Exploration of PBPK Model-Calculation of Drug Time Course in Tissue Using IV Bolus Drug Plasma Concentration-Time Profile and the Physiological Parameters of the Organ.

An uncommon innovative consideration of the well-stirred linear physiologically based pharmacokinetic model and the drug plasma concentration-time profile, which is measured in routine intravenous bolus pharmacokinetic study, was applied for the calculation of the drug time course in human tissues. This cannot be obtained in the in vivo pharmacokinetic study. The physiological parameters of the organ such as organ tissue volume, organ blood flow rate, and its vascular volume were used in the calculation.

On the accuracy of calculation of the mean residence time of drug in the body and its volumes of distribution based on the assumption of central elimination.

1. The steady state and terminal volumes of distribution, as well as the mean residence time of drug in the body (Vss, Vβ, and MRT) are the common pharmacokinetic parameters calculated using the drug plasma concentration-time profile (Cp(t)) following intravenous (iv bolus or constant rate infusion) drug administration. 2.

Practical permeability-based hepatic clearance classification system (HepCCS) in drug discovery.

Background: The use of liver microsomes and hepatocytes to predict total in vivo clearance is standard practice in the pharmaceutical industry; however, metabolic stability data alone cannot always predict in vivo clearance accurately.

Results: Apparent permeability generated from Mardin-Darby canine kidney cells and rat hepatocyte uptake for 33 discovery compounds were obtained.

Conclusion: When there is underprediction of in vivo clearance, compounds with low apparent permeability (less than 3 × 10(-6) cm/s) all exhibited hepatic uptake.

On the maintenance of hepatocyte intracellular pH 7.0 in the in-vitro metabolic stability assay.

The account of pH difference between hepatocytes (intracellular pH 7.0) and extracellular water (pH 7.4) leads to the novel equation for hepatic clearance (Berezhkovskiy, J Pharma Sci 100:1167-1683, 2011).

Lead identification of novel and selective TYK2 inhibitors.

A therapeutic rationale is proposed for the treatment of inflammatory diseases, such as psoriasis and inflammatory bowel diseases (IBD), by selective targeting of TYK2. Hit triage, following a high-throughput screen for TYK2 inhibitors, revealed pyridine 1 as a promising starting point for lead identification. Initial expansion of 3 separate regions of the molecule led to eventual identification of cyclopropyl amide 46, a potent lead analog with good kinase selectivity, physicochemical properties, and pharmacokinetic profile.

On the accuracy of a one-compartment approach for determination of drug terminal half-life.

The drug terminal half-life (t(1/2)) is commonly predicted by a simplified one-compartment approach (t(1/2) = ln 2V(ss)/CL), where V(ss) and CL are the steady-state volume of distribution and the total body clearance of drug, respectively. The analysis of the accuracy of this approach is provided. It turns out that most often a simplified one-compartment calculation underestimates t(1/2) by no more than 25% for human, 26% for dog, 20% for monkey, 19% for rat, and 23% for mouse.

Prediction of drug terminal half-life and terminal volume of distribution after intravenous dosing based on drug clearance, steady-state volume of distribution, and physiological parameters of the body.

The steady state, V(ss), terminal volume of distribution, V(β), and the terminal half-life, t(1/2), are commonly obtained from the drug plasma concentration-time profile, C(p)(t), following intravenous dosing. Unlike V(ss) that can be calculated based on the physicochemical properties of drugs considering the equilibrium partitioning between plasma and organ tissues, t(1/2) and V(β) cannot be calculated that way because they depend on the rates of drug transfer between blood and tissues. Considering the physiological pharmacokinetic model pertinent to the terminal phase of drug elimination, a novel equation that calculates t(1/2) (and consequently V(β)) was derived.

An alternative approach for quantitative bioanalysis using diluted blood to profile oral exposure of small molecule anticancer drugs in mice.

A quantitative bioanalytical method for pharmacokinetic studies using diluted whole blood from serially bled mice was developed. Oral exposure profiles in mice for five model anticancer compounds dacarbazine, gefitinib, gemcitabine, imatinib, and topotecan were determined following discrete and cassette (five-in-one) dosing. Six micro blood samples per animal were collected and added to a fixed amount of water.

Conceptual underestimation of the total body clearance by the sum of clearances of individual organs in physiologically based pharmacokinetics.

It is commonly assumed for linear pharmacokinetics that the total body clearance (CL) is equal to the sum of clearances of individual elimination organs. This is not quite valid because, in general, the concentration of drug in arterial blood entering the elimination organ is not the same as the measured venous blood concentration that is used to calculate CL. Consideration of physiologically based pharmacokinetic model that differentiates between venous and arterial blood shows that CL exceeds the sum of clearances provided by individual organs.

Determination of hepatic clearance with the account of drug-protein binding kinetics.

Binding of drugs to plasma proteins is commonly considered in pharmacokinetics as being in an instantaneous equilibrium. Although if the timescale of dissociation of drug-protein complex becomes comparable to the time that a drug molecule spends in blood while passing through the elimination organ, the kinetics of protein binding may influence the organ clearance. This appears possible for the compounds that have large dissociation energy from protein.

On the accuracy of determination of unbound drug fraction in tissue using diluted tissue homogenate.

The unbound drug fraction in tissue, f(ut) , is commonly measured in vitro using the diluted tissue homogenate. An appraisal of the calculation procedure that is routinely applied to obtain f(ut) is presented. An accurate detailed calculation that takes into account the drug protein binding in tissue extracellular water and the pH difference between extra- and intracellular water is considered.

Preclinical stereoselective disposition and toxicokinetics of two novel MET inhibitors.

The R- and S-enantiomer of N-(4-(3-(1-ethyl-3,3-difluoropiperidin-4-ylamino)-1H-pyrazolo[3,4-b]pyridin-4-yloxy)-3-fluorophenyl)-2-(4-fluorophenyl)-3-oxo-2,3-dihydropyridazine-4-carboxamide are novel MET kinase inhibitors that have been investigated as potential anticancer agents. The effect of the chirality of these compounds on preclinical in vivo pharmacokinetics and toxicity was studied. The plasma clearance for the S-enantiomer was low in mice and monkeys (23.

Consistency of the novel equations for determination of hepatic clearance and drug time course in liver that account for the difference in drug ionization in extracellular and intracellular tissue water.

Intrinsic clearances of seven diverse compounds in rat liver microsomes were measured at intracellular pH 7.0 and extracellular pH 7.4.

Evaluation of dried blood spot sampling following cassette dosing in drug discovery.

Background: Dried blood spot (DBS) sampling has received growing interest mainly in regulatory preclinical and clinical studies while not routinely used in exploratory discovery pharmacokinetic screening. An intravenous bolus cassette dose of six compounds in rats followed by hemolyzed blood sample (HBS) and DBS sampling was evaluated in this study.

Results: A sensitive liquid chromatography tandem mass spectrometry method was developed and qualified for the simultaneous determination of six compounds in rat whole blood using DBS or HBS techniques.

A convenient method to measure blood-plasma concentration ratio using routine plasma collection in in vivo pharmacokinetic studies.

A practical time-saving method of determination of equilibrium blood-plasma concentration ratio is described. The method is based on the analysis of compound plasma concentrations in regular blood sample and the blood sample diluted with blank plasma. Since only plasma concentrations are analyzed, the method can be conveniently applied in routine pharmacokinetic studies with minimal additional work for obtaining blood-plasma ratio.

The influence of hepatic transport on the distribution volumes and mean residence time of drug in the body and the accuracy of estimating these parameters by the traditional pharmacokinetic calculations.

The influence of hepatic uptake and efflux, which includes passive diffusion and transporter-mediated component, on drug distribution volumes [steady-state volume of distribution (V(ss)) and terminal volume of distribution (V(β))], mean residence time (MRT), clearance, and terminal half-life is considered using a simplified physiologically based pharmacokinetic model. To account for hepatic uptake, liver is treated as two-compartmental unit with drug transfer from extracellular water into hepatocytes. The exactly calculated distribution volumes and MRT are compared with that obtained by the traditional equations based on the assumption of central elimination.

The corrected traditional equations for calculation of hepatic clearance that account for the difference in drug ionization in extracellular and intracellular tissue water and the corresponding corrected PBPK equation.

The estimation of hepatic clearance, Clh, using in vitro data on metabolic stability of compound, its protein binding and blood–plasma equilibrium concentration ratio is commonly performed using well-stirred, parallel tube or dispersion models. It appears that for ionizable drugs there is a difference of the steady-state concentrations in extracelluar and intracellular water (at hepatocytes), where metabolism takes place. This occurs due to the different pH of extra- and intracellular water (7.

On the accuracy of estimation of basic pharmacokinetic parameters by the traditional noncompartmental equations and the prediction of the steady-state volume of distribution in obese patients based upon data derived from normal subjects.

The steady-state and terminal volumes of distribution, as well as the mean residence time of drug in the body (V(ss), V(β), and MRT) are the common pharmacokinetic parameters calculated using the drug plasma concentration-time profile C(p) (t) following intravenous (i.v. bolus or constant rate infusion) drug administration.

Preclinical absorption, distribution, metabolism, excretion, and pharmacokinetic-pharmacodynamic modelling of N-(4-(3-((3S,4R)-1-ethyl-3-fluoropiperidine-4-ylamino)-1H-pyrazolo[3,4-b]pyridin-4-yloxy)-3-fluorophenyl)-2-(4-fluorophenyl)-3-oxo-2,3-dihydropyridazine-4-carboxamide, a novel MET kinase inhibitor.

GNE-A (AR00451896; N-(4-(3-((3S,4R)-1-ethyl-3-fluoropiperidine-4-ylamino)-1H-pyrazolo[3,4-b]pyridin-4-yloxy)-3-fluorophenyl)-2-(4-fluorophenyl)-3-oxo-2,3-dihydropyridazine-4-carboxamide) is a potent, selective MET kinase inhibitor being developed as a potential drug for the treatment of human cancers. Plasma clearance was low in mice and dogs (15.8 and 2.

On the possibility of self-induction of drug protein binding.

The equilibrium unbound drug fraction (f(u)) is an important pharmacokinetic parameter, which influences drug elimination and distribution in the body. Commonly the drug plasma concentration is substantially less then that of drug binding proteins, so that f(u) can be assumed constant independent of drug concentration. A general consideration of protein binding based on the mass-action law provides that the unbound drug fraction increases with the increase of drug concentration, which is also a usual experimental observation.

On the influence of protein binding on pharmacological activity of drugs.

The effect of variable protein binding (taken as independent parameter) on pharmacological activity of drugs is considered in terms of the exposure or the steady state concentration of unbound drug at targeted tissue. Based on the application of the parallel tube or dispersion models it is shown that for the most common case of orally administered drugs eliminated mainly by hepatic metabolism the increase of protein binding may be beneficial for drug action. In contrary, consideration of this case using the well-stirred model suggests that changes in protein binding do not influence drug efficiency.

A valid equation for the well-stirred perfusion limited physiologically based pharmacokinetic model that consistently accounts for the blood-tissue drug distribution in the organ and the corresponding valid equation for the steady state volume of distribution.

A consistent account of the assumptions of the well-stirred perfusion limited model leads to the equation for the organ tissue that does not coincide with that often presented in books and papers. The difference in pharmacokinetic profiles calculated by the valid and the commonly used equations could be quite significant, particularly due to contribution of the organs with relatively large perfusion volume, and especially for drugs with small tissue-plasma partition coefficient and high blood-plasma concentration ratio. Application of the valid equation may result in much faster initial drop of drug plasma concentration time curve and significantly longer terminal half-life, especially for low extraction ratio drugs.

Prediction of the possibility of the secondary peaks of iv bolus drug plasma concentration time curve by the model that directly takes into account the transit time through the organ.

The article considers the problem of determination of organ clearance and the time course of drug plasma concentration using the model for which the drug transit time through the organ is regarded as one of the parameters. The suggested nonsteady state approach to the determination of organ clearance conceptually corresponds to the parallel tube model, and directly takes into account the delay of drug exit from the organ due to the transit time tau. The considered model is linear, so that the definition of mean organ clearance as D(o)/AUC, where D(o) is the quantity of drug eliminated by the organ and AUC is the area under drug plasma concentration time curve, is relevant and yields the same value as obtained at steady state.