Novel Pathways Of Ponatinib Disposition Catalysed By CYP1A1 Involving Generation Of Potentially Toxic Metabolites

Ponatinib, a pan-BCR-ABL tyrosine kinase inhibitor for the treatment of chronic myeloid leukemia (CML), causes severe side-effects including vascular occlusions, pancreatitis and liver toxicity, although the underlying mechanisms remain unclear. Modification of critical proteins through reactive metabolites are thought to be responsible for a number of adverse drug reactions. In vitro metabolite screening of ponatinib with human liver microsomes and glutathione revealed unambiguous signals of glutathionedrug (P-GSH) adducts. Further profiling of human P450s indicated that CYP1A1 was the predominant P450 enzyme driving this reaction. P-GSH conjugate formation paralleled the disappearance of hydroxylated ponatinib metabolites, suggesting the initial reaction was epoxide generation. Mouse glutathione S-transferase p1 (mGstp1) further enhanced P-GSH adduct formation in vitro. Ponatinib pharmacokinetics were determined in vivo in WT mice and mice humanised for CYP1A1/2 and treated with the CYP1A1 inducers 2,3,7,8-tetrachlorodibenzodioxin (TCDD) or 3-methylcholanthrene (3-MC). Ponatinib exposure was significantly decreased in treated mice compared to controls (7.7- and 2.2 fold for WT and humanised CYP1A1/2, respectively). Interestingly, the P-GSH conjugate was only found in the feces of CYP1A1-induced mice, not in control animals. Proteinadducts were also identified by LC-MS/MS analysis of mGstp1 tryptic digests. These results indicate not only that CYP1A1 could be involved in ponatinib disposition, which has not been previously reported, but also that electrophilic intermediates resulting from CYP1A1 metabolism in normal tissues may contribute to ponatinib toxicity. These data are consistent with a recent report that CML patients who smoke are at a greater risk of disease progression and premature death. (Lauseker et al., 2017).