Physiologically Based Pharmacokinetic Modeling of the Drug-Drug Interaction Between CYP3A4 Substrate Glasdegib and Moderate CYP3A4 Inducers in Lieu of a Clinical Study.

Glasdegib (DAURISMO) is a hedgehog pathway inhibitor approved for the treatment of acute myeloid leukemia (AML). Cytochrome P450 3A4 (CYP3A4) has been identified as a major metabolism and clearance pathway for glasdegib. The role of CYP3A4 in the clearance of glasdegib has been confirmed with clinical drug-drug interaction (DDI) studies following the coadministration of glasdegib with the strong CYP3A4 inhibitor ketoconazole and the strong inducer rifampin. To evaluate potential drug interactions with CYP3A4 modulators, the coadministration of glasdegib with a moderate CYP3A4 inducer, efavirenz, was evaluated using physiologically based pharmacokinetic (PBPK) modeling using the Simcyp simulator. The glasdegib compound file was developed using measured physicochemical properties, data from human intravenous and oral pharmacokinetics, absorption, distribution, metabolism, and excretion studies, and in vitro reaction phenotyping results. The modeling assumptions, model parameters, and assignments of fractional CYP3A4 metabolism were verified using results from clinical pharmacokinetics (PK) and DDI studies with ketoconazole and rifampin. The verified glasdegib and efavirenz compound files, the latter of which was available in the Simcyp simulator, were used to estimate the potential impact of efavirenz on the PK of glasdegib. PBPK modeling predicted a glasdegib area under the concentration-time curve ratio of 0.45 and maximum plasma concentration ratio of 0.75 following coadministration with efavirenz. The PBPK results, in lieu of a formal clinical study, informed the drug label, with the recommendation to double the clinical dose of glasdegib when administered in conjunction with a moderate CYP3A4 inducer, followed by a resumption of the original dose 7 days post-discontinuation.

Enzalutamide and Apalutamide: In Vitro Chemical Reactivity Studies and Activity in a Mouse Drug Allergy Model.

Enzalutamide and apalutamide are two androgen receptor inhibitors approved for the treatment of castration-resistant prostate cancer (CRPC) and nonmetastatic castration-resistant prostate cancer (nmCRPC), respectively. Apalutamide is associated with an increased incidence of skin rash above the placebo groups in the SPARTAN trial in nmCRPC and in the TITAN trial in metastatic castration-sensitive prostate cancer patients. On the contrary, the rate of skin rash across all clinical trials (including PROSPER [nmCRPC]) for enzalutamide is similar to the placebo. We hypothesized that the apalutamide-associated increased skin rash in patients could be linked to a structural difference. The 2-cyanophenyl and dimethyl moieties in enzalutamide are substituted in apalutamide with 2-cyanopyridine and cyclobutyl, respectively. In our evaluations, the 2-cyanopyridine moiety of apalutamide was chemically reactive with the thiol nucleophile glutathione, resulting in rearranged thiazoline products. Radiolabeled apalutamide, but not radiolabeled enzalutamide, was shown to react with mouse and human plasma proteins. Thiol nucleophiles decreased the extent of covalent binding to the model protein bovine serum albumin, whereas amine and alcohol nucleophiles had no effect, suggesting reactivity with cysteine of proteins. Subcutaneous administration of apalutamide dose dependently increased lymphocyte cellularity in draining lymph nodes in a mouse drug allergy model (MDAM). Enzalutamide, and its known analogue RD162 in which the cyanophenyl was retained but the dimethyl was replaced by cyclobutyl, demonstrated substantially less covalent binding activity and negative results in the MDAM assay. Collectively, these data support the hypothesis that the 2-cyanopyridine moiety in apalutamide may react with cysteine in proteins forming haptens, which may trigger an immune response, as indicated by the activity of apalutamide in the MDAM assay, which in turn may be leading to increased potential for skin rash versus placebo in patients in the SPARTAN and TITAN clinical trials.

Novel Application of the Two-Period Microtracer Approach to Determine Absolute Oral Bioavailability and Fraction Absorbed of Ertugliflozin.

Ertugliflozin, a sodium glucose cotransporter-2 inhibitor, is approved in the United States for treatment of type 2 diabetes mellitus. A novel two-period study design with 14 C microtracer dosing in each period was used to determine absolute oral bioavailability (F) and fraction absorbed (Fa ) of ertugliflozin. Eight healthy adult men received 100-µg i.v. 14 C-ertugliflozin (400 nCi) dose 1 h after a 15-mg oral unlabeled ertugliflozin dose (period 1), followed by 100 µg 14 C-ertugliflozin orally along with 15 mg oral unlabeled ertugliflozin (period 2). Unlabeled ertugliflozin plasma concentrations were determined using high-performance liquid-chromatography tandem mass spectrometry (HPLC-MS/MS). 14 C-ertugliflozin plasma concentrations were determined using HPLC-accelerator mass spectrometry (AMS) and 14 C urine concentrations were determined using AMS. F ((area under the curve (AUC)p.o. /14 C-AUCi.v. )*(14 C-Dosei.v. /Dosep.o. )) and Fa ((14 C_Total_Urinep.o. /14 C_Total_Urinei.v. )* (14 C-Dosei.v. /14 C-Dosep.o. )) were estimated. Estimates of F and Fa were 105% and 111%, respectively. Oral absorption of ertugliflozin was complete under fasted conditions and F was ∼100%. Ertugliflozin was well tolerated.

Role of Hepatic Organic Anion Transporter 2 in the Pharmacokinetics of R- and S-Warfarin: In Vitro Studies and Mechanistic Evaluation.

Interindividual variability in warfarin dose requirement demands personalized medicine approaches to balance its therapeutic benefits (anticoagulation) and bleeding risk. Cytochrome P450 2C9 ( CYP2C9) genotype-guided warfarin dosing is recommended in the clinic, given the more potent S-warfarin is primarily metabolized by CYP2C9. However, only about 20-30% of interpatient variability in S-warfarin clearance is associated with CYP2C9 genotype. We evaluated the role of hepatic uptake in the clearance of R- and S-warfarin. Using stably transfected HEK293 cells, both enantiomers were found to be substrates of organic anion transporter (OAT)2 with a Michaelis-Menten constant ( Km) of ∼7-12 µM but did not show substrate affinity for other major hepatic uptake transporters. Uptake of both enantiomers by primary human hepatocytes was saturable ( Km ≈ 7-10 µM) and inhibitable by OAT2 inhibitors (e.g., ketoprofen) but not by OATP1B1/1B3 inhibitors (e.g., cyclosporine). To further evaluate the potential role of hepatic uptake in R- and S-warfarin pharmacokinetics, mechanistic modeling and simulations were conducted. A "bottom-up" PBPK model, developed assuming that OAT2-CYPs interplay, well recovered clinical pharmacokinetics, drug-drug interactions, and CYP2C9 pharmacogenomics of R- and S-warfarin. Clinical data were not available to directly verify the impact of OAT2 modulation on warfarin pharmacokinetics; however, the bottom-up PBPK model simulations suggested a proportional change in clearance of both warfarin enantiomers with inhibition of OAT2 activity. These results suggest that variable hepatic OAT2 function, in conjunction with CYP2C, may contribute to the high population variability in warfarin pharmacokinetics and possibly anticoagulation end points and thus warrant further clinical investigation.