SELECTION AND CHARACTERIZATION OF HEAT-RESISTANT VARIANTS OF MULTIDRUG-RESISTANT HUMAN GASTRIC CARCINOMA CELL LINES
Aim: To generate heat resistant variants selected from established human gastric carcinoma cell lines exhibiting different types of multidrug resistance (MDR) phenotype, i.e. EPG85-257P, the drug sensitive parental cell-line, EPG85-257RDB, a classical MDR subline and EPG85-257RNOV, which is an atypical multidrug resistant subline. Methods: Thermoresistance was induced by stepwise increase of the growth temperature from 37.0 to 39.4 °C. Thermoresistance was determined by change of population doubling time (PDT) and clonogenic survival after acute hyperthermia at 42, 43, 44 and 45 °C. Results: Most of the cells exhibited necrosis at elevated culture temperature. The PDT of the surviving thermoresistant variants were increased two-fold (EPG85-257P-TR) and 1.2-fold (EPG85-257RNOV-TR), respectively. No PDT change was observed with the lowest thermoresistant subline EPG85-257RDB-TR. Dose response curves after acute hyperthermia indicated a stable increase of thermotolerance of the parental cell line and the atypical MDR subline (50-90-fold at 45 °C), but not of the classical MDR subline, which was only increased at 43 °C (3-4-fold). Acquired thermoresistance did not change after freezing/thawing procedures. Conclusion: All cell lines achieved chronically induced thermoresistance. Thermotolerance after acute hyperthermia was present in the drug sensitive parental cell line and the atypical MDR subline, but not in cells exhibiting a classical MDR phenotype.
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