Ian Jardine

Analysis of the anticancer drugs VP 16-213 and VM 26 and their metabolites by high-performance liquid chromatography

A rapid and convenient high-performance liquid chromatographic procedure for the analysis of the clinically useful anticancer agents VP 16-213 and VM 26 is described. The drugs, which are semi-synthetic derivatives of the natural product podophyllotoxin, are extracted from plasma with chloroform. The extracts are evaporated to dryness, reconstituted in methanol, and chromatographed on a reversed-phase microparticle C18 column using isocratic elution with a mixture of methanol--water (60:40). Each drug is used as the internal standard for the other. Quantitation to 500 ng/ml (0.85 nmole/ml) plasma is based on peak height ratios using UV detection at 254 nm. Patient plasma concentration versus time data agree well with previously published data obtained using radiolabelled drug. Investigations into the nature of the hydroxy acid metabolite of VP 16-213, carried out using paired-ion chromatography with tetrabutylammonium bromide and fluorescence detection, are described. Also, a unique separation of VP 16-213 and a possible metabolite, the isomer, picro VP 16-213, is described.

IRREVERSIBLE BINDING OF 6-THIOPURINE TO RAT HEPATIC MICROSOMAL PROTEINS IN VITRO AND IN VIVO

Publisher Summary This chapter discusses the irreversible binding of 6-thiopurine to rat hepatic microsomal proteins in vitro and in vivo. The use of the anti-neoplastic agent 6-thiopurine is limited because of drug-induced hepatotoxicity. 6-thiopurine can be biotransformed by rat hepatic microsomes into a reactive metabolite that subsequently binds to hepatic microsomal protein in vitro and in vivo. This binding is inhibited by glutathione. Data suggests the involvement of cytochrome P-450 in the metabolic activation of 6-thiopurine to a metabolite capable of binding to hepatic microsomal protein both in vitro and in vivo. The metabolite appears to bind to protein by formation of a disulfide bond that is not easily cleaved. Glutathione protects against protein binding by competing with protein thiols for the metabolite. The chapter illustrates a possible mechanism for these metabolic routes of 6-thiopurine.