G-CSF supplementation with chemotherapy can promote revascularization and subsequent tumor regrowth: prevention by a CXCR4 antagonist.

Recombinant granulocyte colony-stimulating factor (G-CSF) is used to accelerate recovery from chemotherapy-induced myelosuppression. G-CSF has been recently shown to stimulate angiogenesis mediated by several types of bone marrow-derived cell populations. To investigate whether G-CSF may alter tumor response to therapy, we studied Lewis lung and EMT/6 breast carcinomas in mice treated with paclitaxel (PTX) chemotherapy in combination with G-CSF. We compared the results obtained to mice treated with PTX and AMD3100, a small-molecule drug antagonist of CXCR4 which, like G-CSF, can be used to mobilize hematopoietic cells. We show that PTX combined with G-CSF treatment facilitates revascularization, leading to an improvement in blood perfusion in LLC tumors, and a decrease in hypoxia in EMT/6 tumors, thus enhancing tumor growth in comparison to PTX or PTX and AMD3100 therapies. We found that hemangiocytes but not Gr-1(+) CD11b(+) cells colonize EMT/6 tumors after treatment with PTX and G-CSF, but not PTX and AMD3100, and therefore may contribute to angiogenesis. However, increases in hemangiocyte colonization were not observed in LLC PTX and G-CSF-treated tumors, suggesting distinct mechanisms of tumor revascularization after G-CSF. Overall, our observations suggest that despite its known considerable clinical benefits, G-CSF might contribute to tumor revascularization by various mechanisms, and diminish the antitumor activity of chemotherapy, an effect that can be prevented by AMD3100.