Effect of oridonin on cell-free DNA synthesis in vitro

Oridonin is an antitumor agent isolated from Rabdosia mbescens Hemsl. The DNA synthesis system was sensitive to oridonin in a concentration-dependent manner. When the system was exposed to oridonin 40 ltg/ml for 60 min, the DNA synthesis was inhibited by 62.5%. This inhibition was not reversed by increasing the DNA concentration. The preincubation of oridonin with partially purified DNA polymerase II of Ehrlich ascites tumor cells produced a stronger inhibition, but that of oridonin with DNA or deoxynucleoside triphosphates did not. The inhibitory rates of oridonin 40 ltg/ml were 47 and 78% in the groups preincubated without and with oridonin, respectively. These results suggest that oridonin exerts an inhibitory action on DNA polymerase II.