AIMTo investigate the synergetic effect and the mechanism of antitumor action of the antibiotic lidamycin in combination with cisplatin in vitro.

METHODSCytotoxicity of the drugs was measured by clonogenic assay. Chromatin condensation was observed by co-staining with fluorescent dyes, Hoechst 33342 and propidium iodide. Apoptotic sub-G1 was detected by flow cytometry and DNA ladder was observed using agarose gel electrophoresis. Bcl-2 protein level was detected by Western blot assay.

RESULTSBy using clonogenic assay, lidamycin in combination with cisplatin was found to have synergetic effects on the proliferation of human hepatoma BEL-7402 cells. The data showed that BEL-7402 cells treated with cisplatin and lidamycin in combination produced internucleosomal DNA fragmentation analysed by agarose gel electrophoresis. The results of flow cytometry showed that cisplatin and lidamycin administrated in combination showed no obvious change in G1 phase distribution compared with single treatment. However, this combination reduced the S phase arrest and reversed the reduction of G2/M phase induced by single treatment. The results also showed that there was 11.3% or 9.37% of cells undergoing apoptosis in BEL-7402 cells treated with cisplatin or lidamycin, respectively, while it showed 32.4% of apoptotic cells in combination treatment. Cisplatin, lidamycin and combination of cisplatin and lidamycin was shown to induce typical chromatin condensation in BEL-7402 cells. The study showed that 0.5 mumol.L-1 cisplatin or 1 x 10(-4) mumol.L-1 lidamycin alone decreased Bcl-2 protein level, while lidamycin in combination with cisplatin strongly inhibited expression of Bcl-2 proteins in BEL-7402 cells.

CONCLUSIONThe results suggest that lidamycin enhancement of cisplatin-induced apoptosis associates with decrease of Bcl-2 protein expression, which may be useful for cancer chemotherapy.