Abstract 3227: Bioactivity and metabolic stability of indirubins

Abstract

Abstract Indirubins are known to induce cell cycle arrest in G1/S and/or G2/M followed by apoptosis and potently inhibit proliferation of human tumor cells. In general, they have unfavorable pharmacokinetic properties as a consequence of poor solubility, resulting in low bioavailability. They are CYP450 substrates, undergoing deactivating metabolic transformations by formation of hydroxylated metabolites, especially in 6- and 7’-positions. The antiproliferative activity of these metabolites was decreased or nearly completely abrogated. To improve metabolic stability and solubility, novel indirubins were synthesized: hydrophilic N-methylpiperazinoethyl (E748) or N,N-dimethylaminophenyl groups were attached to the indirubin core by a 5-carboxamide anchor (E748 and E 744, respectively) or by a 3’-oxime ether link (E857). Moreover, to block 7’-hydroxylation, 7’-aza-5-methylindirubin (E844) was synthesized. Compounds were incubated in vitro with liver microsomes and metabolites were analyzed. E844 yielded as main metabolites 7’-aza-5-methyl-6-hydroxy-indirubin and 7’-aza-5-hydroxymethyl-indirubin. E748 yielded the 7’-hydroxy derivative as main metabolite. In contrast to E748, E744 did not appear to undergo detectable metabolic transformation. In addition, E857 and its water soluble hydrochloride (E857a) were not found to be hydroxylated at the respective bisindole positions. Main biotransformation of E857 rather occurred in the side chain, resulting in the formation of N- methylpiperazinoethyl-N-oxide. In contrast to E 857, the hydrochloride E857a was found hydroxylated at the methylpiperazino group. The results demonstrate that deactivating metabolic transformation of indirubins can be mitigated by introducing N-atoms into the bisindole core, and/or by directing metabolic attack into the 3’ side chain, through attachment of hydrophilic substituents. In summary, the metabolic stability of the bisindole pharmacophore can be increased by appropriate molecular modifications that also improve pharmacokinetics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3227. doi:10.1158/1538-7445.AM2011-3227