DEVELOPMENT AND CHARACTERIZATION OF NOVEL HUMAN MULTIDRUG-RESISTANT MAMMARY-CARCINOMA LINES IN-VITRO AND IN-VIVO

Clinical chemotherapy of breast carcinomas must be considered insuffic ient, mainly due to the appearance of drug resistance. The multidrug r esistance (MDR) phenotype, either intrinsically occurring or acquired, e.g., against a panel of different antineoplastic drugs, is discussed in relation to several MDR-associated genes such as the MDR-gene mdrI encoding the P-glycoprotein (PGP), the MRP gene (multidrug resistance protein) encoding an MDR-related protein or the LRP gene encoding the lung resistance protein. Numerous experimental and clinical approache s aiming at reversing resistance require well-characterised in vitro a nd in vive models. The aim of our work was to develop multidrug resist ant sublines from human xenotransplanted breast carcinomas, in additio n to the broadly used line MCF-7 and its multidrug resistant subline M CF-7/Adr(R). MDR was induced in vitro with increasing concentrations o f Adriablastin (ADR) for several weeks, resulting in a 3.5- to 35-fold increase in IC50 values using the MTT-test. Cell lines were cross-res istant toward another MDR-related drug, vincristine, but remained sens itive to non-MDR-related compounds such as cisplatin and methotrexate. The resistance toward Adriamycin and vincristine was confirmed in viv o by a lack of tumour growth inhibition in the nude mouse system. Gene expression data for the mdrI/PGP, MRP/MRP and LRP/LRP on both the mRN A (RT-PCR) and the protein levels (immunoflow cytometry) demonstrated that induction of mdrI gene expression was responsible for the acquire d MDR phenotype, Rhodamine efflux data, indicated by PGP overexpressio n, underlined the development of this MDR mechanism in the newly estab lished breast carcinoma lines MT-I/ADR, MT-3/ADR and MaTu/ADR. (C) 199 7 Wiley-Liss, Inc.