Chloroacetaldehyde (CA) is a nephrotoxic and neurotoxic metabolite of the anticancer drug ifosfamide (IFA) and is a dose-limiting factor in IFA-based chemotherapy. Plasma levels of CA in IFA-treated cancer patients are often difficult to determine due to the lack of a sufficiently sensitive and specific analytical method. We have developed a simple and sensitive HPLC method with fluorescence detection to measure CA formation catalyzed by liver cytochrome P450 enzymes, either in vivo in IFA-injected rats or in vitro in liver microsomal incubations. This method is based on the formation of the highly fluorescent adduct 1-N(6)-ethenoadenosine from the reaction of CA with adenosine (10 mM) at pH 4.5 upon heating at 80 degrees C for 2 h. The derivatization mixture is directly injected onto a C18 HPLC column and is monitored with a fluorescence detector. Calibration curves are linear (r > 0.999) over a wide range of CA concentrations (5-400 pmol). The limit of detection of CA in plasma using this method is <0.1 microM and only 50 microl of plasma is required for the assay. By coupling this method with a recently described HPLC-fluorescent method to determine acrolein, a cytochrome P450 metabolite of IFA formed during the activation of the drug by 4-hydroxylation, the two major, alternative P450-catalyzed pathways of IFA metabolism can be monitored from the same plasma samples or liver microsomal incubations and the partitioning of drug between these two pathways thereby quantitated. This assay may prove to be useful for studies of IFA metabolism aimed at identifying factors that contribute to individual differences in CA formation and in developing approaches to minimize CA formation while maximizing IFA cytotoxicity.
Copyright 1999 Academic Press.