A novel series of 1,2,4-triazolyl octahydropyrrolo[2,3-b]pyrroles showing high affinity and selectivity at the DA D3 receptor is reported here. Compounds endowed with high selectivity over the hERG channel were identified and their pharmacokinetic properties thoroughly analyzed. A few derivatives with appropriate developability characteristics were selected for further studies and progression along the screening cascade. In particular, derivative 60a, (DA D3 pKi=8.4, DA D2 pKi=6.0 and hERG fpKi=5.2) showed a balanced profile and further refinements are in progress around this molecule.

A novel series of 1,2,4-triazolyl 5-azaspiro[2.4]heptanes with high affinity and selectivity at the dopamine (DA) D3 receptor (D3R) is described. Some of these compounds also have high selectivity over the hERG channel and were characterized with respect to their pharmacokinetic properties both in vitro and in vivo during lead identification and early lead optimization phases. A few derivatives with overall favorable developability characteristics were selected for further late lead optimization studies.

A new series of morpholine derivatives has been identified as selective DA D3 receptor antagonists; their in vitro profile and pharmacokinetic data are provided.

Toxicity remains a leading cause of attrition at all stages of the drug development process. The majority of safety-related attrition occurs preclinically, suggesting that approaches to identify “predictable” preclinical safety liabilities earlier in the drug development process should lead to the design and/or selection of better drug candidates that have increased probabilities of becoming marketed drugs. In this chapter, we discuss how the application of discovery toxicology tools, both new molecular technologies as well as more established approaches such as standard repeat-dose rodent toxicology studies, together with early estimation or simulation of human exposure can identify predictable safety risks earlier in the testing paradigm. The earlier identification and characterization of dose-limiting toxicities will provide chemists and toxicologists with the opportunity to determine structure–toxicity relationships and minimize or circumvent adverse safety liabilities.

The last two decades have provided a large weight of preclinical data implicating the neurokinin-1 receptor (NK1) and its cognate ligand substance P (SP) in a broad range of both central and peripheral disease conditions. However, to date, only the NK1 receptor antagonist aprepitant has been approved as a therapeutic and this is to prevent chemotherapy-induced nausea & vomiting (CINV). The belief remained that the full therapeutic potential of NK1 receptor antagonists had yet to be realized; therefore clinical evidence that NK1 receptor antagonists may be effective in major depression disorder, resulted in a significant further investment in discovering novel CNS penetrant druggable NK1 receptor antagonists to address this condition. At GlaxoSmithKline after the discovery of casopitant, that went on to demonstrate efficacy as a novel antidepressant in the clinic, additional novel analogues of this NK1 receptor antagonist were designed to further enhance its drug developability characteristics. Herein, we therefore describe the discovery process and the vivo pharmacological and pharmacokinetic profile of the new NK1 receptor antagonist 3a (also called orvepitant), selected as clinical candidate and further progressed into clinical studies for major depressive disorder. Moreover, molecular modeling studies enabled us to improve the pharmacophore model of the NK1 receptor antagonists with the identification of a region able to accommodate a variety of heterocycle moieties.

The constant decline in drug discovery productivity despite the continuous growth in R&D investments has been on the table for many years and is driving changes in the current business model. We have focused our attention on what appears to be by far the major cause of attrition, the intrinsic quality of drug candidates; with the assumption that candidate quality can be designed and assessed at a rather early stage in drug discovery we have developed tools such as CNS chemical space mapping through PLS analysis, Drug Efficiency (DRUGeff) and the mechanistic PK/PD hypothesis. We also introduced best practices that were found extremely valuable which will be discussed in this article.

The hypothalamic peptides orexin-A and orexin-B are potent agonists of two G-protein coupled receptors, namely the OX1 and the OX2 receptor. These receptors are widely distributed, though differentially, in the rat brain. In particular, the OX1 receptor is highly expressed throughout the hypothalamus, whilst the OX2 receptor is mainly located in the ventral posterior nucleus. A large body of compelling evidence, both pre-clinical and clinical, suggests that the orexin system is profoundly implicated in sleep disorders. In particular, modulation of the orexin receptors activation by appropriate antagonists was proven to be an efficacious strategy for the treatment of insomnia in man. A novel, drug-like bis-amido piperidine derivative was identified as potent dual OX1 and OX2 receptor antagonists, highly effective in a pre-clinical model of sleep.

INTRODUCTION:The ultimate objective of optimizing adsorption, distribution, metabolism and excretion (ADME) parameters in drug discovery is to maximize the unbound concentration at the site of action for a given dose level. This has the added benefit of minimizing the efficacious dose, reducing the potential for attrition related to drug burden and direct organ toxicity. The concept of drug efficiency was formulated as a tool to obtain a balanced profile between target affinity and ADME properties during lead optimization.AREAS COVERED:The authors discuss how it is possible to maximize the in vivo pharmacological potential addressing whether drug efficiency adds value to the decision-making process and whether it is possible to introduce a single optimization parameter, the drug efficiency index (DEI), linking target affinity and ADME properties, as a marker of in vivo efficacy.EXPERT OPINION:In the absence of a clear hypothesis-driven approach at the beginning of the program (i.e., pharmacokinetic-pharmacodynamic link), the objective to select molecules with a low therapeutic dose is still a major hurdle in drug discovery. The authors believe that a greater strategic focus on mechanistically relevant measures of the determinants of receptor occupancy would help the optimization and selection process. In this respect, the introduction of the DEI, which can be seen as a correction of target affinity by the in vivo pharmacokinetic potential, may help drug discovery to select and promote those molecules with the highest probability to interact with the biological target and with the best balance between target affinity and ADME properties.

Estimating the unbound fraction of drugs in brain has become essential for the evaluation and interpretation of the pharmacokinetics and pharmacodynamics of new central nervous system drug candidates. Dialysis-based methods are considered to be accurate for estimating the fraction unbound in brain; however, these techniques are hampered by a low throughput. In this study, we present a novel, matrix-free, high-throughput method for estimating the unbound fraction, based on a sample pooling approach combining the TRANSIL brain absorption assay with liquid chromatography-mass spectrometry. The base measurement of the TRANSIL approach is the affinity to brain membranes, and this method is used directly to predict the free fraction in brain. The method was evaluated by comparing the free fraction of drugs in brain [f(u,brain) (%)] obtained using the TRANSIL brain absorption assay and equilibrium dialysis methods for a test set of 65 drugs (27 marketed and 38 proprietary drugs). A good correlation (r(2) > 0.93) of f(u,brain) (%) between the TRANSIL brain absorption assay and equilibrium dialysis was observed. Moreover, we compared the lipid composition of rat and porcine brain and analyzed the influence of the brain albumin content on brain tissue binding measurement. The comparison of the lipid composition indicated only minor differences between rat and porcine brain, and albumin appears to have a low impact on brain tissue binding measurements. The TRANSIL brain absorption assay with sample pooling methodology not only significantly reduces the biological matrix required but also increases the throughput, compared with the conventional dialysis methods.

Amphetamines are a group of sympathomimetic drugs that exhibit strong central nervous system stimulant effects. d-Amphetamine ((+)-alpha-methylphenetylamine) is the parent drug in this class to which all others are structurally related. In drug discovery, d-amphetamine is extensively used either for the exploration of novel mechanisms involving the catecholaminergic system, or for the validation of new behavioural animal models. Due to this extensive use of d-amphetamine in drug research and its interest in toxicologic–forensic investigation, a specific and high-throughput method, with minimal sample preparation, is necessary for routine analysis of d-amphetamine in biological samples. We propose here a sensitive, specific and high-throughput bioanalytical method for the quantitative determination of d-amphetamine in rat blood using MS3 scan mode on a hybrid triple quadrupole-linear ion trap mass spectrometer (LC–MS/MS/MS). Blood samples, following dilution with water, were prepared by fully automated protein precipitation with acetonitrile containing an internal standard. The chromatographic separation was achieved on a Waters XTerra C18 column (2.1mm×30mm, 3.5μm) using gradient elution at a flow rate of 1.0mL/min over a 2min run time. An Applied Biosystems API4000 QTRAP™ mass spectrometer equipped with turbo ion-spray ionization source was operated simultaneously in MS3 scan mode for the d-amphetamine and in multiple reaction monitoring (MRM) for the internal standard. The MS/MS/MS ion transition monitored was m/z 136.1→119.1→91.1 for the quantitation of d-amphetamine and for the internal standard (rolipram) the MS/MS ion transition monitored was m/z 276.1→208.2. The linear dynamic range was established over the concentration range 0.5–1000ng/mL (r2=0.9991). The method was rugged and sensitive with a lower limit of quantification (LLOQ) of 0.5ng/mL. All the validation data, such as accuracy, precision, and inter-day repeatability, were within the required limits. This method was successfully applied to evaluate the pharmacokinetics of d-amphetamine in rat. On a more general extent, this work demonstrated that the selectivity of the fragmentation pathway (MS3) can be used as alternative approach to significantly improve detection capability in complex situation (e.g., small molecules in complex matrices) rather than increasing time for sample preparation and chromatographic separation.

As a result of their wide acceptance and conceptual simplicity, drug-like concepts are having a major influence on the drug discovery process, particularly in the selection of the 'optimal' absorption, distribution, metabolism, excretion and toxicity and physicochemical parameters space. While they have an undisputable value when assessing the potential of lead series or in evaluating inherent risk of a portfolio of drug candidates, they result much less useful in weighing up compounds for the selection of the best potential clinical candidate. We introduce the concept of drug efficiency as a new tool both to guide the drug discovery program teams during the lead optimization phase and to better assess the developability potential of a drug candidate.

A novel series of 1,2,4-triazol-3-yl-azabicyclo[3.1.0]hexanes with high affinity and selectivity for the DA D(3) receptor and excellent pharmacokinetic profiles was recently reported. We also recently discussed the role of the linker associated with the triazole moiety. In this manuscript, we are reporting a detailed exploration of the region of the receptor interacting with the amine terminus of the scaffold wherein SAR and developability data associated with these novel templates was undertaken.

A pharmacophore model for triple reuptake inhibitors and the new class of 1-(aryl)-6-[alkoxyalkyl]-3-azabicyclo[3.1.0]hexanes were recently reported. Further investigation in this area led to the identification of a new series of potent and selective triple reuptake inhibitors endowed with good developability characteristics. Excellent bioavailability and brain penetration are associated with this series of 6-(3,4-dichlorophenyl)-1-[(methyloxy)methyl]-3-azabicyclo[4.1.0]heptanes together with high in vitro potency and selectivity at SERT, NET, and DAT. In vivo microdialysis experiments in different animal models and receptor occupancy studies in rat confirmed that derivative 17 showed an appropriate profile to guarantee further progression of the compound.

A direct and specific comparison of a trifluoromethyl group with the corresponding pentafluorosulfanyl group is made in terms of primary affinity and pharmacokinetic properties.

The discovery of new highly potent and selective triple reuptake inhibitors is reported. The new classes of 1-(aryl)-6-[alkoxyalkyl]-3-azabicyclo[3.1.0]hexanes and 6-(aryl)-6-[alkoxyalkyl]-3-azabicyclo[3.1.0]hexanes are described together with detailed SAR. Appropriate decoration of the scaffolds was achieved with the help of a triple reuptake inhibitor pharmacophore model detailed here. Selected derivatives showed good oral bioavailability (>30%) and brain penetration (B/B > 4) in rats associated with high in vitro potency and selectivity at SERT, NET, and DAT. Among these compounds, microdialysis and in vivo experiments confirm that derivative 15 has an appropriate developability profile to be considered for further progression.

Herein we report a detailed description of the structure-activity relationships for a novel series of "C-linked" 1,2,4-triazolylazabicyclo[3.1.0]hexanes. These derivatives are endowed with very high in vitro affinity and selectivity for the dopamine D(3) receptor. An optimization with respect to undesired affinity toward the hERG potassium channel is also reported. Members of this compound series also show excellent in vitro and in vivo pharmacokinetic properties.

IMPORTANCE OF THE FIELD:The incorporation of brain tissue binding routinely in CNS drug discovery screening strategies has markedly changed the way CNS drug discovery is performed and is proving to be a valuable tool in identifying new therapies for CNS diseases. For many years emphasis has been placed on the magnitude of the brain to blood ratio, the bigger the better, even though, in many cases, brain total concentration (C(brain)) has no or, at best, poor correlation with receptor occupancy/pharmacodynamic readout. Today, C(brain) values measured during in vivo experiments are corrected for the fraction unbound measured through in vitro experiments using brain tissue homogenate or brain tissue slice to obtain an estimate of the brain unbound concentration (C(u,brain)), and this has been demonstrated across a range of CNS targets to give a much better correlation with receptor occupancy/pharmacodynamic readout. This apparently simple change in CNS lead optimisation strategy has de facto revolutionised the vision of the brain penetration concepts.AREAS COVERED IN THIS REVIEW:This review will provide an overview of the use and applications of assessing brain free fraction to determine C(u,brain).TAKE HOME MESSAGE:Assessing brain free fraction to determine C(u,brain) in CNS lead optimisation strategies is the surrogate of choice for rapidly assessing biophase concentration for the majority of CNS targets.

The discovery of new highly potent and selective dopamine (DA) D(3) receptor antagonists has recently allowed the characterization of the DA D(3) receptor in a range of preclinical animal models of drug addiction. A novel series of 1,2,4-triazol-3-yl-azabicyclo[3.1.0]hexanes, members of which showed a high affinity and selectivity for the DA D(3) receptor and excellent pharmacokinetic profiles, is reported here. Members of a group of derivatives from this series showed good oral bioavailability and brain penetration and very high in vitro affinity and selectivity for the DA D(3) receptor, as well as high in vitro potency for antagonism at this receptor. Several members of this series also significantly attenuate the expression of conditioned place preference (CPP) to nicotine and cocaine.

The lead optimization process to identify new selective dopamine D(3) receptor antagonists is reported. DMPK parameters and binding data suggest that selective D(3) receptor antagonists as potential PET ligands might have been identified.