Characterization of the urinary metabolites of merbarone in cancer patients.
Phase-I clinical trials in cancer patients of merbarone (MB), a thiobarbituric acid derivative with curative activity against the murine leukemias, were recently completed. Reverse-phase HPLC of urine samples from treated patients showed the presence of two major metabolites, identified as 4'-hydroxymerbarone and 2-oxo-desthiomerbarone, eluting prior to the parent drug. In addition, a third polar metabolite, largely masked in liquid chromatograms by poorly retained endogenous urinary constituents, was detected and characterized as 4'-hydroxy-2-oxo-desthiomerbarone. Several minor metabolites, one of greater polarity and several less polar than MB, remain to be identified. Initial structural elucidations were ascertained from methane chemical ionization mass spectroscopy upon isolating MB and its metabolites from patient urine by solid-phase extraction. Quasi-molecular ion patterns at masses consistent with the drug and three oxidative metabolites were apparent. Molecular ion shifts that occurred after treating the urine isolate with acetic anhydride under Schotten-Baumann conditions indicated that two of the metabolites were phenolic derivatives. A high-resolution 1H-NMR spectrum (500 MHz) of the urine isolate exhibited a well-resolved aromatic region containing peaks consistent with those determined for synthetically prepared reference standards of each metabolite. This evidence was further substantiated by obtaining UV spectra during HPLC with a diode array detector. Chromatographic peak identification was established from the correspondence of retention times and UV spectra with the synthetic compounds. These studies demonstrate that MB is subject to extensive oxidative metabolism in humans. However, metabolite plasma levels are exceedingly low throughout the course of a 5-day continuous infusion, suggesting that metabolite excretion rates may exceed their rates of formation. Furthermore, since the relative concentrations of the major metabolites in urine are appreciably higher than that of MB, metabolite renal clearance is apparently greater than that of the drug.
Supko
J G
JG
Ohio State University College of Pharmacy.
Malspeis
L
L
D000107:Acetylation; D000970:Antineoplastic Agents / Q000378:metabolism / Q000652:urine*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D009369:Neoplasms / Q000652:urine*; D010636:Phenols / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013858:Thiobarbiturates / Q000378:metabolism / Q000652:urine*
D000970:Antineoplastic Agents; D010636:Phenols; D013858:Thiobarbiturates; C045459:merbarone