Impact of model misspecification on model-based tests in PK studies with parallel design: real case and simulation studies.

This article evaluates the performance of pharmacokinetic (PK) equivalence testing between two formulations of a drug through the Two-One Sided Tests (TOST) by a model-based approach (MB-TOST), as an alternative to the classical non-compartmental approach (NCA-TOST), for a sparse design with a few time points per subject. We focused on the impact of model misspecification and the relevance of model selection for the reference data. We first analysed PK data from phase I studies of gantenerumab, a monoclonal antibody for the treatment of Alzheimer's disease. Using the original rich sample data, we compared MB-TOST to NCA-TOST for validation. Then, the analysis was repeated on a sparse subset of the original data with MB-TOST. This analysis inspired a simulation study with rich and sparse designs. With rich designs, we compared NCA-TOST and MB-TOST in terms of type I error and study power. With both designs, we explored the impact of misspecifying the model on the performance of MB-TOST and adding a model selection step. Using the observed data, the results of both approaches were in general concordance. MB-TOST results were robust with sparse designs when the underlying PK structural model was correctly specified. Using the simulated data with a rich design, the type I error of NCA-TOST was close to the nominal level. When using the simulated model, the type I error of MB-TOST was controlled on rich and sparse designs, but using a misspecified model led to inflated type I errors. Adding a model selection step on the reference data reduced the inflation. MB-TOST appears as a robust alternative to NCA-TOST, provided that the PK model is correctly specified and the test drug has the same PK structural model as the reference drug.

Application of Modeling and Simulation to Identify a Shortened Study Duration and Novel Bioequivalence Metric for a Long-Acting Intrauterine System.

An intrauterine system (IUS) can be implanted in the uterus and deliver drug directly at the site of pharmacological action. Mirena was the first FDA-approved levonorgestrel (LNG) releasing IUS without an approved generic form. Its 5-year application duration presents challenges for bioequivalence (BE) assessment using the conventional in vivo studies with pharmacokinetic and/or comparative clinical endpoints. Conventionally, along with other conditions, BE could be established if the 90% confidence interval (CI) of the ratio of geometric means of residual LNG at the end of 5 years is within the BE limits of 80.00% and 125.00%. Modeling and simulation were conducted to identify a shortened BE study duration and its corresponding BE acceptance limit that can be used as a surrogate for the conventional limit for a 5-year study. Simulation results suggest that having the 90% CI of the residual LNG 12 months post insertion within 95.00-105.26% would ensure that residual LNG amount at 5 years to be within 80.00-125.00%. This modeling and simulation practice leads to the current BE recommendation: if a test IUS is made of the same material in the same concentration and has the same physical dimensions as the Mirena, its BE could be established by showing (1) comparative physicochemical and mechanical properties; (2) comparative in vitro drug release behavior for 5 years; and (3) performance in a comparative short-term in vivo study and BE based on 90% confidence interval of test and reference ratio of residual LNG to be within 95.00-105.26% at month 12.

Efficient model-based bioequivalence testing.

The classical approach to analyze pharmacokinetic (PK) data in bioequivalence studies aiming to compare two different formulations is to perform noncompartmental analysis (NCA) followed by two one-sided tests (TOST). In this regard, the PK parameters area under the curve (AUC) and $C_{\max}$ are obtained for both treatment groups and their geometric mean ratios are considered. According to current guidelines by the U.S. Food and Drug Administration and the European Medicines Agency, the formulations are declared to be sufficiently similar if the $90\%$ confidence interval for these ratios falls between $0.8$ and $1.25 $. As NCA is not a reliable approach in case of sparse designs, a model-based alternative has already been proposed for the estimation of $\rm AUC$ and $C_{\max}$ using nonlinear mixed effects models. Here we propose another, more powerful test than the TOST and demonstrate its superiority through a simulation study both for NCA and model-based approaches. For products with high variability on PK parameters, this method appears to have closer type I errors to the conventionally accepted significance level of $0.05$, suggesting its potential use in situations where conventional bioequivalence analysis is not applicable.

Use of Partial Area Under the Curve in Bioavailability or Bioequivalence Assessments: A Regulatory Perspective.

Peak drug concentration (Cmax ) and total exposure, such as area under the concentration-time curve (AUC) from time zero to infinity may be insufficient for assessing relative bioavailability (BA) or bioequivalence (BE) among two products in cases where rapid onset of action or controlled duration of effect is needed to ensure similar drug efficacy. Regulatory agencies have recommended the use of partial AUC (pAUC) as an additional exposure measure for relative BA or BE assessments. The pAUC metric describes pharmacokinetic profiles with the focus on quantification of exposures over specific time intervals to support the determination of relative BA or BE for these drug products in relation to respective reference products. The principles and rationales for using pAUCs are included in the US Food and Drug Administration (FDA)'s general BA or BE guidances. Specific pAUC recommendations are also reflected in product-specific guidances for generic drug development published by the FDA. Rationales for the use of pAUCs in relative BA or BE assessments are based on drug-specific and product-specific considerations. This white paper introduces the general framework, including rationales for pAUC recommendations, and provides an overview of the current status, challenges, and the FDA considerations on the use of pAUC for relative BA or BE assessments in the United States.

Applications of Physiologically Based Biopharmaceutics Modeling (PBBM) to Support Drug Product Quality: A Workshop Summary Report.

This report summarizes the proceedings for Day 3 of the workshop titled "Current State and Future Expectations of Translational Modeling Strategies toSupportDrug Product Development, Manufacturing Changes and Controls". From a drug product quality perspective, patient-centric product development necessitates the development of clinically relevant drug product specifications (CRDPS). In this regard, Physiologically Based Biopharmaceutics modeling (PBBM) is a viable tool to establish links between in-vitro to in-vivo data, and support with establishing CRDPS. The theme of day 3 was practical applications of PBBM to support drug product quality. In this manuscript, case studies from US FDA, EMA and pharmaceutical industry on applications of PBBM in drug product quality are summarized which include 1) regulatory agency's perspectives on establishing the safe space and achieving study waivers, 2) model-informed risk assessment on the effects of acid reducing agents, bridging of dissolution methods, food effect, and formulation selection, and 3) understanding clinical formulation performance. Breakout session discussions focused on four topics - 1) terminologies related to physiologically based modeling in support of drug product quality, 2) regulatory harmonization on evidentiary standards, 3) CRDPS approaches and 4) bridging between biorelevant and quality control (QC) dissolution methods.

New Model-Based Bioequivalence Statistical Approaches for Pharmacokinetic Studies with Sparse Sampling.

In traditional pharmacokinetic (PK) bioequivalence analysis, two one-sided tests (TOST) are conducted on the area under the concentration-time curve and the maximal concentration derived using a non-compartmental approach. When rich sampling is unfeasible, a model-based (MB) approach, using nonlinear mixed effect models (NLMEM) is possible. However, MB-TOST using asymptotic standard errors (SE) presents increased type I error when asymptotic conditions do not hold. In this work, we propose three alternative calculations of the SE based on (i) an adaptation to NLMEM of the correction proposed by Gallant, (ii) the a posteriori distribution of the treatment coefficient using the Hamiltonian Monte Carlo algorithm, and (iii) parametric random effects and residual errors bootstrap. We evaluate these approaches by simulations, for two-arms parallel and two-period, two-sequence cross-over design with rich (n = 10) and sparse (n = 3) sampling under the null and the alternative hypotheses, with MB-TOST. All new approaches correct for the inflation of MB-TOST type I error in PK studies with sparse designs. The approach based on the a posteriori distribution appears to be the best compromise between controlled type I errors and computing times. MB-TOST using non-asymptotic SE controls type I error rate better than when using asymptotic SE estimates for bioequivalence on PK studies with sparse sampling.

Model-Based Analysis of Cannabidiol Dose-Exposure Relationship and Bioavailability.

INTRODUCTION: There is a large variation in cannabidiol (CBD) pharmacokinetics and little information on its bioavailability. This study aims to establish the CBD dose-exposure relationship and to evaluate the effects of dosage forms, food, and doses on CBD absorption. METHODS: Single-dose (range: 5-6000 mg) CBD plasma concentration-time profiles administered as oral solution (OS), oral capsule (OC), or oromucosal spray/drop (OM) from healthy volunteers were extracted from 15 published clinical studies. A dose-exposure proportionality assessment was performed, and a population-based meta-analysis of CBD pharmacokinetics and systemic bioavailability was conducted with a nonlinear mixed-effects modeling. A three-compartment model with a Weibull or zero-order absorption model was used to describe CBD disposition and absorption kinetics. Dosage form, food, and dose were assessed for covariation. RESULTS: Oral solution CBD exposures increased less than proportionally with doses of 750 mg or greater, and bioavailability (6.5% at 3000 mg) decreased with increasing dose. The bioavailability of OC (5.6%) and fed-state OM (6.2%) were similar, whereas it was lower in fasted-state OM (0.9%). The Weibull absorption model best described OS, OC, and fed-state OM profiles. The slowest absorption rate was observed in OS, resulting in a time of maximum concentration of 4.75 hours, followed by fed-state OM (3.13 hrs) and OC (2.1 hrs). The absorption kinetics of fasted-state OM was best described by a zero-order absorption for the duration of 1.71 hours. CONCLUSION: The effects of doses, dosage forms, and feeding status on CBD pharmacokinetics were quantified and should be taken into consideration for dose optimization.

An in vitro approach for evaluating the oral abuse deterrence of solid oral extended-release opioids with properties intended to deter abuse via chewing.

The introduction of prescription opioids with abuse-deterrent (AD) properties to the marketplace has created a need for new testing methodologies to evaluate the performance of potentially abuse-deterrent opioid products. Drug abusers may attempt to chew solid oral extended-release (ER) opioids prior to ingestion to bypass the ER mechanism of the formulation to achieve euphoria. In the present study, a chewing apparatus was utilized to develop an in vitro chewing method for Hysingla ER tablets, a prescription opioid with labeling describing abuse deterrence via the oral route when chewed. Simulated chewing of Hysingla resulted in initially faster drug release during chewing while subsequent dissolution testing demonstrated that the masticated tablets still maintained ER properties. The degree of mastication and corresponding drug release were influenced by the compression gap and the resulting chewing forces. Simulated chewing followed by dissolution testing with different strengths of Hysingla indicated similar AD performance across strengths. By contrast, an opioid product with labeling that does not describe abuse-deterrent properties showed lower resistance to chewing resulting in higher drug release. The results of the present study suggest that the chewing methodology evaluated in this work may provide a useful in vitro tool for the comparative evaluation of AD properties.

Physiologically Based Pharmacokinetic and Absorption Modeling for Osmotic Pump Products.

Physiologically based pharmacokinetic (PBPK) and absorption modeling approaches were employed for oral extended-release (ER) drug products based on an osmotic drug delivery system (osmotic pumps). The purpose was to systemically evaluate the in vivo relevance of in vitro dissolution for this type of formulation. As expected, in vitro dissolution appeared to be generally predictive of in vivo PK profiles, because of the unique feature of this delivery system that the in vitro and in vivo release of osmotic pump drug products is less susceptible to surrounding environment in the gastrointestinal (GI) tract such as pH, hydrodynamic, and food effects. The present study considered BCS (Biopharmaceutics Classification System) class 1, 2, and 3 drug products with half-lives ranging from 2 to greater than 24 h. In some cases, the colonic absorption models needed to be adjusted to account for absorption in the colon. C max (maximum plasma concentration) and AUCt (area under the concentration curve) of the studied drug products were sensitive to changes in colon permeability and segmental GI transit times in a drug product-dependent manner. While improvement of the methodology is still warranted for more precise prediction (e.g., colonic absorption and dynamic movement in the GI tract), the results from the present study further emphasized the advantage of using PBPK modeling in addressing product-specific questions arising from regulatory review and drug development.

"Target-Site" Drug Metabolism and Transport.

The recent symposium on "Target-Site" Drug Metabolism and Transport that was sponsored by the American Society for Pharmacology and Experimental Therapeutics at the 2014 Experimental Biology meeting in San Diego is summarized in this report. Emerging evidence has demonstrated that drug-metabolizing enzyme and transporter activity at the site of therapeutic action can affect the efficacy, safety, and metabolic properties of a given drug, with potential outcomes including altered dosing regimens, stricter exclusion criteria, or even the failure of a new chemical entity in clinical trials. Drug metabolism within the brain, for example, can contribute to metabolic activation of therapeutic drugs such as codeine as well as the elimination of potential neurotoxins in the brain. Similarly, the activity of oxidative and conjugative drug-metabolizing enzymes in the lung can have an effect on the efficacy of compounds such as resveratrol. In addition to metabolism, the active transport of compounds into or away from the site of action can also influence the outcome of a given therapeutic regimen or disease progression. For example, organic anion transporter 3 is involved in the initiation of pancreatic ß-cell dysfunction and may have a role in how uremic toxins enter pancreatic ß-cells and ultimately contribute to the pathogenesis of gestational diabetes. Finally, it is likely that a combination of target-specific metabolism and cellular internalization may have a significant role in determining the pharmacokinetics and efficacy of antibody-drug conjugates, a finding which has resulted in the development of a host of new analytical methods that are now used for characterizing the metabolism and disposition of antibody-drug conjugates. Taken together, the research summarized herein can provide for an increased understanding of potential barriers to drug efficacy and allow for a more rational approach for developing safe and effective therapeutics.

Systems pharmacology approaches for optimization of antiangiogenic therapies: challenges and opportunities.

Targeted therapies have become an important therapeutic paradigm for multiple malignancies. The rapid development of resistance to these therapies impedes the successful management of advanced cancer. Due to the redundancy in angiogenic signaling, alternative proangiogenic factors are activated upon treatment with anti-VEGF agents. Higher doses of the agents lead to greater stimulation of compensatory proangiogenic pathways that limit the therapeutic efficacy of VEGF-targeted drugs and produce escape mechanisms for tumor. Evidence suggests that dose intensity and schedules affect the dynamics of the development of this resistance. Thus, an optimal dosing regimen is crucial to maximizing the therapeutic benefit of antiangiogenic agents and limiting treatment resistance. A systems pharmacology approach using multiscale computational modeling can facilitate a mechanistic understanding of these dynamics of angiogenic biomarkers and their impacts on tumor reduction and resistance. Herein, we discuss a systems pharmacology approach integrating the biology of VEGF-targeted therapy resistance, including circulating biomarkers, and pharmacodynamics to enable the optimization of antiangiogenic therapy for therapeutic gains.

Pulmonary metabolism of resveratrol: in vitro and in vivo evidence.

The role of pulmonary metabolism in trans-resveratrol (RES) pharmacokinetics was studied in a mouse model. Plasma concentrations of RES and its major metabolites trans-resveratrol-3-sulfate (R3S) and trans-resveratrol-3-glucuronide (R3G) were compared after administration of RES by intravenous (IV) and intra-arterial (IA) routes. Total area under the curve (AUC) of RES decreased by approximately 50% when RES was administered by the IV route compared with the IA route. The AUC of R3G was also significantly higher in mice administered RES by the IV route compared with the IA route. In vitro studies performed with mouse and human lung fractions confirmed pulmonary metabolism of RES. Interestingly, mouse-lung fractions gave rise to both R3S and R3G, whereas human lung fractions yielded R3S. This indicates marked interspecies variation in RES conjugation, especially in the context of extrapolating rodent data to humans. Taken together, the results presented here underline, for the first time, the impact of pulmonary metabolism on resveratrol pharmacokinetics and interspecies differences in RES pulmonary metabolism.

In vivo-formed versus preformed metabolite kinetics of trans-resveratrol-3-sulfate and trans-resveratrol-3-glucuronide.

Metabolites in safety testing have gained a lot of attention recently. Regulatory agencies have suggested that the kinetics of preformed and in vivo-formed metabolites are comparable. This subject has been a topic of debate. We have compared the kinetics of in vivo-formed with preformed metabolites. trans-3,5,4'-Trihydroxystilbene [trans-resveratrol (RES)] and its two major metabolites, resveratrol-3-sulfate (R3S) and resveratrol-3-glucuronide (R3G) were used as model substrates. The pharmacokinetics (PK) of R3S and R3G were characterized under two situations. First, the pharmacokinetics of R3S and R3G were characterized (in vivo-formed metabolite) after administration of RES. Then, synthetic R3S and R3G were administered (preformed metabolite) and their pharmacokinetics were characterized. PK models were developed to describe the data. A three-compartment model for RES, a two-compartment model for R3S (preformed), and an enterohepatic cycling model for R3G (preformed) was found to describe the data well. These three models were further combined to build a comprehensive PK model, which was used to perform simulations to predict in vivo-formed metabolite kinetics. Comparisons were made between in vivo-formed and preformed metabolite kinetics. Marked differences were observed in the kinetics of preformed and in vivo-formed metabolites.

Analytical method development for synthesized conjugated metabolites of trans-resveratrol, and application to pharmacokinetic studies.

Trans-3,5,4'-trihydroxystilbene (trans-resveratrol, RES) exhibits very low bioavailability due to extensive conjugative metabolism. Whether RES metabolites exhibit pharmacologic activity is of great interest. The present study aimed at synthesis of monoconjugates of RES - the 3- and 4' monosulfates (R3S and R4'S), and the 3- and 4' monoglucuronides (R3G and R4'G). Synthesis, purification, and yield are described. Synthesized metabolites were utilized to develop a sensitive LC-MS(n) assay for direct quantitation of all analytes. The assay was validated for intra- and inter-day precision and accuracy. Synthesis of RES conjugates and development and validation of a sensitive bioanalytical assay were applied to pharmacokinetic evaluation of RES and its circulating monoconjugates in C57BL mice. The study is a first report of direct quantitation of RES monosulfates and monoglucuronides. These results will aid in characterizing the disposition of RES and its major or active metabolites in vivo.

Chebulagic acid, a COX-LOX dual inhibitor isolated from the fruits of Terminalia chebula Retz., induces apoptosis in COLO-205 cell line.

ETHNOPHARMACOLOGICAL RELEVANCE: Terminalia chebula has an esteemed origin in Indian mythology; its fruits are used to treat many diseases such as digestive, diabetes, colic pain, chronic cough, sore throat, asthma, etc. AIM OF THE STUDY: The water or ethanolic extracts of the fruits were reported to have anti-oxidant, anti-inflammatory, anti-cancer and radio-protector properties. The present study is to isolate and identify the compounds that inhibit COX and 5-LOX, the key enzymes involved in inflammation and carcinogenesis. MATERIALS AND METHODS: The ethanolic extract of the fruits was fractionated by RP-HPLC and fractions were tested for enzyme inhibition activity against COX and 5-LOX. One of the fractionated compounds showed potent dual inhibition against COX and 5-LOX. It was identified as chebulagic acid by LC-MS, NMR and IR analyses. The chebulagic acid was also tested for anti-proliferative activity. RESULTS: Chebulagic acid showed potent COX-LOX dual inhibition activity with IC(50) values of 15+/-0.288, 0.92+/-0.011 and 2.1+/-0.057 microM for COX-1, COX-2 and 5-LOX respectively. It also showed anti-proliferative activity against HCT-15, COLO-205, MDA-MB-231, DU-145 and K562 cell lines. Further mechanistic studies on COLO-205 cells revealed induction of apoptosis by chebulagic acid. CONCLUSIONS: Chebulagic acid, a COX-2 and 5-LOX dual inhibitor isolated from the fruits of Terminalia chebula, induces apoptosis in COLO-205 cells.