MTBITC mediates cell cycle arrest and apoptosis induction in human HepG2 cells despite its rapid degradation kinetics in the in vitro model.

Despite the great variety of structure homologous, experimental research on the cancer preventive properties of isothiocyanates (ITCs) is limited to only a fractional amount thereof so far. Especially the degradation of these compounds in the experimental system has not been investigated so far. In this study, we investigated the effect of 4-methylthiobutyl isothiocyante (MTBITC) on the proliferation of human hepatoma (HepG2) cells and underlying mechanisms. A concentration and time-dependent reduction in proliferation activity could be observed in cells treated with MTBITC exceeding 10 microM. At these concentrations MTBITC-induced apoptosis in HepG2 cells could be observed by internucleosomal DNA fragmentation, flow cytometry analysis, and the detection of single-stranded apoptotic DNA. In all the three assays, clear apoptotic events were present after 6-hr exposure to MTBITC. Apoptosis induction was accompanied by a time-dependent arrest of HepG2 cells at the G2/M phase of the cell cycle. This study shows for the first time the inhibitory potency of MTBITC on metabolically competent hepatoma cells, whereas the loss of reduced glutathione and its impact on mitochondria seem to be the major processes involved in the initiation and execution of the apoptotic cell death. The results of this study also showed that irrespective of the intense degradation kinetics of MTBITC, the strong cytostatic effect of the ITC was not markedly affected by it and suggests that although ITCs are only present at maximum concentrations in a living system for a rather short time, this might be sufficient to exert their therapeutic effects.