Hexahydrocurcumin enhances inhibitory effect of 5-fluorouracil on HT-29 human colon cancer cells

AIM:To investigate the ability of hexahydrocurcumin(HHC) to enhance 5-fluorouracil(5-FU) in inhibiting the growth of HT-29 cells by focusing on cyclooxygenase(COX)-2 expression.METHODS:Antiproliferative effects of HHC and 5-FU,alone and in combination,on growth of HT-29 human colon cancer cells were assessed using 5-diphenyltetrazolium bromide(MTT) reduction assay.In combination treatment,low doses of 5-FU were used combined with various concentrations of HHC to minimize the toxicity and side effects of 5-FU.The therapeutic effects of these drugs on down-regulation of COX-2 mRNA and protein expression were examined using semi-quantitative reverse transcription-polymerase chain reaction(RT-PCR) and Western blotting analysis.RESULTS:MTT reduction assay indicated that HHC alone markedly decreased the viability of HT-29 human colon cancer cells compared to control.Semi-quantitative RT-PCR analysis indicated that HHC is a selective COX-2 inhibitor.This finding was supported by the observation that HHC significantly down-regulates COX-2 mRNA expression compared to the control(control:100.05% ± 0.03% vs HHC:61.01% ± 0.35%,P < 0.05) but does not alter COX-1 mRNA.In combined treatment,addition of HHC to a low dose of 5-FU exerts a synergistic effect against the growth of HT-29 cells by markedly reducing cell viability to a greater degree than monotherapy.Semi-quantitative RT-PCR indicated that 5-FU at the concentration of 5 μmol/L in combination with HHC at the concentration of 25 μmol/L significantly down-regulates COX-2 mRNA expression when compared with values in cells treated with 5-FU or HHC alone(HHC + 5-FU:31.93% ± 5.69%,5-FU:100.66% ± 4.52% vs HHC:61.01% ± 0.35%,P < 0.05).CONCLUSION:HHC together with 5-FU exerts a synergistic effect and may prove chemotherapeutically useful in treating human colon cancer.