Effects of PPP in combination with cytotoxic drugs and pharmacologic inhibitors. (A) RPMI 8226 cells were incubated for 24 hours with 0.3 μM PPP before treatment with dexamethasone, doxorubicin, and melphalan for another 24 hours followed by analysis using the resazurin assay. (B) RPMI 8226 cells were treated simultaneously with PPP and rapamycin or SB203580 for 48 hours followed by analysis using the resazurin assay. Three independent experiments were performed in triplicate and 1 representative is shown. Data are presented as means ± SD. Error bars not visible are included within the symbols (P < .001).