Abstract 5126: The link between therapy-induced senescence and anti-tumor immune microenvironment in melanoma
Authors: Vilgelm Anna E. , Johnson C Andrew , Prasad Nripesh , Yang Jinming , Chen Sheau-Chiann , Ayers Gregory D. , Sosman Jeffrey A. , Ecsedy Jeffrey A. , Yu Shyr , Levy Shawn E. , Richmond Ann 
Published: July 2016

Abstract
Tumor cell senescence is often induced by cancer therapeutics. Senescent cells secrete many proteins that may affect both malignant and non-malignant components of the tumor. The goal of this study was to determine how therapy-induced senescence (TIS) affects the immune microenvironment in melanoma. We used inhibitors of cell cycle kinases AURKA and CDK4/6 (AURKAi, CDK4/6i) to induce senescence in melanoma tumors. RNA sequencing analysis of AURKAi-treated syngeneic mouse tumors demonstrated that response to AURKA inhibition was strongly associated with induction of an immune transcriptome (p = 3.5E-29). Immunofluorescent staining and flow cytometric analysis of digested tumors showed correlation between the numbers of tumor-infiltrating leukocytes (TILs) and AURKAi response (Spearman r = -0.87, p&lt;0.001). T cells were among the TILs recruited into AURKAi-sensitive tumors. Therapeutic benefit of AURKAi was limited in immunodeficient host (67% of tumors regressed in immunocompetent mice vs 0% in immunodeficient mice, p = 0.01) suggesting that recruitment of TILs augments response to senescence-inducing therapy. We found that TILs were driven into tumors in response to chemokine CCL5 that was induced in AURKAi and CDK4/6i-treated melanoma cells (up to 20 fold, p≤0.005) on mRNA and secreted protein levels. Knockdown of CCL5 (KD) inhibited leukocyte recruitment (6.8% in KD vs 29.5% in control, p = 0.002) and response to AURKAi in vivo (p = 0.61 in KD vs p = 0.02 in control). In contrast, therapeutic benefit was greatly enhanced when senescence-inducing therapy was combined with T cell-activating immunotherapy using CD137 (4-1BB) agonist (p&lt;0.001). We also evaluated CCL5 expression in human melanoma tumors in relation with TIS and TIL markers. Expression of CCL5 was induced by AURKAi and/or CDK4/6i in patient derived xenografts (3 patients, 3 mice each, p≤0.02), in tumors from patients who responded on AURKAi clinical trial (3 patients, before/after therapy) and was associated with expression of “Immune response” genes in The Cancer Genome Atlas (TCGA) dataset of 278 melanoma tumors (p = 1.40E-93). In conclusion, our data demonstrates that TIS promotes recruitment of TILs via the induction of CCL5 which, in turn, augment therapeutic response in melanoma. Further improvement of melanoma outcome is achieved when senescence-inducing drugs are combined with immunotherapy that promotes tumor cells killing by TILs. This study presents a novel promising approach to improve melanoma therapy by utilizing TIS to reprogram tumor immune microenvironment.
Citation Format: Anna E. Vilgelm, C Andrew Johnson, Nripesh Prasad, Jinming Yang, Sheau-Chiann Chen, Gregory D. Ayers, Jeffrey A. Sosman, Jeffrey A. Ecsedy, Shyr Yu, Shawn E. Levy, Ann Richmond. The link between therapy-induced senescence and anti-tumor immune microenvironment in melanoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5126.