Purpose: Immunotherapy in the clinic has demonstrated its potential to control cancer through disinhibiting the immune system, especially for immune checkpoint inhibitors such as anti-programmed cell death protein 1/anti-programmed death-ligand 1 (anti-PD1/anti-PD-L1). However, although these new immunotherapies have resulted in durable clinical responses in various cancers, multiple mechanisms of immune resistance and suppression exist in tumors. One significant barrier to efficacy of anti-PD1 against colon cancer may be the recruitment of myeloid-derived suppressor cells (MDSCs) into the tumor microenvironment. Here we demonstrated functional inhibition of G-MDSC with (-)-4-O-(4-O-β-D-glucopyranosylcaffeoyl) quinic acid (QA), an inhibitor of PI3Kδ/γ, reshaped the tumor immune microenvironment and promoted cytotoxic T cell-mediated tumor regression, resultantly enhancing responses to anti-PD1 treatment in colon tumor model.
Methods: A syngeneic colon tumor mouse model was used to study the effects of QA on tumor immune microenvironment and its potential synergistic effects with anti-PD1 blockade.
Results: QA treatment inhibited G-MDSC function in the tumor tissue. Additionally, combination treatment induced CD8+ T lymphocyte-dependent tumor growth delay and prolonged survival time in colon cancer.
Conclusions: Our results offered opportunities for new combination strategies using a selective small molecule PI3Kδ/γ inhibitor, to suppress MDSCs to enhance responses to immune checkpoint blockade in colon cancer.
Keywords: (−)-4-O-(4-O-β-D-glucopyranosylcaffeoyl) quinic acid; MDSCs; anti-PD1 blockade; colon carcinoma.