Difference in cytotoxicity of paclitaxel against neoplastic and normal cells.

The difference in growth response between neoplastic and contact-sensitive normal cells was investigated by cell growth curve, colony forming efficiency and flow cytometric analysis. Neoplastic cells (MKN-28, MKN-45, and MCF-7), treated with paclitaxel at a concentration of 0.01 mM, showed growth inhibition, low colony-forming efficiency and a prolonged G2+M phase accumulation. Normal cells (Balb/c 3T3 cells and human fibroblasts originating from stomach cancer tissue), treated with paclitaxel at a concentration of less than 0.5 microM, showed no growth inhibition and no decrease in colony-forming efficiency. Normal cells treated with 1 microM of paclitaxel showed low accumulation in G2+M phases. The results show that paclitaxel at concentrations ranging from 0.01 to 0.5 microM had a cytotoxic effect against neoplastic cells but not against normal cells, such as fibroblasts around the cancer cells.