It was the aim of this study to compare drug-resistant sublines of the murine P388 in relation to resistance markers, the resistant phenotype and immunogenicity. Resistance to drugs either belonging to the MDR type (Doxorubicin, Vincristine, Mitoxantrone) or to the non-MDR type (Methotrexate) was generated in vivo in order to mimic the clinical situation. All resistant sublines expressed the mdr1 gene and the p-glycoprotein determined on m-RNA level or immunohistochemically, while no expression was registered in the parent P388. The rhodamine 123 fluorescence 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 indicates that the rhodamine efflux is a more function-related marker for MDR than the mdr1 gene and the pgp. The in vivo characterization of the sublines as regards their sensitivity to cytostatics revealed a clear-cut cross-resistance to MDR drugs in the MDR-lines, while the Methotrexate resistant subline was only cross-resistant to Cytarabine. In each resistant subline collateral sensitivity to certain but different cytostatics was observed. Experiments to overcome resistance by concomitant 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 registered in the original P388. Vaccination with lethally irradiated drug-resistant cells resulted in a substantial rejection of viable tumor cells of the same line. With the P388/Mitox and P388/Vinc also an over-cross immunization was possible. This generation of immunogenicity as a concomitant characteristic of resistance should be considered as therapeutic potential also in the treatment of clinical cancer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMedDate not supplied

Multidrug resistance of murine leukemia cells characterization and correlation with cytochrome P-450 dependent activities, cytosolic calcium and cell cycle state.

This paper reports studies on P388 leukemic cells sensitive and resistant to ADR and VCR. The P450 dependent enzyme system and the cytosolic calcium were estimated and are discussed in relation to MDR. It could be shown, in comparison to sensitive P388 cells, that the plasma membrane permeability for fluorescent dyes like rhodamine 123 and fura-2 and the biotransformation of xenobiotics are changed in resistant cells. Whereas the transport behaviour for the dyes is similarly induced in resistant cells independent of the drug which made the MDR, the P450 dependent enzyme activities are strongly increased in P388/ADR in comparison to the P388 and P388/VCR. The cell cycle analysis shows the same effect. Many more cells of P388/ADR are in the S-phase in comparison to P388 or P388/VCR. The LI is also increased in this direction. Therefore, it can be concluded that, depending on the kind of drug which made the MDR, different biochemical mechanisms are activated.

ATP Binding Cassette Transporter, Subfamily B, Mem↗