The effect of hydroxycamptothecin in the activity of RNA and DNA polymerases prepared from murine hepatoma cells

Hydroxycamptothecin (HCPT) is an antitumor alkaloid isolated from Camptotheca acuminata indigenous to China. It could reduce the activity of nuclear RNA polymerase II and I(III) of hepatoma cells. HCPT at 25-100 microM caused a remarkable inhibition on DNA polymerase alpha whilst only a slight inhibition on beta. The inhibitory action on alpha was restored by increasing amounts of enzyme or DNA template, but unchanged by varying amounts of substrate. It is suggested that HCPT may exert a stronger inhibition on DNA replication process.

Cytotoxicity and sister chromatid exchanges induced in vitro by six anticancer drugs developed in the People's Republic of China

Growth inhibition in the Chinese hamster cell line V79 and in the human lymphoid cell line Raji and induction of sister chromatid exchange(s) (SCE) in V79 cells after treatment with six anticancer drugs [harringtonine (HRT), homoharringtonine (HHRT), camptothecin (CPT), hydroxycamptothecin (HCPT), lycobetaine (LBT), and oxalysine (OXL)] developed in the People's Republic of China were studied. OXL is a new antibiotic; all other drugs are plant extracts. All drugs caused a dose-dependent growth inhibition in both cell types, as evidenced by decreases in plating efficiencies of V79 cells and in viable cell counts of Raji. However, the degree of inhibition differed widely among the drugs. HRT, HHRT, CPT, and HCPT were the most potent growth inhibitors, LBT was next, and OXL was the least effective inhibitor. SCE analyses were made in V79 cells treated with a drug in the presence or absence of the metabolic activation system S9 mixture (S9 mix), except for the HRT assay in which the S9 mix was not used. CPT, HCPT, and LBT induced a dose-dependent increase in SCE frequencies, while HRT, HHRT, and OXL caused no SCE induction at any dose level used. CPT was the most powerful SCE inducer. HCPT induced SCE but at a much reduced rate when compared to that of CPT. LBT was a weak SCE inducer; SCE induction was seen only in cultures treated with 40 micrograms or more LBT/ml. Addition of the S9 mix did not alter SCE frequencies, indicating that the drugs were direct-acting agents. HRT and HHRT were highly toxic, but they induced no increases in SCE frequency, indicating that cytotoxicity of a compound does not necessarily correlate with SCE induction.

The influence of several anticancer agents on cell proliferation, differentiation and the cell cycle of murine erythroleukemia cells

The influence of homoharringtonine, hydroxycamptothecin and lycobetaine on the cell cycle progression of murine erythroleukemia cells was studied by using flow microfluorometry (FMF) technique and centrifugal elutriation to obtain specific fractions of the cell cycle. FMF histogram analysis showed that homoharringtonine could strongly arrest cells in the G1 phase of the immediate cell cycle. This effect was more pronounced and persisted longer with G1 cells than with S or G2 cells. Hydroxycamptothecin mainly delayed the progression of S cells of the subsequent cell cycle (daughter cells). Lycobetaine caused a marked accumulation of G2 cells. These 3 compounds possess a relatively specific action on cell progression through the cell cycle. Homoharringtonine and hydroxycamptothecin can inhibit the cell proliferation of murine erythroleukemia cells (MELC) at low concentrations (ng/ml) whereas lycobetaine, cantharidin and oxalysine are less potent. Among them only hydroxycamptothecin had a weak activity to induce MELC differentiation. These results may provide some basic knowledge for designing new protocols of the combination treatment of neoplastic diseases.