Syntheses of radiolabeled ABT‐578 for ADME studies

Several isotopomers of ABT‐578 ( I , II , III , and IV ) were prepared starting from different labeled precursors: [5'‐³H]‐tetrazole ( 1 ), [5'‐¹⁴C]‐tetrazole ( 2 ), [40‐³H]rapamycin ( 3 ), and [2,11,31‐³H]rapamycin ( 4 ). It was shown that the tritium label at the 40 position of rapamycin is lost during an attempted synthesis of [40‐³H]ABT‐578 ( III ). Copyright © 2006 John Wiley & Sons, Ltd.     

Drug discovery information integration: virtual humans for pharmacokinetics

The ‘virtual human’ refers to simulation models based on explicit mathematical models of mammalian physiology. When applied to pharmacokinetics (PK), the virtual human embodies models that can be parameterised for different species, different individuals and populations of individuals, and that allow simulation of PK from measured and/or predicted in vitro properties. The models are independent of the properties of any specific drug, and can be used for the prediction of drug behaviour in specific human individuals and in pre-clinical species. The hope is that these models will allow the prediction of PK throughout the drug discovery and development process, enabling effective targeting of synthetic chemistry efforts to compounds with the required therapeutic effect, careful evaluation of multiple candidates for development, assessment of the potential for drug-drug interactions, evaluation of multiple formulations, efficient clinical trial design and other benefits, including reduction of animal usage in drug discovery. However, we believe that the biggest impact on drug discovery productivity would accrue from achieving two clear objectives: an estimate of human in vivo activity on every compound synthesised and a reliable prioritisation, based on predictions of human in vivo activity, for the next round of synthesis. It is realistic to believe that the benefits of delivering these objectives could, through shortening the time to decision and increasing the chance of success, lead to a five- to ten-fold increase in discovery output. It is also now possible to demonstrate that a combination of virtual human simulation software and industrial-scale absorption, distribution, metabolism and elimination (ADME) testing can deliver both of these objectives.     

Design,synthesis, evaluation,and molecular modeling studies of indolyl oxoacetamides as potential pancreatic lipase inhibitors

A series of indolyl oxoacetamide analogs was synthesized, characterized, and evaluated for their pancreatic lipase inhibitory activity using porcine pancreatic lipase (type II) and 4-nitrophenyl butyrate. Compound 8d exhibited a potent inhibition, with an IC₅₀ value of 4.53 µM, followed by 8c (IC₅₀ = 5.12 µM), compared with the standard drug, orlistat (IC₅₀ = 0.99 µM). Furthermore, analogs 8c and 8d exhibited a reversible competitive inhibition, similar to orlistat. Molecular docking studies of the compounds 7a–f and 8a – f were in agreement with the in vitro results, wherein 8d exhibited a potential MolDock score of −163.052 kcal/mol. A 10-ns molecular dynamics simulation of 8d complexed with pancreatic lipase confirmed the role of π–π stacking and π–cation interactions with the lid domain and Arg 256, respectively, in stabilizing the ligand at the active site (maximum observed root mean square deviation ≈ 2 Å). The present study led to the identification of novel indolyl oxoacetamides ( 8a – d ) as potential pancreatic lipase inhibitory leads that might further result in enhanced potency through lead optimization.     

Lipophilicity and biomimetic properties to support drug discovery

Introduction: Lipophilicity, expressed as the octanol-water partition coefficient, constitutes the most important property in drug action, influencing both pharmacokinetic and pharmacodynamics processes as well as drug toxicity. On the other hand, biomimetic properties defined as the retention outcome on HPLC columns containing a biological relevant agent, provide a considerable advance for rapid experimental – based estimation of ADME properties in early drug discovery stages.

Areas covered: This review highlights the paramount importance of lipophilicity in almost all aspects of drug action and safety. It outlines problems brought about by high lipophilicity and provides an overview of the drug-like metrics which incorporate lower limits or ranges of logP. The fundamental factors governing lipophilicity are compared to those involved in phospholipophilicity, assessed by Immobilized Artificial Membrane Chromatography (IAM). Finally, the contribution of biomimetic properties to assess plasma protein binding is evaluated.

Expert opinion: Lipophilicity and biomimetic properties have important distinct and overlapping roles in supporting the drug discovery process. Lipophilicity is unique in early drug design for library screening and for the identification of the most promising compounds to start with, while biomimetic properties are useful for the experimentally-based evaluation of ADME properties for the synthesized novel compounds, supporting the prioritization of drug candidates and guiding further synthesis.     

A physiologically based kinetic (PBK) model describing plasma concentrations of quercetin and its metabolites in rats

Biological activities of flavonoids in vivo are ultimately dependent on the systemic bioavailability of the aglycones as well as their metabolites. In the present study, a physiologically based kinetic (PBK) model was developed to predict plasma concentrations of the flavonoid quercetin and its metabolites and to tentatively identify the regiospecificity of the major circulating metabolites. The model was developed based on in vitro metabolic parameters and by fitting kinetic parameters to literature available in vivo data. Both exposure to quercetin aglycone and to quercetin-4′-O-glucoside, for which in vivo data were available, were simulated. The predicted plasma concentrations of different metabolites adequately matched literature reported plasma concentrations of these metabolites in rats exposed to 4′-O-glucoside. The bioavailability of aglycone was predicted to be very low ranging from 0.004%-0.1% at different oral doses of quercetin or quercetin-4′-O-glucoside. Glucuronidation was a crucial pathway that limited the bioavailability of the aglycone, with 95–99% of the dose being converted to monoglucuronides within 1.5–2.5 h at different dose levels ranging from 0.1 to 50 mg/kg bw quercetin or quercetin-4′-O-glucoside. The fast metabolic conversion to monoglucuronides allowed these metabolites to further conjugate to di- and tri-conjugates. The regiospecificity of major circulating metabolites was observed to be dose-dependent. As we still lack in vivo kinetic data for many flavonoids, the developed model has a great potential to be used as a platform to build PBK models for other flavonoids as well as to predict the kinetics of flavonoids in humans.     

Prediction of ARA/PPI Drug-Drug Interactions at the Drug Discovery and Development Interface

Advances in understanding of human disease have prompted the U.S. Food and Drug Administration to classify certain molecules as “break-through therapies,” providing an accelerated review that may potentially enhance the quality of patient lives. With this designation come compressed timelines to develop drug products, which are not only suitable for clinic trials but can also be approved and brought to the market rapidly. Early risk identification for decreased oral absorption due to drug-drug interactions with proton pump inhibitors (PPIs) or acid-reducing agents (ARAs) is paramount to an effective drug product development strategy. An early ARA/PPI drug-drug interaction (DDI) risk identification strategy has been developed using physiologically based absorption modeling that readily integrates ADMET predictor generated in silico estimates or measured in vitro solubility, permeability, and ionization constants. Observed or predicted pH-solubility profile data along with pKas and drug dosing parameters were used to calculate a fraction of drug absorbed ratio in absence and presence of ARAs/PPIs. An integrated physiologically based pharmacokinetic absorption model using GastroPlus? with pKa values fitted to measured pH-solubility profile data along with measured permeability data correctly identified the observed ARA/PPI DDI for 78% (16/22) of the clinical studies. Formulation strategies for compounds with an anticipated pH-mediated DDI risk are presented.     

Pharmacokinetic aspects and in vitro–in vivo correlation potential for lipid-based formulations

Lipid-based formulations have been an attractive choice among novel drug delivery systems for enhancing the solubility and bioavailability of poorly soluble drugs due to their ability to keep the drug in solubilized state in the gastrointestinal tract. These formulations offer multiple advantages such as reduction in food effect and inter-individual variability, ease of preparation, and the possibility of manufacturing using common excipients available in the market. Despite these advantages, very few products are available in the present market, perhaps due to limited knowledge in the in vitro tests (for prediction of in vivo fate) and lack of understanding of the mechanisms behind pharmacokinetic and biopharmaceutical aspects of lipid formulations after oral administration. The current review aims to provide a detailed understanding of the in vivo processing steps involved after oral administration of lipid formulations, their pharmacokinetic aspects and in vitro in vivo correlation (IVIVC) perspectives. Various pharmacokinetic and biopharmaceutical aspects such as formulation dispersion and lipid digestion, bioavailability enhancement mechanisms, impact of excipients on efflux transporters, and lymphatic transport are discussed with examples. In addition, various IVIVC approaches towards predicting in vivo data from in vitro dispersion/precipitation, in vitro lipolysis and ex vivo permeation studies are also discussed in detail with help of case studies.KEY WORDS: Pharmacokinetics, Lipolysis, IVIVC, Efflux transporters, Lymphatic delivery, Food effectAbbreviations: ADME, absorption/distribution/metabolism/elimination; AUC, area under the curve; BCS, biopharmaceutics classification system; BDDCS, biopharmaceutics drug disposition classification system; CACO, human epithelial colorectal adenocarcinoma cells; C_max, maximum plasma concentration; CMC, critical micellar concentration; CYP, cytochrome; DDS, drug delivery systems; FaSSGF, fasted-state simulated gastric fluid; FaSSIF, fasted-state simulated intestinal fluid; FeSSIF, fed-state simulated intestinal fluid; GIT, gastrointestinal tract; IVIVC, in vitro in vivo correlation; LCT, long chain triglyceride; LFCS, lipid formulation classification system; log P, n-octanol/water partition coefficient; MCT, medium chain triglyceride; MDCK, Madin–Darby canine kidney cells; NCE, new chemical entity; P-app, apparent permeability; P-gp, permeability glycoprotein; SCT, short chain triglyceride; SEDDS, self-emulsifying drug delivery system; SIF, simulated intestinal fluid; SMEDDS, self-microemulsifying drug delivery system; SNEDDS, self-nanoemulsifying drug delivery system; Vit E, vitamin E     

Strategies for more effective and reliable ADME

This conference was organised by Vision in Business, in order to address the issue that ‘more than 40% of drug preclinical failure is due to ADME-related issues and many drugs are later withdrawn because of unanticipated drug–drug interactions (C Masimirembwa, AstraZeneca Mölndal, Sweden). Academic and industrial scientists were brought together to discuss and present current knowledge/theories on subjects of importance in preclinical and clinical drug development. These included in vivo/in vitro correlations, approaches and experimental models used, in silico models and methods, metabolic databases and their application, as well as safety and financial outcomes. Participants were challenged by the issues covered and encouraged to share their own experiences and opinions during extensive discussions with other scientists.     

系统生物学在中药ADME性质研究中的应用

本文从中医的研究角度综述了系统生物学的定义、研究框架、范围和方法论特点,并以PBPK和PBPD研究为实例,详述了系统生物学方法论在药学研究中的最新应用和进展,阐明了系统生物学是还原论基础上的整体论。中医药是中医整体辩证理论指导下的复杂体系,拟乘系统生物学之势将面对诸多基础问题的挑战,然而中药ADME性质的阐明将成为中医药系统生物学研究的基石,从而将分子水平和整体水平有力地衔接起来。本文中同时简略地综述了作者研究组在该领域的有益尝试,结果表明中药的早期ADME性质研究方法将是揭开中药之谜并过渡到系统生物学水平的有力手段。