Midostaurin Modulates Tumor Microenvironment and Enhances Efficacy of Anti-PD-1 against Colon Cancer

Simple Summary Colon cancer is one of the most common types of cancer worldwide. Immune checkpoint inhibitors have promising effects on various types of cancers with limited efficacy in colon cancer. Midostaurin (PKC412) is currently used for the treatment of patients with acute myeloid leukemia harboring FLT3-mutation. The aim of this study was to assess the potential effect of midostaurin on the modulation of TME and the efficacy of anti-PD-1 against colon cancer. We showed midostaurin inhibited colorectal adenocarcinoma cell growth and induced multinucleation and micronuclei formation. Midostaurin inhibited colorectal adenocarcinoma cell growth associated with the formation of dsDNA and ssDNA; the up-regulation of mRNA expression of cGAS, STING, IRF3, and IFNAR1; the down-regulation of Trex-1, c-Kit, and Flt3 protein expression. The tumor-implanted model displayed a combination of midostaurin-enhanced efficacy of anti-PD-1 to suppress tumor growth. In TME, midostaurin diminished Treg cells and increased M1 macrophage. The expressions of STING and INF beta proteins were elevated in the tumor specimens. Our results suggest that midostaurin may have the potential to enhance immunotherapy in clinical practice. Immunotherapy modulating the tumor microenvironment (TME) immune function has a promising effect on various types of cancers, but it remains as a limited efficacy in colon cancer. Midostaurin (PKC412) has been used in the clinical treatment of fms-like tyrosine kinase 3 (FLT3)-mutant acute myeloid leukemia and has demonstrated immunomodulatory activity. We aimed to evaluate the effect of midostaurin on the modulation of TME and the efficacy of anti-programmed cell death protein 1 (PD-1) against colon cancer. Midostaurin inhibited the growth of murine CT26 and human HCT116 and SW480 cells with multinucleation and micronuclei formation in morphology examination. The cell cycle arrested in the G2/M phase and the formation of the polyploid phase was noted. The formation of cytosolic DNA, including double-strand and single-strand DNA, was increased. Midostaurin increased mRNA expressions of cGAS, IRF3, and IFNAR1 in colorectal adenocarcinoma cells and mouse spleen macrophages. The protein expressions of Trex-1, c-KIT, and Flt3, but not PKC alpha/beta/gamma and VEGFR1, were down-regulated in midostaurin-treated colorectal adenocarcinoma cells and macrophages. Trex-1 protein expression was abrogated after FLT3L activation. In vivo, the combination of midostaurin and anti-PD-1 exhibited the greatest growth inhibition on a CT26-implanted tumor without major toxicity. TME analysis demonstrated that midostaurin alone decreased Treg cells and increased neutrophils and inflammatory monocytes. NKG2D(+) and PD-1 were suppressed and M1 macrophage was increased after combination therapy. When combined with anti-PD-1, STING and INF beta protein expression was elevated in the tumor. The oral administration of midostaurin may have the potential to enhance anti-PD-1 efficacy, accompanied by the modulation of cytosolic DNA-sensing signaling and tumor microenvironment.