Blockade of dopamine D3 receptor in ventral tegmental area attenuating contextual fear memory

The abnormal fear memory will lead to the onset of stress disorders, such as post-traumatic stress disorder (PTSD) and so on. Therefore, the intervention in the formation of abnormal fear memory will provide a new strategy for the prevention and treatment of PTSD. In our previous studies, we found that blockade of dopamine D3 receptor (DRD3) with highly selective antagonist YQA14 or knockout of DRD3 was able to attenuate the expression or retrieval of fear memory in PTSD animal models. However, the neurobiological mechanism of regulation of DRD3 in fear is unclear. In the present research, we clarified that DRD3 was expressed in the dopaminergic (DAergic) neurons in the ventral tegmental area (VTA). Then, we identified that microinjection of YQA14 (1 μg/0.2 μl/side) in VTA before the aversive stimuli in the training session or during days subsequent to the shock significantly meliorated the freezing behaviors in the inescapable electric foot-shock model. At last, using fiber photometry system, we found that microinjection of YQA14 in VTA promoted the dopamine neurotransmitter release in the basolateral amygdala (BLA), and pre-training YQA14 infusion in VTA lowered the increase of dopamine (DA) in BLA induced by shock during the training session or by context during the retrieval session. All above the results demonstrated that YQA14 attenuated the fear learning through the blockade of DRD3 in VTA decreasing the excitability of the projection to BLA. This study may provide new mechanisms and potential intervention targets for stress disorders with abnormal fear memory.

Application of physiologically based pharmacokinetic models to promote the development of veterinary drugs with high efficacy and safety

Physiologically based pharmacokinetic (PBPK) models have become important tools for the development of novel human drugs. Food-producing animals and pets comprise an important part of human life, and the development of veterinary drugs (VDs) has greatly impacted human health. Owing to increased affordability of and demand for drug development, VD manufacturing companies should have more PBPK models required to reduce drug production costs. So far, little attention has been paid on applying PBPK models for the development of VDs. This review begins with the development processes of VDs; then summarizes case studies of PBPK models in human or VD development; and analyzes the application, potential, and advantages of PBPK in VD development, including candidate screening, formulation optimization, food effects, target-species safety, and dosing optimization. Then, the challenges of applying the PBPK model to VD development are discussed. Finally, future opportunities of PBPK models in designing dosing regimens for intracellular pathogenic infections and for efficient oral absorption of VDs are further forecasted. This review will be relevant to readers who are interested in using a PBPK model to develop new VDs.

Comparable Intestinal and Hepatic First-Pass Effect of YL-IPA08 on the Bioavailability and Effective Brain Exposure, a Rapid Anti-PTSD and Anti-Depression Compound

YL-IPA08, exerting rapid antidepressant-like and anxiolytic-like effects on behaviors by translocator protein (TSPO) mediation, is a novel compound that has been discovered and developed at our institute. Fit-for-purpose pharmacokinetic properties is urgently needed to be discovered as early as possible for a new compound. YL-IPA08 exhibited low bioavailability (∼6%) during the preliminary pharmacokinetics study in rats after oral administration. Our aim was to determine how metabolic disposition by microsomal P450 enzymes in liver and intestine limited YL-IPA08’s bioavailability and further affected brain penetration to the target. Studies of in vitro metabolic stability and permeability combined with in vivo oral bioavailability, panel CYP inhibitor co-administration via different routes, and double cannulation rats were conducted to elucidate the intestinal and hepatic first-pass effect of YL-IPA08 on bioavailability. Unbound brain-to-plasma ratio (K_p,uu) in rats was determined at steady state. Results indicated that P450-mediated elimination appeared to be important for its extensive first-pass effect with comparative contribution of gut (35%) and liver (17%), and no significant species difference was observed. The unbound concentration of YL-IPA08 in rat brain (6.5 pg/ml) was estimated based on K_p,uu (0.18) and was slightly higher than in vitro TSPO-binding activity (4.9 pg/ml). Based on the onset efficacy of YL-IPA08 toward TPSO in brain and K_p,uu, therapeutic human plasma concentration was predicted to be ∼27.2 ng/ml would easily be reached even with unfavorable bioavailability.

Assessment and Confirmation of Species Difference in Nonlinear Pharmacokinetics of Atipamezole with Physiologically Based Pharmacokinetic Modeling

Atipamezole, an α ₂-adrenoceptor antagonist, displayed nonlinear pharmacokinetics (PK) in rats. The aim of this study was to understand the underlying mechanisms of nonlinear PK in rats and linear PK in humans and develop physiologically based PK models (PBPK) to capture and validate this phenomenon. In vitro and in vivo data were generated to show that metabolism is the main clearance pathway of atipamezole and species differences exist. Where cytochrome P450 (P450) was responsible for the metabolism in rats with a low Michaelis constant, human-specific UDP-glucuronosyltransferase 2B10- and 1A4-mediated N-glucuronidation was identified as the leading contributor to metabolism in humans with a high V _max capacity. Saturation of metabolism was observed in rats at pharmacologically relevant doses, but not in humans at clinically relevant doses. PBPK models were developed using GastroPlus software to predict the PK profile of atipamezole in rats after intravenous or intramuscular administration of 0.1 to 3 mg/kg doses. The model predicted the nonlinear PK of atipamezole in rats and predicted observed exposures within 2-fold across dose levels. Under the same model structure, a human PBPK model was developed using human in vitro metabolism data. The PBPK model well described human concentration-time profiles at 10-100 mg doses showing dose-proportional increases in exposure. This study demonstrated that PBPK is a useful tool to predict human PK when interspecies extrapolation is not applicable. The nonlinear PK in rat and linear PK in human were characterized in vitro and allowed the prospective human PK via intramuscular dosing to be predicted at the preclinical stage. SIGNIFICANCE STATEMENT: This study demonstrated that PBPK is a useful tool for predicting human PK when interspecies extrapolation is not applicable due to species unique metabolism. Atipamezole, for example, is metabolized by P450 in rats and by N-glucuronidation in humans that were hypothesized to be the underlying reasons for a nonlinear PK in rats and linear PK in humans. This was testified by PBPK simulation in this study.

Metabolic stability and its role in the discovery of new chemical entities

Determination of metabolic profiles of new chemical entities is a key step in the process of drug discovery, since it influences pharmacokinetic characteristics of therapeutic compounds. One of the main challenges of medicinal chemistry is not only to design compounds demonstrating beneficial activity, but also molecules exhibiting favourable pharmacokinetic parameters. Chemical compounds can be divided into those which are metabolized relatively fast and those which undergo slow biotransformation. Rapid biotransformation reduces exposure to the maternal compound and may lead to the generation of active, non-active or toxic metabolites. In contrast, high metabolic stability may promote interactions between drugs and lead to parent compound toxicity. In the present paper, issues of compound metabolic stability will be discussed, with special emphasis on its significance, in vitro metabolic stability testing, dilemmas regarding in vitro-in vivo extrapolation of the results and some aspects relating to different preclinical species used in in vitro metabolic stability assessment of compounds.

Selective dopamine D3 receptor antagonist YQA14 inhibits morphine-induced behavioral sensitization in wild type, but not in dopamine D3 receptor knockout mice

Increasing preclinical evidence demonstrates that dopamine D3 receptor (D3R) antagonists are a potential option for the treatment of drug addiction. The reinstatement of the addiction can be triggered by environmental stimuli that acquire motivational salience through repeated associations with the drug's effects. YQA14 is a novel D3R antagonist that has exhibited pharmacotherapeutic efficacy in reducing cocaine and amphetamine reward and relapse to drug seeking in mice. In this study we investigated the effects of YQA14 on morphine-induced context-specific locomotor sensitization in mice. We showed that repeated injection of YQA14 (6.25-25 mg/kg every day ip) prior to morphine (10 mg/kg every day sc) not only inhibited the acquisition, but also significantly attenuated the expression of morphine-induced locomotor sensitization. Furthermore, in the expression phase, one single injection of YQA14 (6.25-25 mg/kg, ip) dose-dependently inhibited the expression of morphine-induced behavioral sensitization. Moreover, YQA14 inhibited the expression of morphine-induced behavioral sensitization in wild mice (WT), but not in D3R knockout (D3R^-/-) mice in the expression phase. In addition, D3R^-/- mice also displayed the reduction in the expression phase compared with WT mice. In summary, this study demonstrates that blockade or knockout of the D3R inhibits morphine-induced behavior sensitization, suggesting that D3R plays an important role in the pathogenesis and etiology of morphine addiction, and it might be a potential target for clinical management of opioid addiction.

Prediction of a Therapeutic Dose for Buagafuran, a Potent Anxiolytic Agent by Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling Starting from Pharmacokinetics in Rats and Human

Physiologically based pharmacokinetic (PBPK)/pharmacodynamic (PD) models can contribute to animal-to-human extrapolation and therapeutic dose predictions. Buagafuran is a novel anxiolytic agent and phase I clinical trials of buagafuran have been completed. In this paper, a potentially effective dose for buagafuran of 30 mg t.i.d. in human was estimated based on the human brain concentration predicted by a PBPK/PD modeling. The software GastroPlus^TM was used to build the PBPK/PD model for buagafuran in rat which related the brain tissue concentrations of buagafuran and the times of animals entering the open arms in the pharmacological model of elevated plus-maze. Buagafuran concentrations in human plasma were fitted and brain tissue concentrations were predicted by using a human PBPK model in which the predicted plasma profiles were in good agreement with observations. The results provided supportive data for the rational use of buagafuran in clinic.

Predicting Oral Drug Absorption: Mini Review on Physiologically-Based Pharmacokinetic Models

Most marketed drugs are administered orally, despite the complex process of oral absorption that is difficult to predict. Oral bioavailability is dependent on the interplay between many processes that are dependent on both compound and physiological properties. Because of this complexity, computational oral physiologically-based pharmacokinetic (PBPK) models have emerged as a tool to integrate these factors in an attempt to mechanistically capture the process of oral absorption. These models use inputs from in vitro assays to predict the pharmacokinetic behavior of drugs in the human body. The most common oral PBPK models are compartmental approaches, in which the gastrointestinal tract is characterized as a series of compartments through which the drug transits. The focus of this review is on the development of oral absorption PBPK models, followed by a brief discussion of the major applications of oral PBPK models in the pharmaceutical industry.

PBPK modeling and simulation in drug research and development

Physiologically based pharmacokinetic (PBPK) modeling and simulation can be used to predict the pharmacokinetic behavior of drugs in humans using preclinical data. It can also explore the effects of various physiologic parameters such as age, ethnicity, or disease status on human pharmacokinetics, as well as guide dose and dose regiment selection and aid drug-drug interaction risk assessment. PBPK modeling has developed rapidly in the last decade within both the field of academia and the pharmaceutical industry, and has become an integral tool in drug discovery and development. In this mini-review, the concept and methodology of PBPK modeling are briefly introduced. Several case studies were discussed on how PBPK modeling and simulation can be utilized through various stages of drug discovery and development. These case studies are from our own work and the literature for better understanding of the absorption, distribution, metabolism and excretion (ADME) of a drug candidate, and the applications to increase efficiency, reduce the need for animal studies, and perhaps to replace clinical trials. The regulatory acceptance and industrial practices around PBPK modeling and simulation is also discussed.

P-Glycoprotein (ABCB1) limits the brain distribution of YQA-14, a novel dopamine D3 receptor antagonist

YQA-14 is a promising agent for treating addiction to cocaine and opioids. However, previous studies have showed there is marked contrast between the relatively small differences in pharmacological action in vivo and the large differences in their respective receptor binding properties in vitro. We hypothesized that the conflict between the in vivo and in vitro outcomes was attributable to poor brain exposure to YQA-14 caused by drug efflux transporters. To address this issue, we investigated the directional flux of YQA-14 across Caco-2 cells at 37°C or 4°C and the bidirectional transport in the presence and absence of transporter chemical inhibitors. These phenomena were further investigated by an in vivo determination of the brain and blood pharmacokinetics (PK) profile of YQA-14 following intraperitoneal administration with and without inhibitor. The efflux ratio of YQA-14 on Caco-2 cell monolayers was 2.39 and the efflux was temperature-dependent. When co-incubated with GF120918 or LY335979, the efflux of YQA-14 was markedly decreased. However, there was no significant difference in the permeability of YQA-14 when the cells were treated with Ko143. In vivo experiments showed that the brain-to-plasma ratio increased by more than 75-fold and 20-fold with co-administration of GF120918 and LY335979, respectively. Use of Ko143 did not change the brain-to-blood ratio of YQA-14. The results indicate that the brain distribution of YQA-14 was restricted because of active efflux transport at the blood brain barrier. In addition, P-glycoprotein (P-gp) played a dominant role in limiting the distribution of YQA-14 to the brain.

A selective D3 receptor antagonist YQA14 attenuates methamphetamine-induced behavioral sensitization and conditioned place preference in mice

AIM

We have reported that a selective dopamine D3 receptor antagonist YQA14 attenuates cocaine reward and relapse to drug-seeking in mice. In the present study, we investigated whether YQA14 could inhibit methamphetamine (METH)-induced locomotor sensitization and conditioned place preference (CPP) in mice.

METHODS

Locomotor activity was monitored in mice treated with METH (1 mg/kg, ip) daily on d 4-13, followed by a challenge with METH (0.5 mg/kg) on d 21. CPP was examined in mice that were administered METH (1 mg/kg) or saline alternately on each other day for 8 days (METH conditioning). YQA14 was injected intraperitoneally 20 min prior to METH or saline.

RESULTS

Both repetitive (daily on d 4-13) and a single injection (on the day of challenge) of YQA14 (6.25, 12.5 and 25 mg/kg) dose-dependently inhibited the acquisition and expression of METH-induced locomotor sensitization. However, repetitive injection of YQA14 (daily during the METH conditioning) did not alter the acquisition of METH-induced CPP, whereas a single injection of YQA14 (prior to CPP test) dose-dependently attenuated the expression of METH-induced CPP. In addition, the repetitive injection of YQA14 dose-dependently facilitated the extinction and decreased the reinstatement of METH-induced CPP.

CONCLUSION

Brain D3 receptors are critically involved in the reward and psychomotor-stimulating effects of METH. Thus, YQA14 deserves further study as a potential medication for METH addiction.

Preclinical pharmacokinetics of TPN729MA, a novel PDE5 inhibitor, and prediction of its human pharmacokinetics using a PBPK model

AIM

TPN729MA is a novel selective PDE5 inhibitor currently under clinical development in China for the treatment of erectile dysfunction. In this study we characterized its preclinical pharmacokinetics (PK) and predict its human PK using a physiologically based pharmacokinetic (PBPK) model.

METHODS

The preclinical PK of TPN729MA was studied in rats and dogs. Human clearance (CL) values for TPN729MA were predicted from various allometric methods and from intrinsic CL determined in human liver microsomes. Human PK and plasma concentration versus time profiles of TPN729MA were predicted by using a PBPK model in GastroPlus. Considering the uncertainties in the prediction, a preliminary human study was conducted in 3 healthy male volunteers with an oral dose of 25 mg.

RESULTS

After a single intravenous administration of TPN729MA at a dose of 1 mg/kg in rats and 3 mg/kg in dogs, the plasma CL was 69.7 mL·min(-1)·kg(-1) in rats and 26.3 mL·min(-1)·kg(-1) in dogs, and the steady-state volumes of distribution (V(ss)) were 7.35 L/kg in rats and 6.48 L/kg in dogs. The oral bioavailability of TPN729MA was 10% in rats and above 34% in dogs. Profiles of predicted plasma concentration versus time were similar to those observed in humans at 25 mg, and the predicted T(max), C(max) and AUC values were within 2-fold of the observed values.

CONCLUSION

TPN729MA demonstrates good preclinical PK. This compound is a valuable candidate for further clinical development. This study shows the benefits of using a PBPK model to predict PK in humans.

Characterization of preclinical in vitro and in vivo pharmacokinetics properties for KBP-7018, a new tyrosine kinase inhibitor candidate for treatment of idiopathic pulmonary fibrosis

KBP-7018 is a novel selective tyrosine kinase inhibitor with potential for the treatment of idiopathic pulmonary fibrosis. The objective of this study was to characterize the preclinical pharmacokinetics of KBP-7018 in vitro and in vivo, and then to assess the likelihood of developing KBP-7018 as a clinical candidate. The systemic clearance (CL) of KBP-7018 was relatively low in rodents and monkeys with a value of less than 30% of hepatic blood flow, while it was high in dogs. The steady-state volume of distribution (V_ss) ranged from 1.51 L/kg to 4.65 L/kg across the species tested. The maximum concentration (C_max) of KBP-7018 occurred at 0.25–6 hours after oral dosing, and the bioavailability was moderate (21%–68%). The human CL (~20% of hepatic blood flow) and V_ss (1.6–5.3 L/kg) were predicted by allometric scaling method and together with the other modeling methods indicated low metabolism and acceptable half-time (4.8–19.3 hours) in vivo. Overall, the preclinical data make it amenable to further oral solid dosage from design for the upcoming Phase I trials in human.