Cell-cycle specificity of sulforaphane-mediated apoptosis in Jurkat T-leukemia cells.

Background: Sulforaphane (SFN) is an isothiocyanate that is present in widely consumed vegetables. Previous studies have shown that SFN is effective in preventing carcinogenesis induced by carcinogens in rodents. Recently it was found that SFN could also inhibit cell proliferation and induce apoptosis in several tumor cell lines. In the present study, the possible cell-cycle specificity of SFN-mediated apoptosis was investigated. Materials and Methods: Cells were synchronized by thymidine block. Analysis of the cell-cycle and apoptosis induction was performed using flow cytometry. Results: Flow cytometric assessment of the extent of apoptosis in cells synchronized by thymidine block revealed that cells were most sensitive to SFN in the G1-phase, less sensitive in the G2/M-phase and least sensitive during the S-phase. Conclusion: These findings suggest that cell vulnerability to SFN-mediated apoptosis is subject to regulation by cell-cycle- dependent mechanisms. Isothiocyanates are agents that occur as glucosinolates in a variety of cruciferous vegetables. In vitro and in vivo studies show that isothiocyanates are potent anticarcinogenic compounds (1-5). Sulforaphane (SFN) is one of the most studied isothiocyanates. Accumulating evidence suggests that SFN is an effective inhibitor of chemically induced tumors in rodents (1, 6-7) through the induction of phase II detoxification enzymes (8). Moreover, in vitro studies suggest that SFN also modulates the growth of tumor cells through induction of apoptosis, inhibition of cell proliferation and regulation of the cell-cycle (9). Taken together, these findings identify SFN as a potential anticancer agent. However, it is not clear whether its proapoptotic activity is cell-cycle specific. The cell-cycle phase is believed to play a critical role in the mechanism for the action of a plethora of cytotoxic drugs. There are a lot of good examples in this context. Azathioprine is a purine antagonist and has classically been described as a cell-cycle specific drug, an S-phase inhibitor (10); the apoptotic effect of methotrexate is only realized in cells that are in the S- phase of cell replication (11); taxanes target tubulin and mitosis (12). This study was undertaken to investigate the possible cell- cycle specificity of SFN-mediated apoptosis induction in Jurkat T leukemia cells synchronized in the different cell- cycle phases.