked the evolution over time of tumor and microenvironment cells, differentially expressed genes and signatures within each cell population, and TCR clonal dynamics. Results: ARIANES enrolled 130 pts, including 27 DDRd mCRPC pts. In the latter, ORR was 22% (6/27) by PCWG3-mRECISTv1.1, and mPFS (modified Progression Free Survival) 6.7 months (95% CI 2.7 - 11.1) at data cut-off. High-quality profiling data were obtained for 41 samples (17 pts) and 16 samples (6 pts) by bulk and scRNA+TCR-Seq, respectively. When focusing on bulk RNA-Seq data of pts with clinical benefit (CB, i.e. response or PFS > 6 months; n = 4, 3, 3 at B, on R, on R+A, respectively) vs pts with no CB (NCB, n = 10, 8, 12 at B, on R, on R+A, respectively), we found that 7/23 pathways significantly enriched on R+A were related to innate immunity (including IL6_JAK_STAT3 and INFa signaling), whereas DNA_REPAIR and MITOTIC_SPINDLE were significantly downregulated. At the gene level, FANCA, HJURP and RAD54L were downregulated on R+A, whereas ZBP1 was downregulated on R and R+A. scRNA-Seq of a BRCA2-mutant mCRPC pt with prolonged PR (Partial Response) consistently showed gradual increase on R and R+A of cGAS-STING innate immune sensing and JAK/STAT pathways activation, both in tumor and immune cells, together with CCL5 expression; scTCR-Seq revealed the expansion of specific T-cell clonotypes on R + A. This was not observed in progressing patients. Conclusion: Multi-omics analysis on sequential pts samples reveals that R displays immunomodulatory properties in pt tumors and confirms the potential of (i) R to activate innate immune pathways in tumor cells, and (ii) R + A to induce T-cell activation and clonal expansion. To our knowledge, this is the first study providing a longitudinal and multi-omics bulk/sc resolution analysis of evolution of tumor and immune cells in pts on PARPi and PARPi + anti-PD-L1. Citation Format: Thibault Thomas-Bonafos, Julien Vibert, Arnaud Pagès, Léo Colmet-Daage, Roman Chabanon, Aurore Jeanson, Lambros Tselikas, Marlène Garrido, Clémence Hénon, Aurélien Parpaleix, Marianne Chasseriaud, Alice Bernard-Tessier, Nicolas Dorvault, Baptiste Bonnet, Clémence Astier, Anas Gazzah, Ronan Flippot, Natacha Naoun, Anna Patrikidou, Pernelle Lavaud, Aline Fuerea, Laurence Albiges, Yohann Loriot, Stéphane Champiat, Capucine Baldini, Fanny Bouquet, Nathalie Droin, Karim Fizazi, Damien Vasseur, Christophe Massard, Etienne Rouleau, Patricia Martin-Romano, Kaissa Ouali, Sophie Postel-Vinay. Clinical and translational results of the academic ARIANES Phase 2 basket study: Longitudinal bulk and single-cell RNAseq analyses of patient tumors identify biological correlates of response to PARP inhibitors and anti-PD-L1 therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr CT089.