Four phase 1 trials to evaluate the safety and pharmacokinetic profile of single and repeated dosing of SCO-101 in adult male and female volunteers.

SCO-101 (Endovion) was discontinued 20 years ago as a new drug under development against sickle cell anaemia. Data from the phase 1 studies remained unpublished. New data indicate that SCO-101 might be efficacious as add-on therapy in cancer. Thus, we report the results from the four phase 1 trials performed between 2001 and 2002. Adult volunteers received SCO-101 or placebo in four independent trials. Adverse events were recorded, and SCO-101 was determined for pharmacokinetic analysis. Ninety-two volunteers completed the trials. The most remarkable adverse effect was a transient and dose-dependent increase in unconjugated bilirubin. Plasma SCO-101 elimination was approximately log linear, with apparent oral clearances of between 315 and 2103 mL/h for single doses, and between 121 and 2433 mL/h at steady state following oral administration. There was a marked decrease in clearance with increasing dose, and for repeated dose versus single dose. Tmax was greater, and Cmax and AUC∞ were lower in the fed state compared to the fasted state. Exposure was equivalent in males and females and for African Americans and Caucasians. In conclusion, SCO-101 appears to be a safe drug with a predictable PK profile. Its efficacy as add-on to standard anticancer drugs has yet to be defined.

Anti-Tremor Action of Subtype Selective Positive Allosteric Modulators of GABAA Receptors in a Rat Model of Essential Tremors.

Essential tremor (ET) is among the most prevalent neurological disorders and the most common cause of abnormal tremors. It is characterized by postural and action tremors ranging from 4 to 12 Hz. The treatments of choice for ET are propranolol and primidone, but their use is associated with adverse effects like hypotension, depression, and cognitive impairments. Benzodiazepines, which nonselectively enhances the effect of GABA at the GABAA α1/2/3/5 receptors, have been shown to be effective in treating ET. Their use, however, is limited due to sedation, ataxia, tolerance development and memory impairment. Sedation and ataxia are attributed to the activity at the α1 subunit while cognitive impairment is ascribed to the action on the α5 subunit of the GABAA receptors. It can be hypothesized that subtype selective GABAA receptor modulators only acting via the α2, and α3 subunits may have an improved side effect profile while retaining the beneficial effects. Here, we have evaluated the effect of subtype selective GABAA α2/3/5 receptor modulators on harmaline-induced tremors in rats. The tremors were automatically quantified in tremor boxes. We show that the GABAA α2/3 subtype selective modulator NS16085 significantly and dose-dependently inhibits harmaline-induced tremors in rats, indicating that potentiation of α2- and α3-containing GABAA receptors is sufficient to ameliorate harmaline-induced tremors. These results provide the first support for a therapeutic role of a subtype selective GABAA α2/3 modulator in the treatment of ET.

Characterization of AN317, a novel selective agonist of α6ß2-containing nicotinic acetylcholine receptors.

Neuronal nicotinic acetylcholine receptors (nAChRs) are crucial mediators of central presynaptic, postsynaptic, and extrasynaptic signaling, and they are implicated in a range of CNS disorders. The numerous nAChR subtypes are differentially expressed and mediate distinct functions throughout the CNS, and thus there is considerable interest in developing subtype-selective nAChR modulators, both for use as pharmacological tools and as putative therapeutics. α6ß2-containing (α6ß2*) nAChRs are highly expressed in and regulate the activity of midbrain dopaminergic neurons, which makes them attractive drug targets in several psychiatric and neurological diseases, including nicotine addiction and Parkinson's disease. This paper presents the preclinical characterization of AN317, a novel α6ß2* agonist exhibiting functional selectivity toward other nAChRs, including α4ß2, α3ß4 and α7 receptors. AN317 induced [3H]dopamine release from rat striatal synaptosomes and augmented dopaminergic neuron activity in substantia nigra pars compacta brain slices in Ca2+ imaging and electrophysiological assays. In line with this, AN317 alleviated the high-frequency tremors arising from reserpine-mediated dopamine depletion in rats. Finally, AN317 mediated significant protective effects on cultured rat mesencephalic neurons treated with the dopaminergic neurotoxin MPP+. AN317 displays good bioavailability and readily crosses the blood-brain barrier, which makes it a unique tool for both in vitro and in vivo studies of native α6ß2* receptors in the nigrostriatal system and other dopaminergic pathways. Altogether, these findings highlight the potential of selective α6ß2* nAChR activation as a treatment strategy for symptoms and possibly even deceleration of disease progression in neurodegenerative diseases such as Parkinson's disease.

The Delta-Subunit Selective GABA A Receptor Modulator, DS2, Improves Stroke Recovery via an Anti-inflammatory Mechanism.

Inflammatory processes are known to contribute to tissue damage in the central nervous system (CNS) across a broad range of neurological conditions, including stroke. Gamma amino butyric acid (GABA), the main inhibitory neurotransmitter in the CNS, has been implicated in modulating peripheral immune responses by acting on GABA A receptors on antigen-presenting cells and lymphocytes. Here, we investigated the effects and mechanism of action of the delta-selective compound, DS2, to improve stroke recovery and modulate inflammation. We report a decrease in nuclear factor (NF)-κB activation in innate immune cells over a concentration range in vitro. Following a photochemically induced motor cortex stroke, treatment with DS2 at 0.1 mg/kg from 1 h post-stroke significantly decreased circulating tumor necrosis factor (TNF)-α, interleukin (IL)-17, and IL-6 levels, reduced infarct size and improved motor function in mice. Free brain concentrations of DS2 were found to be lower than needed for robust modulation of central GABA A receptors and were not affected by the presence and absence of elacridar, an inhibitor of both P-glycoprotein and breast cancer resistance protein (BCRP). Finally, as DS2 appears to dampen peripheral immune activation and only shows limited brain exposure, we assessed the role of DS2 to promote functional recovery after stroke when administered from 3-days after the stroke. Treatment with DS2 from 3-days post-stroke improved motor function on the grid-walking, but not on the cylinder task. These data highlight the need to further develop subunit-selective compounds to better understand change in GABA receptor signaling pathways both centrally and peripherally. Importantly, we show that GABA compounds such as DS2 that only shows limited brain exposure can still afford significant protection and promote functional recovery most likely via modulation of peripheral immune cells and could be given as an adjunct treatment.

Characterization of a novel high-potency positive modulator of K(v)7 channels.

K(v)7 channel activators decrease neuronal excitability and might potentially treat neuronal hyperexcitability disorders like epilepsy and mania. Here we introduce NS15370 ((2-(3,5-difluorophenyl)-N-[6-[(4-fluorophenyl)methylamino]-2-morpholino-3-pyridyl]acetamide)hydrochloride, an in vitro high-potency chemical analogue of retigabine, without effects on GABA(A) receptors. NS15370 activates recombinant homo- and heteromeric K(v)7.2-K(v)7.5 channels in HEK293 cells at sub-micromolar concentrations (EC50~100 nM, as quantified by a fluorescence based Tl⁺-influx assay). In voltage clamp experiments NS15370 exhibits a complex, concentration-dependent mode-of-action: At low concentrations it accelerates voltage-dependent activation rates, slows deactivations, and increases steady-state current amplitudes. Quantified by the peak-tail current method, the V½ value of the steady-state activation curve is shifted towards hyperpolarized potentials at concentrations ~100 times lower than retigabine. However, in contrast to retigabine, NS15370 also introduces a distinct time-dependent current decrease, which eventually, at higher concentrations, causes suppression of the current at depolarized potentials, and an apparent "cross-over" of the voltage-activation curve. In brain slices, NS15370 hyperpolarizes and increases spike frequency adaptation of hippocampal CA1 neurons and the compound reduces the autonomous firing of dopaminergic neurons in the substantia-nigra pars compacta. NS15370 is effective in rodent models of hyperexcitability: (i) it yields full protection against mouse 6 Hz seizures and rat amygdala kindling discharges, two models of partial epilepsia; (ii) it reduces (+)-MK-801 hydrogen maleate (MK-801)-induced hyperactivity as well as chlordiazepoxide (CDP)+d-amphetamine (AMP)-induced hyperactivity, models sensitive to classic anti-psychotic and anti-manic treatments, respectively. Our findings with NS15370 consolidate neuronal K(v)7 channels as targets for anti-epileptic and psychiatric drug development.

Selective positive modulator of calcium-activated potassium channels exerts beneficial effects in a mouse model of spinocerebellar ataxia type 2.

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disorder caused by a polyglutamine expansion within the Ataxin-2 (Atxn2) protein. Purkinje cells (PC) of the cerebellum fire irregularly and eventually die in SCA2. We show here that the type 2 small conductance calcium-activated potassium channel (SK2) play a key role in control of normal PC activity. Using cerebellar slices from transgenic SCA2 mice we demonstrate that SK channel modulators restore regular pacemaker activity of SCA2 PCs. Furthermore, we also show that oral delivery of a more selective positive modulator of SK2/3 channels (NS13001) alleviates behavioral and neuropathological phenotypes of aging SCA2 transgenic mice. We conclude that SK2 channels constitute a therapeutic target for SCA2 treatment and that the developed selective SK2/3 modulator NS13001 holds promise as a potential therapeutic agent for treatment of SCA2 and possibly other cerebellar ataxias.