Characterization of AZD4694, a novel fluorinated Abeta plaque neuroimaging PET radioligand.

Positron emission tomography (PET) radioligands that bind selectively to beta-amyloid plaques (Abeta) are promising imaging tools aimed at supporting the diagnosis of Alzheimer's disease and the evaluation of new drugs aiming to modify amyloid plaque load. For extended clinical use, there is a particular need for PET tracers labeled with fluorine-18, a radionuclide with 110 min half-life allowing for central synthesis followed by wide distribution. The development of fluorinated radioligands is, however, challenging because of the lipophilic nature of aromatic fluorine, rendering fluorinated ligands more prone to have high non-specific white matter binding. We have here developed the new benzofuran-derived radioligand containing fluorine, AZD4694 that shows high affinity for beta-amyloid fibrils in vitro (K(d) = 2.3 +/- 0.3 nM). In cortical sections from human Alzheimer's disease brain [(3)H]AZD4694 selectively labeled beta-amyloid deposits in gray matter, whereas there was a lower level of non-displaceable binding in plaque devoid white matter. Administration of unlabeled AZD4694 to rat showed that it has a pharmacokinetic profile consistent with good PET radioligands, i.e., it quickly entered and rapidly cleared from normal rat brain tissue. Ex vivo binding data in aged Tg2576 mice after intravenous administration of [(3)H]AZD4694 showed selective binding to beta-amyloid deposits in a reversible manner. In Tg2576 mice, plaque bound [(3)H]AZD4694 could still be detected 80 min after i.v. administration. Taken together, the preclinical profile of AZD4694 suggests that fluorine-18 labeled AZD4694 may have potential for PET-visualization of cerebral beta-amyloid deposits in the living human brain.

AZD2184: a radioligand for sensitive detection of beta-amyloid deposits.

The presence of beta-amyloid plaques in brain is a hallmark of Alzheimer's disease (AD) and serves as a biomarker for confirmation of diagnosis postmortem. Positron emission tomography (PET) radioligands such as Pittsburgh compound B ([(11)C]-2-(3-fluoro-4-methylamino-phenyl)-benzothiazol-6-ol) (PIB) binds selectively to beta-amyloid and are promising new tools supporting the clinical diagnoses of AD. In addition, such methodology may be useful for evaluation of new drugs aiming at reduction of amyloid plaque load. The objective of this study is to develop a new amyloid selective PET radioligand with higher signal-to-background ratio when compared with existing amyloid PET ligands. The lead compound, AZD2184, (2-[6-(methylamino)pyridin-3-yl]-1,3-benzothiazol-6-ol) was found to have high affinity for amyloid fibrils in vitro (K(d): 8.4 +/- 1.0 nM). Two minutes after i.v. administration in rats, about 1% of the dose was in brain. In vitro autoradiography on cortical brain sections from amyloid-beta precursor protein/presenilin 1 (APP/PS1) mice and AD patients showed that while [(3)H]AZD2184 and [(3)H]PIB are mutually displaceable, [(3)H]AZD2184 displays a higher signal-to-background ratio primarily by virtue of lower background binding levels. The ratio of binding ability in prefrontal cortex (high plaque load) to subcortical white matter (background) was 4.5 for [(3)H]AZD2184 and 0.8 for [(3)H]PIB at 1 nM. In adjacent cortical sections from APP/PS1 mouse as well as from AD cortical tissue, [(3)H]AZD2184 and antibodies to human beta-amyloid labeled identical structures. In vivo administration of [(3)H]AZD2184 to APP/PS1 mice further showed that [(3)H]AZD2184 labels amyloid deposits with low non-specific background binding. Taken together, the pre-clinical profile of AZD2184 in relation to the reference ligand PIB, suggests that (11)C-labeled AZD2184 is a potential radioligand for PET-visualization of beta-amyloid deposits in the living human brain.

In vitro-in vivo correlation in man of a topically applied local anesthetic agent using numerical convolution and deconvolution.

The aim of this study was to evaluate the relevance of the in vitro permeation method used at our laboratory in predicting in vivo dermal and transdermal absorption. Two different emulsions, a submicron oil-in-water (o/w) emulsion and a semisolid water-in-oil (w/o) emulsion, containing a model compound were investigated. The in vitro permeation rate of the compound from these emulsions was measured using static diffusion cells with human skin as membrane. The emulsions were allowed to remain in contact with the skin in the donor chamber for 15, 60, and 240 min. The study was monitored for 240 min and the steady state flux was calculated. The systemic concentration of the compound was measured in vivo as a function of time after dermal application to healthy volunteers with 15 and 60 min of application. A short-lasting i.v. infusion study in healthy volunteers was used to simulate the i.v. bolus dose. Numerical convolution was used to predict the in vivo plasma concentration of the compound while the in vivo absorption rate of the compound was estimated using numerical deconvolution. To establish correlation, the predicted in vivo flux was compared with the corresponding observed in vitro parameter after adjusting for the lag time. No major differences were seen in the systemic plasma levels between the two emulsions, which is in close agreement with the steady state flux measured in vitro. A linear correlation representing a point-to-point relationship was established for each of the investigated formulations and application times. The longer application time was predicted more accurately for both emulsions.

Physicochemical interaction of local anesthetics with lipid model systems--correlation with in vitro permeation and in vivo efficacy.

In dermal/transdermal drug administration stratum corneum (SC) is often the rate-limiting step. Furthermore, the intercellular lipid domain of SC is nowadays widely accepted as the major contributor to the skin barrier. The current work investigates whether the difference in the level of topical efficacy of local anesthetic compounds correlates with the type of interaction between the drug and the intercellular lipids of SC. Therefore, local anesthetics of varying topical efficacy were evaluated with respect to their effect on the morphology of various model lipid systems using small and wide angle X-ray diffraction (SWAXD) and differential scanning calorimetry (DSC). The model lipids used were glyceryl monooleate, sphingomyelin and lipids isolated from human SC. Furthermore, partitioning into isolated human SC as well as permeation through isolated human SC and human tape-stripped skin were investigated in vitro. The results indicate that local anesthetics may act as their own permeation enhancers by increasing the degree of hydrocarbon chain fluidity of the intercellular lipids. Eventually these interactions may induce non-lamellar reversed types of liquid crystalline structures locally in SC, which further facilitate the drug mobility. The large difference in topical efficacy of the investigated local anesthetics could not be explained simply by looking at their effect on the phase behavior of lipid model systems. Despite the similarities in physicochemical properties of these substances, the in vitro skin permeability differed markedly (AD>EMLA>lidocaine>prilocaine>sameridine). Thus, it was concluded that sufficient drug permeability over SC is essential to obtain local anesthesia by blocking the superficial nociceptors.