Exploring the Impact of Pharmacological Target-Mediated Low Plasma Exposure in Lead Compound Selection in Drug Discovery - A Modeling Approach

Small-molecule drug development faces the challenge of low success rate. In this paper, we propose one potential cause that may occur in the preclinical phase and has rarely been brought up before - the neglected target-mediated low plasma exposure, and the subsequent lead compound mis-selection due to conventional pharmacokinetic criteria requiring sufficient plasma exposure and desired half-life. To evaluate the concept of target-mediate low plasma exposure, we established a minimal physiologically-based pharmacokinetic (mPBPK) model to evaluate the concentration-time profiles of a group of virtual lead series analogs in plasma and in tissues with and without pharmacological target expression. Simulation results demonstrated that the candidate with the highest target binding has the lowest plasma exposure due to target-mediated tissue retention. The traditional PK criteria, such as the requirement of sufficient plasma exposure and desired half-life, may potentially result in lead compound mis-selection by discarding the appropriate and best candidate(s). The mPBPK model was partially validated using 4 tyrosine kinase inhibitors based on our in-house PK and tissue distribution data obtained in animals. The association rate constant (Kass) was estimated to be 49.8 h-1, 31.4 h-1, 8.58 h-1, and 1.91 h-1 for afatinib, dasatinib, gefitinib, and sorafenib, respectively. Among these four model drugs, a strong correlation was observed between their Kass values and AUChigh-perfused tissue /AUCplasma ratios, a metric of tissue retention. Our mPBPK modeling and simulation results indicated that the concept of target-mediated low plasma exposure should be kept in mind during the lead compound selection process.

Characterizing the Nonlinear Pharmacokinetics and Pharmacodynamics of BI 187004, an 11β-Hydroxysteroid Dehydrogenase Type 1 Inhibitor, in Humans by a Target-Mediated Drug Disposition Model

BI 187004, a selective small-molecule inhibitor of 11β-hydroxysteroid dehydrogenase-1 (11β-HSD1), displayed complex nonlinear pharmacokinetics (PK) in humans. Following nine single oral doses, BI 187004 exhibited nonlinear PK at low doses and linear PK at higher doses. Notably, substantial hepatic 11β-HSD1 inhibition (50%) was detected in a very low-dose group, achieving a consistent 70% hepatic enzyme inhibition in subsequent ascending doses without any dose-dependent effects. The unusual PK and PD profiles of BI 187004 suggest the presence of pharmacological target-mediated drug disposition (TMDD), arising from the saturable binding of BI 187004 compound to its high-affinity and low-capacity target 11β-HSD1. The non-intuitive dose, exposure, and response relationship for BI 187004 pose a significant challenge in rational dose selection. This study aimed to construct a TMDD model to explain the complex nonlinear PK behavior and underscore the importance of recognizing TMDD in this small-molecule compound. Among the various models explored, the best model was a two-compartment TMDD model with three transit absorption components. The final model provides insights into 11β-HSD1 binding-related parameters for BI 187004, including the total amount of 11β-HSD1 in the liver (estimated to be 8000 nmol), the second order association rate constant (estimated to be 0.102 nM-1h-1), and the first-order dissociation rate constant (estimated to be 0.11 h-1). Our final population PK model successfully characterized the intricate nonlinear PK of BI 187004 across a wide dose range. This modeling work serves as a valuable reference for the rational selection of the dose regimens for BI 187004's future clinical trials.

Population Target-Mediated Pharmacokinetic/Pharmacodynamic Modeling to Evaluate SPI-62 Exposure and Hepatic 11β-Hydroxysteroid Dehydrogenase Type 1 (HSD-1) Inhibition in Healthy Adults

INTRODUCTION

SPI-62 is a small-molecule 11β-hydroxysteroid dehydrogenase type 1 (HSD-1) inhibitor exhibiting complicated nonlinear pharmacokinetics (PK) in human. Previously, we developed a target-mediated drug disposition (TMDD) model to characterize the substantial nonlinear PK of SPI-62.

OBJECTIVE

The aim of the current analysis was to perform population PK/PD analysis to further link SPI-62 exposure (i.e., PK) with its response (i.e., inhibition of hepatic HSD-1 activity) to gain a quantitative understanding of the SPI-62 dose-exposure-response relationship.

METHODS

PK and PD data from the first-in-human (FIH) clinical trials, including single ascending dose (SAD) and multiple ascending dose (MAD) studies, were used for model development. During the model development process, the final model selection was based on biological and physiological plausibility, goodness-of-fit plots, stability of parameter estimates, and objective function value. The nonlinear-mixed effect modeling (NONMEM) software was used for both the implementation of the PK/PD model and model simulation. SPI-62 plasma levels and hepatic HSD-1 inhibition over time following various dose regimens were simulated.

RESULTS

The final model was a two-compartment TMDD model component for SPI-62 and an inhibitory Imax model component for hepatic HSD-1 activity. The TMDD-hepatic PD model that we established adequately characterized all remarkable PK and PD behaviors of SPI-62, such as extremely low plasma exposures following the first low doses, nonlinear PK turned into linear PK after repeated low doses, and substantial and long-lasting hepatic HSD-1 inhibition following low doses. SPI-62 was estimated to bind to the target with a second-order association rate constant (Kon) of 8.43 nM-1 h-1 and first-order dissociation rate constant (Koff) value of 0.229 h-1, indicating that SPI-62 binds rapidly to, and dissociates slowly from, its pharmacological target. The estimated target capacity (Rtot) of 5460 nmol corresponds to approximately 2.2 mg of SPI-62, which comports well with the dose range in which PK nonlinearity is prominent. Model simulation results reveal that a 6 mg once-daily regimen can lead to long-lasting and substantial hepatic HSD-1 inhibition.

CONCLUSIONS

A population TMDD-PD model that explains SPI-62 nonlinear PK and hepatic HSD-1 inhibition following different dose regimens in healthy adults was successfully established. Our simulation results provide a solid foundation for model-informed development of SPI-62.

Epigenetic Mechanisms Contribute to Intraindividual Variations of Drug Metabolism Mediated by Cytochrome P450 Enzymes

Significant interindividual and intraindividual variations on cytochrome P450 (CYP)-mediated drug metabolism exist in the general population globally. Genetic polymorphisms are one of the major contribution factors for interindividual variations, but epigenetic mechanisms mainly contribute to intraindividual variations, including DNA methylation, histone modifications, microRNAs, and long non-coding RNAs. The current review provides analysis of advanced knowledge in the last decade on contributions of epigenetic mechanisms to intraindividual variations on CYP-mediated drug metabolism in several situations, including (1) ontogeny, the developmental changes of CYP expression in individuals from neonates to adults; (2) increased activities of CYP enzymes induced by drug treatment; (3) increased activities of CYP enzymes in adult ages induced by drug treatment at neonate ages; and (4) decreased activities of CYP enzymes in individuals with drug-induced liver injury (DILI). Furthermore, current challenges, knowledge gaps, and future perspective of the epigenetic mechanisms in development of CYP pharmacoepigenetics are discussed. In conclusion, epigenetic mechanisms have been proven to contribute to intraindividual variations of drug metabolism mediated by CYP enzymes in age development, drug induction, and DILI conditions. The knowledge has helped understanding how intraindividual variation are generated. Future studies are needed to develop CYP-based pharmacoepigenetics to guide clinical applications for precision medicine with improved therapeutic efficacy and reduced risk of adverse drug reactions and toxicity. SIGNIFICANCE STATEMENT: Understanding epigenetic mechanisms in contribution to intraindividual variations of CYP-mediated drug metabolism may help to develop CYP-based pharmacoepigenetics for precision medicine to improve therapeutic efficacy and reduce adverse drug reactions and toxicity for drugs metabolized by CYP enzymes.

Pharmacokinetics and bioequivalence study of esomeprazole magnesium enteric-coated tablets 20 mg in healthy Chinese subjects under fasting and fed conditions

Objective: The main purpose of this study was to evaluate the pharmacokinetics, bioequivalence, and safety properties between a new generic and a brand reference formulation of esomeprazole enteric-coated tablets 20 mg in healthy Chinese subjects under fasting and fed conditions. Methods: The fasting study was an open-label, randomized, two-period crossover study conducted in 32 healthy Chinese volunteers, and the fed study was a four-period crossover study conducted in 40 healthy Chinese volunteers. Blood samples were collected at the specified time points and determined to obtain the plasma concentrations of esomeprazole. The primary pharmacokinetic parameters were calculated using the non-compartment method. Bioequivalence was analyzed by the geometric mean ratios (GMRs) of the two formulations and the corresponding 90% confidence intervals (CIs). The safety of the two formulations was assessed. Results: The fasting and fed study showed that the pharmacokinetics of the two formulations was similar. Under the fasting condition, the 90% CIs of GMRs of the test-to-reference formulation were 87.92%-104.36% for C_max, 87.82%-101.45% for AUC_0-t, and 87.99%-101.54% for AUC_0-∞; under the fed condition, the 90% CIs of GMRs of the test-to-reference formulation were 80.53%-94.95% for C_max, 87.46%-97.26% for AUC_0-t, and 87.46%-97.16% for AUC_0-∞. The 90% CIs of GMRs fall within the bioequivalence range of 80.00%-125.00%. The two formulations had good safety and were well-tolerated, and no serious adverse events occurred. Conclusion: According to relevant regulatory standards, esomeprazole enteric-coated generic and reference products exhibited bioequivalence and good safety in healthy Chinese subjects. Clinical Trials Registration: http://www.chinadrugtrials.org.cn/index.html, identifier CTR20171347 and CTR20171484.

Importance of Target-Mediated Drug Disposition (TMDD) of Small-Molecule Compounds and Its Impact on Drug Development-Example of the Class Effect of HSD-1 Inhibitors

With more potent drug candidates being developed, the incidence of target-mediated drug disposition (TMDD) in small-molecule compounds has significantly increased in the past decade. Moreover, TMDD appears to apply to some small-molecule compound classes. The main purpose of the current review is to increase the awareness of TMDD in a series of small-molecule inhibitors of 11β-hydroxysteroid dehydrogenase type 1 (HSD-1) using ABT-384, SPI-62, MK-0916, BMS-823778, and BI-187004 as case examples. Although developed independently by different pharmaceutical companies, these HSD-1 inhibitors demonstrated strikingly similar nonlinear pharmacokinetic behaviors when wide dose ranges were evaluated in first-in-human (FIH) single ascending dose (SAD) and multiple ascending dose (MAD) studies. Recognizing TMDD in small-molecule compounds is important, as the information can be leveraged to select the appropriate dose regimen, improve clinical trial design, as well as predict pharmacological target occupancy. In this review, we summarize the general pharmacokinetic features that facilitate the recognition of small-molecule TMDD, provide case examples of specific HSD-1 inhibitors, highlight the importance of recognizing TMDD of small-molecule compounds during clinical development, and comment on the importance of utilizing pharmacometric modeling to facilitate the quantitative understanding of small-molecule compounds exhibiting TMDD.

Physiologically based pharmacokinetic modeling of brivaracetam and its interactions with rifampin based on CYP2C19 phenotypes

Brivaracetam (BRV), a third-generation antiepileptic drug (AED), is primarily metabolized through amidase hydrolysis and CYP2C19-mediated hydroxylation in vivo. This study utilized physiologically based pharmacokinetic (PBPK) modeling to explore the pharmacokinetics of BRV and drug interactions between BRV and rifampin (RIF), a CYP2C19 inducer, based on CYP2C19 genetic polymorphisms. A PBPK model of BRV was developed in the general population and in individuals with different CYP2C19 phenotypes by adjusting catalytic rate constants (k_cat), and the model was validated with observed clinical data. The model was then extrapolated to predict BRV steady-state plasma concentration in individuals with different CYP2C19 phenotypes, with or without coadministration of RIF. The developed model adequately described BRV exposure in the abovementioned populations. The predicted steady-state area under the curve (AUC_τ-ss) increases by 20% in heterozygous extensive metabolizers (hEMs) and 55% in poor metabolizers (PMs), compared to homozygous extensive metabolizer (EMs). When coadministered with RIF, the model predicted the most significant magnitude of drug-drug interaction (DDI) in EMs, while the exposure change of BRV was minimal in PMs. Referencing the recommended concentration for therapeutic drug monitoring (TDM), we concluded that the current clinical maintenance dose of BRV is acceptable regardless of CYP2C19 polymorphisms and coadministration with RIF.

Intestinal Excretion, Intestinal Recirculation, and Renal Tubule Reabsorption Are Underappreciated Mechanisms That Drive the Distribution and Pharmacokinetic Behavior of Small Molecule Drugs

Drug reabsorption following biliary excretion is well-known as enterohepatic recirculation (EHR). Renal tubular reabsorption (RTR) following renal excretion is also common but not easily assessed. Intestinal excretion (IE) and enteroenteric recirculation (EER) have not been recognized as common disposition mechanisms for metabolically stable and permeable drugs. IE and intestinal reabsorption (IR:EHR/EER), as well as RTR, are governed by dug concentration gradients, passive diffusion, active transport, and metabolism, and together they markedly impact disposition and pharmacokinetics (PK) of small molecule drugs. Disruption of IE, IR, or RTR through applications of active charcoal (AC), transporter knockout (KO), and transporter inhibitors can lead to changes in PK parameters. The impacts of intestinal and renal reabsorption on PK are under-appreciated. Although IE and EER/RTR can be an intrinsic drug property, there is no apparent strategy to optimize compounds based on this property. This review seeks to improve understanding and applications of IE, IR, and RTR mechanisms.

Pharmacokinetics and Pharmacodynamics of Esomeprazole/Sodium Bicarbonate Immediate-Release Capsules in Healthy Chinese Volunteers: A Cross-Over, Randomized Controlled Trial

INTRODUCTION

Esomeprazole delayed release tablets (ESO) are one of the most effective treatments for acid-related disorders. The purpose of this study is to compare the safety, pharmacokinetics (PK) and pharmacodynamics (PD) of an immediate-release capsule formulation containing esomeprazole 20 mg and sodium bicarbonate 1100 mg (IR-ESO) compared to those of the esomeprazole delayed release tablet 20 mg (ESO). In addition, the impact of CYP2C19 gene polymorphisms on PK and PD was evaluated.

METHODS

A single-center, open-label, randomized, 2-treatment, 2-sequence, and 2-period crossover study was conducted in 40 healthy Chinese subjects. Subjects received either IR-ESO or ESO for 5 days. After single- and multiple-dosing administration, blood samples were collected for PK analysis, and intragastric pH was assessed by 24-h pH monitoring. The CYP2C19 gene polymorphisms were analyzed by Sanger sequencing.

RESULTS

The geometric mean ratios (90% confidence interval) [GMR (95%CI)] of IR-ESO/ESO for AUC_inf [single dose: 103.60% (96.58%, 111.14%), multiple doses: 101.65% (97.88%, 105.57%)] were within the range of 80.00-125.00%. The AUC_inf showed an increasing trend between CYP2C19 extensive metabolizer (EM), intermediate metabolizer (IM), and poor metabolizer (PM) after single-dose and multiple-dose administration (p < 0.05). The GMR (95%CI) of IR-ESO/ESO for 24-h integrated gastric acidity from baseline [single dose: 101.07% (96.56%, 105.78%), multiple doses: 101.24% (97.74%, 104.86%)] were within the range of 80.00-125.00%. The percentage changes in 24-h integrated gastric acidity from baseline was significant difference between EM, IM, and PM after single-dose IR-ESO and ESO (p < 0.05). Drugs were all well tolerated, and there were no significant differences in adverse events between IR-ESO and ESO.

CONCLUSION

This study showed that IR-ESO can inhibit the secretion of gastric acid rapidly and continuously, and that the PK and PD of IR-ESO are affected by CYP2C19 genotypes. The GMR (95% CI) of IR-ESO/ESO for AUC_inf and the percentage changes in 24-h integrated gastric acidity from baseline were all within the range of 80.00-125.00%.

TRIAL REGISTRATION

Chinese Clinical Trial Registry: ChiCTR1900024935.

Progress in 11β-HSD1 inhibitors for the treatment of metabolic diseases: A comprehensive guide to their chemical structure diversity in drug development

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) is a key metabolic enzyme that catalyzing the intracellular conversion of inactive glucocorticoids to physiologically active ones. Work over the past decade has demonstrated the aberrant overexpression of 11β-HSD1 contributed to the pathophysiological process of metabolic diseases like obesity, type 2 diabetes mellitus, and metabolic syndromes. The inhibition of 11β-HSD1 represented an attractive therapeutic strategy for the treatment of metabolic diseases. Therefore, great efforts have been devoted to developing 11β-HSD1 inhibitors based on the diverse molecular scaffolds. This review focused on the structural features of the most important 11β-HSD1 inhibitors and categorized them into natural products derivatives and synthetic compounds. We also briefly discussed the optimization process, binding modes, structure-activity relationships (SAR) and biological evaluations of each inhibitor. Moreover, the challenges and directions for 11β-HSD1 inhibitors were discussed, which might provide some useful clues to guide the future discovery of novel 11β-HSD1 inhibitors.

Discovery of Clinical Candidate BMS-823778 as an Inhibitor of Human 11β-Hydroxysteroid Dehydrogenase Type 1 (11β-HSD-1)

BMS-823778 (2), a 1,2,4-triazolopyridinyl-methanol derived analog, was identified as a potent and selective inhibitor of human 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1) enzyme (IC₅₀ = 2.3 nM) with >10,000-fold selectivity over 11β-HSD-2. Compound 2 exhibits robust acute pharmacodynamic effects in cynomolgus monkeys (ED₅₀ = 0.6 mg/kg) and in diet-induced obese (DIO) mice (ED₅₀ = 34 mg/kg). Compound 2 also showed excellent inhibition in an ex vivo adipose DIO mouse model (ED₅₀ = 5.2 mg/kg). Oral bioavailability ranges from 44% to 100% in preclinical species. Its favorable development properties, pharmacokinetics, high adipose-to-plasma concentration ratio, and preclinical pharmacology profile have prompted the evaluation of 2 for the treatment of type 2 diabetes and metabolic syndrome in phase 2 clinical trials.

Physiologically-based pharmacokinetic modelling of a CYP2C19 substrate, BMS-823778, utilizing pharmacogenetic data

AIMS

Previous studies demonstrated direct correlation between CYP2C19 genotype and BMS-823778 clearance in healthy volunteers. The objective of the present study was to develop a physiologically-based pharmacokinetic (PBPK) model for BMS-823778 and use the model to predict PK and drug-drug interaction (DDI) in virtual populations with multiple polymorphic genes.

METHODS

The PBPK model was built and verified using existing clinical data. The verified model was simulated to predict PK of BMS-823778 and significance of DDI with a strong CYP3A4 inhibitor in subjects with various CYP2C19 and UGT1A4 genotypes.

RESULTS

The verified PBPK model of BMS-823778 accurately recovered observed PK in different populations. In addition, the model was able to capture the exposure differences between subjects with different CYP2C19 genotypes. PK simulation indicated higher exposures of BMS-823778 in CYP2C19 poor metabolizers who were also devoid of UGT1A4 activity, compared to those with normal UGT1A4 functionality. Moderate DDI with itraconazole was predicted in subjects with wild-type CYP2C19 or UGT1A4. However, in subjects without CYP2C19 or UGT1A4 functionality, significant DDI was predicted when BMS-823778 was coadministered with itraconazole.

CONCLUSIONS

A PBPK model was developed using clinical data that accurately predicted human PK in different population with various CYP2C19 phenotypes. Simulations with the verified PBPK model indicated that UGT1A4 was probably an important clearance pathway in CYP2C19 poor metabolizers. DDI with itraconazole is likely to be dependent on the genotypes of CYP2C19 and UGT1A4.