Anti-edema and antioxidant combination therapy for ischemic stroke via glyburide-loaded betulinic acid nanoparticles.

Stroke is a deadly disease without effective pharmacotherapies, which is due to two major reasons. First, most therapeutics cannot efficiently penetrate the brain. Second, single agent pharmacotherapy may be insufficient and effective treatment of stroke requires targeting multiple complementary targets. Here, we set to develop single component, multifunctional nanoparticles (NPs) for targeted delivery of glyburide to the brain for stroke treatment. Methods: To characterize the brain penetrability, we radiolabeled glyburide, intravenously administered it to stroke- bearing mice, and determined its accumulation in the brain using positron emission tomography-computed tomography (PET/CT). To identify functional nanomaterials to improve drug delivery to the brain, we developed a chemical extraction approach and tested it for isolation of nanomaterials from E. ulmoides, a medicinal herb. To assess the therapeutic benefits, we synthesized glyburide-loaded NPs and evaluated them in stroke- bearing mice. Results: We found that glyburide has a limited ability to penetrate the ischemic brain. We identified betulinic acid (BA) capable of forming NPs, which, after intravenous administration, efficiently penetrate the brain and significantly reduce ischemia-induced infarction as an antioxidant agent. We demonstrated that BA NPs enhance delivery of glyburide, leading to therapeutic benefits significantly greater than those achieved by either glyburide or BA NPs. Conclusion: This study suggests a new direction to identify functional nanomaterials and a simple approach to achieving anti-edema and antioxidant combination therapy. The resulting glyburide- loaded BA NPs may be translated into clinical applications to improve clinical management of stroke.

Synthesis and in Vivo Evaluation of a Novel PET Radiotracer for Imaging of Synaptic Vesicle Glycoprotein 2A (SV2A) in Nonhuman Primates.

Structural disruption and alterations of synapses are associated with many brain disorders including Alzheimer's disease, epilepsy, depression, and schizophrenia. We have previously developed the PET radiotracer 11C-UCB-J for imaging and quantification of synaptic vesicle glycoprotein 2A (SV2A) and synaptic density in nonhuman primates and humans. Here we report the synthesis of a novel radiotracer 18F-SDM-8 and its in vivo evaluation in rhesus monkeys. The in vitro binding assay of SDM-8 showed high SV2A binding affinity ( Ki = 0.58 nM). 18F-SDM-8 was prepared in high molar activity (241.7 MBq/nmol) and radiochemical purity (>98%). In the brain, 18F-SDM-8 displayed very high uptake with peak standardized uptake value (SVU) greater than 8 and fast and reversible kinetics. A displacement study with levetiracetam and blocking studies with UCB-J and levetiracetam demonstrated its binding reversibility and specificity toward SV2A. Regional binding potential values were calculated and ranged from 0.8 in the brainstem to 4.5 in the cingulate cortex. By comparing to 11C-UCB-J, 18F-SDM-8 displayed the same attractive imaging properties: very high brain uptake, appropriate tissue kinetics, and high levels of specific binding. Given the longer half-life of F-18 and the feasibility for central production and multisite distribution, 18F-SDM-8 holds promise as an excellent radiotracer for SV2A and as a biomarker for synaptic density measurement in neurodegenerative diseases and psychiatric disorders.

Comparative evaluation of two glycine transporter 1 radiotracers [11C]GSK931145 and [18F]MK-6577 in baboons.

Glycine transporter type-1 (GlyT1) has been proposed as a target for drug development for schizophrenia. PET imaging with a GlyT1 specific radiotracer will allow for the measurement of target occupancy of GlyT1 inhibitors, and for in vivo investigation of GlyT1 alterations in schizophrenia. We conducted a comparative evaluation of two GlyT1 radiotracers, [(11) C]GSK931145, and [(18) F]MK-6577, in baboons. Two baboons were imaged with [(11) C]GSK931145 and [(18) F]MK-6577. Blocking studies with GSK931145 (0.3 or 0.2 mg/kg) were conducted to determine the level of tracer specific binding. [(11) C]GSK931145 and [(18) F]MK-6577 were synthesized in good yield and high specific activity. Moderately fast metabolism was observed for both tracers, with ∼ 30% of parent at 30 min post-injection. In the brain, both radiotracers showed good uptake and distribution profiles consistent with regional GlyT1 densities. [(18) F]MK-6577 displayed higher uptake and faster kinetics than [(11) C]GSK931145. Time activity curves were well described by the two-tissue compartment model. Regional volume of distribution (VT ) values were higher for [(18) F]MK-6577 than [(11) C]GSK931145. Pretreatment with GSK931145 reduced tracer uptake to a homogeneous level throughout the brain, indicating in vivo binding specificity and lack of a reference region for both radiotracers. Linear regression analysis of VT estimates between tracers indicated higher specific binding for [(18) F]MK-6577 than [(11) C]GSK931145, consistent with higher regional binding potential (BPND ) values of [(18) F]MK-6577 calculated using VT from the baseline scans and non-displaceable distribution volume (VND ) derived from blocking studies. [(18) F]MK-6577 appears to be a superior radiotracer with higher brain uptake, faster kinetics, and higher specific binding signals than [(11) C]GSK931145.