Antiproliferative effects of paclitaxel (Taxol) on human renal clear cell carcinomas in vitro

The aim of this study was to analyse the direct antiproliferative effects of paclitaxel on 20 different renal clear cell carcinoma (RCCC) cell lines comparing the effects of paclitaxel dissolved in either DMSO or Cremophor EL/ethanol (Taxol). The MTT assay was used to determine the growth inhibition of the cell lines by paclitaxel. In addition, micronuclei and microtubule alterations were examined by light and immunofluorescence microscopy. A significant (P < 0.05) dose-dependent inhibition of proliferation was evident in 19 out of 20 cell lines after exposure to paclitaxel dissolved in DMSO and in all cell lines after exposure to paclitaxel in Cremophor EL/ethanol. The extent of response markedly varied between the different cell lines ranging from modest effects to reduction of cell viability down to 1-2% of the control. The effects of paclitaxel in Cremophor EL/ethanol proved to be more pronounced than the effects of paclitaxel dissolved in DMSO. This observation could be explained by additional growth inhibitory effects of Cremophor EL alone. Light microscopy revealed extensive micronucleus formation after treatment with paclitaxel. However, the failure to demonstrate differences of micronucleus formation in paclitaxel-responsive and non-responsive RCCC cell lines argued against a causal relationship between micronucleus formation and growth inhibition. Immunofluorescence microscopy revealed no differences in the formation of abnormal microtubules in cell lines responsive or non-responsive to the growth inhibitory effects of paclitaxel. Further investigations, therefore, are needed to understand the mechanisms determining the response of RCCCs to paclitaxel treatment.