We previously synthesized several K-
vitamin derivatives, which are potent
growth inhibitors of human
tumor cells, including Hep3B human
hepatoma cells. Among these, Cpd 5 was the most potent. However, being a
quinone derivative, Cpd 5 has the potential for generating toxic
reactive oxygen species (ROS). We therefore synthesized a fluorinated derivative of Cpd 5, F-Cpd 5. The calculated reduction potential of F-Cpd 5 was much higher than that for Cpd 5 and it was not predicted to generate ROS. This was supported by our observation that F-Cpd 5 generated significantly lower ROS than Cpd 5. F-Cpd 5 was three times more potent than Cpd 5 in inhibiting Hep3B cell growth. Interestingly, under identical culture conditions, F-Cpd 5 inhibited
mitogen-induced
DNA synthesis in normal rat hepatocytes 12-fold less potently than Hep3B cells. F-Cpd 5 was found to induce
caspase-3 cleavage and nuclear
DNA laddering, evidences for apoptosis. It preferentially inhibited the activities of the cell cycle controlling
phosphatases Cdc25A and Cdc25B, by binding to their catalytic cysteines. Consequently, inhibitory
tyrosine phosphorylation of the Cdc25 substrate
kinases Cdk2 and Cdk4 were induced. F-Cpd 5 also induced phosphorylation of the MAPK
proteins ERK1/2, JNK1/2 and p38 in Hep3B cells and the MAPK inhibitors (
U0126, JNKI-II, and
SB 203580) antagonized its growth inhibition. F-Cpd 5 inhibited the action of cytosolic ERK
phosphatase activity, which likely caused the ERK phosphorylation. F-Cpd 5 thus differentially inhibited growth of normal and
tumor cells by preferentially inhibiting the actions of Cdc25A and Cdc25B
phosphatases and inducing MAPK phosphorylation.