Establishment and characterization of cisplatin-resistant sublines of human lung cancer cell lines

Human lung cancer sublines resistant to cisplatin (CDDP) have been developed by continuously exposing cells to gradually increasing doses of CDDP and use of the limiting dilution technique. The cell lines used were PC-7, PC-9 and PC-14 (pulmonary adenocarcinoma) and H69 and N231 (small-cell lung cancer). The resistant phenotype of the resistant sublines was stable for more than 2 months in the absence of drug. PC-7/1.2 (i.e., PC-7 cells growing stably in medium containing 1.2 micrograms/ml of CDDP), PC-9/0.5, PC-14/1.5, H69/0.4, and N231/0.2 have been developed, which are 22.9, 7.1, 3.1, 25.6, and 8.4 times more resistant to CDDP than the respective parent cell line in terms of IC50 in the soft agar colony assay with continuous drug exposure. Cloning efficiency decreased significantly in N231/0.2. The doubling times increased significantly in most of the resistant sublines. Cellular DNA contents increased in all resistant sublines, but statistical significance was observed only in H69/0.4 (p less than 0.05). Cells of the resistant sublines of PC-7, PC-9, PC-14 and H69 were larger than cells of the parent lines, but the differences were not significant. The growth morphologies of all resistant sublines in the drug-free medium were similar to those of parent cell lines. All resistant sublines tested were significantly cross-resistant to carboplatin. The patterns of cross-resistance, cross-sensitivity and collateral sensitivity to adriamycin, mitomycin-C, 5-fluorouracil, vindesine, etoposide, aclacinomycin and vincristine were different in each resistant subline. Verapamil (3.3 micrograms/ml) showed little modifying effect on CDDP resistance in 5 CDDP-resistant sublines tested except N231/0.2 (Modification Index: 0.49). Cyclosporin A (5.0 micrograms/ml) modified CDDP resistance in CDDP-resistant small-cell lung cancer sublines (H69/0.4 and N231/0.2) (Modification Index: 0.45 and 0.07, respectively), while in CDDP-resistant NSCLC sublines (PC-7/1.0 and PC-9/0.5), cyclosporin A reduced the sensitivity to CDDP.