Structural attributes influencing unbound tissue distribution.

Unbound tissue-to-plasma partition coefficients (K) were determined for 56 structurally diverse compounds in rats following intravenous infusion. Five tissues were included in the study: white adipose, brain, heart, liver, and skeletal muscle. The rank ordering of the median tissue K values was: liver (4.

Liver-Targeted Small-Molecule Inhibitors of Proprotein Convertase Subtilisin/Kexin Type 9 Synthesis.

Targeting of the human ribosome is an unprecedented therapeutic modality with a genome-wide selectivity challenge. A liver-targeted drug candidate is described that inhibits ribosomal synthesis of PCSK9, a lipid regulator considered undruggable by small molecules. Key to the concept was the identification of pharmacologically active zwitterions designed to be retained in the liver.

In Vitro-In Vivo Extrapolation of Intestinal Availability for Carboxylesterase Substrates Using Portal Vein-Cannulated Monkey.

Prediction of intestinal availability (FF) of carboxylesterase (CES) substrates is of critical importance in designing oral prodrugs with optimal properties, projecting human pharmacokinetics and dose, and estimating drug-drug interaction potentials. A set of ester prodrugs were evaluated using in vitro permeability (parallel artificial membrane permeability assay and Madin-Darby canine kidney cell line-low efflux) and intestinal stability (intestine S9) assays, as well as in vivo portal vein-cannulated cynomolgus monkey. In vitro-in vivo extrapolation (IVIVE) of FF was developed with a number of modeling approaches, including a full physiologically based pharmacokinetic (PBPK) model as well as a simplified competitive-rate analytical solution.

Fluid resuscitation mediates the association between inhalational burn injury and acute kidney injury in the major burn population.

Background: It is known that acute respiratory distress syndrome and acute lung injury are independent risk factors for developing acute kidney injury (AKI) through complex pathophysiologic mechanisms. Our specific aim is to evaluate the risk factors for AKI postburn injury and whether inhalation thermal injury is an independent risk factor for developing AKI in the major burn population.

Methods: This is an institutional review board-approved, retrospective cohort study of patients admitted to a tertiary burn intensive care unit between 2011 and 2013.

Projecting ADME Behavior and Drug-Drug Interactions in Early Discovery and Development: Application of the Extended Clearance Classification System.

Purpose: To assess the utility of Extended Clearance Classification System (ECCS) in understanding absorption, distribution, metabolism, and elimination (ADME) attributes and enabling victim drug-drug interaction (DDI) predictions.

Methods: A database of 368 drugs with relevant ADME parameters, main metabolizing enzymes, uptake transporters, efflux transporters, and highest change in exposure (%AUC) in presence of inhibitors was developed using published literature. Drugs were characterized according to ECCS using ionization, molecular weight and estimated permeability.

Evaluation of a Mathematical Model of Rat Body Weight Regulation in Application to Caloric Restriction and Drug Treatment Studies.

The purpose of this work is to develop a mathematical model of energy balance and body weight regulation that can predict species-specific response to common pre-clinical interventions. To this end, we evaluate the ability of a previously published mathematical model of mouse metabolism to describe changes in body weight and body composition in rats in response to two short-term interventions. First, we adapt the model to describe body weight and composition changes in Sprague-Dawley rats by fitting to data previously collected from a 26-day caloric restriction study.

Insights From an Integrated Physiologically Based Pharmacokinetic Model for Brain Penetration.

Central-nervous-system, physiologically based pharmacokinetic (PBPK) models predict exposure profiles in the brain, that is, the rate and extent of distribution. The current work develops one such model and presents improved methods for determining key input parameters. A simple linear regression statistical model estimates the passive permeability at the blood-brain barrier from brain uptake index data and descriptors, and a novel analysis extracts the relative active transport parameter from in vitro assays taking into consideration both paracellular transport and unstirred water layers.

Rapid Method To Determine Intracellular Drug Concentrations in Cellular Uptake Assays: Application to Metformin in Organic Cation Transporter 1-Transfected Human Embryonic Kidney 293 Cells.

Because of the importance of intracellular unbound drug concentrations in the prediction of in vivo concentrations that are determinants of drug efficacy and toxicity, a number of assays have been developed to assess in vitro unbound concentrations of drugs. Here we present a rapid method to determine the intracellular unbound drug concentrations in cultured cells, and we apply the method along with a mechanistic model to predict concentrations of metformin in subcellular compartments of stably transfected human embryonic kidney 293 (HEK293) cells. Intracellular space (ICS) was calculated by subtracting the [(3)H]-inulin distribution volume (extracellular space, ECS) from the [(14)C]-urea distribution volume (total water space, TWS).

Toward a unified model of passive drug permeation II: the physiochemical determinants of unbound tissue distribution with applications to the design of hepatoselective glucokinase activators.

In this work, we leverage a mathematical model of the underlying physiochemical properties of tissues and physicochemical properties of molecules to support the development of hepatoselective glucokinase activators. Passive distribution is modeled via a Fick-Nernst-Planck approach, using in vitro experimental data to estimate the permeability of both ionized and neutral species. The model accounts for pH and electrochemical potential across cellular membranes, ionization according to Henderson-Hasselbalch, passive permeation of the neutral species using Fick's law, and passive permeation of the ionized species using the Nernst-Planck equation.

Towards a unified model of passive drug permeation I: origins of the unstirred water layer with applications to ionic permeation.

In this work, we provide a unified theoretical framework describing how drug molecules can permeate across membranes in neutral and ionized forms for unstirred in vitro systems. The analysis provides a self-consistent basis for the origin of the unstirred water layer (UWL) within the Nernst-Planck framework in the fully unstirred limit and further provides an accounting mechanism based simply on the bulk aqueous solvent diffusion constant of the drug molecule. Our framework makes no new assumptions about the underlying physics of molecular permeation.

Mechanistic insights from comparing intrinsic clearance values between human liver microsomes and hepatocytes to guide drug design.

Metabolic stability of drug candidates are often determined in both liver microsome and hepatocyte assays. Comparison of intrinsic clearance values between the two assays provides additional information to guide drug design. Intrinsic clearance values from human liver microsomes and hepatocytes were compared for a set of commercial drugs with known metabolic pathways and transporter characteristics.

Design of a Potent CB1 Receptor Antagonist Series: Potential Scaffold for Peripherally-Targeted Agents.

Antagonism of cannabinoid-1 (CB1) receptor signaling has been demonstrated to inhibit feeding behaviors in humans, but CB1-mediated central nervous system (CNS) side effects have halted the marketing and further development of the lead drugs against this target. However, peripherally restricted CB1 receptor antagonists may hold potential for providing the desired efficacy with reduced CNS side effect profiles. In this report we detail the discovery and structure-activity-relationship analysis of a novel bicyclic scaffold (3) that exhibits potent CB1 receptor antagonism and oral activity in preclinical feeding models.

Discovery and evaluation of spirocyclic derivatives as antagonists of the neuropeptide Y5 receptor.

A novel series of spirocyclic derivatives was synthesized and evaluated as NPY Y5R antagonists for the treatment of obesity. Cis and trans analogs 7a and 8a were equipotent in a Y5R binding assay (K(i)'s ≤ 1 nM) and displayed good stability in human and rat liver microsome preparations. Compound 7a failed to demonstrate weight loss activity in a diet-induced obese (DIO) rat model at unbound drug levels in the brain that exceeded the Y5R K(i) value by 25-fold over a 24-h time-period.

Discovery of new piperidine amide triazolobenzodiazepinones as intestinal-selective CCK1 receptor agonists.

New cholecystokinin-1 receptor (CCK1R) agonist 'triggers' were identified using iterative library synthesis. Structural activity relationship studies led to the discovery of compound 10e, a potent CCK1R agonist that demonstrated robust weight loss in a diet-induced obese rat model with very low systemic exposure. Pharmacokinetic data suggest that efficacy is primarily driven through activation of CCK1R's located within the intestinal wall.

Impact of genetic polymorphisms of cytochrome P450 2 C (CYP2C) enzymes on the drug metabolism and design of antidiabetics.

CYP2C enzymes are responsible for the oxidative metabolism of a diverse number of drugs for the treatment of type 2 diabetes mellitus, a severe metabolic disorder with high prevalence. Various clinical studies found the close association between CYP2C polymorphisms and altered pharmacokinetics, toxicological profiles, and drug-drug interactions of antidiabetic drugs. In this brief review, we discussed the impact of CYP2C polymorphisms on the metabolic fate of small-molecule antidiabetics including sulfonylureas, meglitinides, thiazolidinediones, gliptins, and gliflozins, with the key drug-protein molecular interactions highlighted.

Systematic and pairwise analysis of the effects of aromatic halogenation and trifluoromethyl substitution on human liver microsomal clearance.

Fluorine- and chlorine-containing moieties have been strategically integrated into chemical structures to optimize the pharmacokinetic and metabolic properties of therapeutic agents, based partly on the concept that the addition of these substituents may lower microsomal clearance. A large-scale systematic mechanistic study of drug metabolic alteration by aromatic halogenation has hitherto not been possible due to the lack of either large clearance databases or adequate data mining tools. To address this, we systematically searched compound pairs in Pfizer's human liver microsomal clearance database of over 220,000 unique compounds to assess the effects of fluoro-, chloro- and trifluoromethyl-substitution on phenyl derivatives.

Excretion, metabolism, and pharmacokinetics of CP-945,598, a selective cannabinoid receptor antagonist, in rats, mice, and dogs.

1-(8-(2-Chlorophenyl)-9-(4-chlorophenyl)-9H-purin-6-yl)-4-(ethylamino)piperidine-4-carboxamide (CP-945,598) is an orally active antagonist of the cannabinoid CB-1 receptor that progressed into phase 3 human clinical trials for the treatment of obesity. In this study, we investigated the metabolic fate and disposition of CP-945,598 in rats, Tg-RasH2 mice, and dogs after oral administration of a single dose of [(14)C]CP-945,598. Total mean recoveries of the radioactive dose were 97.

Metabolism of 4-Aminopiperidine Drugs by Cytochrome P450s: Molecular and Quantum Mechanical Insights into Drug Design.

4-Aminopiperidines are a variety of therapeutic agents that are extensively metabolized by cytochrome P450s with CYP3A4 as a major isoform catalyzing their N-dealkylation reaction. However, its catalytic mechanism has not been fully elucidated in a molecular interaction level. Here, we applied theoretical approaches including the molecular mechanics-based docking to study the binding patterns and quantum mechanics-based reactivity calculations.

Species independence in brain tissue binding using brain homogenates.

Species independence of brain tissue binding was assessed with a large number of structurally diverse compounds using equilibrium dialysis with brain homogenates of seven species and strains (Wistar Han rat, Sprague-Dawley rat, CD-1 mouse, Hartley guinea pig, beagle dog, cynomolgus monkey, and human). The results showed that the fractions unbound of the seven species and strains were strongly correlated with correlation coefficients ranging from 0.93 to 0.

Discovery of N-benzyl-2-[(4S)-4-(1H-indol-3-ylmethyl)-5-oxo-1-phenyl-4,5-dihydro-6H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-6-yl]-N-isopropylacetamide, an orally active, gut-selective CCK1 receptor agonist for the potential treatment of obesity.

We describe the design, synthesis, and structure-activity relationships of triazolobenzodiazepinone CCK1 receptor agonists. Analogs in this series demonstrate potent agonist activity as measured by in vitro and in vivo assays for CCK1 agonism. Our efforts resulted in the identification of compound 4a which significantly reduced food intake with minimal systemic exposure in rodents.

Quantitative in vitro and in vivo pharmacological profile of CE-178253, a potent and selective cannabinoid type 1 (CB1) receptor antagonist.

Background: Cannabinoid 1 (CB1) receptor antagonists exhibit pharmacological properties favorable for the treatment of obesity and other related metabolic disorders. CE-178253 (1-[7-(2-Chlorophenyl)-8-(4-chlorophenyl)-2-methylpyrazolo[1,5-a]-[1,3,5]triazin-4-yl]-3-ethylaminoazetidine-3-carboxylic acid hydrochloride) is a recently discovered selective centrally-acting CB1 receptor antagonist. Despite a large body of knowledge on cannabinoid receptor antagonists little data exist on the quantitative pharmacology of this therapeutic class of drugs.

Strategic use of plasma and microsome binding to exploit in vitro clearance in early drug discovery.

Apparent intrinsic clearance (CLia) determined from microsomal stability assays is a cornerstone in drug discovery. Categorical bins are routinely applied to this end point to facilitate analysis. However, such bins ignore the interdependent nature of apparent intrinsic microsome clearance on several ADME parameters.

In vitro and in vivo pharmacology of CP-945,598, a potent and selective cannabinoid CB(1) receptor antagonist for the management of obesity.

Cannabinoid CB(1) receptor antagonists exhibit pharmacologic properties favorable for the treatment of metabolic disease. CP-945,598 (1-[9-(4-chlorophenyl)-8-(2-chlorophenyl)-9H-purin-6-yl]-4-ethylamino piperidine-4-carboxylic acid amide hydrochloride) is a recently discovered selective, high affinity, competitive CB(1) receptor antagonist that inhibits both basal and cannabinoid agonist-mediated CB(1) receptor signaling in vitro and in vivo. CP-945,598 exhibits sub-nanomolar potency at human CB(1) receptors in both binding (K(i)=0.

Structure-based drug metabolism predictions for drug design.

Significant progress has been made in structure-based drug design by pharmaceutical companies at different stages of drug discovery such as identifying new hits, enhancing molecule binding affinity in hit-to-lead, and reducing toxicities in lead optimization. Drug metabolism is a major consideration for modifying drug clearance and also a primary source for drug metabolite-induced toxicity. With major cytochrome P450 structures identified and characterized recently, structure-based drug metabolism prediction becomes increasingly attractive.