Synergistic antitumor activity by dual blockade of CCR1 and CXCR2 expressed on myeloid cells within the tumor microenvironment

Abstract

Abstract Background Chemokine signaling within the tumor microenvironment can promote tumor progression. Although CCR1 and CXCR2 on myeloid cells could be involved in tumor progression, it remains elusive what effect would be observed if both of those are blocked. Methods We employed two syngeneic colorectal cancer mouse models: a transplanted tumor model and a liver metastasis model. We generated double-knockout mice for CCR1 and CXCR2, and performed bone marrow (BM) transfer experiments in which sub-lethally irradiated wild-type mice were reconstituted with BM from either wild-type, Ccr1−/−, Cxcr2−/− or Ccr1−/−Cxcr2−/− mice. Results Myeloid cells that express MMP2, MMP9 and VEGF were accumulated around both types of tumors through CCR1- and CXCR2-mediated pathways. Mice reconstituted with Ccr1−/−Cxcr2−/− BM exhibited the strongest suppression of tumor growth and liver metastasis compared with other three groups. Depletion of CCR1+CXCR2+ myeloid cells led to a higher frequency of CD8+ T cells, whereas the numbers of Ly6G+ neutrophils, FOXP3+ Treg cells and CD31+ endothelial cells were significantly decreased. Furthermore, treatment with a neutralizing anti-CCR1 mAb to mice reconstituted with Cxcr2−/− BM significantly suppressed tumor growth and liver metastasis. Conclusion Dual blockade of CCR1 and CXCR2 pathways in myeloid cells could be an effective therapy against colorectal cancer.