Effect of 10-hydroxycamptothecin on nuclear RNA polymerase activity in hepatoma cells in mice

10-Hydroxycamptothecin (HC) is an effective antitumor alkaloid isolated from Camptotheca acuminata. The nuclei from mouse hepatoma cells were isolated and purified. Under light and electron microscopes, the nuclei were intact and clean without cytoplasmic contaminants. In vitro experiment: 30 min after incubation of the nuclei with HC 10-100 Μm at 37 ºC, the activies of RNA polymerase II and I(III) were suppressed gradually. The dise for 50% of inhibition≈ 50μM. The suppressive effect of HC 50 and 100μM on RNA polymerase II appeared generally at 10-15 min after incubation, whilst a similar effect on polymerase I(II) was seen at 30 min. In vivo experiment: 4 h after the last ip injection of HC 10 mg/kg qd×3 to tumorbearing mice, the activities of RNA polymerase II and I(II) in hepatoma nuclei were inhibited by 47% and 43%, respectively.