Functional effects of cytochrome P450 variants on drug metabolism and adverse drug reactions: developing and extending high throughput P450 protein technology platforms

Abstract

Cytochrome P450 (CYPs) are a superfamily of heme containing enzymes that catalyse a diverse range of biological reactions. They are responsible for over 80% of primary metabolism of currently available drugs and are therefore central to its medical importance. Investigating the effects of these enzymes on drugs by metabolite detection and kinetic studies is a step forward to the vision of personalised medicine. The enzyme family is known to be associated with the development of adverse drug reactions which are usually only discovered in late stages of drug development, therefore screening for potential adverse drug reactions earlier on would aid minimising such adverse events occurring. There is therefore a need to analyse the interaction profile of new drugs with CYPs in a cost effective and high throughput manner for early stage screening, since drug discovery efforts tend to utilise large compound libraries. Recently, a novel functional CYP microarray has been developed in the Blackburn laboratory at UCT to enable label-dependent analysis of metabolism of substrates by the major CYP3A4 isoform in a high throughput manner. This thesis describes efforts involved in expanding the functional CYP microarray format to the other major CYP isoforms namely, CYP2C9 and CYP2D6 and developing a new immobilisation-free technology with label-free mass spectrometric identification and quantitation of metabolites formed. The goals of expansion of functional CYP microarrays were achieved by using microarray or confocal fluorescence scanning in conjunction with atomic force microscopy to more accurately quantitate active CYP3A4, CYP2C9 and CYP2D6 protein levels for catalytic substrate-dependent turnover rates. Finally the label- and immobilisation-free CYP technology was evaluated using probe substrates and a complex drug, rifampicin. These two platforms are primed to be a useful tool in pre-clinical drug screening for use in the drug discovery field by the academic, pharmaceutical and biotechnology industries.