COLLATERAL SENSITIVITY OF HUMAN-MELANOMA MULTIDRUG-RESISTANT VARIANTSTO THE POLYAMINE ANALOG, N-1,N-11-DIETHYLNORSPERMINE

Certain N-alkylated analogues of the natural polyamine spermine, such as N-1,N-11-diethylnorspermine (DENSPM), rapidly deplete intracellular polyamine pools by down-regulating the biosynthetic enzymes, ornithin e decarboxylase and S-adenosylmethionine decarboxylase, and by potentl y up-regulating the polyamine catabolizing enzyme, spermidine/spermine N-1-acetyltransferase. On the basis of previously reported antitumor activity in human tumor xenograft model systems, DENSPM is currently u ndergoing Phase I clinical trials against human melanoma and other sol id tumors. The antiproliferative activity of this analogue against the multidrug resistance (MDR) phenotype was examined in three MDR sublin es of human melanoma RPMI-7932 cells, which were shown to be 2-to 10-f old resistant to classical MDR agents. These MDR lines had been separa tely derived using different selecting agents (Lemontt et at, Cancer R es., 48: 6344-6353, 1988). Subline functional resistance due to P-glyc oprotein was confirmed by decreased retention of rhodamine 123 relativ e to parent cells as detected by flow cytometry. Although the three su blines were 2- to 10-fold less sensitive than the parent line to class ical MDR-type agents, they were found in dose-response studies to be s ignificantly more sensitive to DENSPM than the parent line. In additio n, they showed a distinct cytotoxic response after a 48-h treatment wi th 10 mu M DENSPM, which was not apparent in the parent line. Growth s ensitivity of the sublines to the ornithine decarboxylase inhibitor, c u-difluoromethylornithine, or the S-adenosylmethionine decarboxylase i nhibitor, CGP-48664, was found to be similar to parent cells. The rati o of the key biosynthetic enzyme activities for ornithine decarboxylas e and S-adenosylmethionine decarboxylase was found to be 3.5- to 5-fol d higher in all three sublines, due mainly to increases in the former enzyme. This imbalance produced unusually high putrescine pools. Altho ugh DENSPM down-regulation of decarboxylase activities and potent up-r egulation of spermidine/spermine N-1-acetyltransferase activity occurr ed similarly in both parent and variant lines, polyamine depletion was greater in the variant lines. Collateral sensitivity of the MDR subli nes to DENSPM is partially attributable to the finding that analogue ( and spermidine) uptake in the sublines was about 2-fold higher (after 2 h) than in the parent cells. The presence of disturbances in polyami ne homeostasis and increased sensitivity to DENSPM in three independen tly selected cell line variants suggests that they may be generally as sociated with the MDR phenotype in human melanoma and possibly other t umor tells. The collateral sensitivity of human melanoma MDR variants to DENSPM represents a possible therapeutic indication which should be considered during the ongoing clinical evaluation of this drug.