Sigma-1 and dopamine D2/D3 receptor occupancy of pridopidine in healthy volunteers and patients with Huntington disease: a [18F] fluspidine and [18F] fallypride PET study.

PURPOSE: Pridopidine is an investigational drug for Huntington disease (HD). Pridopidine was originally thought to act as a dopamine stabilizer. However, pridopidine shows highest affinity to the sigma-1 receptor (S1R) and enhances neuroprotection via the S1R in preclinical studies. Using [18F] fluspidine and [18F] fallypride PET, the purpose of this study was to assess in vivo target engagement/receptor occupancy of pridopidine to the S1R and dopamine D2/D3 receptor (D2/D3R) at clinical relevant doses in healthy volunteers (HVs) and as proof-of-concept in a small number of patients with HD. METHODS: Using [18F] fluspidine PET (300 MBq, 0-90 min), 11 male HVs (pridopidine 0.5 to 90 mg; six dose groups) and three male patients with HD (pridopidine 90 mg) were investigated twice, without and 2 h after single dose of pridopidine. Using [18F] fallypride PET (200 MBq, 0-210 min), four male HVs were studied without and 2 h following pridopidine administration (90 mg). Receptor occupancy was analyzed by the Lassen plot. RESULTS: S1R occupancy as function of pridopidine dose (or plasma concentration) in HVs could be described by a three-parameter Hill equation with a Hill coefficient larger than one. A high degree of S1R occupancy (87% to 91%) was found throughout the brain at pridopidine doses ranging from 22.5 to 90 mg. S1R occupancy was 43% at 1 mg pridopidine. In contrast, at 90 mg pridopidine, the D2/D3R occupancy was only minimal (~ 3%). CONCLUSIONS: Our PET findings indicate that at clinically relevant single dose of 90 mg, pridopidine acts as a selective S1R ligand showing near to complete S1R occupancy with negligible occupancy of the D2/D3R. The dose S1R occupancy relationship suggests cooperative binding of pridopidine to the S1R. Our findings provide significant clarification about pridopidine's mechanism of action and support further use of the 45-mg twice-daily dose to achieve full and selective targeting of the S1R in future clinical trials of neurodegenerative disorders. Clinical Trials.gov Identifier: NCT03019289 January 12, 2017; EUDRA-CT-Nr. 2016-001757-41.

Metoprolol-pridopidine drug-drug interaction and food effect assessments of pridopidine, a new drug for treatment of Huntington's disease.

AIMS: Pridopidine is an oral drug in clinical development for treatment of patients with Huntington's disease. This study examined the interactions of pridopidine with in vitro cytochrome P450 activity and characterized the effects of pridopidine on CYP2D6 activity in healthy volunteers using metoprolol as a probe substrate. The effect of food on pridopidine exposure was assessed. METHODS: The ability of pridopidine to inhibit and/or induce in vitro activity of drug metabolizing enzymes was examined in human liver microsomes and fresh hepatocytes. CYP2D6 inhibition potency and reversibility was assessed using dextromethorphan. For the clinical assessment, 22 healthy subjects were given metoprolol 100 mg alone and concomitantly with steady-state pridopidine 45 mg twice daily. Food effect on a single 90 mg dose of pridopidine was evaluated in a crossover manner. Safety assessments and pharmacokinetic sampling occurred throughout the study. RESULTS: Pridopidine was found to be a metabolism dependent inhibitor of CYP2D6, the main enzyme catalysing its own metabolism. Flavin-containing monooxygenase heat inactivation of liver microsomes did not affect pridopidine metabolism-dependent inhibition of CYP2D6 and its inhibition of CYP2D6 was not reversible with addition of FeCN3 . Exposure to metoprolol was markedly increased when coadministered with pridopidine; the ratio of the geometric means (90% confidence interval) for maximum observed plasma concentration, and area under the plasma concentration-time curve from time 0 to the time of the last quantifiable concentration and extrapolated to infinity were 3.5 (2.9, 4.22), 6.64 (5.27, 8.38) and 6.55 (5.18, 8.28), respectively. Systemic exposure to pridopidine was unaffected by food conditions. CONCLUSIONS: As pridopidine is a metabolism-dependent inhibitor of CYP2D6, systemic levels of drugs metabolized by CYP2D6 may increase with chronic coadministration of pridopidine. Pridopidine can be administered without regard to food.

Chronic Cannabis Users: A New Special Population to Consider for Drug Development.

The use and acceptance of cannabis, either medically or recreationally, has substantially outpaced the collection of data necessary to evaluate it's use in any population. However, the mere widespread availability does not imply the absence of risk or confirmation of efficacy and should not be treated as such. There is enough data to suggest that not only does the potential for pharmacokinetic and metabolic interactions exist, but also that baseline characteristics for a given population could be different in chronic cannabis users. Either or both of these may impact the safety and efficacy profile for any new drug in development. As such, we encourage drug developers to consider that the cannabis user may very well be a special population that warrants its own clinical pharmacology evaluation.

Framework for the Design of Cannabis-Mediated Phase I Drug-Drug Interaction Studies.

Cannabis has become legal in much of the United States similar to many other countries, for either recreational or medical use. The use of cannabis products is rapidly increasing while the body of knowledge of its myriad of effects still lags. In vitro and clinical data show that cannabis' main constituents, delta-9-tetrahydrocannabinol and cannabidiol, can affect pharmacokinetics (PK), safety, and pharmacodynamics (PD) of other drugs. Within the context of clinical drug development, the widespread and frequent use of cannabis products has essentially created another special population: the cannabis user. We propose that all clinical drug development programs include a Phase 1 study to assess the drug-drug interaction potential of cannabis as a precipitant on the PK, safety, and if applicable, the PD of all new molecular entities (NMEs) in a combination of healthy adult subjects as well as frequent and infrequent cannabis users. This data should be required to inform drug labeling and aid health care providers in treating any patient, as cannabis has quickly become another common concomitant medication and cannabis users, a new special population.

Pharmacokinetics, Pharmacodynamics, Pharmacogenomics, Safety, and Tolerability of Avatrombopag in Healthy Japanese and White Subjects.

Avatrombopag, an orally administered, small-molecule thrombopoietin receptor (c-Mpl) agonist, is currently in clinical development for the potential treatment of severe thrombocytopenia in patients with chronic liver disease undergoing an elective procedure. The objectives of this study were to characterize and compare the pharmacokinetics (including the food effect) and pharmacodynamics (platelet count) of avatrombopag following single doses in Japanese and white subjects. Following single dosing under fasted and fed conditions, mean peak concentrations occurred at 5 to 8 hours and subsequently declined with a half-life of 16 to 18 hours in Japanese and white subjects. Administration with food did not alter the rate or extent of avatrombopag absorption but substantially reduced pharmacokinetic variability relative to the fasted state. CYP2C9 polymorphism (*2, *3) was associated with higher pharmacokinetic variability but not with any clinically important effect on variability in platelet response. Plasma exposures of avatrombopag increased in a dose-proportional manner over the dose range tested. After a single dose, platelet count increased in a dose-related manner, reaching a maximum by day 11 and returning to baseline levels by day 27. No clinically important differences were found when avatrombopag pharmacokinetics and pharmacodynamics were compared between Japanese and white subjects. Administration of avatrombopag was generally well tolerated.

Incorporation of the genetic control of alcohol dehydrogenase into a physiologically based pharmacokinetic model for ethanol in humans.

The assessment of the variability of human responses to foreign chemicals is an important step in characterizing the public health risks posed by nontherapeutic hazardous chemicals and the risk of encountering adverse reactions with drugs. Of the many sources of interindividual variability in chemical response identified to date, hereditary factors are some of the least understood. Physiologically based pharmacokinetic modeling linked with Monte Carlo sampling has been shown to be a useful tool for the quantification of interindividual variability in chemical disposition and/or response when applied to biological processes that displayed single genetic polymorphisms. The present study has extended this approach by modeling the complex hereditary control of alcohol dehydrogenase, which includes polygenic control and polymorphisms at two allelic sites, and by assessing the functional significance of this hereditary control on ethanol disposition. The physiologically based pharmacokinetic model for ethanol indicated that peak blood ethanol levels and time-to-peak blood ethanol levels were marginally affected by alcohol dehydrogenase genotypes, with simulated subjects possessing the B2 subunit having slightly lower peak blood ethanol levels and shorter times-to-peak blood levels compared to subjects without the B2 subunit. In contrast, the area under the curve (AUC) of the ethanol blood decay curve was very sensitive to alcohol dehydrogenase genotype, with AUCs from any genotype including the ADH1B2 allele considerably smaller than AUCs from any genotype without the ADH1B2 allele. Furthermore, the AUCs in the ADH1C1/C1 genotype were moderately lower than the AUCs from the corresponding ADH1C2/C2 genotype. Moreover, these simulations demonstrated that interindividual variability of ethanol disposition is affected by alcohol dehydrogenase and that the degree of this variability was a function of the ethanol dose.