Mcl-1 downregulation sensitizes glioma to bortezomib-induced apoptosis

Glioma is the most aggressive form of primary brain tumor, with dismal patient outcome and no effective therapeutic approaches available. Targeting the ubiquitin-proteasome pathway has recently emerged as a potent rational anticancer strategy. Bortezomib, a specific proteasome inhibitor, has been approved for the treatment of relapsed or refractory multiple myeloma and other hematological malignancies as a single agent or as part of a combination therapy. However, bortezomib alone or in combination showed only minimal effects in the treatment of solid tumors. Myeloid cell leukemia-1 (Mcl-1) is an anti-apoptotic protein which protects tumor cells against spontaneous and chemotherapy-induced apoptosis. In multiple myeloma, specific downregulation of Mcl-1 induces apoptosis. Furthermore, previous studies demonstrated that proteasome inhibitors induce Mcl-1 accumulation that, in turn, slows down their pro-apoptotic effects, and the cell survival in multiple myeloma is highly dependent on Mcl-1. In the present study, we investigated the role of Mcl-1 downregulation in bortezomib-induced apoptosis in gliomas. We observed that bortezomib triggers caspase-3 and PARP activation, upregulates cytochrome c expression and induces apoptosis. Furthermore, we demonstrated that effective targeting of Mcl-1 in glioma cells by gene silencing technology augments the glioma cell sensitivity to bortezomib-induced apoptosis. In conclusion, the present study demonstrates that Mcl-1 plays a critical role in bortezomib-induced apoptosis. Mcl-1 inhibitor in combination with bortezomib present a promising novel strategy to trigger cell death pathways in the treatment of gliomas.