COMPARISON AND CHARACTERIZATION OF GROWTH-INHIBITION IN L1210 CELLS BY ALPHA-DIFLUOROMETHYLORNITHINE, AN INHIBITOR OF ORNITHINE DECARBOXYLASE, AND N1,N8-BIS(ETHYL)SPERMIDINE, AN APPARENT REGULATOR OF THE ENZYME

Abstract

The cellular effects of .alpha.-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and N1,N8-bis(ethyl)spermidine (BES), an apparent regulator of the enzyme were compared in cultured L1210 cells. Unlike DFMO, BES had no direct inhibitory effect on ODC activity. Rather the polyamine analogue is believed, from previous studies, to behave similarly to exogenous spermidine in it''s ability to suppress intracellular ODC activity but not in it''s ability to perform functions required for cell growth. The kinetics and extent of growth inhibition by 30 .mu.M or 100 .mu.M BES and 1 mM DFMO were nearly identical as were their effects on macromolecular precursor incorporation with leucine being the first and most significantly affected. By flow cytometry, neither BES nor DFMO induced obvious perturbations in the cell cycle. Both compounds effectively eliminated ODC activity in treated cells and depleted putrescine and spermidine pools with very similar kinetics of decline. These close similarities in drug effects between BES and DFMO, an established polyamine inhibitor, support previous indications that BES induces growth inhibition by depletion of cellular polyamines. BES differed distinctly from the ODC inhibitor by decreasing spermine pools, and by not increasing S-adenosyl-methionine decarboxylase activity, S-adenosylmethionine pools, or stimulating cellular uptake of polyamines. These data suggest that enzyme regulation by polyamine analogues such as BES represents a viable alternative to enzyme inhibition as an antiproliferative strategy directed at polyamine biosynthesis.