Inhibition of human UDP-glucuronosyltransferase (UGT) enzymes by kinase inhibitors: Effects of dabrafenib, ibrutinib, nintedanib, trametinib and BIBF 1202

We have demonstrated previously that the kinase inhibitors (KIs) lapatinib, pazopanib, regorafenib and sorafenib are potent inhibitors of UGT1A1 and UGTs 1A7-1A10. The present study characterised the effects of four additional drugs in this class, dabrafenib, ibrutinib, nintedanib and trametinib, on human UGT enzyme activities in vitro. Dabrafenib, ibrutinib, nintedanib and trametinib were potent inhibitors of human liver microsomal UGT1A1; K_i,u values ranged from 1.1 to 7.5 µM. Similarly, these KIs inhibited UGT 1A7, 1A8, 1A9 and 1A10, albeit less potently than UGT1A1. Despite the potent inhibition of UGT1A1, in vitro – in vivo extrapolation excluded the likelihood that dabrafenib, ibrutinib, nintedanib and trametinib would precipitate drug-drug interactions (DDIs) due to the low unbound plasma concentrations of these drugs observed in patients. The structures of dabrafenib, ibrutinib, lapatinib, nintedanib, pazopanib, regorafenib, trametinib and 22 other KIs overlaid well on that of sorafenib, a potent inhibitor of UGT1A1 and UGTs 1A7-1A10. Taken together, kinetic and computational modelling data suggest that all currently marketed KIs are likely to be potent inhibitors of UGT1A1, and are also likely to inhibit UGTs 1A7-1A10 to some extent due to the structural and chemical features shared in common by these drugs. By contrast, BIBF 1202, the major metabolite of nintedanib, did not appreciably inhibit human UGTs, due to the presence of a terminal electronegative group which appears to disfavor enzyme inhibition. Given the potent inhibition of several UGT enzymes, especially UGT1A1, by KIs, characterisation of the DDI potential of newly developed agents in this class is warranted.