The effect of polyamine homologation on the transport and cytotoxicity properties of polyamine-(DNA-intercalator) conjugates

efficient five-step synthetic method was developed to access a homologous s eries of spermidine-acridine and spermidine-anthracene conjugates. The deri vatives were comprised of a spermidine fragment covalently tethered at its N4 position to either an acridine or anthracene nucleus via an aliphatic ch ain (e.g., spermidine-[aliphatic tether]-acridine). The distance separating the spermidine and aromatic nucleus was altered by using different tethers comprised of four or five methylene units, respectively. These ligands (2- 5) were shown to inhibit human DNA topoisomerase-ll (TOPO-II) activity at 1 0 mu M Enzymatic activity was assessed as the ability to unknot (decatenate ) and cleave kinetoplast DNA (kDNA). Polyamine conjugation did not disrupt the ability of the acridine-spermidine conjugates 2 and 3 to inhibit TOPO-I I activity as compared with the 9-aminoacridine and 9-(N-butyl)aminoacridin e controls (at 10 mu M) In general, the acridine derivatives (2 and 3) show ed higher TOPO-II inhibitory activity than their anthracene counterparts (4 and 5). However, this trend was reversed in a whole cell assay with L1210 (murine leukemia) cells, wherein the anthracene analogues were more potent than their acridine counterparts. In this regard the qualitative enzyme-bas ed assay did not predict the trends in the corresponding IC50 values. Withi n either series insertion of an additional methylene unit did not significa ntly alter activity. While the appended spermidine unit did not disrupt TOP O II inhibition by the tethered DNA intercalator, it did provide an alterna tive made of entry into the cell as demonstrated by spermidine protection a ssays. These results were compared with a spermine-intercalator analogue. O f all the conjugates tested the N-4-(4-(9-aminoacridinyl)butyl)spermine hex ahydrochloride (conjugate 16)resulted in the highest degree of L1210 cell r escue upon cotreatment of the cells with exogenous spermidine. It was concl uded that the monoalkylated spermine motif present in 16 holds promise as a better vector than its N4 monoalkylated spermidine counterpart.