Interaction of a Polyamine Analogue, 1,19-bis-(Ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4), with DNA and Effect on Growth, Survival, and Polyamine Levels in Seven Human Brain Tumor Cell Lines

Computer graphics modeling and physicochemical studies of spermine-DNA interactions, as well as experiments in cell culture, indicate that a polyamine analogue with strong affinity for nucleic acids but poor ability to condense and aggregate DNA in vitro should act as an antiproliferative agent if it can enter cells. On the basis of our studies of polyamine-DNA interactions, we designed a pentamine, 1,19-bis(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4), that had these characteristics. Measurement of melting temperature and ultraviolet light scattering studies show that the affinity of this analogue for calf-thymus DNA is about 4 times higher than that of spermine, whereas its ability to aggregate DNA is slightly poorer than that of spermine. Studies in U-87 MG, U-251 MG, SF-126, SF-188, SF-763, SF-767, and DAOY human brain tumor cells in tissue culture showed that treatment for more than 96 h with concentrations of 5 μm BE-4-4-4-4 or greater inhibited growth; decreased levels of putrescine, spermidine, and spermine; and decreased colony-forming ability in all cell lines. The cytotoxicity of the analogue varied among cell lines; DAOY and SF-767 were the most sensitive and the most resistant lines, respectively. In SF-763 cells, growth inhibition by BE-4-4-4-4 could be partially reversed by the addition of putrescine, spermidine, or spermine 1 day after BE-4-4-4-4 addition, but in U-251 MG cells, growth inhibition was reversed only by spermine and not by other polyamines. When any of the naturally occurring polyamines was added simultaneously with BE-4-4-4-4, growth inhibition was completely blocked. The data suggest that a threshold intracellular concentration of BE-4-4-4-4 is needed to manifest the growth-inhibitory and cytotoxic effects. In most cell lines, once that threshold level is reached, the growth-inhibitory and cytotoxic properties of the analogue are manifest irrespective of cellular polyamine levels. Further increases in the BE-4-4-4-4 concentration or incubation time reduce the intracellular polyamine levels but do not significantly increase growth inhibition. In U-87 MG and DAOY cells, however, prolonged incubation with higher concentrations of BE-4-4-4-4 causes additional growth inhibition along with depletion of intracellular polyamines. Thus, it appears that polyamine analogues having higher affinity for DNA than natural polyamines can inhibit cell growth even in the presence of natural polyamines, if they are taken up by cells to a sufficient degree to compete with and displace natural polyamines from their binding sites on DNA.