@article {Shirley1144, author = {Michael A. Shirley and Pat Wheelan and Stanley R. Howell and Robert C. Murphy}, title = {Oxidative Metabolism of a Rexinoid and Rapid Phase II Metabolite Identification by Mass Spectrometry}, volume = {25}, number = {10}, pages = {1144--1149}, year = {1997}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {LGD1069 (Targretin), a retinoid {\textquotedblleft}X{\textquotedblright} receptor-selective ligand, or rexinoid, is in clinical trials for treating cancer. Biologically-active oxidized LGD1069 metabolites have been observed in patient plasma samples, making corresponding structural characterizations necessary. Formation of multiple metabolite isomersin vivo has created technical challenges in metabolite structural analysis; however, mass spectrometry (MS) was able to pinpoint two sites of Phase I metabolism. A carbon-13 trideuterated analog was used as an isotopic marker to probe Phase II metabolism of LGD1069. Rats were orally gavaged with an equimolar mixture of LGD1069 and [13C2H3]LGD1069, then anesthetized prior to bile-duct cannulation. Bile was collected for 7 hr, extracted, and concentrated. Recovered metabolites were analyzed by narrow-bore, gradient liquid chromatography (LC) with negative ion, electrospray ionization MS detection. When resultant total ion chromatograms were interrogated for mass spectra exhibiting isotope clusters separated by 4 daltons, 13 such clusters corresponding to Phase II LGD1069 metabolites of nine different molecular weights were detected. Acyl-glucuronide and taurine conjugates of both parent compound and hydroxy-LGD1069 were observed. The sulfate and taurine conjugates of oxo-LGD1069 were also identified, as were 6,7-dihydroxy-LGD1069 taurine, LGD1069 ether glucuronide, and a secondary conjugate (taurine) of the latter. Identities of selected conjugates were confirmed by MS/MS. The results of this study demonstrate that when combined with traditional GC/MS and MS/MS data, the isotope cluster technique can provide powerful selectivity in identifying numerous Phase II drug metabolites during a single LC/MS analysis. The American Society for Pharmacology and Experimental Therapeutics}, issn = {0090-9556}, URL = {https://dmd.aspetjournals.org/content/25/10/1144}, eprint = {https://dmd.aspetjournals.org/content/25/10/1144.full.pdf}, journal = {Drug Metabolism and Disposition} }