Cytokinetic effects of oridonin on leukemia L1210 cells

Oridonin is a diterpenoid isolated from Rabdosia rubescens. An ip injection of 1*10(6) L1210 cells gave rise to an exponential growth during the first 7 d.The doubling time was about 0.61 d. The growth curve reached a plateau phase in 8 d. The cell killing rates of oridonin 15 mg/kg ip on d 5 and d 8 upon L1210 cells were 73 and 39% respectively. The labeled mitotic curve of L1210 cells showed the prolonged T(C), T(G2+M) and T(S) after ip oridonin 15 mg/kg. Oridonin was injected ip 15 mg/kg 30 min after the pulse labeled with [3H] TdR, LI decreased gradually from 28% to 9%.The L1210 cells showed a remarkable nuclear damage without noticeable damage of cytoplasm in 1 h. The damaged labeled and unlabeled cells amounted to 22 and 16% respectively.By continuous labeling with [3H]TdR for 24 h, the fraction of cells in G0 phase of L1210 cells on d 8 was 64%, the damaged cells in G0 phase were about 34%. Using the colchicines-blocking technique in combination with the pulse and continuous labeling technique with [3H]TdR, T(G2), T(S) and T(G1) were 2.3,12.3 and 3.0 h. The time of G2 and S phase were prolonged, while T(G1) was unchanged. Thus,oridonin appears to be a cell cycle non-specific agent.