Assessment of the biodistribution of an [ 18 F]FDG‐loaded perfluorocarbon double emulsion using dynamic micro‐PET in rats

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97497/1/cmmi1532.pd

Increased capillary tortuosity and pericapillary basement membrane thinning in skeletal muscle of mice undergoing running wheel training.

To work out which microvascular remodeling processes occur in murine skeletal muscle during endurance exercise, we subjected C57BL/6-mice to voluntary running wheel training for 1 week (1wk-t) or 6 weeks (6wks-t). By means of morphometry, the capillarity as well as the compartmental and sub-compartmental structure of the capillaries were quantitatively described at the light microscopy and at the electron microscopy level, respectively, in the plantaris muscle (PLNT) of the exercising mice in comparison to untrained littermates. In the early phase of the training (1wk-t), angiogenesis (32%-higher capillary-fiber (CF)-ratio; P0.05), further reduction of CBMT (16.5%; P<0.05) and additional shortening of the intraluminal protrusion length (23%; P<0.05), all compared to controls. Other structural indicators such as capillary profile sizes, profile area densities, perimeters of the capillary compartments and concentrations of endothelium-pericyte peg-socket junctions were not significantly different between the mouse groups. Besides angiogenesis, increase of capillary tortuosity and reduction of CBMT represent the most striking microvascular remodeling processes in skeletal muscle of mice that undergo running wheel training

Ultrasound-Induced Mechanical Compaction in Acoustically Responsive Scaffolds Promotes Spatiotemporally Modulated Signaling in Triple Negative Breast Cancer

Cancer cells continually sense and respond to mechanical cues from the extracellular matrix (ECM). Interaction with the ECM can alter intracellular signaling cascades, leading to changes in processes that promote cancer cell growth, migration, and survival. The present study used a recently developed composite hydrogel composed of a fibrin matrix and phase-shift emulsion, termed an acoustically responsive scaffold (ARS), to investigate effects of local mechanical properties on breast cancer cell signaling. Treatment of ARSs with focused ultrasound drives acoustic droplet vaporization (ADV) in a spatiotemporally controlled manner, inducing local compaction and stiffening of the fibrin matrix adjacent to the matrix–bubble interface. Combining ARSs and live single cell imaging of triple-negative breast cancer cells, it is discovered that both basal and growth-factor stimulated activities of protein kinase B (also known as Akt) and extracellular signal-regulated kinase (ERK), two major kinases driving cancer progression, negatively correlate with increasing distance from the ADV-induced bubble both in vitro and in a mouse model. Together, these data demonstrate that local changes in ECM compaction regulate Akt and ERK signaling in breast cancer and support further applications of the novel ARS technology to analyze spatial and temporal effects of ECM mechanics on cell signaling and cancer biology.The study uses a smart hydrogel system with focused ultrasound for precise temporal and spatial control of tissue compaction. Incorporating breast cancer cells into this hydrogel system reveals that ultrasound-triggered increases in compaction of extracellular matrix promotes signaling through pathways known to drive proliferation and aggressive features in breast cancer and other malignancies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172808/1/adhm202101672_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172808/2/adhm202101672.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172808/3/adhm202101672-sup-0001-SuppMat.pd

4‑[¹⁸F]Fluoro‑<i>m</i>‑hydroxyphenethylguanidine: A Radiopharmaceutical for Quantifying Regional Cardiac Sympathetic Nerve Density with Positron Emission Tomography

4-[¹⁸F]­Fluoro-<i>m</i>-hydroxyphenethylguanidine ([¹⁸F]­4F-MHPG, [¹⁸F]<b>1</b>) is a new cardiac sympathetic nerve radiotracer with kinetic properties favorable for quantifying regional nerve density with PET and tracer kinetic analysis. An automated synthesis of [¹⁸F]<b>1</b> was developed in which the intermediate 4-[¹⁸F]­fluoro-<i>m</i>-tyramine ([¹⁸F]<b>16</b>) was prepared using a diaryliodonium salt precursor for nucleophilic aromatic [¹⁸F]­fluorination. In PET imaging studies in rhesus macaque monkeys, [¹⁸F]<b>1</b> demonstrated high quality cardiac images with low uptake in lungs and the liver. Compartmental modeling of [¹⁸F]<b>1</b> kinetics provided net uptake rate constants <i>K</i>_i (mL/min/g wet), and Patlak graphical analysis of [¹⁸F]<b>1</b> kinetics provided Patlak slopes <i>K</i>_p (mL/min/g). In pharmacological blocking studies with the norepinephrine transporter inhibitor desipramine (DMI), each of these quantitative measures declined in a dose-dependent manner with increasing DMI doses. These initial results strongly suggest that [¹⁸F]<b>1</b> can provide quantitative measures of regional cardiac sympathetic nerve density in human hearts using PET

Synthesis and Evaluation of [¹⁸F]RAGER: A First Generation Small-Molecule PET Radioligand Targeting the Receptor for Advanced Glycation Endproducts

The receptor for advanced glycation endproducts (RAGE) is a 35 kDa transmembrane receptor that belongs to the immunoglobulin superfamily of cell surface molecules. Its role in Alzheimer’s disease (AD) is complex, but it is thought to mediate influx of circulating amyloid-β into the brain as well as amplify Aβ-induced pathogenic responses. RAGE is therefore of considerable interest as both a diagnostic and a therapeutic target in AD. Herein we report the synthesis and preliminary preclinical evaluation of [¹⁸F]­RAGER, the first small molecule PET radiotracer for RAGE (<i>K</i>_d = 15 nM). Docking studies proposed a likely binding interaction between RAGE and RAGER, [¹⁸F]­RAGER autoradiography showed colocalization with RAGE identified by immunohistochemistry in AD brain samples, and [¹⁸F]­RAGER microPET confirmed CNS penetration and increased uptake in areas of the brain known to express RAGE. This first generation radiotracer represents initial proof-of-concept and a promising first step toward quantifying CNS RAGE activity using PET. However, there were high levels of nonspecific [¹⁸F]­RAGER binding <i>in vitro</i>, likely due to its high log <i>P</i> (experimental log <i>P</i> = 3.5), and rapid metabolism of [¹⁸F]­RAGER in rat liver microsome studies. Therefore, development of second generation ligands with improved imaging properties would be advantageous prior to anticipated translation into clinical PET imaging studies

Investigation of Proposed Activity of Clarithromycin at GABA_A Receptors Using [¹¹C]Flumazenil PET

Clarithromycin is a potential treatment for hypersomnia acting through proposed negative allosteric modulation of GABA_A receptors. We were interested whether this therapeutic benefit might extend to Parkinson’s disease (PD) patients because GABAergic neurotransmission is implicated in postural control. Prior to initiating clinical studies in PD patients, we wished to better understand clarithromycin’s mechanism of action. In this work we investigated whether the proposed activity of clarithromycin at the GABA_A receptor is associated with the benzodiazepine binding site using <i>in vivo</i> [¹¹C]­flumazenil positron emission tomography (PET) in primates and <i>ex vivo</i> [³H]­flumazenil autoradiography in rat brain. While the studies demonstrate that clarithromycin does not change the <i>K</i>_d of FMZ, nor does it competitively displace FMZ, there is preliminary evidence from the primate PET imaging studies that clarithromycin delays dissociation and washout of flumazenil from the primate brain in a dose-dependent fashion. These findings would be consistent with the proposed GABA_A allosteric modulator function of clarithromycin. While the results are only preliminary, further investigation of the interaction of clarithromycin with GABA receptors and/or GABAergic medications is warranted, and therapeutic applications of clarithromycin alone or in combination with flumazenil, to treat hyper-GABAergic status in PD at minimally effective doses, should also be pursued

Synthesis of Diverse ¹¹C‑Labeled PET Radiotracers via Direct Incorporation of [¹¹C]CO₂

Three new positron emission tomography (PET) radiotracers of interest to our functional neuroimaging and translational oncology programs have been prepared through new developments in [¹¹C]­CO₂ fixation chemistry. [¹¹C]­QZ (glutaminyl cyclase) was prepared via a tandem trapping of [¹¹C]­CO₂/intramolecular cyclization; [¹¹C]­tideglusib (glycogen synthase kinase-3) was synthesized through a tandem trapping of [¹¹C]­CO₂ followed by an intermolecular cycloaddition between a [¹¹C]­isocyanate and an isothiocyanate to form the 1,2,4-thiadiazolidine-3,5-dione core; [¹¹C]­ibrutinib (Bruton’s tyrosine kinase) was synthesized through a HATU peptide coupling of an amino precursor with [¹¹C]­acrylic acid (generated from [¹¹C]­CO₂ fixation with vinylmagnesium bromide). All radiochemical syntheses are fully automated on commercial radiochemical synthesis modules and provide radiotracers in 1–5% radiochemical yield (noncorrected, based upon [¹¹C]­CO₂). All three radiotracers have advanced to rodent imaging studies and preliminary PET imaging results are also reported