For preclinical and clinical assessment of therapeutically relevant unbound, free, brain concentrations, the pharmacokinetic parameter fraction of unbound drug in brain (fu,brain) is commonly used to compensate total drug concentrations for nonspecific brain tissue binding (BTB). As, homogenous BTB is assumed between species and in health and disease, rat BTB is routinely used. The impact of Alzheimer’s disease (AD) on drug BTB in brain regions of interest (ROI), i.e., fu,brain,ROI, is yet unclear. This study for the first time provides insight into regional drug BTB and the validity of employing rat fu,brain,ROI as a surrogate of human BTB, by investigating five marketed drugs in post-mortem tissue from AD patients (n = 6) and age-matched controls (n = 6). Heterogeneous drug BTB was observed in all within group comparisons independent of disease and species. The findings oppose the assumption of uniform BTB, highlighting the need of case-by-case evaluation of fu,brain,ROI in translational CNS research.

The blood-brain barrier (BBB) is suggested to be compromised in Alzheimer's disease (AD). The concomitant presence of vascular amyloid beta (Aβ) pathology, so called cerebral amyloid angiopathy (CAA), also predisposes impairment of vessel integrity. Additionally, immunotherapy against Aβ may lead to further damage of the BBB. To what extent this affects the BBB passage of molecules is debated. The current study aimed to investigate BBB integrity to large molecules in transgenic mice displaying abundant Aβ pathology and age matched wild type animals, with or without acute anti-Aβ antibody treatment. Animals were administered a single i.v. injection of PBS or 3D6 (10 mg/kg), i.e. the murine version of the clinically investigated Aβ antibody bapineuzumab, supplemented with [125I]3D6. Three days post injections, a 4 kDa FITC and a 150 kDa Antonia Red dextran were administered i.v. to all animals. After termination, fluorescent detection in brain and serum was used for the calculation of dextran brain-to-blood concentration ratios. Further characterization of antibody fate and the presence of CAA were investigated using radioactivity measurements and Congo red staining. BBB passage of large molecules was equally low in wild type and transgenic mice, suggesting an intact BBB despite Aβ pathology. Neither was the BBB integrity affected by acute 3D6 treatment. However, CAA was confirmed in the transgenes and local antibody accumulations were observed in the brain, indicating CAA-antibody interactions. The current study shows that independently of Aβ pathology or acute 3D6 treatment, the BBB is intact, without extensive permeability to large molecules, including the 3D6 antibody.

Pathophysiological impairment of the neurovascular unit, including the integrity and dynamics of the blood-brain barrier (BBB), has been denoted both a cause and consequence of neurodegenerative diseases. Pathological impact on BBB drug delivery has also been debated. The aim of the present study was to investigate BBB drug transport, by determining the unbound brain-to-plasma concentration ratio (K-p,K-uu,K-brain), in aged A beta PP-transgenic mice, alpha-synuclein transgenic mice, and wild type mice. Mice were dosed with a cassette of five compounds, including digoxin, levofloxacin (1 mg/kg, s.c.), paliperidone, oxycodone, and diazepam (0.25 mg/kg, s.c.). Brain and blood were collected at 0.5,1, or 3 h after dosage. Drug concentrations were measured using LC-MS/MS. The total brain-to-plasma concentration ratio was calculated and equilibrium dialysis was used to determine the fraction of unbound drug in brain and plasma for all compounds. Together, these three measures were used to determine the Kp,uu,brain value. Despite A beta or alpha-synuclein pathology in the current animal models, no difference was observed in the extent of drug transport across the BBB compared to wild type animals for any of the compounds investigated. Hence, the present study shows that the concept of a leaking barrier within neurodegenerative conditions has to be interpreted with caution when estimating drug transport into the brain. The capability of the highly dynamic BBB to regulate brain drug exposure still seems to be intact despite the presence of pathology. (C) 2017 The Authors. Published by Elsevier Ltd.

Methods to investigate blood-brain barrier transport and pharmacologically active drug concentrations in the human brain are limited and data translation between species is challenging. Hence, there is a need to further develop the read-out of techniques like positron emission tomography (PET) for studying neuropharmacokinetics. PET has a high translational applicability from rodents to man and measures total drug concentrations in vivo. The aim of the present study was to investigate the possibility of translating total drug concentrations, acquired through PET, to unbound concentrations, resembling those measured in the interstitial fluid by microdialysis sampling. Simultaneous PET scanning and brain microdialysis sampling were performed in rats throughout a 60min infusion of [N-methyl-11C]oxycodone in combination with a therapeutic dose of oxycodone and during a 60min follow up period after the end of infusion. The oxycodone concentrations acquired with PET were converted into unbound concentrations by compensating for brain tissue binding and brain intracellular distribution, using the unbound volume of distribution in brain (Vu,brain), and were compared to microdialysis measurements of unbound concentrations. A good congruence between the methods was observed throughout the infusion. However, an accumulating divergence in the acquired PET and microdialysis data was apparent and became more pronounced during the elimination phase, most likely due to the passage of radioactive metabolites into the brain. In conclusion, the study showed that PET can be used to translate non-invasively measured total drug concentrations into unbound concentrations as long as the contribution of radiolabelled metabolites is minor or can be compensated for.

CONTEXT:Natural strain variation and rapid resistance development makes development of broad spectrum hepatitis C virus (HCV) drugs very challenging and evaluation of inhibitor selectivity and resistance must account for differences in the catalytic properties of enzyme variants.OBJECTIVE:To understand how to study selectivity and relationships between efficacy and genotype or resistant mutants for NS3 protease inhibitors.MATERIALS AND METHODS:The catalytic properties of NS3 protease from genotypes 1a, 1b and 3a, and their sensitivities to four structurally and mechanistically different NS3 protease inhibitors have been analysed under different experimental conditions.RESULTS:The optimisation of buffer conditions for each protease variant enabled the comparison of their catalytic properties and sensitivities to the inhibitors. All inhibitors were most effective against genotype 1a protease, with VX-950 having the broadest selectivity.DISCUSSION AND CONCLUSION:A new strategy for evaluation of inhibitors relevant for the discovery of broad spectrum HCV drugs was established.

To aid the design of next generation hepatitis C virus (HCV) drugs, the kinetics of the interactions between NS3 protease inhibitors and enzyme from genotypes 1a, 1b, and 3a have been characterized. The linear mechanism-based inhibitors VX-950 (telaprevir) and SCH 503034 (boceprevir) benefited from covalent adduct formation. However, the apparent affinities were rather weak (VX-950, K(D)* of 340, 8.5, and 1000 nM for genotypes 1a, 1b and 3a, respectively; SCH 503034, K(D)* of 90 and 3.9 nM for 1b and 3a, respectively). The non-mechanism-based macrocyclic inhibitors BILN-2016 (ciluprevir) and ITMN-191 (danoprevir) had faster association and slower dissociation kinetics, indicating that rigidification is kinetically favorable. ITMN-191 had nanomolar affinities for all genotypes (K(D)* of 0.13, 1.6, and 0.52 nM), suggesting that a broad spectrum drug is conceivable. The data show that macrocyclic scaffolds and mechanism-based inhibition are advantageous but that there is considerable room for improvement of the kinetics of HCV protease targeted drugs.

In this thesis, different approaches based on inhibition and interactions studies, have been used to characterize inhibitors of the non-structural protein 3 (NS3) from the hepatitis C virus (HCV). This involves identification of enzyme inhibitory effects and characterization of interaction mechanisms and kinetics, as well as effects on replication in a cell based system and serum protein binding. All this information contributes to HCV drug discovery.By using an inhibition assay it was possible to evaluate the effects of NS3 protease inhibitors, tested or used in the clinic, on NS3 variants, representing different model systems often used for drug discovery. This study illustrates the importance of accounting for differences in catalytic properties in comparative analyses, for making relevant interpretations of inhibition data. An SPR biosensor-based assay expanded the first study, and provided kinetic and mechanistic information, by direct interaction analyses of the inhibitors. It revealed significant differences between the different genotypes and model systems, and provided data that can be used to better understand the efficacy of inhibitors.Additionally, novel NS3 protease inhibitors were evaluated with respect to their potential to interfere with protease activity, their sensitivity to resistant mutants and effect on HCV replication. The most potent compounds were also characterized by their bioavailability, solubility and metabolic stability. This provides information for design of improved NS3 protease inhibitors, suggesting potential peptidomimetic structures for the backbone as well as for peptide substituents. These modification strategies allowed inhibitors to be truncated and less peptide-like, still with retained inhibitory effect.A new strategy for analysis of serum protein binding, of importance for drug distribution was also developed. By defining and using the concept of binding efficiency, serum protein interactions of moderate affinity, as described by rapid kinetics, were characterized. This strategy is also applicable for analysis of low affinity interactions.Taken together, all these studies provide knowledge and strategies for HCV drug discovery, and by using this information we might take a step closer to the final goal, which is to eradicate HCV.