KAAD-cyclopamine augmented TRAIL-mediated apoptosis in malignant glioma cells by modulating the intrinsic and extrinsic apoptotic pathway

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic. The main obstacle in TRAIL-based therapy is that many glioma cells are resistant. In this study glioblastoma cell lines, human glioblastoma short-term cultures and human astrocytes were treated with 3-keto-N-aminoethylaminoethylcaproyldihydrocinnamoyl cyclopamine (KAAD-cyclopamine), tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) or the combination of both. Single treatment with KAAD-cyclopamine or TRAIL does not induce cytotoxicity in malignant glioma cells. However, treatment with KAAD-cyclopamine in combination with TRAIL induces rapid apoptosis in TRAIL-resistant glioma cells. Notably, normal human astrocytes were not affected by the combination treatment consisting of KAAD-cyclopamine and TRAIL. KAAD-cyclopamine led to an upregulation of death receptor 4 and 5 and down-regulation of bcl-2 and c-FLIP. Furthermore, over-expression of both bcl-2 and c-FLIP attenuated KAAD-cyclopamine facilitated TRAIL-mediated apoptosis. Taken together, we provided evidence that KAAD-cyclopamine facilitated TRAIL-mediated apoptosis at the level of the intrinsic and extrinsic apoptotic pathways in malignant glioma cells.