PI3K inhibitors sensitize CLL cells to fludarabine. CLL B cells were cultured with or without marrow stromal cells and treated with PI3K inhibitors alone (single agents) or a combination of PI3K inhibitors and fludarabine (+F-ara-A). (A) Contour plots of viable (bottom right quadrant), apoptotic (bottom left quadrant), and dead (top left quadrant) CLL cells from a representative patient, cultured on marrow stromal cells, and treated with the reagents indicated above or below each of the plots. Next to each of these cell populations, the relative proportion of viable, apoptotic, and dead cells is displayed. Pretreatment of CLL cells with the PI3-K inhibitors Ly 294002, PI-103, and PIK-90 enhanced the cytotoxicity of fludarabine and also partially reversed the protective effect of stromal cells on fludarabine-induced apoptosis. In this case, F-ara-A treatment alone did not affect CLL viability, and treatment with PIK-90 at 1 μM reduced the viability to 75.6% from 87.8% in the controls. However, the combination of both drugs decreased the viability to 23%, suggesting synergism at this concentration. (B) This graph summarizes the effects of PI3K inhibitors alone and in combination with F-ara-A in cultures with or without marrow stromal cells in 10 different CLL cell samples and at 3 different time points. The viability of CLL cells was assessed at the time points indicated on the horizontal axis by staining with DiOC6 and PI. Each data point in panel B represents the mean (± SEM; n = 10) relative viability of treated CLL B cells compared with the untreated controls (100%).
