Identification and anti-human glioblastoma activity of tagitinin C from Tithonia diversifolia methanolic extract

The Tithonia diversifolia methanolic extract (TDM), which showed antiproliferative activity against human glioblastoma U373 cells, with an IC50 value of 59.2±3.7 μg mL(-1), was passed through silica gel chromatography and successively eluted with different percentages of EtOAc/hexane. The 10-60% EtOAc/hexane subfractions, which exhibited a comparatively higher antiproliferative activity, were isolated, and then structural identification was proceeded with 1H nuclear magnetic resonance. The isolated compound was tagitinin C, a kind of sesquiterpenoid. The IC50 value was 6.1±0.1 μg mL(-1) in U373 treated with tagitinin C. In flow cytometric analysis and inhibition of pan-caspase, the results showed that the anti-glioblastoma effect was apoptosis-independent. In PARP, p-p38, ULK1, and LC3-II expression, the anti-glioblastoma induced by tagitinin C was likely via autophagy. In the ULK1 siRNA transfection experiment, autophagy blockade counteracted the suppression induced by tagitinin C. The result suggested that tagitinin C induces U373 cell death dependent upon autophagy under certain conditions.