Epidemiologic studies have indicated that n-3 polyunsaturated fatty acids (PUFAs) supplementation may reduce the incidence of breast cancer, also in vivo and in vitro studies have shown that n-3 PUFAs have an inhibitory effect on breast cancer cells. One important n-3 PUFA are eiocosapentaenoic acid (EPA), which are metabolized to five regioisomeric epoxyeicosatetraenoic acids (epoxy-EPAs) by the cytochromes P450 system. Further, these epoxides are metabolized by epoxide hydrolase (EH), which can be inhibited by N, N`-dicyclohexylurea (DCU), an epoxide hydrolase inhibitor (EHI). The effect of these five epoxy-EPAs and the combination of epoxy-EPAs and EHI on breast cancer cells is not known.
In this study the effect of 8, 9-epoxy-EPA on the human estrogen responsive breast cancer cell line MCF-7 was tested. MCF-7 cells were treated with 8, 9-epoxy-EPA, DCU and a combination of 8, 9-epoxy-EPA + DCU. Both the treatment with 8, 9-epoxy-EPA and the combination of 8, 9-epoxy-EPA + DCU inhibited the growth of MCF-7 cells in the presence of FBS. Treatment with 8, 9-epoxy-EPA in the absence of FBS did not result in a change in cell viability, which indicates that the growth inhibition on MCF-7 cells by 8, 9-epoxy-EPA requires an additional proliferative stimulus. To examine the effects of 8, 9-epoxy-EPA on MCF-7 cell growth flow cytometry was used to monitor cell cycle progression. Cells treated with 8, 9-epoxy-EPA and the combination of 8, 9-epoxy-EPA + DCU for 16 and 24 hours were found to be arrested in G0/G1-phase, and did not progress through the cell cycle at the same rate as control cells. 8, 9-epoxy-EPA treatment for 24 hours also resulted in a corresponding decrease in G2/M-phase. The adding of DCU did not enhance the effect of the 8, 9-epoxy-EPA treatment on cell cycle progression significantly. Treatment in the absence of FBS showed no alteration in the progression of the cell cycle. The growth inhibition effect on MCF-7 cells of 8, 9-epoxy-EPA was further studied by examining changes in expression of different cell cycle regulatory proteins. The protein levels were found to be unaltered after 8, 9-epoxy-EPA treatment. The growth inhibition effect may be due to increased cell apoptosis as an alternative to decreased proliferation in MCF-7 cells. This possibility should be evaluated in further studies.||en