Abstract A184: T-cell rejuvenation is associated with vorinostat-induced immune response in combination with immune checkpoint blockade

Abstract

Background: Immune checkpoint inhibitors targeting the PD-1/PD-L1 axis have shown clinical benefit in solid tumor patients, including renal cell carcinoma (RCC). However, the rate of clinical response remains modest. Growing evidence suggests that epigenetic modifying agents may have an immunomodulatory role. Our group has previously demonstrated that the selective class I histone deacetylase (HDAC) inhibitor entinostat decreases the function of regulatory T-cells (Treg) and myeloid-derived suppressor cells (MDSC), and synergizes with PD-1 blockade. In this study, we assessed the immunomodulatory activity and efficacy of combining PD-1 blockade with the pan-HDAC inhibitor vorinostat in a RCC model. Methods: To test the efficacy of a combination therapy with a PD-1 inhibitor, mDX-400 (10 and 20 mg/kg I.P) (Merck & Co., Inc.) and a pan-HDAC inhibitor, vorinostat (100 and 150 mg/kg I.P) (Merck & Co., Inc.), we utilized a syngeneic mouse model of metastatic RCC following orthotopic implantation of luciferase expressing RENCA cells in immunocompetent BALB/c mice. Antitumor activity was assessed by bioluminescence technique as well as end point measurements of tumor weights. Immune landscape profiling of tumor infiltrating lymphocytes (TILs) was performed by flow cytometry, immunohistochemistry, and immunofluorescence. Survival analysis was performed by Kaplan–Meier estimates and log-rank statistic. Differences in chromatin accessibility in peripheral blood mononuclear cells (PBMC) were assessed by Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq). Results: Statistically significant reductions in end point tumor weights, as well as lung metastases nodules, were observed in mice treated with the combination of vorinostat (100 mg/kg P=0.0391; 150 mg/kg P=0.0165) and mDX-400 (20 mg/kg) compared to vehicle, while no statistical significant reduction was observed in those treated with single-agent mDX-400. Combination therapy also significantly lengthened the survival of the mice (median survival = 60 days; P=0.009) compared to treatment with the single agent mDX-400 (median survival=42 days). Immune landscape profiling did not demonstrate a significant increase in CD8+ tumor infiltration (P=0.479), but a statistically significant increase in natural killer cell infiltration (P=0.048) was observed. Though the CD8+ tumor infiltration was unchanged, a significant reduction (P=0.049) of exhausted CD8+ T-cells (CD8+PD1+) was observed in the combination treatment compared to mDX400 alone. Furthermore, a decrease was observed in the immunosuppressive Tregs (CD4+FOXP4+) and MDSC (CD11b+Gr1+) in the combination group compared to mDX400 alone. Bioinformatic analyses of ATAC-seq data from the PBMC cells of mice in the combination treatment and mDX400 alone showed increased chromatin accessibility between the two conditions. Pathway analysis of genes associated with more accessible chromatin in the combination treatment than mDX400 treatment identified enrichment of cell cycle control and immune cell activation pathways. Conclusions: Our results demonstrate that the pan-HDAC inhibitor vorinostat augments the antitumor effect of immune checkpoint inhibitor mDX-400 and prolongs survival in the RENCA model. This combination advantage was achieved by changing the immune landscape in TILs, especially by decreasing the exhausted subset of T-cells. The combination of these drugs is associated with higher chromatin accessibility near genes involved in cell cycle progression and immune cell activation. Taken together, our results support the clinical testing of pan-HDAC inhibitors in combination of PD-1 inhibitors and provide a novel potential immunomodulatory effect of epigenetic drugs. Citation Format: Nur P. Damayanti, Justin A. Budka, Josue D. Ordaz, Ashley Orillion, Khunsha Ahmed, Xioana Chu, Yue Wang, Yunlong Liu, Roberto Pili. T-cell rejuvenation is associated with vorinostat-induced immune response in combination with immune checkpoint blockade [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A184.