As previously demonstrated, the synthetic
bile acid derivatives mediate anti-proliferative properties in a variety of human
cancer cells. In the present study, the effects of the synthetic derivatives of
ursodeoxycholic acid (UDCA),
HS-1030 and
HS-1183, and
chenodeoxycholic acid (CDCA),
HS-1199 and
HS-1200, on the proliferation of HT-29 human
colon cancer cells were investigated. Whereas UDCA and CDCA had no effect on the growth of cells in the concentration ranges we have tested,
HS-1199 and
HS-1200 completely inhibited cell proliferation, while
HS-1030 and
HS-1183 showed weak inhibitory activities. Simultaneous estimation of cell cycle parameters and apoptosis by flow cytometry showed that the synthetic
bile acid derivatives produced the arrest of cell cycle progression at the G1 phase and ensuing increase of sub-G1 fraction, which resulted in the induction of apoptosis. The induction of apoptosis was confirmed by observation of cleavages of
poly(ADP-ribose) polymerase and DNA fragmentation. Furthermore, Western blot analysis showed decreased expression levels of
cyclin D1,
cyclin E,
cyclin A, Cdk2, Cdk4, and Cdk6
proteins. In addition, the synthetic
bile acid derivatives markedly induced the level of Cdk inhibitor, p21WAF1/CIP1, in a p53-independent manner. Furthermore, the exposure of cells to the synthetic
bile acid derivatives resulted in a decrease in the level of pRb and enhanced binding between pRb and E2F-1. Based on these data, these synthetic
bile acid derivatives may serve as potential lead compounds in the treatment of
colon cancer.