Fluorescent chemosensors for the detection of biological amines

Chemical sensing has become an important field for the study of bioanalytes and provides key information pertaining to disease pathogenesis, and the physiological mechanisms underlying cellular processes. Discussed herein is a brief introduction to fluorescence methods for bioanalyte detection along with the design and synthesis of novel chemical sensors for important bioamines. First, we report a chemical sensor for kynurenine, a molecule known to contribute to tumor growth and the development of neurodegenerative diseases. Several coumarin dimers were developed for the two-point binding of kynurenine, but showed poor solubility in aqueous media. Later, a coumarin monomer was developed that showed high selectivity for kynurenine and a pronounced fluorescence response at low pH. Next, we produced pH-sensitive chemical sensors for neurotransmitters. The sensors are designed to produce a turn-on fluorescence response upon exocytosis. Secretion from the acidic vesicle into the neutral synaptic cleft deprotonates the sensor and makes it highly fluorescent. The sensor's fluorescence response is easily tuned by altering the pKa of the pH-sensitive group through a single coupling reaction. By slightly altering the coumarin core, we then achieved a three-input sensor for pH, glutamate, and zinc as the latter two molecules are copackaged in high concentrations in glutamatergic boutons. An 11-fold fluorescence enhancement of the sensor-glutamate-zinc bound complex was observed at the pH values germane to exocytosis

Development of a Fluorescent Chemosensor for the Detection of Kynurenine

Kynurenine, a metabolite of tryptophan, is known to contribute to cancer progression when overproduced. A method for facile fluorescent sensing of kynurenine using sensor <b>1</b> has been developed. When bound at low pH, sensor <b>1</b> undergoes a very large bathochromic shift because kynurenine extends the conjugation of the fluorophore. This unusual mechanism of activation provides a 390-fold fluorescence enhancement that is very specific to kynurenine and a wavelength of fluorescence that extends into the red

Three-Input Logic Gates with Potential Applications for Neuronal Imaging

Convenient methods for the direct visualization of neurotransmitter trafficking would bolster investigations into the development of neurodegenerative diseases. Here, tunable fluorescent molecular logic gates with applications to neuronal imaging have been developed. The three-input AND molecular logic gates are based on the coumarin-3-aldehyde scaffold and designed to give a turn-on fluorescence response upon the corelease of glutamate and zinc from secretory vesicles via exocytosis. Spectroscopic studies reveal an 11-fold fluorescence enhancement under conditions mimicking exocytosis. Methylation of the scaffold was used to optimize the spectral profile of the sensors toward desired excitation wavelengths. A binding study that elucidates the sensor-analyte interactions is presented. These sensors serve as a proof-of-concept toward the direct imaging of neurotransmitters released upon exocytosis using fluorescent molecular logic gates

BLZ945 derivatives for PET imaging of colony stimulating factor-1 receptors in the brain

Background: The kinase colony stimulating factor-1 receptor (CSF-1R) has recently been identified as a novel therapeutic target for decreasing tumor associated macrophages and microglia load in cancer treatment. In glioblastoma multiforme (GBM), a high-grade cancer in the brain with extremely poor prognosis, macrophages and microglia can make up to 50% of the total tumor mass. Currently, no non-invasive methods are available for measuring CSF-1R expression in vivo. The aim of this work is to develop a PET tracer for imaging of CSF-1R receptor expression in the brain for future GBM patient selection and treatment monitoring. Methods: BLZ945 and a derivative that potentially allows for fluorine-18 labeling were synthesized and evaluated in vitro to determine their affinity towards CSF-1R. BLZ945 was radiolabeled with carbon-11 by N-methylation of des-methyl-BLZ945 using [11C]CH3I. Following administration to healthy mice, metabolic stability of [11C]BLZ945 in blood and brain and activity distribution were determined ex vivo. PET scanning was performed at baseline, efflux transporter blocking, and CSF-1R blocking conditions. Finally, [11C]BLZ945 binding was evaluated in vitro by autoradiography on mouse brain sections. Results: BLZ945 was the most potent compound in our series with an IC50 value of 6.9 ± 1.4 nM. BLZ945 was radiolabeled with carbon-11 in 20.7 ± 1.1% decay corrected radiochemical yield in a 60 min synthesis procedure with a radiochemical purity of >95% and a molar activity of 153 ± 34 GBq·μmol−1. Ex vivo biodistribution showed moderate brain uptake and slow wash-out, in addition to slow blood clearance. The stability of BLZ945 in blood plasma and brain was >99% at 60 min post injection. PET scanning demonstrated BLZ945 to be a substrate for efflux transporters. High brain uptake was observed, which was shown to be mostly non-specific. In accordance, in vitro autoradiography on brain sections revealed high non-specific binding. Conclusions: [11C]BLZ945, a CSF-1R PET tracer, was synthesized in high yield and purity. The tracer has high potency for the target, however, future studies are warranted to address non-specific binding and tracer efflux before BLZ945 or derivatives could be translated into humans for brain imaging