CHARACTERIZATION OF 4 DRUG-RESISTANT P388 SUBLINES - RESISTANCE SENSITIVITY IN-VIVO, RESISTANCE-MARKERS AND PROLIFERATION-MARKERS, IMMUNOGENICITY/

It was the aim of this study to compare drug-rsistant sublines of the murine P388 in relation to resistance markers, the resistant phenotype and immunogenicity. Resistance to drugs either belonging to the MDR t ype (Doxorubicin, Vincristine, Mitoxantrone) or to the non-MDR type (M ethotrexate) was generated in vivo in order to mimic the clinical situ ation. All resistant sublines expressed the mdr1 gene and the p-glycop rotein determined on m-RNA level or immunohistochemically, while no ex pression was registered in the parent P388. The rhodamine 123 fluoresc ence as marker for the energy dependent drug efflux pump was decreased only in the MDR-sublines, while the parent P388 and the Methotrexate- resistant line retained 100% or 90% of the dye, respectively. This ind icates that the rhodamine efflux is a more function-related marker for MDR than the mdr1 gene and the pgp. The in vivo characterization of t he sublines as regards their sensitivity to cytostatics revealed a cle ar-cut cross-resistance to MDR drugs in the MDR-lines, while the Metho trexate resistant subline was only cross-resistant to Cytarabine. In e ach resistant subline collateral sensitivity to certain but different cytostatics was observed. Experiments to overcome resistance by concom itant treatment with the modulators Nifedipine, Verapamil, Cyclosporin A and Chloroquin led to only limited success. The sublines P388/Mitox , P388/Vinc and P388/MTX developed immunogenicity which was never regi stered in the original P388. Vaccination with lethally irradiated drug -resistant cells resulted in a substantial rejection of viable rumor c ells of the same line. With the P388/Mitox and P388/Vinc also an overc ross immunization was possible. This generation of immunogenicity as a concomitant characteristic of resistance should be considered as ther apeutic potential also in the treatment of clinical cancer.