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

Abstract

Bis(9-methylphenazine-1-carboxamides) joined by a variety of dicationic (CH(2))(n)()NR(CH(2))(m)NR(CH(2))(n) linkers of varying length (carboxamide N-N distances from 11.0 to 18.4 A) 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 (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 IC(50) ratios of <1 in the resistant Jurkat lines, consistent with topo II inhibition not being the primary mechanism of action. Analogues joined by an (CH(2))(2)NR(CH(2))(2)NR(CH(2))(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, (CH(2))(2)NR(CH(2))(3)NR(CH(2))(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 [IC(50) in JL(C) cells 0.08 nM; superior to that for the clinical bis(naphthalimide) LU 79553]. Overall, the IC(50)s of analogues with linker chains (CH(2))(n)NH(CH(2))(m)NH(CH(2))(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.

Antitumour activity of XR5944 in vitro and in vivo in combination with 5-fluorouracil and irinotecan in colon cancer cell lines

“…XR5944 is a novel bis-phenazine that has shown potent cytotoxic activity in a range of human and murine tumour cell lines in vitro, as well as significant antitumour activity against human tumour xenografts in vivo and ex vivo (Cree et al, 2001;Gamage et al, 2001;Stewart et al, 2001). XR5944 has recently entered phase I clinical trials.…”

“…Although the initial report suggested that XR5944 might act through the joint inhibition of topoisomerase I and II , other studies have demonstrated that topoisomerases are not the primary cellular targets, and that the compound may work via a novel mechanism of action. For example, XR5944 was evaluated in the NCI human cell line panel (Gamage et al, 2001) and COMPARE analysis showed lack of correlation with known topoisomerase poisons and suggested a unique mechanism of action (data not shown). Furthermore, potency of XR5944 was not impaired in human cell lines or in the yeast Saccharomyces cerevisiae with reduced levels of topoisomerase enzymes (Gamage et al, 2001;Sappal et al, 2004).…”

“…For example, XR5944 was evaluated in the NCI human cell line panel (Gamage et al, 2001) and COMPARE analysis showed lack of correlation with known topoisomerase poisons and suggested a unique mechanism of action (data not shown). Furthermore, potency of XR5944 was not impaired in human cell lines or in the yeast Saccharomyces cerevisiae with reduced levels of topoisomerase enzymes (Gamage et al, 2001;Sappal et al, 2004). Gene expression profiles of XR5944 and irinotecan-treated human tumour xenografts were distinct, revealing clusters of differentially regulated genes by the two drugs (Sappal et al, 2004).…”

Antineoplastic DNA-Binding Compounds: Intercalating and Minor Groove Binding Drugs

“…Figure 3) is a novel bisphenazine originating from a drug development programme aimed at developing new compounds as drugs for the treatment of solid tumours (34). This agent expressed strong cytotoxic activity in a variety of in vitro and in vivo tumour models.…”

Considerations for Treatment Development in Rhabdomyosarcoma: In Vitro Assessment of Novel DNA Binding Drugs

“…These compounds were designed as bisintercalating topoisomerase I and II poisons (Spicer et al, 2000), but their actual mechanism of action is complex and appears to involve both transcription inhibition, along with topoisomerase I poisoning (Byers et al, 2005). The three compounds studied here are potently cytotoxic in mouse leukemia P388, mouse Lewis lung and Jurkat human leukemia cells (Gamage et al, 2001). The toxicity of SN26700 and SN26871 however, is diminished some 35 to 2200 times in the RMS panel, with their IC 50 s clustering around m or greatly exceeding it ( Figure 2).…”