Tamoxifen-Induced Cell Death of Malignant Glioma Cells Is Brought About by Oxidative-Stress-Mediated Alterations in the Expression of BCL2 Family Members and Is Enhanced on miR-21 Inhibition.

High-grade gliomas are refractory to the current mode of treatment primarily due to their inherent resistance to cell death. Tamoxifen has been reported to inhibit growth and induce cell death of glioma cells in vitro, in an estrogen-receptor-independent manner. Delineating the molecular mechanism underlying tamoxifen-induced cell death of human glioma cells would help in identifying pathways/genes that could be targeted to induce tumor-cell-specific cell death. In the present study, tamoxifen was found to bring about autophagic cell death of human glioma cells that was accompanied by oxidative stress induction, JNK activation, downregulation of anti-autophagic BCL2 family members, viz. BCL2 and BCL-XL, and increased expression of the pro-autophagic members BCL-Xs and BAK. Oxidative stress induction appears to be primarily responsible for the tamoxifen-induced cell death since the cell death, JNK activation, and the alterations in the expression levels of BCL2 family members were abrogated on pretreatment with antioxidant vitamin E. MiR-21, an oncogenic miRNA, is known to be highly upregulated in malignant glioma. Inhibition of miR-21 activity was found to enhance tamoxifen-induced cell death of U87 MG malignant glioma cells. Tamoxifen treatment coupled with miR-21 inhibition could therefore be an effective strategy for the treatment of malignant gliomas.