Characterization of a Taxol‐resistant Human Small‐cell Lung Cancer Cell Line

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Abstract
Taxol is a novel anticancer agent with activity against a broad range of tumors. It has a unique ability to stabilize polymerized tubulin into microtubule bundles within the cell. We have established a taxol‐resistant human small‐cell lung cancer cell line (H69/Txl) by exposing H69 cells to stepwise increases in taxol concentration. The resistance of H69/Txl cells to taxol was 4.7‐fold that of the original H69 cells: the IC50 values for H69 and H69/Txl were 113.7 ± 56.54 nM and 538.7 ± 214.7 nM by the tetrazolium dye assay, respectively. Removal of the drug from the medium resulted in a 38% decrease in the growth rate of H69/Txl as compared with that in the presence of 30 nM taxol, suggesting that the growth of H69/Txl was partially dependent on taxol. H69/Txl showed higher sensitivity to vinca alkaloids such as vindesine, vincristine and vinblastine than the parental H69. There was no significant difference in intracellular [3H]taxol content between H69 and H69/Txl cells. No MDR‐1 mRNA was detected in H69/Txl by the reverse transcription polymerase chain reaction. There was no significant difference of total and polymerized tubulin content between H69 and H69/Txl cells. Altered mobility of one of the α‐tubulin isoforms in H69/Txl was revealed by using isoelectric focusing and Western blotting with anti‐α‐tubulin antibody. In H69, two α‐tubulin isoforms were observed, whereas three were evident in H69/Txl, two of them comigrating with the isoforms of H69 and the other being more acidic. We observed the increased acetylation of α‐tubulin in H69/Txl cells as compared with that in H69 cells. The acetylation of α‐tubulin may be responsible for the taxol resistance and/or taxol‐dependent growth of H69/Txl.