Mesenchymal stem cells regulate melanoma cancer cells extravasation to bone and liver at their perivascular niche

Skeleton and liver are preferred organs for cancer dissemination in metastatic melanoma negatively impacting quality of life, therapeutic success and overall survival rates. At the target organ, the local microenvironment and cell-to-cell interactions between invading and resident stromal cells constitute critical components during the establishment and progression of metastasis. Mesenchymal stem cells (MSCs) possess, in addition to their cell progenitor function, a secretory capacity based on cooperativity with other cell types in injury sites including primary tumors (PT). However, their role at the target organ microenvironment during cancer dissemination is not known. We report that local MSCs, acting as pericytes, regulate the extravasation of melanoma cancer cells (MCC) specifically to murine bone marrow (BM) and liver. Intra-arterially injected wildtype MCC fail to invade those selective organs in a genetic model of perturbed pericyte coverage of the vasculature (PDGF-B ret/ret), similar to CD146-deficient MCC injected into wild type mice. Invading MCC interact with resident MSCs/pericytes at the perivascular space through co-expressed CD146 and Sdf-1/CXCL12-CXCR4 signaling. Implanted engineered bone structures with MSCs/pericytes deficient of either Sdf-1/CXCL12 or CD146 become resistant to invasion by circulating MCC. Collectively, the presence of MSCs/pericytes surrounding the target organ vasculature is required for efficient melanoma metastasis to BM and liver.