Effects of novel spermine analogues on cell cycle progression and apoptosis in MALME-3M human melanoma cells.
On the basis of encouraging preclinical findings, polyamine analogues have emerged as a novel class of experimental antitumor agents. The spermine derivative N1,N11-diethylnorspermine (DE-333, also known as DENSPM) is currently undergoing Phase I clinical trials against solid tumors. A series of systematically modified DE-333 analogues differing in intra-amine carbon distances and in N-alkyl terminal substituents (i.e., methyl, ethyl, and propyl) were evaluated in MALME-3M human melanoma cells, a cell line known to be cytotoxically affected by DE-333 and especially responsive to analogue induction of the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase. Analogues accumulated to comparable intracellular concentrations and similarly affected cell growth with IC50 values in the 0.5-1.0 microM range. During prolonged incubations, diethyl and dipropyl analogues were cytotoxic, whereas two dimethyl analogues were cytostatic. Cell cycle analysis following treatment with the cytotoxic analogues revealed a prominent G1 block apparent as an accumulation of cells in G0/G1 and depletion of S-phase cells as well as a less restrictive G2 block. By contrast, cytostatic analogues incompletely arrested cells in G1, leaving a significant number of S-phase cells. Morphological and immunocytochemical analysis of detached cells revealed a far greater proportion of apoptotic cells with cytotoxic analogues than with cytostatic analogues. Although spermidine/spermine N1-acetyltransferase activity was differentially induced by the analogues, there was no obvious correlation with cell cycle effects. Overall, these data indicate a previously unrecognized combined effect of polyamine analogues on cell cycle progression and apoptosis. On the basis of structure-function relationships, these activities may be manipulated to optimize therapeutic efficacy.