Stromal reaction inhibitor and immune-checkpoint inhibitor combination therapy attenuates excluded-type colorectal cancer in a mouse model.

Abstract

Despite recent advances in cancer immunotherapy, the efficacy of colorectal cancer (CRC) immunotherapy regimens is limited. This study evaluated the combined effect of an anti-PD-1 antibody and a platelet-derived growth factor receptor inhibitor (imatinib) on CRC progression using an orthotopic transplanted mouse model that reproduced the three histological phenotypes of CRC (inflamed-, excluded-, and desert-type). The frequency of each of these phenotypes in 196 human CRC tissue samples was also evaluated. Excluded-type CRC had the highest frequency in human tissue samples. In the mouse model, imatinib suppressed stromal reaction and increased sensitivity to anti-PD-1 treatment in excluded-type CRC. Antitumor effect was observed in mice with excluded-type tumors only after concomitant administration of anti-PD-1 antibody and imatinib. Immunohistological analysis revealed a reduction in stromal volume and an increase in the number of CD8-positive T cells in the tumor nest following combination therapy. RNA sequencing revealed significant activation of immune-related pathways and suppression of stromal-related pathways in transplanted tumors treated with combination therapy compared with tumors treated with anti-PD-1 antibody monotherapy. This combination therapy may prove effective for CRC cases that are unresponsive to anti-PD-1 antibody monotherapy.