Influence of polyamine architecture on the transport and topoisomerase II inhibitory properties of polyamine DNA-interealator conjugates

An efficient five-step synthetic method was developed to access a series of spermine derivatives containing appended acridine, anthracene, and 7-chlor oquinoline motifs. The derivatives were composed of a spermine fragment cov alently tethered at its N4 and N9 positions to an aromatic nucleus via an a liphatic chain (e.g., 8: acridine -[C4 aliphatic tether]-spermine-[C4 aliph atic tether]-acridine). The distance separating the spermine and aromatic n uclei was altered via different tethers composed of four or five methylene units. These bis ligands (8, 9, 12, and 13) were shown to inhibit human DNA topoisomerase II (topo II) activity at 5 muM. Enzymatic activity was asses sed as the ability to unknot (decatenate) and cleave kinetoplast DNA (kDNA) . Polyamine conjugation did not disrupt the ability of the acridine-spermin e conjugates 8 and 9 to inhibit topo II activity as compared with the 9-ami noacridine and 9-(N-butyl)aminoacridine controls (at 5 muM). The parent pol yamines, spermine (5 muM) and spermidine (10 muM), had little effect on top o II activity. In general, the bis-substituted spermine derivatives (8, 9, 12, and 13) were more efficient topo II inhibitors at 5 uM than their monos ubstituted spermidine counterparts (22-25) at 10 muM. Within the bisinterca lator spermine series, insertion of an additional methylene unit (i.e., C5 tethers) increased potency 2-fold (8, bis-C4-acridine, 47 h IC50 = 40 muM; 9, bis-C5-acridine, IC50 = 17 muM). Comparison of the bis- and monoacridine spermine motifs (8 and 17) revealed a 4-fold increase in potency for the l atter architecture (94 h IC50 for 8, 74 muM; for 17, 17 muM). In general th e bisintercalators (8, 9, 12, and 13) behaved as cytostatic agents, while t he monosubstituted acridine and anthracene derivatives (22-25) were cytotox ic. Anthracene-containing conjugates were generally more toxic than their a cridine counterparts in an L1210 (murine leukemia) cell assay. Of the conju gates tested the (monointercalator)-spermine motif (e.g., 17) had the highe st affinity for the L1210 polyamine transporter as revealed by spermidine p rotection experiments.