Prediction of the Transporter-Mediated Drug-Drug Interaction Potential of Dabrafenib and Its Major Circulating Metabolites RUNNING TITLE: Risk for transporter-mediated drug-drug interactions for dabrafenib and metabolites

Abbreviations: AB, Apical to basolateral; BA, Basolateral to apical; BA/AB ratio, P app BA /P app AB ; BCRP, breast cancer resistance protein; CHO, Chinese hamster ovary cell line; DDI, drug-drug interaction; DMEM, Dulbecco's Modified Eagle Medium; DMF, dimethyl formamide; DMSO, dimethyl sulphoxide; DPBS, Dulbecco's Phosphate Buffered Saline; ITC, International Transporter Consortium; K m , affinity constant; MDCK = Madin Darby canine kidney cells; MDR1, multi-drug resistance protein 1; OATP, organic anion transporting polypeptide; OAT, organic anion transporter; OCT, organic cation transporter; P-gp, P-glycoprotein; P app , apparent permeability; V max , maximum uptake rate. ABSTRACT The BRAF inhibitor dabrafenib was recently approved for the treatment of certain BRAF V600 mutation-positive tumors, either alone or in combination therapy with the MEK inhibitor trametinib. This article presents the dabrafenib transporter-mediated drug-drug interaction risk assessment, which is currently an important part of drug development, regulatory submission and drug registration. Dabrafenib and its major circulating metabolites (hydroxy-, carboxy-and desmethyl-dabrafenib) were investigated as inhibitors of the clinically relevant transporters Pgp, BCRP, OATP1B1, OATP1B3, OCT2, OAT1 and OAT3. The DDI Guidance risk assessment decision criteria for inhibition of BCRP, OATP1B1 and OAT3 were slightly exceeded and therefore a minor DDI effect resulting from inhibition of these transporters remained possible. Biliary secretion is the major excretion pathway of dabrafenib-related material (71.1% of orally administered radiolabeled dose recovered in feces), while urinary excretion was observed as well (22.7% of the dose). In vitro uptake into human hepatocytes of the dabrafenib metabolites, but not of dabrafenib parent compound, was mediated, at least in part, by hepatic uptake transporters. The transporters responsible for uptake of the pharmacologically active hydroxy-and desmethyl dabrafenib could not be identified, whereas carboxy-dabrafenib was a substrate of several OATPs. Dabrafenib, hydroxyand desmethyl dabrafenib were substrates of P-gp and BCRP, while carboxy-dabrafenib was not. While a small increase in exposure to carboxy-dabrafenib upon inhibition of OATPs and an increase in exposure to desmethyl-dabrafenib upon inhibition of P-gp or BCRP cannot be excluded, the clinical significance of such increases is likely to be low