Cytotoxic effect through Fas/APO-1 expression due to vitamin K in human glioma cells

Congeners of vitamin K have been found to inhibit growth in various rodent and human tumor cells, but the mechanisms of the inhibitory action are stil l not well understood. To investigate the modes of actions of vitamin K, we used several vitamin K analogs and examined their cytotoxic effect for hum an glioma cell lines RBR17T and U251. The analogs included vitamin K-1 (VK1 ), vitamin K-2 (VK2), vitamin K-3 (VK3), and geranylgeraniol (GGO) which fo rm an unsaturated side chain of VK2. Cell viability was estimated by MTT as say. DNA fragmentation was demonstrated by gel electrophoresis and flow cyt ometry. In order to study the mechanism of apoptosis, we measured the chang es of intracellular reactive oxygen intermediates (ROI) and Fas/APO-1 expre ssion by flow cytometry. The results showed: (1) VK2, VK3, and GGO inhibite d cell growth; (2) VK3 had a more potent cytotoxic effect than VK2, and VK3 enhanced the cytotoxic effect of antitumor agents (ACNU and IFN-beta) in R BR17T cells; (3) VK2, VK3, and GGO induce apoptosis; (4) VK3 increased the expression of Fas/APO-1 although VK2 and GGO did not increase its expressio n in glioma cells; (5) VK3 increased the production of intracellular ROI. C atalase and reduced glutathione (GSH) inhibited production of intracellular ROI and antagonized inhibition of cell-growth induced by VK2, but failed t o antagonize that of VK2 and GGO. We hypothesize that VK3 induces apoptosis by promoting the generation of intracellular ROI and Fas/APO-1 expression. On the other hand, VK2 and GGO induce apoptosis but most likely by some ot her unknown pathway.