CYP3A4-Mediated\nBioactivation of the β‑Amyloid\nPrecursor Protein-Cleaving Enzyme 1 Inhibitor JNJ-54861911 Results\nin Redox-Neutral Addition of Glutathione via Catalysis by Glutathione\nS‑Transferase α1, Identified as the Major Target Protein\nin H

The β-amyloid precursor protein-cleaving enzyme\n1 (BACE1)\ninhibitor JNJ-54861911, a candidate for the treatment of Alzheimer’s\ndisease, was withdrawn from clinical trials due to drug-induced liver\ninjury (DILI). This paper describes our investigation of the metabolism\nof JNJ-54861911 to understand the potential contribution to the observed\nDILI. In human hepatocytes, JNJ-54861911 is metabolized by CYP450\n3A4 to a reactive intermediate (RI), which undergoes glutathione (GSH)\naddition at C6 of the 2-amino-4-methyl-1,3-thiazin-4-yl moiety via\nglutathione S-transferase α1 (GSTA1) catalysis. Despite the\npreponderant role of CYP3A4 as an enabler, the adduct has the same\nlevel of oxidation as that of JNJ-54861911. The exact mechanism of\nRI formation might involve a sulfoxide (with further reduction) or\ntautomeric forms of JNJ-54861911 bearing a reactive thiazinium cation\nactivating both the C2 and C6 positions. The cell pellet from the\nhuman hepatocyte incubated with <sup>14</sup>C-JNJ-54861911 was analyzed\nvia gel electrophoresis, resulting in the identification of a major\nprotein adduct on GSTA1, a cross-link resulting from the addition\nof GSH and lysine 120 to JNJ-54861911, most likely on position C6\nand on the nitrile, respectively. Ultimately, this major adduct might\nonly account for 15–25% of the total covalent binding (CVB).\nOther important contributors to CVB might exist, like the bioactivation\nof the major diaminothiazine metabolite (DIAT). The level of covalent\nbinding (CVB) burden (fraction of the dose resulting in CVB) is clearly\nbelow 1 mg/day, with a low daily dose of 25 mg. Despite this limited\nmagnitude of CVB, it could still contribute to the liver enzyme elevations\nobserved in approximately 20% of the patients and to the few cases\nof severe immune-mediated DILI. The latter could occur through a haptenization\nphenomenon and/or by inducing stress in hepatocytes. Such stress may\nactivate an innate immune response, which, in turn, promotes the adaptive\nimmune response.