Enhanced apoptosis and radiosensitization by combined 13-cis-retinoic acidand interferon-alpha 2a; Role of RAR-beta gene

Purpose: Combined use of 13-cis-retinoic acid (cRA) and interferon-alpha 2a (IFN alpha) induced significant radiosensitization in human cervical cance r ME-180 cell line, whereas it failed to achieve similar radiation enhancem ent in HeLa cells. The differential radiosensitization could be from the di fference of retinoic acid receptor (RAR) expression because RAR-beta was hi ghly expressed in ME-180 cells in contrast to the HeLa cells where RAR-beta was not detectable. We examined the role of this gene in mediating radiose nsitization by cRA and IFN alpha, and explored the mechanism of radiation-i nduced cell killing. Methods and Materials: Human cervical cancer cell lines, ME-180 and HeLa, w ere treated with cRA and IFN alpha followed by radiation. Apoptosis and rad iosensitization were quantitated by TUNEL assay (in situ DNA nick end label ing) and colony-forming ability of surviving cells. The cells were transfec ted with bcl-2 gene and RAR-beta gene to test the role of these genes in me diating radiosensitization and apoptosis. Results: Synergistic radiosensitization and apoptosis was observed by combi ned use of cRA and IFN alpha with radiation in ME-180 cells which express h igh level of RAR-beta mRNA, whereas these were not seen in HeLa cells where RAR-beta mRNA is not detectable. Both radiosensitization and apoptosis wer e abolished by bcl-2 gene in ME-180 cells. RAR-beta gene transfection induc ed similar radiation enhancement and apoptosis in HeLa cells. Conclusion: Apoptosis and radiation response were enhanced in the cells wit h high level of RAR-beta mRNA expression. The RAR-beta gene appears to medi ate the radiation-induced apoptosis by cRA and IFN alpha. These findings in dicate that presence of RAR-beta in the cancer cells could be exploited for patient selection in using these drugs for apoptosis. and radiosensitizati on. (C) 2001 Elsevier Science Inc.