Combination Effects of Polyphenols Present in Sugarcane on Proliferation in MCF-7 Human Breast Cancer Cells

Sugarcane is one of the most important crops in the world and rich in polyphenols. In this study, quercetin, apigenin, luteolin, tricin and p-coumaric acid, the major polyphenols in sugarcane, were used to evaluate the antiproliferative activities toward MCF-7 human breast cancer cells independently and in combination. These five polyphenols all showed inhibitory effects against MCF-7 cells within different dose ranges. The combinations of luteolin and three polyphenols (quercetin, apigenin, p-coumaric acid) were studied. p-Coumaric acid together with luteolin exhibited synergistic effects at all concentrations tested: the CI (Combination Index) values at 50%, 75% and 90% inhibition of MCF-7 cell growth were 0.68 ± 0.06, 0.70 ± 0.08 and 0.83 ± 0.09, respectively. Although the two-way combination of luteolin and apigenin showed moderate antagonistic effect (CI, 1.26 ± 0.24) at EC₅₀, the CI value dropped as the inhibition rate increased, showing a synergistic effect at the inhibition rate above 70%. The combination of luteolin and quercetin indicated antagonistic effect at the inhibition rate above 50% (Fa_0.5, CI = 1.10 ± 0.05). p-Coumaric acid with quercetin exhibited antagonistic actions (Fa_0.5, CI = 1.62 ± 0.22) at all concentrations tested. In addition, the EC₅₀ values of luteolin and quercetin against MCF-7 cells decreased by 1.91 and 2.62-fold after combining with 20 µM tricin. The results provide evidence of synergistic relation among polyphenols present in sugarcane in inhibition of cancer cell growth and of their potential clinical application.