Purpose: Hepatocellular carcinoma (HCC) is resistant to conventional chemotherapeutics such as doxorubicin. Milk thistle extract, or its active constituent silymarin has been used by cancer patients as an alternative and complementary agent. Telomerase activation is one of the initial events of HCC. In this study, we applied doxorubicin and silymarin for 72 hrs in order to test individual and combined effect of the agents on telomerase activity.
Methods: The effects of doxorubicin, silymarin, and their combination on the proliferation of HepG2 cell line were tested by MTT assay, and Checkerboard micro plate method was applied to define the nature of doxorubicin and silymarin interactions on the cells. Lipid peroxidations were assessed by thiobarbituric acid reactive substance (TBARS) level. Telomerase activity was determined according to the telomeric repeat amplification protocol (TRAP). Untreated cells were used as control group.
Results: Doxorubicin-silymarin combination had indifferent antiproliferative effects on HepG2 cells. Telomerase activity of the cells incubated with IC50 of doxorubicin and silymarin decreased to 72% (p<0.05). IC50 combinations of doxorubicin and silymarin caused 70% (p<0.05) reduction. All treatments except for the 1/2IC50 of silymarin caused significant increase in lipid peroxidation levels when compared to controls. TBARS levels did not significantly increase when doxorubicin and silymarin were applied in combination, which is in concordance with the indifferent drug interaction.
Conclusion: IC50 of both doxorubicin and silymarin alone and in combination inhibited telomerase activity. Mechanism of inhibition may be elucidated by further molecular studies.