ABROGATED ENERGY-DEPENDENT UPTAKE OF CISPLATIN IN A CISPLATIN-RESISTANT SUBLINE OF THE HUMAN OVARIAN-CANCER CELL-LINE IGROV-1

The parental IGROV-1 human ovarian adenocarcinoma cell line was interm ittently exposed to increasing concentrations of cisplatin to obtain r esistant sublines. A stable resistant subline with a resistance factor of 8.4 had been developed after 9 months and 28 passages, which was d enoted IGROV(CDDP). A high correlation coefficient of 0.97 was found b etween the log cell survival and the DNA-adduct peak level during the process of resistance development. IGROV(CDDP) was strongly cross-resi stant to carboplatin and doxorubicin and moderately cross-resistant to etoposide, docetaxel, and topotecan. Only minor resistance against 5- fluorouracil was observed, whereas IGROV(CDDP) was not cross-resistant to methotrexate. Intracellular accumulation of cisplatin was 65% lowe r in IGROV(CDDP) as compared with parental IGROV-1 at 37 degrees C und er normal conditions. Coincubation of cisplatin with the Na+/K+-ATPase inhibitor ouabain resulted in a more pronounced decrease in platinum accumulation in IGROV-1 (44% decrease) than in IGROV(CDDP) (26% decrea se). Under energy-depleting conditions the accumulation of cisplatin i n the parental cell line was approximately 60% lower than that observe d under normal (energy [i.e., ATP] rich) culture conditions, In contra st, the accumulation in IGROV(CDDP) was not affected by ATP-depletion. There appeared to be no significant difference between the intracellu lar accumulation of platinum in the resistant and sensitive cells unde r conditions of energy deprivation or when the uptake was studied at 0 degrees C. In conclusion, abrogation of energy-dependent accumulation in IGROV(CDDP) seems to be a major mechanism of resistance to cisplat in in this cell line.