Dicationic Bis(9-methylphenazine-1-carboxamides): Relationships between Biological Activity and Linker Chain Structure for a Series of Potent Topoisomerase Targeted Anticancer Drugs

Bis(9-methylphenazine-1-carboxamides) joined by a variety of dicationic (CH2)nNR(CH2)mNR(CH2)n linkers of varying length (carboxamide N−N distances from 11.0 to 18.4 Å) and rigidity were prepared by reaction of 9-methylphenazine-1-carboxylic acid imidazolide with the appropriate polyamines. The compounds were evaluated for growth inhibitory properties in P388 leukemia, Lewis lung carcinoma, and wild-type (JLC) and mutant (JLA and JLD) forms of human Jurkat leukemia with low levels of topoisomerase II (topo II). The compounds all had IC50 ratios of <1 in the resistant Jurkat lines, consistent with topo II inhibition not being the primary mechanism of action. Analogues joined by an (CH2)2NR(CH2)2NR(CH2)2 linker were extremely potent cytotoxins, with selectivity toward the human cell lines, but absolute potencies declined sharply from R = H through R = Me to R = Pr and Bu. In contrast, (CH2)2NR(CH2)3NR(CH2)2 compounds showed reverse effects, with the R = Me analogue being more potent than the R = H one as well as being the most potent in the series [IC50 in JLC cells 0.08 nM; superior to that for the clinical bis(naphthalimide) LU 79553]. Overall, the IC50s of analogues with linker chains (CH2)nNH(CH2)mNH(CH2)n were inversely proportional to linker length. Constraining the rigidity of the linker chain by incorporating a piperazine ring did not decrease potency significantly. A representative compound bound tightly to DNA with high selectivity for GC sites, compatible with recent work suggesting that compounds of this type place their side chains in the major groove, making specific contacts with guanine bases. Representative compounds were susceptible to transport mediated resistance, being much less effective in cells that overexpressed P-glycoprotein. Overall the results suggest these compounds have a similar mode of action, mediated primarily by poisoning of topo I (possibly with some involvement of topo II). The bis(9-methylphenazine-1-carboxamides) show very high in vitro growth inhibitory potencies compared to their monomeric analogues. Two compounds showed in vivo activity in murine colon 38 syngeneic and HT29 human colon tumor xenograft models using intraperitoneal dosing.