First-in-Human Brain Imaging of [18F]TRACK, a PET tracer for Tropomyosin Receptor Kinases.

The tropomyosin receptor kinase TrkA/B/C family is responsible for human neuronal growth, survival, and differentiation from early nervous system development stages onward. Downregulation of TrkA/B/C receptors characterizes numerous neurological disorders including Alzheimer's disease (AD). Abnormally expressed Trk receptors or chimeric Trk fusion proteins are also well-characterized oncogenic drivers in a variety of neurogenic and non-neurogenic human neoplasms and are currently the focus of intensive clinical research. Previously, we have described the clinical translation of a highly selective and potent carbon-11-labeled pan-Trk radioligand and the preclinical characterization of the optimized fluorine-18-labeled analogue, [18F]TRACK, for in vivo Trk positron emission tomography (PET) imaging. We describe herein central nervous system selectivity assessment and first-in-human study of [18F]TRACK.

An aqueous extract of the marine sponge Ectyoplasia ferox stimulates L-type Ca2+-current by direct interaction with the Cav1.2 subunit.

Marine organisms have attracted much attention as a source of pharmacological tools or potential drugs. We have produced and screened a library of sponge extracts in search of biologically active compounds that may contain useful pharmaceutical lead structures. Sponges were collected from various locations and their aqueous extracts were freeze dried. Murine right and left atria were used to screen 75 extracts for putative cardiac effects. Among seven extracts with a positive inotropic and chronotropic effect the extract C47 from Ectyoplasia ferox proved to be the most active and was chosen for further analysis. C47 also produced a beta-adrenoceptor-independent, propranolol-resistant positive inotropic effect in human atrial trabeculae. To elucidate one possible mode of action the effects of C47 on L-type Ca(2+) current (I(Ca,L)) were measured with a standard patch-clamp technique. In isolated human atrial myocytes exposure to C47 increased peak amplitude of I(Ca,L) in a concentration-dependent manner. The threshold concentration was 15 microg/ml. In addition, voltage dependency of activation and steady-state inactivation were shifted to more negative potentials. C47 slowed the initial phase of time-dependent current inactivation and the recovery from inactivation. In cell-attached patches of HEK 293 cells expressing human Ca(v)1.2 addition of C47 to the bath solution did not affect gating properties, whereas inclusion of the extract into the pipette solution strongly increased single-channel activity, suggesting a direct effect on the pore-forming channel subunit. Despite its robust effect on I(Ca,L) C47 enhanced cardiac force of contraction by only a fraction of the maximum increase caused by high extracellular concentrations of Ca(2+) and failed to increase vascular tone. These findings suggest that the effect of C47 is restricted to the Ca(2+) channel.

Different responses to drugs against overactive bladder in detrusor muscle of pig, guinea pig and mouse.

Direct comparison of experimental data for drugs commonly used in the treatment of overactive bladder is difficult because of possible species differences. In this study, we compare the effects of atropine, propiverine, oxybutynin and tolterodine in strips of pig, guinea pig and mouse detrusor muscle. In the three species, we observed slight differences in potency of carbachol-induced biphasic contractile responses between the species (guinea pig>pig>mouse). Cumulative concentration-response curves for carbachol were shifted to the right by atropine, propiverine, oxybutynin and tolterodine. However, at higher concentrations of the latter three antagonists, the maximum response to carbachol was also reduced. Therefore, propiverine, oxybutynin and tolterodine must have additional pharmacological actions beyond competitive antagonism at muscarinic receptors. Electric field stimulation (30 Hz) of detrusor strips led to contraction amplitudes, which remained constant over time (210 min) in pig, decreased by 17+/-5% in guinea pig, and increased by 28+/-9% in mouse detrusor muscle. Electric field stimulation-evoked contractions were suppressed to 18% of pre-drug control by high concentrations of atropine (10 microM) in pig, but to a much lesser extent in guinea pig and mouse (to 46% and 70%, respectively). In all three species, a myogenic component of contraction was observed in the presence of tetrodotoxin (1 microM). Compared to atropine, the bladder spasmolytic agents propiverine, oxybutynin and tolterodine also reduced electrically evoked contractions in the three species, though higher concentrations were required. The differences in the reported effects of the spasmolytic agents commonly used for treating overactive bladder suggest that drug action is strongly dependent on the species. Thus, a comparison of drug effects is only feasible in the same animal model and the results cannot easily be transferred to humans.

Pharmacological characterization of the P2X(7) receptor on human macrophages using the patch-clamp technique.

Whole-cell patch-clamp recordings were made from macrophages derived from human monocytes that had been cultured for 5-7 days. The P2X agonists ATP (100 microM) and 2',3'-(4-benzoyl)-benzoyl ATP (BzATP, 100 microM) induced inward currents. A second application of the agonists was characterized by strong desensitisation of the maximum current. Pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), a non-specific P2X antagonist, and 1-( N, O- bis[5-isoquinolinesulphonyl]- N-methyl- L-tyrosyl)-4-phenylpiperazine (KN62), a potent P2X(7) antagonist at the human receptor, both reduced the ATP-induced inward current. KN62 also inhibited the BzATP-induced current. The P2X(7) antagonist Coomassie Brilliant Blue G (BBG), believed to be potent at the human but even more so potent at the rat receptor, did not reduce the BzATP-induced inward current significantly. These results indicate that the native P2X(7) receptor subtype is expressed in human macrophages and that this receptor subtype is involved in the ATP-mediated inward current. Our experiments suggest that other P2X receptors also appear to be involved in the ATP-mediated current in human monocyte-derived macrophages.