Abstract
Puromycin-resistant (PurR) mutants/variants of a human carcinoma cell line (HeLa), which show greatly reduced cellular uptake of 3H-puromycin and 3H-daunomycin have been isolated after one- and two-step selections in presence of the drug. The cross-resistance pattern of these mutant cell lines towards numerous anticancer drugs and other inhibitors has been examined. Both the first- and the second-step mutants exhibited increased resistance to a number of antimitotic drugs (viz. vinblastine, vincristine, colchicine, taxol and maytansine), several protein synthesis inhibitors (viz. chalcomycin, bruceantin, harringtonine, homoharringtonine), a large number of DNA interactive compounds (viz. aclacinomycin A, actinomycin D, adriamycin, m-AMSA, chromomycin A3, coralyne sulphoacetate, daunomycin, ellipticine, mithramycin, mitoxantrone, 5-methoxysterigmatocystin, rubidazone, variamycin, VM26 and VP16-213) and a number of other drugs acting via other mechanisms (viz. Baker's antifol, nitidine chloride and rhodamine 123). Whereas the first-step mutants showed stable resistance to these drugs, the second-step lines partially reverted upon growth in non-selective medium. Further, treatment of these mutant lines with non-cytotoxic doses of the calcium channel blocker verapamil reverted or abolished their resistance to the above drugs in a dose-dependent manner. In contrast to the above compounds, the PurR mutants showed no significant cross-resistance to a large number of other drugs which included asaley, AT-125, 5-azacytidine, azaserine, cyclocytidine, cis-platin, cytosine arabinoside, chlorambucil, chlorpromazine, alpha-difluoromethyl ornithine, 5-fluorouracil, ftorafur, gallium nitrate, hydroxyurea, ICRF-159, ICRF-187, imipramine, methotraxate, 6-methylmercaptopurine riboside, mycophenolic acid, melphalan, mitomycin C, methyl GAG, nafoxidine, reumycin, 6-selenoguanosine, 6-thioguanine, tiazofurin, tamoxifen, thalicarpine, tiapamil and verapamil). These cross-resistance data should prove useful in developing suitable drug combinations to which cellular resistance would not develop readily.
Highlights
HeLa and its drug-resistant variants were grown routinely in monolayers in alpha MEM supplemented with 5% foetal bovine serum at 37°C in 95% air, 5% CO2 atmosphere (Singh & Gupta, 1985)
The degree of resistance of any cell line towards a given drug was determined by seeding 100 and 250 cells of the parental and the mutant cell lines in duplicate into the wells of 24-well tissue culture dishes containing 0.5 ml of various drug dilutions made twice the final concentrations desired in the growth medium
The drug doses were chosen based on initial toxicity studies with the sensitive and resistance cell lines and were such that the D1o value of various cell lines lay within this range
Summary
Cell lines and culture conditionsHeLa (clone S3) and its drug-resistant variants were grown routinely in monolayers in alpha MEM supplemented with 5% foetal bovine serum at 37°C in 95% air, 5% CO2 atmosphere (Singh & Gupta, 1985). The degree of resistance of any cell line towards a given drug was determined by seeding 100 and 250 cells of the parental and the mutant cell lines in duplicate (in 0.5 ml of growth medium) into the wells of 24-well tissue culture dishes containing 0.5 ml of various drug dilutions made twice the final concentrations desired in the growth medium. In most of these experiments, 12 or more drug doses differing from each other by a factor of 2 were employed. The control cells were treated with an equivalent amount of solvent in which the drug was made
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