Preclinical development of GNTbm-38, a novel class I histone deacetylase inhibitor, while combined with anti-VEGFR TKI or anti-PD-1 Ab: Assessment of immune activation and immune memory in cancer immunotherapy.

2574 Background: Several clinical trials explored ICI-based combinations in MSS mCRC patients, and the promising outcomes are lacking. Histone deacetylase inhibitors (HDACis) for cancer therapy may boost antitumor immune activity, reduce immunosuppressive cells, and play a crucial role in controlling tumor progression. Therefore, rational drug combinations, containing class I HDACi or other immune-modulating drugs, may provide opportunities in immunotherapy. Methods: The activities of GMTbm-38 were assessed in vitro, including H3 acetylation and cancer cell growth inhibition, etc. The murine colon cancer CT-26 model was used to test antitumor efficacy in wild type and transgenic humanized PD1/PD-L1 mice. GNTbm-38 was combined with an anti-VEGFR TKI or murine/human PD1 antibody to test the antitumor synergistic effect. RNA-seq, flow cytometry, and IHC were performed to illustrate the potential mechanisms. Results: GNTbm-38 induced histone 3 acetylation and inhibited the cell growth of varieties of human cancer cells. By using CT-26 model, GNTbm-38 showed a superior efficacy profile in WT mice compared to immune-deficient mice. The antitumor activity related to induced immune activation and immune memory was dependent on CD8 + T cell activation. Treatment with GNTbm-38 showed an increased number of intratumoral CD8 + CTLs, a decreased number of MDSCs, and induced normalization of tumor vessels. GNTbm-38 substantially induced the expression of IFN-γ response genes and enhanced antigen processing and presentation signatures. GNTbm-38 acts as a TME reprogramming regulator in immunotherapy. When combined with TKI, GNTbm-38 significantly improved tumor response rate and survival rate through synergistic effect by normalizing tumor vessels, increasing tumor antigen presentation, increasing activated CD8 + T cell infiltration into tumors, inducing memory T cell persistence, and inhibiting mobilization of immunosuppressive cells into tumors. Treatment with GNTbm-38 plus anti-PD-1 Ab in the CT-26 model showed greatly improved tumor response rate and survival rate with a strong synergistic effect. Furthermore, in B-hPD-1/hPD-L1 mice (humanized model) subcutaneously injected with B-hPD-L1 CT-26 cells, treatment of pembrolizumab and GNTbm-38 resulted in a 46.5% inhibition on tumor growth. Therefore, our data provided a strong rationale to explore the combination of GNTbm-38 with anti-VEGF TKI with or without ICI. Conclusions: Collectively, our data show that GNTbm-38 exhibits markedly superior pharmacokinetics, tolerability, and efficacy in animal models. GNTm-38 has been shown to display powerful induction of immune activation and immune memory in combination therapy with TKI/ICI against colon CT-26 cold tumor.