Aliphatic chain length specificity of the polyamine transport system in ascites L1210 leukemia cells

A series of diamine homologues of putrescine and triamine homologues of spermidine was used to determine the structural specificity of the polyamine transport system in ascites L1210 leukemia cells by measuring their ability to compete with [3H]-putrescine, [3H]spermidine, or [3H]spermine for uptake. Transport specificity among the diamines (as indicated by K1 constants) was greatest for those having chain lengths similar to that of spermidine and least for those similar to putrescine. Among the triamines, transport specificity was greatest for those having an overall chain length similar to those of spermidine and spermine. The homologue competition profiles were relatively the same for [3H]putrescine, [3H]spermidine, or [3H]spermine, suggesting that all three polyamines utilize the same transport system. This was further substantiated by uptake kinetic plots which showed that the three polyamines were competitive inhibitors of one another. In terms of receptor specificity, the ranking order among the polyamines was as follows: spermine (apparent Km, 1.6 microM) greater than spermidine (apparent Km, 2.2 microM) greater than putrescine (apparent Km, 8.5 microM). This information should prove useful in designing anticancer agents which are intended to utilize this transport system.