In vivo evidence and molecular basis for leukemia movement within bone marrow. (A) FLT-1 neutralization reduces actin polymerization in leukemia cells within the BM of inoculated NOD-SCID mice. Top panels (× 630 magnification) show BM sections of control (untreated) NOD-SCID mice 10 days after leukemia cells inoculation, stained and visualized in a fluorescence microscope as described in “Materials and methods.” Green staining shows leukemia cells with evidence for polarization/movement (Phalloidin, stains polymerized actin). Note the almost complete absence of Phalloidin staining in the epiphyseal regions of BM of mice treated with the 6.12 FLT-1-neutralizing Ab (FLT-1Ab, bottom panels, × 630 magnification). These results were obtained from 3 independent experiments. (B) Nystatin, a cholesterol-sequestering agent that impedes lipid raft formation, blocks P1GF-induced leukemia-cell migration. Results show transwell migration assay data, demonstrating that 697 cell migration (mean cell number in 6 HPF, × 400) in response to P1GF (10 ng/mL) is significantly (P < .05) impeded by cotreatment with nystatin, used as described in “Materials and methods.” Results shown are representative of 2 independent experiments. Error bars depict the standard error of the mean.