Impact of calcitriol and an AKT inhibitor, AT7867, on survival of rat C6 glioma cells

Abstract

Glioma is the most prevalent and lethal type of primary tumor of central nervous system. The regulatory role of calcitriol, the active form of vitamin D3, has been determined in various cellular processes including cell survival and apoptosis. To study the impact of AKT-pathway inhibition with or without calcitriol combination on glioma cell viability, the effects of AT7867 (AKT-pathway inhibitor) and calcitriol on cell viability and apoptosis were investigated in glioma C6 cell-line. Optimal doses of calcitriol and AT7867 were determined by MTT- and xCELLigence-assays. Both agents (alone/in combination) effectively suppressed the proliferation of C6 cells. While AT7867 inhibited glioma cell viability more effectively than calcitriol, this inhibitory action of AT7867 was not significantly increased by calcitriol combination. The expression levels of vitamin D receptor(VDR)-triggered molecules, AKT-pathway components and apoptosis factors were compared between calcitriol-, AT7867- and calcitriol + AT7867-treated and non-treated cells. CYP24A1 gene was upregulated and DBP, CYP1A1, CYP27B1, EGFRvIII, AKT-pathway (AKT1, MTOR, CREB, PTEN), apoptosis (BAD, CYC-C, CASP3, APAF-1, BCL2) and MMP3 genes were downregulated by calcitriol treatment.AT7867 treatment induced CYP27B1 upregulation, reduced VDR and AKT-pathway (PI3K, MTOR, CREB, PTEN) gene expression levels but showed a relatively less pronounced effect on apoptosis-related gene levels. The combination of calcitriol and AT7867 treatment generated an effect that was similar to that induced by calcitriol alone. Our results demonstrate that calcitriol and AT7867 have differing actions on AKT- and apoptotic-pathways of C6 glioma cell-line. Calcitriol has a lesser viability reducing impact than AT7867 putatively due to its apoptosis inhibiting action.