Evaluation of Potential Drug-Drug Interaction Risk of Pexidartinib With Substrates of Cytochrome P450 and P-Glycoprotein

Physiologically Based Pharmacokinetic Absorption Model for Pexidartinib to Evaluate the Impact of Meal Contents and Intake Timing on Drug Exposure

Pexidartinib is a systemic treatment for patients with tenosynovial giant cell tumor not amenable to surgery. Oral absorption of pexidartinib is affected by food; administration with a high-fat meal (HFM) or low-fat meal (LFM) increases absorption by approximately 100% and approximately 60%, respectively, compared with the fasted state. Pexidartinib is currently dosed 250 mg orally twice daily with an LFM (approximately 11-14 g of total fat). We developed a physiologically based pharmacokinetic model to determine the impact on drug exposure of dose timing with respect to meals, meal type, and caloric content. A 15%-16% increase in plasma exposure was predicted when consuming an HFM 1 hour after dosing with an LFM, but almost no effect on pharmacokinetics was predicted when an HFM was consumed 3 hours or more before or after pexidartinib dosing with an LFM. Exposure was not significantly affected when pexidartinib was taken with a 500-kcal LFM over the range of fat (approximately 11-14 g of total fat; 20%-25% calories from fat) for an LFM. These findings on timing of pexidartinib dose with respect to meals should be considered by patients and physicians to reduce the potential for side effects.

The latest perspectives of small molecules FMS kinase inhibitors

FMS kinase is a type III tyrosine kinase receptor that plays a central role in the pathophysiology and management of several diseases, including a range of cancer types, inflammatory disorders, neurodegenerative disorders, and bone disorders among others. In this review, the pathophysiological pathways of FMS kinase in different diseases and the recent developments of its monoclonal antibodies and inhibitors during the last five years are discussed. The biological and biochemical features of these inhibitors, including binding interactions, structure-activity relationships (SAR), selectivity, and potencies are discussed. The focus of this article is on the compounds that are promising leads and undergoing advanced clinical investigations, as well as on those that received FDA approval. In this article, we attempt to classify the reviewed FMS inhibitors according to their core chemical structure including pyridine, pyrrolopyridine, pyrazolopyridine, quinoline, and pyrimidine derivatives.

Dosing Recommendation Based on the Effects of Different Meal Types on Pexidartinib Pharmacokinetics in Healthy Subjects: Implementation of Model-informed Drug Development Strategy

Pexidartinib, an oral small molecule inhibitor of the colony-stimulating factor 1 receptor, is approved for treatment of adults with symptomatic tenosynovial giant cell tumor associated with severe morbidity or functional limitations and not amenable to improvement with surgery. The original dosing regimen is 400 mg of pexidartinib (2 × 200-mg capsules) twice daily, administered on an empty stomach at least 1 hour before or 2 hours after a meal or snack. Because pexidartinib is likely to be taken over an extended period of time, the ability to take pexidartinib with a meal would simplify timing of administration and potentially improve compliance. Since administering 400 mg of pexidartinib with a low-fat meal increases exposure by ≈60% relative to the fasted state, administering 250 mg of pexidartinib with a low-fat meal (low-fat meal dosing regimen) was predicted to achieve an exposure similar to 400 mg administered during a fasted state (original dosing regimen). Based on clinical trial simulations with two one-sided t-tests and bootstrapping (ie, resampling) analyses, a bioequivalence study (n = 24) would have >90% power to conclude that the original dosing regimen (400 mg fasted twice daily) and the low-fat meal dosing regimen (250 mg with a low-fat meal twice daily) are bioequivalent. This report provides the outcome of the implementation of the model-informed drug development strategy to recommend and justify a low-fat meal dosing regimen for pexidartinib that has the potential to improve patient compliance while maintaining drug exposure.

Pharmacokinetics of the Multi-kinase Inhibitor Pexidartinib: Mass Balance and Dose Proportionality

Pexidartinib is an oral small-molecule tyrosine kinase inhibitor that selectively targets colony-stimulating factor 1 receptor. Two phase 1 single-center trials were conducted in healthy subjects to determine the absorption, distribution, metabolism, and excretion of pexidartinib using radiolabeled drug and to assess the dose proportionality of pexidartinib following single oral doses. In the mass balance study, eight male subjects received a single oral dose of [¹⁴ C]-pexidartinib 400 mg with radioactivity assessed in plasma, urine, and feces samples taken at various timepoints postdose. In the dose-proportionality study, 18 subjects received single doses of pexidartinib 200, 400, and 600 mg using randomization sequences. Peak pexidartinib and total radioactivity were observed at 1.75-2.0 hours after the oral dose and then declined in a multiphasic manner. The overall mean recovery of administered radioactivity was 92.2% over 240 hours with 64.8% in the feces and 27.4% in the urine. Major components detected in plasma were pexidartinib and glucuronide (M5, ZAAD-1006a), with M5 and pexidartinib detected in urine and feces, respectively. A glucuronide of dealkylated form (M1) in the urine and multiple oxidized forms (M2, M3, and M4) in feces were detected. The dose-proportionality study found dose-proportional drug exposure between the 200- and 400-mg doses and slightly less than proportional exposure between the 400- and 600-mg doses. These results from these studies provide insight into pexidartinib disposition after oral administration and support the development of dosing guidance in subjects with renal or hepatic impairment or subjects taking cytochrome P450 3A and uridine disphosphate-glucuronosyl transferase inhibitors and inducers.

Eco-Friendly, Simple, Fast, and Sensitive UPLC-MS/MS Method for Determination of Pexidartinib in Plasma and Its Application to Metabolic Stability

Pexidartinib is the first drug approved by the U.S. Food and Drug Administration specifically to treat the rare joint tumor tenosynovial giant cell tumor. In the current study, a validated, selective, and sensitive UPLC-MS/MS assay was developed for the quantitative determination of pexidartinib in plasma samples using gifitinib as an internal standard (IS). Pexidartinib and IS were extracted by liquid-liquid extraction using methyl tert-butyl ether and separated on an acquity BEH C18 column kept at 40 °C using a mobile phase of 0.1% formic acid in acetonitrile: 0.1% formic acid in de-ionized water (70:30). The flow rate was 0.25 mL/min. Multiple reaction monitoring (MRM) was operated in electrospray (ESI)-positive mode at the ion transition of 418.06 > 165.0 for the analyte and 447.09 > 128.0 for the IS. FDA guidance for bioanalytical method validation was followed in method validation. The linearity of the established UPLC-MS/MS assay ranged from 0.5 to 1000 ng/mL with r > 0.999 with a limit of quantitation of 0.5 ng/mL. Moreover, the metabolic stability of pexidartinib in liver microsomes was estimated.

Evaluation of Absorption and Metabolism-Based DDI Potential of Pexidartinib in Healthy Subjects

BACKGROUND AND OBJECTIVE

Pexidartinib is a novel oral small-molecule inhibitor that selectively targets colony-stimulating factor 1 receptor, KIT proto-oncogene receptor tyrosine kinase, and FMS-like tyrosine kinase 3 harboring an internal tandem duplication mutation. It is approved in the United States for the treatment of adult patients with symptomatic tenosynovial giant cell tumor (TGCT) associated with severe morbidity or functional limitations and not amenable to improvement with surgery. Pexidartinib in vitro data indicate the potential for absorption- and metabolism-related drug-drug interactions (DDIs). The objective was to present a comprehensive DDI risk assessment of agents that can impact pexidartinib exposure by altering its absorption and metabolism potentially affecting efficacy and safety of pexidartinib.

METHODS

Four open-label crossover studies were performed to assess the effects of a pH modifier (esomeprazole), a strong cytochrome P450 (CYP) 3A4 inhibitor (itraconazole), a strong CYP3A/5'-diphospho-glucuronosyltransferase (UGT) inducer (rifampin), and a UGT inhibitor (probenecid) on the single-dose pharmacokinetics of pexidartinib. In addition, a physiologically based pharmacokinetic model was developed to predict the effect of a moderate CYP3A4 inhibitor (fluconazole) and a moderate CYP3A inducer (efavirenz) on the pharmacokinetics of pexidartinib.

RESULTS

Co-administration of pexidartinib with esomeprazole modestly decreased pexidartinib exposure (maximum plasma concentration [C_max], ng/mL: geometric mean ratio [90% confidence interval (CI)], 45.4% [36.8-55.9]; area under the drug plasma concentration-time curve from time 0 to infinity [AUC_∞], ng•h/mL: geometric mean ratio [90% CI], 53.1% [47.4-59.3]), likely related to decreased solubility of pexidartinib at increased pH levels. As expected, the strong CYP3A4 inhibitor itraconazole increased pexidartinib exposure (C_max, ng/mL: geometric mean ratio [90% CI], 148.3% [127.8-172.0]; AUC_∞, ng•h/mL: geometric mean ratio [90% CI], 173.0% [160.7-186.3]) while the strong CYP3A/UGT inducer rifampin decreased exposure (C_max, ng/mL: geometric mean ratio [90% CI], 67.1% [53.1-84.8]; AUC_∞, ng•h/mL: geometric mean ratio [90% CI], 37.0% [30.6-44.8]). In addition, UGT inhibition increased pexidartinib exposure (C_max, ng/mL: geometric mean ratio [90% CI], 105.8% [92.4-121.0]; AUC_∞, ng•h/mL: geometric mean ratio [90% CI], 159.8% [143.4-178.0]), consistent with the fact that pexidartinib is a substrate of the UGT1A4 enzyme, which is responsible for the generation of the major metabolite, ZAAD-1006a.

CONCLUSIONS

The physiologically based pharmacokinetic model predicted that a moderate CYP3A4 inhibitor and a moderate CYP3A inducer would produce modest increases and decreases, respectively, in pexidartinib exposure. These results provide a basis for pexidartinib dosing recommendations when administered concomitantly with drugs with drug-drug interaction potential, including dose adjustments when concomitant administration cannot be avoided.

CLINICAL TRIAL REGISTRATION

Probenecid: phase I trial, NCT03138759, 3 May, 2017; esomeprazole, itraconazole, rifampin: phase I trials, not registered with ClinicalTrials.gov.