Objective To observe the effect of concomitant administration of hederagenin（ HG） and 5-fluorouracil（ 5-FU） / oxaliplatin（ Oxa） on the proliferation of human colon adenocarcinoma cell line HT19 and its possible mechanism. Methods Using MTT

the single and concomitant effect of HG

5-FU and Oxa on HT-29 during exponential phase of proliferation were assayed. By performing statistical analysis such as Median-effect Equation

the response curves are plotted and the drug-drug interaction by establishing the drug combination-response model predicted. By colony formation assay

we have measured the effect of single and concomitant usage of the 3 drugs on the colony formation. Using RT-qRCP

the effects on mRNA expressions of OPRT

TS

ERCC1 and BRCA1 were tested.Result As the dose increased

the inhibiting effect of HG

5-FU and Oxa on HT-29 proliferation

singly or concomitantly administered

also increased with the synergistic effect in high concentration enhanced. The effect of concomitant administration of HG and 5-FU / Oxa produced favorable synergistic effect. The inhibitory rate for HG

5-FU

Oxa

HG + 5-FU and HG + Oxa groups were 39. 34%

45. 37%

51. 01%

70. 43% and 70. 96%

respectively

and their differences to control group showed statical significance（ P < 0. 01）. After the administration of HG

TS mRNA was down-regulated to 1. 655

ERCC1 mRNA down-regulated to 0. 182

BRCA1 mRNA down-regulated to0. 44 and OPPRT mRNA up-regulated to 1. 655 with statistical significances to control group（ P < 0. 05 or P < 0. 01）.Conclusion the concomitant administration of hederagenin（ HG） and 5-fluorouracil（ 5-FU） / oxaliplatin（ Oxa）showed significant inhibitory effect on the proliferation of human colon adenocarcinoma cell line HT19 with the efficacy concomitantly enhanced. The one of the synergistic mechanisms is possibly the down-regulation of HT-29 in TS

ERCC1 and BRCA1 expressions and up-regulation of OPRT expression.