Retinamide-induced apoptosis in glioblastomas is associated with down-regulation of Bcl-xL and Bcl-2 proteins

Glioblastomas are among the most difficult neoplasms to treat with continued poor prognosis for long-term survival. Glioblastomas have developed effective mechanisms to resist chemotherapy including levels anti-apoptotic proteins, Bcl-xL and Bcl-2. Chemotherapy agents that promote down-regulation of Bcl-xL and Bcl-2 may enhance sensitivity to chemotherapy in glioblastomas. The ability of the synthetic retinoid N-(4-hydroxyphenyl) retinamide to modulate these anti-apoptotic proteins and to enhance apoptosis and chemotherapy was examined in glioblastoma cells. Expression of Bcl-2 family member proteins Bcl-xL and Bcl-2 were assessed in glioblastomas from three cell lines including U87, U251, and U138. Cells were treated with either retinamide alone or in combination with the chemotherapy agent, BCNU. The incidence of apoptosis was determined with flow cytometry analysis (FACS). Based on Western blots the levels of Bcl-2 and Bcl-xL were decreased in glioblastoma cells after treatment with retinamide. Retinamide treatment resulted in increased ratios of deamidated verses transamidated levels of Bcl-xL in U87 cells. BCNU chemotherapy combined with retinamide markedly down-regulated levels of both Bcl-xL and Bcl-2 proteins in glioblastoma and enhanced the incidence of apoptosis in U87 cells. These studies demonstrate that modulation of levels of the anti-apoptotic proteins, Bcl-xL and Bcl-2, may enhance the sensitivity of glioblastoma toward chemotherapy.