UGT1A1 and UGT1A9 substrates
In vitro data indicate that regorafenib as well as its active metabolites M-2 inhibits
glucuronidation mediated by uridine diphosphate glucuronosyl transferases UGT1A1 (Ki values
of 0.6 to 3.1 µM) and UGT1A9 (Ki values of 2.1 to 4.3 µM) whereas M-5 only inhibits UGT1A1
(Ki value of 1.1 µM) at concentrations which are achieved in vivo at steady state. Administration
of regorafenib with a 5-day break prior to administration of irinotecan resulted in an increase of
approximately 44% in mean exposure (AUC) to SN-38, a substrate of UGT1A1 and an active
metabolite of irinotecan. An increase in mean exposure to irinotecan of approximately 28% was
also observed. This indicates that co-administration of regorafenib may increase systemic
exposure to UGT1A1 and UGT1A9 substrates. The clinical significance of these findings is
unknown.