Idiosyncratic adverse drug reactions (IADRs) in humans can result in a broad range of clinically significant toxicities leading to attrition during drug development as well as postlicensing withdrawal or labeling. IADRs arise from both drug and patient related mechanisms and risk factors. Drug related risk factors, resulting from parent compound or metabolites, may involve multiple contributory mechanisms including organelle toxicity, effects related to compound disposition, and/or immune activation. In the current study, we evaluate an in vitro approach, which explored both cellular effects and covalent binding (CVB) to assess IADR risks for drug candidates using 36 drugs which caused different patterns and severities of IADRs in humans. The cellular effects were tested in an in vitro Panel of five assays which quantified (1) toxicity to THLE cells (SV40 T-antigen-immortalized human liver epithelial cells), which do not express P450s, (2) toxicity to a THLE cell line which selectively expresses P450 3A4, (3) cytotoxicity in HepG2 cells in glucose and galactose media, which is indicative of mitochondrial injury, (4) inhibition of the human bile salt export pump, BSEP, and (5) inhibition of the rat multidrug resistance associated protein 2, Mrp2. In addition, the CVB Burden was estimated by determining the CVB of radiolabeled compound to human hepatocytes and factoring in both the maximum prescribed daily dose and the fraction of metabolism leading to CVB. Combining the aggregated results from the in vitro Panel assays with the CVB Burden data discriminated, with high specificity (78%) and sensitivity (100%), between 27 drugs, which had severe or marked IADR concern, and 9 drugs, which had low IADR concern, we propose that this integrated approach has the potential to enable selection of drug candidates with reduced propensity to cause IADRs in humans.

As part of the drug discovery and development process, it is important to understand the fate of the drug candidate in humans and the relevance of the animal species used for preclinical toxicity and pharmacodynamic studies. Therefore, various in vitro and in vivo studies are conducted during the different stages of the drug development process to elucidate the absorption, distribution, metabolism, and excretion properties of the drug candidate. Although state-of-the-art LC/MS techniques are commonly employed for these studies, radiolabeled molecules are still frequently required for the quantification of metabolites and to assess the retention and excretion of all drug related material without relying on structural information and MS ionization properties. In this perspective, we describe the activities of Isotope Chemistry at AstraZeneca and give a brief overview of different commonly used approaches for the preparation of (14)C- and (3)H-labeled drug candidates. Also various drug metabolism and pharmacokinetic studies utilizing radiolabeled drug candidates are presented with in-house examples where relevant. Finally, we outline strategic changes to our use of radiolabeled compounds in drug metabolism and pharmacokinetic studies, with an emphasis on delaying of in vivo studies employing radiolabeled drug molecules.

Cellulose and cellulose derivatives are biopolymers which are often used as stationary phases for the separation of enantiomers. Describing the mechanism of such separations is a difficult task due to the complexity of these phases. In the present study, we attempt to elucidate the types of interactions occurring between a diol intermediate for a LTD(4) antagonist and a tris(4-methylbenzoate)-derivatized cellulose stationary phase. Thermodynamic studies indicate that, at low temperatures, the enantioselectivity is entropy driven. At higher temperatures, the separation is enthalpy driven. DSC and IR experiments reveal that the transitions between the enthalpic and the entropic regions of the van't Hoff plots are a result of a change in conformation of the stationary phase. Investigation of chromatographic kinetic parameters reveals that, at low temperature, the second eluted enantiomer undergoes sluggish inclusion interactions. Subtle changes in the structure of the analyte indicates that π-π interactions do not contribute to enantioselectivity. Finally, molecular modeling of (R)- and (S)-diol and the stationary phase suggests that hydrogen bonding is a primary factor in the separation, and the calculated energy values obtained from the molecular modeling correlate well with the chromatographic elution order.

A high-throughput pKa screening method based on pressure-assisted capillary electrophoresis (CE) and mass spectrometry (MS) is presented. Effects of buffer type and ionic strength on sensitivity and pKa values were investigated. Influence of dimethyl sulfoxide (DMSO) concentration present in the sample on effective mobility measurement was examined. A series of ten volatile buffers, covering a pH range from 2.5 to 10.5 with the same ionic strength, was employed. The application of volatile background electrolytes resulted in significant signal increase as compared with commonly used non-volatile phosphate buffers. In general, the CE/MS system provided a ten-fold higher sensitivity than conventional UV detection. The newly developed CE/MS method offers high-throughput capacity by pooling a number of compounds into a single sample. Simultaneous measurement of more than 50 compounds was readily achieved in less than 150 min. The measured pKa values are consistent with the published data obtained from the CE/UV method and are also in good agreement with data generated by other methods. Other advantages of using CE/MS for pKa screening are illustrated with typical examples, including poorly soluble compounds and non-UV-absorbing compounds.

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A series of quaternary ammonium compounds that are esters of betaine and fatty alcohols with hydrocarbon chain lengths of 10 to 18 carbon atoms were tested with respect to antimicrobial activities and rates of hydrolysis. When the tetradecyl derivative was tested against some selected microorganisms, the killing effect was comparable to that of the stable quaternary ammonium compound cetyltrimethylammonium bromide. At higher pH values, both the antimicrobial effect and the rate of hydrolysis of the esters increased. However, whereas at pH 6 greater than 99.99% killing of Salmonella typhimurium was achieved with 5 ,ug/ml in 3 min, the rate of hydrolysis was less than 20% in 18 h. At pH 7, a similar killing effect was achieved in 2 min and 50% hydrolysis occurred in ca. 5 h. Thus, it is possible to exploit the rapid microbicidal effect of the compounds before they hydrolyze. The rate of hydrolysis was reduced by the presence of salt. The bactericidal effect of the betaine esters increased with the length of the hydrocarbon chain of the fatty alcohol moiety up to 18 carbon atoms. Since the hydrolysis products are normal human metabolites, the hydrolysis property may extend the use of these quaternary ammonium compounds as disinfectants and antiseptics for food and body surfaces.The membrane-disruptive and antimicrobial activities of cationic surfactants are well recognized. These agents are often active against a broad range of bacteria and other cells and can also inactive certain viruses (16,29). Because of their high affinity for biological membranes, these agents show a low selectivity and can be damaging to a variety of mammalian cells (17,23,24).Since the time needed to kill microorganisms with cationic surfactants is usually short, it could be expected that side effects in the host might be decreased by the use of substances that are subject to hydrolytic degradation. However, the lifetime of the compounds must be sufficiently long to allow proper inactivation of the undesired microorganisms. The products obtained in the degradation steps should also be significantly less toxic than the original compound and should ideally constitute normal metabolites of the host.To explore the possible use of degradable cationic surfactants, we studied a series of amphiphilic betaine esters (Fig. 1). Although the increased rate of base-catalyzed hydrolysis of lower esters of this structure has been investigated and is understood to be caused by an inductive effect from the positive charge (5, 26), this property does not seem to have been considered in connection with biological (10,27) or recent surface chemical (4, 25) studies of compounds of this type. In the present paper, we describe the synthesis of some esters between betaine (trimethylglycine) and long-chain fatty alcohols, their antimicrobial activities, and their rates of hydrolysis. MATERIALS AND METHODSCompounds investigated. The betaine esters were obtained as chlorides by chloroacetylation of the corresponding longchain alcohol, principally as described by Ho...

Although idiosyncratic adverse drug reactions are rare, they are still a major concern to patient safety. Reactive metabolites are widely accepted as playing a pivotal role in the pathogenesis of idiosyncratic adverse drug reactions. While there are today well established strategies for the risk assessment of stable metabolites within the pharmaceutical industry, there is still no consensus on reactive metabolite risk assessment strategies. This is due to the complexity of the mechanisms of these toxicities as well as the difficulty in identifying and quantifying short-lived reactive intermediates such as reactive metabolites. In this review, reactive metabolite risk and hazard assessment approaches are discussed, and their pros and cons highlighted. We also discuss the nature of idiosyncratic adverse drug reactions, using acetaminophen and nefazodone to exemplify the complexity of the underlying mechanisms of reactive metabolite mediated hepatotoxicity. One of the key gaps moving forward is our understanding of and ability to predict the contribution of immune activation in idiosyncratic adverse drug reactions. Sections are included on the clinical phenotypes of immune mediated idiosyncratic adverse drug reactions and on the present understanding of immune activation by reactive metabolites. The advances being made in microphysiological systems have a great potential to transform our ability to risk assess reactive metabolites, and an overview of the key components of these systems is presented. Finally, the potential impact of systems pharmacology approaches in reactive metabolite risk assessments is highlighted.