Monitoring drug–protein interaction

Abstract

A variety of therapeutic drugs can undergo biotransformation via Phase I and Phase II enzymes to reactive metabolites that have intrinsic chemical reactivity toward proteins and cause potential organ toxicity. A drug–protein adduct is a protein complex that forms when electrophilic drugs or their reactive metabolite(s) covalently bind to a protein molecule. Formation of such drug–protein adducts eliciting cellular damages and immune responses has been a major hypothesis for the mechanism of toxicity caused by numerous drugs. The monitoring of protein–drug adducts is important in the kinetic and mechanistic studies of drug–protein adducts and establishment of dose–toxicity relationships. The determination of drug–protein adducts can also provide supportive evidence for diagnosis of drug-induced diseases associated with protein–drug adduct formation in patients. The plasma is the most commonly used matrix for monitoring drug–protein adducts due to its convenience and safety. Measurement of circulating antibodies against drug–protein adducts may be used as a useful surrogate marker in the monitoring of drug–protein adducts. The determination of plasma protein adducts and/or relevant antibodies following administration of several drugs including acetaminophen, dapsone, diclofenac and halothane has been conducted in clinical settings for characterizing drug toxicity associated with drug–protein adduct formation. The monitoring of drug–protein adducts often involves multi-step laboratory procedure including sample collection and preliminary preparation, separation to isolate or extract the target compound from a mixture, identification and determination. However, the monitoring of drug–protein adducts is often difficult because of short half-lives of the protein adducts, sampling problem and lack of sensitive analytical techniques for the protein adducts. Currently, chromatographic (e.g. high performance liquid chromatography) and immunological methods (e.g. enzyme-linked immunosorbent assay) are two major techniques used to determine protein adducts of drugs in patients. The present review highlights the importance for clinical monitoring of drug–protein adducts, with an emphasis on methodology and with a further discussion of the application of these techniques to individual drugs and their target proteins.