Radiosynthesis, Preclinical, and Clinical Positron Emission Tomography Studies of Carbon-11 Labeled Endogenous and Natural Exogenous Compounds

The presence of positron emission tomography (PET) centers at most major hospitals worldwide, along with the improvement of PET scanner sensitivity and the introduction of total body PET systems, has increased the interest in the PET tracer development using the short-lived radionuclides carbon-11. In the last few decades, methodological improvements and fully automated modules have allowed the development of carbon-11 tracers for clinical use. Radiolabeling natural compounds with carbon-11 by substituting one of the backbone carbons with the radionuclide has provided important information on the biochemistry of the authentic compounds and increased the understanding of their in vivo behavior in healthy and diseased states. The number of endogenous and natural compounds essential for human life is staggering, ranging from simple alcohols to vitamins and peptides. This review collates all the carbon-11 radiolabeled endogenous and natural exogenous compounds synthesised to date, including essential information on their radiochemistry methodologies and preclinical and clinical studies in healthy subjects

From Monoamine Oxidase Inhibition to Antiproliferative Activity: New Biological Perspectives for Polyamine Analogs

: Monoamine oxidases (MAOs) are well-known pharmacological targets in neurological and neurodegenerative diseases. However, recent studies have revealed a new role for MAOs in certain types of cancer such as glioblastoma and prostate cancer, in which they have been found overexpressed. This finding is opening new frontiers for MAO inhibitors as potential antiproliferative agents. In light of our previous studies demonstrating how a polyamine scaffold can act as MAO inhibitor, our aim was to search for novel analogs with greater inhibitory potency for human MAOs and possibly with antiproliferative activity. A small in-house library of polyamine analogs (2-7) was selected to investigate the effect of constrained linkers between the inner amine functions of a polyamine backbone on the inhibitory potency. Compounds 4 and 5, characterized by a dianiline (4) or dianilide (5) moiety, emerged as the most potent, reversible, and mainly competitive MAO inhibitors (Ki < 1 μM). Additionally, they exhibited a high antiproliferative activity in the LN-229 human glioblastoma cell line (GI50 < 1 μM). The scaffold of compound 5 could represent a potential starting point for future development of anticancer agents endowed with MAO inhibitory activity

Contribution of Rare and Low-Frequency Variants to Multiple Sclerosis Susceptibility in the Italian Continental Population

Genome-wide association studies identified over 200 risk loci for multiple sclerosis (MS) focusing on common variants, which account for about 50% of disease heritability. The goal of this study was to investigate whether low-frequency and rare functional variants, located in MS-established associated loci, may contribute to disease risk in a relatively homogeneous population, testing their cumulative effect (burden) with gene-wise tests. We sequenced 98 genes in 588 Italian patients with MS and 408 matched healthy controls (HCs). Variants were selected using different filtering criteria based on allelic frequency and in silico functional impacts. Genes showing a significant burden (n = 17) were sequenced in an independent cohort of 504 MS and 504 HC. The highest signal in both cohorts was observed for the disruptive variants (stop-gain, stop-loss, or splicing variants) located in EFCAB13, a gene coding for a protein of an unknown function (p &lt; 10(-4)). Among these variants, the minor allele of a stop-gain variant showed a significantly higher frequency in MS versus HC in both sequenced cohorts (p = 0.0093 and p = 0.025), confirmed by a meta-analysis on a third independent cohort of 1298 MS and 1430 HC (p = 0.001) assayed with an SNP array. Real-time PCR on 14 heterozygous individuals for this variant did not evidence the presence of the stop-gain allele, suggesting a transcript degradation by non-sense mediated decay, supported by the evidence that the carriers of the stop-gain variant had a lower expression of this gene (p = 0.0184). In conclusion, we identified a novel low-frequency functional variant associated with MS susceptibility, suggesting the possible role of rare/low-frequency variants in MS as reported for other complex diseases

Micrometre-long covalent organic fibres by photoinitiated chain-growth radical polymerization on an alkali-halide surface

On-surface polymerization is a promising technique to prepare organic functional nanomaterials that are challenging to synthesize in solution, but it is typically used on metal substrates, which play a catalytic role. Previous examples on insulating surfaces have involved intermediate self-assembled structures, which face high barriers to diffusion, or annealing to higher temperatures, which generally causes rapid dewetting and desorption of the monomers. Here we report the photoinitiated radical polymerization, initiated from a two-dimensional gas phase, of a dimaleimide monomer on an insulating KCl surface. Polymer fibres up to 1 μm long are formed through chain-like rather than step-like growth. Interactions between potassium cations and the dimaleimide’s oxygen atoms facilitate the propagation of the polymer fibres along a preferred axis of the substrate over long distances. Density functional theory calculations, non-contact atomic force microscopy imaging and manipulations at room temperature were used to explore the initiation and propagation processes, as well as the structure and stability of the resulting one-dimensional polymer fibres

Design and synthesis of (pro)electrophilic compounds for investigating the multifactorial nature of neurodegenerative diseases: focus on inflammation-driven events

Neuroinflammation constitutes a major player in the etiopathology of neurodegenerative diseases (NDDs), by orchestrating several neurotoxic pathways which in concert lead to neurodegeneration. A positive feedback loop occurs between inflammation, microglia activation and misfolding processes that, alongside excitotoxicity and oxidative events, represent crucial features of this intricate scenario. The multi-layered nature of NDDs requires a deepen investigation on how these vicious cycles work. This could further help in the search for effective treatments. Electrophiles are critically involved in the modulation of a variety of neuroprotective responses. Thus, we envisioned their peculiar ability to switch on/off biological activities as a powerful tool for investigating the neurotoxic scenario driven by inflammation in NDDs. In particular, in this thesis project, we wanted to dissect at a molecular level the functional role of (pro)electrophilic moieties of previously synthesized thioesters of variously substituted trans-cinnamic acids, to identify crucial features which could interfere with amyloid aggregation as well as modulate Nrf2 and/or NF-κB activation. To this aim, we first synthesized new compounds to identify bioactive cores which could specifically modulate the intended target. Then, we systematically modified their structure to reach additional pathogenic pathways which could in tandem contribute to the inflammatory process. In particular, following the investigation of the mechanistic underpinnings involving the catechol feature in amyloid binding through the synthesis of new dihydroxyl derivatives, we incorporated the identified antiaggregating nucleus into constrained frames which could contrast neuroinflammation also through the modulation of CB2Rs. In parallel, Nrf2 and/or NF-κB antinflammatory structural requirements were combined with the neuroprotective cores of pioglitazone, an antidiabetic drug endowed with MAO-B inhibitory properties, and memantine, which notably contrasts excitotoxicity. By acting as Swiss army knives, the new set of molecules emerge as promising tools to deepen our insights into the complex scenario regulating NDDs

Inhibition of β-Amyloid Aggregation in Alzheimer's Disease: The Key Role of (Pro)electrophilic Warheads

Catechols have been largely investigated as anti-aggregating agents toward beta-amyloid peptide. Herein, as a follow up of a previous series of hydroxycinnamic derivatives, we synthesized a small set of dihydroxy isomers for exploring the role of the reciprocal position of the two hydroxyl functions at a molecular level. Para- and ortho-derivatives effectively reduced amyloid fibrillization, while the meta-analogue was devoid of any activity in this respect. Electrochemical analyses showed that the antiaggregating potency correlates with the oxidation potential, hence indicating the proelectrophilic character as a prerequisite for activity. Interestingly, mass spectrometry studies and quantum mechanical calculations revealed different modes of action for active para- and ortho-derivatives, involving covalent or noncovalent interactions with beta-amyloid. The distinctive mode of action is also translated into a different cytotoxicity profile. This work clearly shows how apparently minimal structural modifications can completely change the compound behavior and generate alternative mechanisms of action of proelectrophilic chemical probes

Development of [¹⁸F]FAMTO: A novel fluorine-18 labelled positron emission tomography (PET) radiotracer for imaging CYP11B1 and CYP11B2 enzymes in adrenal glands

Introduction: Primary aldosteronism accounts for 6\u201315% of hypertension cases, the single biggest contributor to global morbidity and mortality. Whilst ~50% of these patients have unilateral aldosterone-producing adenomas, only a minority of these have curative surgery as the current diagnosis of unilateral disease is poor. Carbon-11 radiolabelled metomidate ([11C]MTO) is a positron emission tomography (PET) radiotracer able to selectively identify CYP11B1/2 expressing adrenocortical lesions of the adrenal gland. However, the use of [11C]MTO is limited to PET centres equipped with on-site cyclotrons due to its short half-life of 20.4 min. Radiolabelling a fluorometomidate derivative with fluorine-18 (radioactive half life 109.8 min) in the para-aromatic position ([18F]FAMTO) has the potential to overcome this disadvantage and allow it to be transported to non-cyclotron-based imaging centres. Methods: Two strategies for the one-step radio-synthesis of [18F]FAMTO were developed. [18F]FAMTO was obtained via radiofluorination via use of sulfonium salt (1) and boronic ester (2) precursors. [18F]FAMTO was evaluated in vitro by autoradiography of pig adrenal tissues and in vivo by determining its biodistribution in rodents. Rat plasma and urine were analysed to determine [18F]FAMTO metabolites. Results: [18F]FAMTO is obtained from sulfonium salt (1) and boronic ester (2) precursors in 7% and 32% non-isolated radiochemical yield (RCY), respectively. Formulated [18F]FAMTO was obtained with >99% radiochemical and enantiomeric purity with a synthesis time of 140 min from the trapping of [18F]fluoride ion on an anion-exchange resin (QMA cartridge). In vitro autoradiography of [18F]FAMTO demonstrated exquisite specific binding in CYP11B-rich pig adrenal glands. In vivo [18F]FAMTO rapidly accumulates in adrenal glands. Liver uptake was about 34% of that in the adrenals and all other organs were <12% of the adrenal uptake at 60 min post-injection. Metabolite analysis showed 13% unchanged [18F]FAMTO in blood at 10 min post-administration and rapid urinary excretion. In vitro assays in human blood showed a free fraction of 37.5%. Conclusions: [18F]FAMTO, a new 18F-labelled analogue of metomidate, was successfully synthesised. In vitro and in vivo characterization demonstrated high selectivity towards aldosterone-producing enzymes (CYP11B1 and CYP11B2), supporting the potential of this radiotracer for human investigation

A Nature-Inspired Nrf2 Activator Protects Retinal Explants from Oxidative Stress and Neurodegeneration

Oxidative stress (OS) plays a key role in retinal dysfunctions and acts as a major trigger of inflammatory and neurodegenerative processes in several retinal diseases. To prevent OS-induced retinal damage, approaches based on the use of natural compounds are actively investigated. Recently, structural features from curcumin and diallyl sulfide have been combined in a nature-inspired hybrid (NIH1), which has been described to activate transcription nuclear factor erythroid-2-related factor-2 (Nrf2), the master regulator of the antioxidant response, in different cell lines. We tested the antioxidant properties of NIH1 in mouse retinal explants. NIH1 increased Nrf2 nuclear translocation, Nrf2 expression, and both antioxidant enzyme expression and protein levels after 24 h or six days of incubation. Possible toxic effects of NIH1 were excluded since it did not alter the expression of apoptotic or gliotic markers. In OS-treated retinal explants, NIH1 strengthened the antioxidant response inducing a massive and persistent expression of antioxidant enzymes up to six days of incubation. These effects resulted in prevention of the accumulation of reactive oxygen species, of apoptotic cell death, and of gliotic reactivity. Together, these data indicate that a strategy based on NIH1 to counteract OS could be effective for the treatment of retinal diseases