HIF-1α inhibition impairs BM homing and BM and spleen colonization. HIF-1α stable silencing (shHIF-1α) in MEC-1 cells impairs homing to BM (A), but not to the spleen (B) in Rag2^−/−γc^−/− mice 16 hours after tail vein injection (n = 6). (C) Spleen weight of Rag2^−/−γc^−/− mice injected with shCTRL and shHIF-1α MEC-1 cells and euthanized when terminally sick (panel F). Data represent mean values ± SEM (n = 6). (D) Histopathological evaluation of organs colonization in mice euthanized when terminally sick. Data represent organ involvement as evaluated by a certified pathologist expressed as mean values ± SEM (n = 6). (E) Representative images (original magnification ×20; hematoxylin and eosin stain) of BM and kidney from Rag2^−/−γc^−/− mice injected with the indicated cells and euthanized when terminally sick. shCTRL BM is filled with leukemic cells, whereas shHIF-1α BM shows normal architecture. In shCTRL kidney, arrows indicate leukemia involvement, whereas shHIF-1α kidney is filled with leukemic cells. (F) Kaplan-Meier survival curve of Rag2^−/−γc^−/− mice injected with MEC-1 shCTRL or shHIF-1α cells and euthanized when terminally sick (n = 6). Representative experiment of 2 with similar results. (G) CD31 immunostaining of spleens colonized by MEC-1 shCTRL or shHIF-1α. The graph (left) shows the average number of microvessels per field (original magnification ×40). Data are represented as mean values ± SEM (n = 3). Representative images are shown (right).