ALDEHYDE DEHYDROGENASE INVOLVEMENT IN A VARIANT OF THE BROWN-NORWAY RAT ACUTE MYELOCYTIC-LEUKEMIA (BNML) THAT ACQUIRED CYCLOPHOSPHAMIDE RESISTANCE IN-VIVO

The development of drug resistance is an important factor contributing to failure of chemotherapy in cancer patients. Cyclophosphamide (CP) is a cytostatic drug widely used in the treatment of haematological ma lignancies and solid tumours. Because CP requires bioactivation to bec ome cytotoxic, an in vivo approach was chosen to generate a subline of the Brown Norway rat acute myelocytic leukaemia (BNML/CPR) highly res istant to CP to serve as a model to investigate the molecular mechanis m(s) of cyclophosphamide resistance. The role of the CP-detoxifying en zyme aldehyde dehydrogenase (ALDH) in the molecular mechanism of CP re sistance in this subline of the BNML has been investigated. Compared t o the parent BNML cell line, the BNML/CPR cell line displayed an appro ximately 6-fold higher level of ALDH enzyme activity. Pretreatment of leukaemic rats with the ALDH inhibitor disulfiram resulted in a restor ation of CP sensitivity of animals carrying the BNML/CPR cells. Furthe rmore, in vitro incubation of BNML/CPR cells with disulfiram prior to incubation with the activated CP derivative mafosfamide resulted in an extra 2-3 log cell kill as indicated by the survival time of rats whi ch were injected with disulfiram pretreated BNML/CPR cells compared to non-pretreated BNML/CPR cells. Data on the glutathione S-transferases (GSTs) isozyme profiles of cytoplasmic liver and spleen extracts of B NML- and BNML/CPR-carrying leukaemic rats indicated that the total GST enzyme amount was lower in BNML/CPR cells than in parent BNML cells. Furthermore, the BNML/CPR subline proved to be sensitive to phosphoram ide mustard, both in vivo and in vitro.