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 degrees C. Thermoresistance was determined by change of population doubling time (PDT) and clonogenic survival after acute hyperthermia at 42, 43, 44 and 45 degrees 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 degrees C), but not of the classical MDR subline, which was only increased at 43 degrees 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.