Effect of oridonin on metabolism of thymine nucleotides in tumor cells in mice

Oridonin is an effective antitumor component isolated from Rabdosia rubescens Hemsl. The incorporation of [3H]TdR into the acid-insoluble fraction (DNA) of Ehrlich ascites tumor cells was distinctly inhibited by oridonin in a concentration-dependent manner, while the concentration of the [3H]thymine nucleotides in the acid-soluble fraction was evidently elevated, especially [3H]TTP. When the concentration of oridonin was 20μg/ml, the incorporation of [3H]TdR was 46% of control in the acid-insoluble fraction and 213% of control in the acid-soluble fraction； the incorporation ratios of [3H]TMP, [3H]TDP and [3H]TTP were 255, 306 and 458，respectively, but the concentration of [3H]TdR in the acid-soluble fraction was the same with that in control. These results suggest that oridonin blocks the polymerization of deoxynucleotides to form DNA, but does not influence the phosphorylation of thymidine or thymine nucleotides.