Dasatinib-induced autophagy is enhanced in combination with temozolomide in glioma

Glioblastoma is defined by its aggressive invasion, microvascular proliferation, and central necrosis. BMS-354825 (dasatinib) is an ATP-competitive small-molecule inhibitor effective in treating drug-resistant tumors with mutant BCR-ABL, KIT, and epidermal growth factor receptor by blocking tyrosine phosphorylation sites that are critical in tumorigenesis. In studying the action of dasatinib in human glioblastoma, we found that levels of phospho-SRC, AKT, and ribosomal protein S6 were decreased in cell lines treated with low nanomolar concentrations of dasatinib at baseline and following stimulation with epidermal growth factor. Furthermore, an increased sensitivity to dasatinib was noted in glioma cells with functional PTEN. Reduction of invasive potential was observed in vitro at concentrations well below the IC50 of dasatinib, which was corroborated by immunofluorescence staining showing disruption of paxillin localization to focal adhesions and decreases in focal adhesion kinase autophosphorylation. Cell cycle analysis revealed minimal G(1) arrest but a significant increase in autophagic cell death in glioma cells treated with dasatinib as assessed by acridine orange staining and a concomitant increase in light chain 3 expression and processing. Combination treatment of glioma cells with dasatinib and temozolomide resulted in a significant increase in cell cycle disruption and autophagic cell death. Dasatinib in combination with temozolomide more effectively increased the therapeutic efficacy of temozolomide than when dasatinib was combined with carboplatin or irinotecan. These results strongly support the clinical use of dasatinib in the treatment of glioblastoma and provide a rationale for combination therapy with dasatinib and temozolomide. [Mol Cancer Ther 2009;8(2):394-406]