Polyamines are believed to be potent vectors for the selective delivery of chemotherapeutic agents into cancer cells. In this paper, we report the effect of spermine conjugation on the cytotoxic and transport properties of acridine. Six derivatives, composed of a spermine chain attached at its N(1) position to an acridine via an aliphatic chain, were synthesized. The aliphatic linker, comprised of 3-5 methylene units, was connected to the position-9 of the heterocycle through either an amide (amidoacridines 8-10) or an amine (aminoacridines 11-13) linkage. Independently of their architecture, all ligands showed a high affinity for DNA binding but a limited DNA sequence selectivity. In a whole cell assay with L1210 and Chinese hamster ovary (CHO) cells, the aminoacridines (IC(50) values around 2 microM) were more potent than the amidoacridines (IC(50) values between 20 and 40 microM). This was related to a less efficient transport for the latter. As determined from competitive uptake studies with [(14)C]spermidine, all conjugates had a high affinity for the polyamine transport system (PTS). However, on the basis of competitive studies with an excess of spermidine and on the differential effect on cell growth and accumulation in CHO and in the mutant PTS deficient CHO-MG cells, the accumulation of the conjugates through the PTS was found to be poor but still more efficient for the aminoacridines. alpha-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, which induces an up-regulation of the activity of the PTS, enhanced accumulation of all acridine conjugates through the PTS and had a synergistic effect on the potency of the acridine conjugates to inhibit cell growth. Despite their high affinity for the PTS, the low amount of derivatives transiting through the PTS is likely to be related to their ability to repress rapidly and efficiently the activity of the PTS and, consequently, to inhibit their own uptake via this system.

SUMMARYThe effects of several N-sulfonyl-polyamines, including N 1 -dansyl-spermine (N 1 -DnsSpm) and N 1 -(n-octanesulfonyl)-spermine (N 1 -OsSpm), were studied at recombinant N-methyl-D-aspartate (NMDA) receptors expressed in Xenopus laevis oocytes. N 1 -DnsSpm and N 1 -OsSpm inhibited NMDA receptors and were ϳ1000-fold more potent than spermine in oocytes voltage-clamped at Ϫ70 mV. Block by N 1 -DnsSpm and N 1 -OsSpm was strongly voltage dependent, being more pronounced at hyperpolarized membrane potentials. With the Woodhull model of voltage-dependent channel block, the values of K d (0) were 779 M, 882 M, and 7.4 mM and those of z␦ were 2.58, 2.57, and 1.07 for N 1 -DnsSpm, N 1 -OsSpm, and spermine, respectively. This suggests that an increase in the voltage dependence of block together with an increase in affinity contributes to the increased potencies of N 1 -DnsSpm and N 1 -OsSpm compared with spermine. Sensitivity to N 1 -DnsSpm was reduced by mutation NR1(N616Q) and was increased by mutations NR1(N616G) and NR2A(N615G). The NR1(N616G) and NR2A(N615G) mutations decreased the K d (0) value of N 1 -DnsSpm without affecting z␦, whereas the NR1(N616Q) mutation reduced z␦. These mutations may alter the accessibility of part of the polyamine binding site within the channel pore or directly alter the properties of that site. Block by N 1 -DnsSpm (0.3 M) was almost complete at Ϫ100 mV, and there was no relief of block at extreme negative membrane potentials (Ϫ100 to Ϫ200 mV) at wild-type NR1/NR2A channels. In contrast, block by N 1 -DnsSpm was partially relieved at extreme negative potentials at receptors containing NR1(N616G) or NR2A(N615G), suggesting that N 1 -DnsSpm can permeate these mutant channels but not wild-type NR1/NR2A channels. This is hypothesized to be due to an increase in the pore size of channels containing NR1(N616G) or NR2A(N615G), which allows passage of the bulky head group of N 1 -DnsSpm. In contrast to N 1 -DnsSpm, N 1 -OsSpm could easily permeate wildtype NR1/NR2A channels, presumably because the head group of N 1 -OsSpm can pass through the narrowest part of the channel pore. N-Sulfonyl-polyamines such as N 1 -DnsSpm and N 1 -OsSpm represent a new class of polyamine antagonists with which to study glutamate receptor ion channels.The endogenous polyamine spermine has a variety of effects on NMDA and non-NMDA glutamate receptors (1, 2). At NMDA receptors, spermine has both stimulatory and inhibitory effects when applied extracellularly (3-7). Inhibition of NMDA receptors by spermine is strongly voltage dependent and may be caused by an open-channel block and/or screening of surface charges around the mouth or vestibule of the ion channel (3,5,8). Intracellular spermine can block the ion channel of some subtypes of AMPA and kainate receptors, an effect that is responsible for inward rectification of these receptors (9 -12) and may be mechanistically similar to the block of inward-rectifier K ϩ channels by polyamines (13,14). When applied extracellularly, spermine is a relatively weak anta...

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Five sets of heterocyclic derivatives of various sizes and complexities coupled by an amidine function to putrescine, spermidine, or spermine were prepared. They were essentially tested to determine the influence of the polyamine chain on their cellular transport. To comment on affinity and on selective transport via the polyamine transport system (PTS), K(i) values for polyamine uptake were determined in L1210 cells, and the cytotoxicity and accumulation of the conjugates were determined in CHO and polyamine transport-deficient mutant CHO-MG cells, as well as in L1210 and alpha-difluoromethylornithine- (DFMO-) treated L1210 cells. Unlike spermine, putrescine and spermidine were clearly identified as selective motifs that enable cellular entry via the PTS. However, this property was clearly limited by the size of substituents: these polyamines were able to ferry a dihydroquinoline system via the PTS but did not impart any selectivity to bulkier substituents.

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The polyamine transport system (PTS) whose activity is up-regulated in cancer cells is an attractive target for drug design. Two heterocyclic (azepine and benzazepine) systems were conjugated to various polyamine moieties through an amidine bound to afford 18 compounds which were evaluated for their affinity for the PTS and their ability to use the PTS for cell delivery. Structure-activity relationship studies and lead optimization afforded two attractive PTS targeting compounds. The azepine-spermidine conjugate 14 is a very selective substrate of the PTS that may serve as a vector for radioelements used for diagnoses or therapeutics in nuclear medicine. The nitrobenzazepine-spermine conjugate 28 is a very powerful PTS inhibitor with very low intrinsic cytotoxicity, able to prevent the growth of polyamine depleted cells in presence of exogenous polyamines.

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