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Abstract
Proadifen (SKF-525A) is a well-known inhibitor of cytochrome P450 monooxygenases.
Besides the prevention of drug metabolism it affects the proliferation of cancer cells,
although the mechanisms of possible anti-cancer activity of proadifen have not been
fully understood yet. The aim of this study therefore was to evaluate the potential
anti-proliferative effect of proadifen on HT-29 colon cancer cells. Our results show
that proadifen inhibited the growth of HT-29 cells by the accumulation of cells in
the G1 phase of the cell cycle, reduction of metabolic activity and colony formation
and by the induction of apoptosis. Analyses of Western blots and flow cytometry revealed
time- and dose-dependent phosphatidylserine externalization, caspase-3 activation
and PARP cleavage. Intense upregulation of NAG-1 and ATF3 and downregulation of Mcl-1
and Egr-1 were also observed. Further investigation showed that NAG-1 gene silencing
by siRNA had no effect on the pro-apoptotic action of proadifen. In contrast, we found
that AR-A014418, the specific inhibitor of glycogen synthase kinase-3 β (GSK-3β),
significantly decreased proadifen-induced apoptosis. Inactivation of GSK-3β (phosphorylation
at serine 9) resulted in changes in phosphatidylserine externalization and caspase-3
activation. These data suggest that GSK-3β is an important factor in the induction
of apoptosis in HT-29 colon cancer cells treated with proadifen.