Notch1 regulates angio-supportive bone marrow–derived cells in mice: relevance to chemoresistance

Host responses to chemotherapy can induce resistance mechanisms that facilitate tumor regrowth. To determine the contribution of bone marrow–derived cells (BMDCs), we exposed tumor-bearing mice to chemotherapeutic agents and evaluated the influx and contribution of a genetically traceable subpopulation of BMDCs (vascular endothelial–cadherin-Cre-enhanced yellow fluorescent protein [VE-Cad-Cre-EYFP]). Treatment of tumor-bearing mice with different chemotherapeutics resulted in a three- to 10-fold increase in the influx of VE-Cad-Cre-EYFP. This enhanced influx was accompanied by a significant increase in angiogenesis. Expression profile analysis revealed a progressive change in the EYFP population with loss of endothelial markers and an increase in mononuclear markers. In the tumor, 2 specific populations of VE-Cad-Cre-EYFP BMDCs were identified: Gr1+/CD11b+ and Tie2high/platelet endothelial cell adhesion moleculelow cells, both located in perivascular areas. A common signature of the EYFP population that exits the bone marrow is an increase in Notch. Inducible inactivation of Notch in the EYFP+ BMDCs impaired homing of these BMDCs to the tumor. Importantly, Notch deletion reduced therapy-enhanced angiogenesis, and was associated with an increased antitumor effect of the chemotherapy. These findings revealed the functional significance of a specific population of supportive BMDCs in response to chemotherapeutics and uncovered a new potential strategy to enhance anticancer therapy. • Exposure to chemotherapy promotes the exit of specific subpopulations of BMDCs with angio-supportive activity.• Notch in BMDCs is required for the exit of these cells from the bone marrow and for chemotherapy-enhanced angiogenesis in tumors.