An investigation into the metabolic activation of novel chloromethylindolines by isoforms of cytochrome P450. Targeting drug metabolising enzymes in cancer: analysis of the role and function of selected cytochrome P450 oxidising novel cancer prodrugs

Abstract

Introduction Cytochromes P450 (CYPs) are the major family of enzymes responsible for detoxification and metabolism of a wide range of both endogenous and xenobiotics chemicals in living organisms. The use of CYPs to activate prodrugs to cytotoxins selectively in tumours has been explored including AQ4N, Phortress and Aminoflavone. CYP1A1, CYP1B1, CYP2W1, and CYP4F11 have been identified as expressed in tumour tissue and surrounding stroma at high frequency compared to most normal tissues. Aim is to investigate the differential metabolism of novel chloromethylindoline by high frequency expressed CYPs in tumours. This differential may be exploited to elicit a selective chemotherapeutic effect by metabolising inert small molecules to potent cytotoxins within the tumour environment. Materials and Methods Sensitive and specific LC/MS/MS techniques have been developed to investigate the metabolism of chloromethylindolines. Recombinant enzymes and transfected cell lines were used to investigate the metabolic profiles with a focus on production of the cytotoxic derivatives of chloromethylindolines. Results Detailed metabolic studies show that (1-(Chloromethyl)-1,2-dihydropyrrolo [3,2-e]indol-3(6H)-yl)(5-methoxy-1H-indol-2-yl) methanone (ICT2700) and other chloromethylindolines are converted by CYP1A1 mediated hydroxylation at the C-5 position leading to highly potent metabolites. In vitro cytotoxicity studies showed differentials of up to 1000-fold was achieved between CYP1A1 activated compared to the non-metabolised parent molecules. The reactivity of metabolites of ICT2700 was also explored using glutathione as a nucleophile. The metabolites were identified by a combination of LC/MS and LC MS/MS techniques. Investigations using mouse and human liver microsomes show that a large number of metabolites are created though none were shown to be associated with a potential anticancer effect. Studies focused on CYP2W1 show that this isoform metabolised ICT2706 to a cytotoxic species and a pharmacokinetic study showed a good distribution of ICT2706 into mouse tissues including tumour. However metabolism of ICT2726 by CYP2W1 resulted only in a non-toxic metabolite profile and may have potential as a biomarker for functional CYP2W1 in tissues. Preliminary studies show that palmitic acid hydroxylation is a useful marker of functional CYP4F11. Summary and conclusion The in vitro results show that the chloromethylindolines are a novel class of agent with potential as prodrugs that following specific hydroxylation by CYP1A1 and CYP2W1 are converted to ultra-potent cytotoxins. Other metabolites are also evident which are not cytotoxic. Studies in vivo show that selected chloromethylindolines possess a good pharmacokinetic profile and show potential as prodrug anticancer agents that require activation by CYP1A1 or CYP2W1. The methods, results, progress and suggestions for future work are presented in this thesis.