HUMAN LARYNX-CARCINOMA CELLS RESISTANT TO CIS-DIAMMINEDICHLOROPLATINUM(II) - MECHANISMS INVOLVED IN THE RESISTANCE

The aim of this study was to characterize two cis-diamminedichloroplat inum (II)(CDDP) resistant cell lines established from human larynx car cinoma HEp2 cells through repeated treatments with increased CDDP conc entrations. CK2 cells obtained by continuous treatments were more resi stant to CDDP than CA3 cells obtained by acute treatments. The examina tion of growth characteristics showed that both CDDP resistant cells h ad doubling times identical to that of the parental cells, but had low er plating efficiency. The possible involvement of glutathione (GSH), glutathione transferases (GST), metallothioneins, P-glycoprotein and d rug accumulation in CDDP resistance was examined. Glutathione contents were elevated in both CDDP resistant lines. However, neither GSH nor GST were involved in CDDP resistance. This was demonstrated by simulta neous incubation of parental and CDDP resistant cells with CDDP and sp ecific inhibitors of GSH and GST alpha and pi (buthionine sulfoximine and ethacrinc acid). Similarly, verapamil, an inhibitor of P-glycoprot ein, did not influence the sensitivity of parental and cells to CDDP. As compared to the parental cells, CK2 cells became resistant and CA3 cells became sensitive to cadmium, indicating increased level of metal lothioneins in CK2 cells, and reduced level in CA3 cells. Measurements of platinum contents in parental and CDDP resistant cells after 1, 3 and 6 hours exposure to 70 mumol CDDP showed reduction in platinum acc umulation after each exposure time in CK2 cells, and after 6 hours exp osure in CA3 cells. This study identified decreased platinum accumulat ion as an important mechanism of CDDP resistance in human larynx carci noma cells.