Induction of apoptosis of human glioma cell lines: Effects of combined treatment with corilagin and temozolomide

Corilagin (beta-1-O-galloyl-3,6-(R)-hexahydroxydiphenoyl-d-glucose), a gallotannin identified in several plants, including Phyllanthus urinaria, has been shown to exhibit versatile medicinal activities. In the present paper, we report experiments aiming at determining the effects of corilagin on nuclear factor kappaB (NF-κB) binding to DNA target and on apoptosis by administering corilagin to two glioma cell lines (U251 and T98G), one of which (T98G) is resistant to temozolomide (TMZ). The data obtained in experiments based on electrophoretic mobility shift assay and in molecular docking simulations demonstrate that corilagin binds to NF-κB and inhibits NF-κB/DNA interactions. The effects on apoptosis were evaluated using the MUSETM instrument and annexin-5 and caspase 3/7 assay kits. The results obtained indicate that corilagin inhibits cell proliferation and induces apoptosis in U251 and T98G glioma cell lines. The effects on cell growth indicate a 60 and 100 µM IC50 of corilagin on U251 and T98G cell lines, respectively. By contrast, dramatic differences were found using TMZ (IC50 75 µM for U251 and 500 µM for T98G). Therefore, corilagin is also effective on the TMZ-resistant T98G glioma cells. This is sustained by further experiments based on the two apoptosis assays and showing that both U251 and T98G cell lines express apoptotic markers when treated with 50 (U251) and 75 (T98G) µM corilagin. Finally, T98G glioma cells treated with sub-optimal concentrations of corilagin (50 µM) expressed high apoptotic levels when they were co-treated with TMZ.