Characterization of an ovarian carcinoma cell line resistant to cisplatin and flavopiridol

Flavopiridol, the first inhibitor of cyclin-dependent kinases to enter clin ical trials, has shown promising antineoplastic activity and is currently u ndergoing Phase II testing. Little is known about mechanisms of resistance to this agent, In the present study, we have characterized an ovarian carci noma cell line [OV202 high passage (hp)] that spontaneously developed drug resistance upon prolonged passage in tissue culture, Standard cytogenetic a nalysis and spectral karyotyping revealed that OV202 hp and the parental lo w passage line OV202 shared several marker chromosomes, confirming the rela tedness of these cell lines. Immunoblotting demonstrated that OV202 and OV2 02 hp contained similar levels of a variety of polypeptides involved in cel l cycle regulation, including cyclin-dependent kinases 2 and 4; cyclins A, D-1, and E; and proliferating cell nuclear antigen, Despite these similarit ies, OV202 hp was resistant to flavopiridol and cisplatin, with increases o f 5- and 3-fold, respectively; in the mean drug concentrations required to inhibit colony formation by 90%. In contrast, OV202 hp and OV202 displayed indistinguishable sensitivities to oxaliplatin, paclitaxel, topotecan, 1,3- bis(2-chloroethyl)-1-nitrosourea, etoposide, doxorubicin, vincristine, and 5-fluorouracil, suggesting that the spontaneously acquired resistance was n ot attributable to altered P-glycoprotein levels or a general failure to en gage the cell death machinery. After incubation with cisplatin, whole cell platinum and platinum-DNA adducts measured using mass spectrometry were low er in OV202 hp cells than OV202 cells. Similarly, after flavopiridol exposu re, whole cell flavopiridol concentrations measured by a newly developed hi gh performance liquid chromatography assay were lower in OV202 hp cells. Th ese data are consistent with the hypothesis that acquisition of spontaneous resistance to flavopiridol and cisplatin in OV202 hp cells is due, at leas t in part, to reduced accumulation of the respective drugs. These observati ons not only provide the first characterization of a flavopiridol-resistant cell line but also raise the possibility that alterations in drug accumula tion might be important in determining sensitivity to this agent.