Rapamycin and CCI-779 induce G₀/G₁ arrest of BM-ECs. Cell-cycle analyses were performed at 24 hours, using flow cytometry bivariate distributions of BrdU incorporation versus DNA content (PI). BM-ECs were stimulated with cytokine media/EGM2 or 10% vol/vol leukemia plasma and treated with rapamycin (10, 100 ng/mL) (A) or with CCI-779 (10 nM) (B). Data represent mean ± SEM of experiments using BM-ECs from 3 different donors and 10 different ALL patients. ^*Significance level of P < .05 using a 2-tailed paired t test. (C) BM-ECs were cytokine/serum deprived for 12 hours (EBM) and then stimulated with cytokine media/EGM2 with or without rapamycin (10 ng/mL) for 12 or 24 hours. Protein levels of cyclin D1, p27^kip1, and p21^cip1 and the phosphorylation status of cdk2 were determined by Western blot. Arrow indicates correct band. Results are representative of 3 (12-hour time point) or 5 (24-hour time point) different BM-ECs tested.