Enhancement of radiation effect by guduchi (Tinospora cordifolia) in HeLa cells

The radiosensitizing effect of various guduchi (Tinospora cordifolia Miers, Menispermaceae) extracts, i.e., pretreatment with 10 mug/ml of methanol (Met), aqueous (Aqu) or methylene chloride (Mch) extracts, was studied in the HeLa cells exposed to 0, 0.5, 1, 2, or 3 Gy of gamma-radiation. The irradiation of cells resulted in a dose-dependent decline in the clonogenicity of cells expressed as reduction in cell survival. Treatment of HeLa cells with Met, Aqu or Mch extract before exposure to different doses of gamma-radiation resulted in a significant decline in the cell survival when compared with the phosphate-buffered saline (PBS) + irradiation group. The highest loss in the clonogenicity was observed in Mch + irradiation group, where the cell survival was lower than doxorubicin (Dox) + irradiation group. Conversely, the frequency of micronuclei increased in a dose-dependent manner in all the groups and a significant elevation in micronuclei frequency was observed in Met + irradiation, Aqu + irradiation, Mch + irradiation and Dox + irradiation groups relative to the PBS + irradiation group. The dose enhancement factor for micronuclei-induction varied between 1.4 to 1.97, depending on the type of extract and dose of irradiation. The dose response for all the groups was linear quadratic. The biological response was determined by plotting the surviving fraction of cells versus micronuclei frequency, respectively, for all the groups. The correlation between cell survival and micronuclei-induction was found to be linear quadratic for all the groups. In spite of a good correlation between micronuclei frequency and cell survival, the frequency of micronuclei was lower in Mch + irradiation group than in the other two groups (i.e., Met and Aqu), owing to the greater cell kill as evidenced by the higher decline in the cell survival in this group when compared to the other groups. However, the statistical difference among all guduchi extracts pretreated groups was not significant. The present study demonstrates that all the guduchi extracts were able to enhance the effect of radiation significantly. However, the most effective extract was Mch, where the reduction in the surviving fraction of cells was higher than either Aqu + irradiation, Met + irradiation or Dox + irradiation group.