Aldehyde dehydrogenase involvement in a variant of the brown Norway rat acute myelocytic leukaemia (BNML) that acquired cyclophosphamide resistance in vivo

Abstract

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 malignancies and solid tumours. Because CP requires bioactivation to become cytotoxic, an in vivo approach was chosen to generate a subline of the Brown Norway rat acute myelocytic leukaemia (BNML/CPR) highly resistant to CP to serve as a model to investigate the molecular mechanism(s) of cyclophosphamide resistance. The role of the CP-detoxifying enzyme aldehyde dehydrogenase (ALDH) in the molecular mechanism of CP resistance in this subline of the BNML has been investigated. Compared to the parent BNML cell line, the BNML/CPR cell line displayed an approximately 6-fold higher level of ALDH enzyme activity. Pretreatment of leukaemic rats with the ALDH inhibitor disulfiram resulted in a restoration of CP sensitivity of animals carrying the BNML/CPR cells. Furthermore, 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 which 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 BNML- 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 phosphoramide mustard, both in vivo and in vitro.