HDAC inhibitor GCJ-490A modulates tumor microenvironment and synergizes with PD-1 antibody against breast and lung cancers in syngeneic murine models

Histone deacetylases (HDAC) inhibition represents one of the few validated strategies in epigenetic cancer therapies, demonstrating significant clinical efficacy in T-cell lymphomas and multiple myeloma, yet exhibiting limited efficacy against solid tumors. GCJ-490A is a novel HDAC inhibitor discovered by medicinal chemists in our institute, which exhibits potent in vitro and in vivo anticancer activity. In this study, we investigated the effects of GCJ-490A on the tumor microenvironment and its potential in synergy with PD-1 antibody in anti-tumor therapy. In syngeneic murine models of breast (EMT6) and lung (LL/2) cancers, we demonstrated that GCJ-490A alone and in combination with PD-1 antibody inhibited tumor growth by regulating T cells and tumor-associated macrophages (TAMs). Specifically, GCJ-490A significantly enhanced T-cell proliferation and cytotoxicity, evidenced by the increased expression of Ki67, CD107a and Granzyme B, and modulated TAMs towards a pro-inflammatory M1 phenotype, while reducing the M2 population. In addition, GCJ-490A upregulated PD-1 on T cells and PD-L1 on myeloid-derived suppressor cells (MDSCs) and TAMs, potentially enhancing PD-1 blockade efficacy. However, the anti-tumor efficacy was less pronounced in LL/2 tumors than in EMT6 tumors, which might be related to the increased infiltration of MDSCs in LL/2 tumors. GCJ-490A promoted MDSCs migration into the tumor by promoting the secretion of CXCL7 from LL/2 cells. In conclusion, GCJ-490A exerts its anti-tumor efficacy by reprogramming the tumor immune microenvironment in EMT6 and LL/2 tumor models, which is augmented when combined with anti-PD-1. However, CXCL7-mediated tumor-type-dependent recruitment of MDSCs by GCJ-490A may limit its therapeutic efficacy, and inhibition of the CXCL7/CXCR1/2 pathway might offer new strategies to address this challenge.