It has been confirmed that multidrug resistant (MDR) human melanoma cells are more sensitive than their wild-type counterparts to H2O2 and aldehydes, the products of bovine serum amine oxidase (BSAO)-catalyzed oxidation of spermine. The metabolites formed by BSAO and spermine are more toxic than exogenous H2O2 and acrolein, even though their concentration is lower during the initial phase of incubation due to their more gradual release than the exogenous products. Both wild-type and MDR cells, after pre-treatment with MDL 72527, an inactivator of polyamine oxidase and a lysosomotropic compound, show to be sensitized to subsequent exposure to BSAO/spermine. Evidence of ultrastructural aberrations and acridine orange release from lysosomes is presented in this work that is in favor of the permeabilization of the lysosomal membrane as the major cause of sensitization by MDL 72527. Owing to its lysosomotropic effect, pre-treatment with MDL 72527 amplifies the ability of the metabolites formed from spermine by oxidative deamination to induce cell death. Since it is conceivable that combined treatment with a lysosomotropic compound and BSAO/spermine would be effective against tumor cells, it is of interest to search for such novel compounds, which might be promising for application in a therapeutic setting.

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