RT Journal Article SR Electronic T1 METABOLIC ACTIVATION OF FLUOROPYRROLIDINE DIPEPTIDYL PEPTIDASE-IV INHIBITORS BY RAT LIVER MICROSOMES JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 121 OP 130 DO 10.1124/dmd.104.001842 VO 33 IS 1 A1 Shiyao Xu A1 Bing Zhu A1 Yohannes Teffera A1 Deborah E. Pan A1 Charles G. Caldwell A1 George Doss A1 Ralph A. Stearns A1 David C. Evans A1 Maria G. Beconi YR 2005 UL http://dmd.aspetjournals.org/content/33/1/121.abstract AB The current study evaluated the potential for two dipeptidyl peptidase-IV (DPP-IV) inhibitor analogs (1S)-1-(trans-4-{[(4-trifluoromethoxyphenyl)sulfonyl]amino}cyclohexyl)-2-[(3S)-3-fluoropyrrolidin-1-yl]-2-oxoethanaminium chloride and (1S)-1-(trans-4-{[(2,4-difluorophenyl)sulfonyl]amino}cyclohexyl)-2-[(3S)-3-fluoropyrrolidin-1-yl]-2-oxoethanaminium chloride (MRL-A and MRL-B), containing a fluoropyrrolidine moiety in the structure, to undergo metabolic activation. The irreversible binding of these tritium-labeled compounds to rat liver microsomal protein was time- and NADPH-dependent and was attenuated by the addition of reduced glutathione (GSH) or N-acetylcysteine (NAC) to the incubation, indicating that chemically reactive intermediates were formed and trapped by these nucleophiles. Mass spectrometric analyses and further trapping experiments with semicarbazide indicated that the fluoropyrrolidine ring had undergone sequential oxidation and defluorination events resulting in the formation of GSH or NAC conjugates of the pyrrolidine moiety. The bioactivation of MRL-A was catalyzed primarily by rat recombinant CYP3A1 and CYP3A2. Pretreatment of rats with prototypic CYP3A1 and 3A2 inducers (pregnenolone-16α-carbonitrile and dexamethasone) enhanced the extent of bioactivation which, in turn, led to a higher degree of in vitro irreversible binding to microsomal proteins (5- and 9-fold increase, respectively). Herein, we describe studies that demonstrate that the fluoropyrrolidine ring is prone to metabolic activation and that GSH or NAC can trap the reactive intermediates to form adducts that provide insight into the mechanisms of bioactivation. The American Society for Pharmacology and Experimental Therapeutics