Abstract
Paclitaxel stabilizes microtubules with inhibition of mitotic spindle formation and has been found effective in several solid cancers. To test whether paclitaxel could be cytotoxic in human HCC cell lines, we used established HuH-7 and HepG2 cell lines. Changes in cell number, DNA synthesis rates and cell viability were determined. We tested whether paclitaxel-treated cells underwent apoptosis, microtubular reorganization, and cell cycle restriction. Studies also examined whether chemosensitization with verapamil enhanced the antitumor activity of paclitaxel. The cell viability was impaired at greater than 0.01 μM paclitaxel concentrations (LD50, 0.8 μM), with flow cytometry indicating accumulation of cells in G2/M, and immunostaining showing polymerized microtubules with characteristic banding patterns. This G2/M restriction was further characterized by flow cytometry, which revealed cyclin A and cdc2 kinase accumulation in paclitaxel-treated cells. Exposure to paclitaxel decreased [3H]thymidine incorporation into DNA in cells at 24 h but this significantly increased at 72 h, most likely due to DNA repair mechanisms related to cell cycle restriction. The cell death was via both apoptotic and non-apoptotic mechanisms. Finally, co-administration of the chemosensitizer verapamil in doses as little as 1 μM increased the antitumor efficacy of paclitaxel by up to five-fold and changed the LD50 of paclitaxel to 0.1 μM. The findings indicate that paclitaxel is cytotoxic to cultured hepatocellular carcinoma cells. Clinical studies of paclitaxel in patients with hepatocellular carcinoma may help determine additional therapies. Copyright (C) 1999.