Increased ceramide and sphingosine are important for synergy with ABT-263.

<p>(<b>A</b>) Summary of the lipids that are altered following treatment of U937 cells with various inhibitors. (<b>B</b>) IC50 values of ABT-263 for individual human leukemia cell lines. Values were calculated in prism as the result of dose response curves determined by alamar blue assay 48 hours after ABT-263 treatment. (<b>C</b>) Total levels of basal ceramide (Cer) and sphingosine-1-phosphate (S1P) in four different cell lines as determined by HPLC-MS/MS. Data are normalized to the levels of lipids in U937. (<b>D</b>) Model depicting how different inhibitors affect sphingolipid metabolism.