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 (CH 2)(n)NR(CH2)(m)NR(CH2)(n) linkers of varying length (carboxamide N-N distan ces from 11.0 to 18.4 Angstrom) and rigidity were prepared by reaction of 9 -methylphenazine-1-carboxylic acid imidazolide with the appropriate polyami nes. The compounds were evaluated for growth inhibitory properties in P388 leukemia, Lewis lung carcinoma, and wild-type (JL(C)) and mutant (JL(A) and JL(D)) 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 o f action. Analogues joined by an (CH2)(2)NR(CH2)(2)NR(CH2)(2) linker were e xtremely potent cytotoxins, with selectivity toward the human cell lines, b ut absolute potencies declined sharply from R = H through R = Me to R = Pr and Bu. In contrast, (CH2)(2)NR(CH2)(3)NR(CH2)(2) compounds showed reverse effects, with the R = Me analogue being more potent than the R = H one as w ell as being the most potent in the series [IC50 in JL(C) cells 0.08 nM; su perior to that for the clinical bis(naphthalimide) LU 79553]. Overall, the IC(50)s Of analogues with linker chains (CH2)(n)NH(CH2)(m)NH(CH2)(n) were i nversely proportional to linker length. Constraining the rigidity of the li nker chain by incorporating a piperazine ring did not decrease potency sign ificantly. A representative compound bound tightly to DNA with high selecti vity for GC sites, compatible with recent work suggesting that compounds of this type place their side chains in the major groove, making specific con tacts with guanine bases. Representative compounds were susceptible to tran sport mediated resistance, being much less effective in cells that overexpr essed P-glycoprotein. Overall the results suggest these compounds have a si milar mode of action, mediated primarily by poisoning of topo I (possibly w ith some involvement of topo II). The bis(9-methylphenazine-1-carboxamides) show very high in vitro growth inhibitory potencies compared to their mono meric analogues. Two compounds showed in vivo activity in murine colon 38 s yngeneic and HT29 human colon tumor xenograft models using intraperitoneal dosing.