Nucleoside Analogs and Nucleoside Precursors as Drugs in the Fight against SARS-CoV-2 and Other Coronaviruses

Coronaviruses (CoVs) are positive-sense RNA enveloped viruses, members of the family Coronaviridae, that cause infections in a broad range of mammals including humans. Several CoV species lead to mild upper respiratory infections typically associated with common colds. However, three human CoV (HCoV) species: Severe Acute Respiratory Syndrome (SARS)-CoV-1, Middle East Respiratory Syndrome (MERS)-CoV, and SARS-CoV-2, are responsible for severe respiratory diseases at the origin of two recent epidemics (SARS and MERS), and of the current COronaVIrus Disease 19 (COVID-19), respectively. The easily transmissible SARS-CoV-2, emerging at the end of 2019 in China, spread rapidly worldwide, leading the World Health Organization (WHO) to declare COVID-19 a pandemic. While the world waits for mass vaccination, there is an urgent need for effective drugs as short-term weapons to combat the SARS-CoV-2 infection. In this context, the drug repurposing approach is a strategy able to guarantee positive results rapidly. In this regard, it is well known that several nucleoside-mimicking analogs and nucleoside precursors may inhibit the growth of viruses providing effective therapies for several viral diseases, including HCoV infections. Therefore, this review will focus on synthetic nucleosides and nucleoside precursors active against different HCoV species, paying great attention to SARS-CoV-2. This work covers progress made in anti-CoV therapy with nucleoside derivatives and provides insight into their main mechanisms of action

Synthesis, self-assembly-behavior and biomolecular recognition properties of thyminyl dipeptides

This article describes the synthesis of Thy-(Phe-Phe) and Thy-(Tyr-Tyr), two thymine-bearing dipeptides based on L-phenylalanine and L-tyrosine, the circular dichroism (CD), UV and dynamic light scattering (DLS) characterization of their self-assemblies, and a CD study of their interaction with nucleic acids (using homoadenine DNA and RNA) and serum proteins (employing BSA as model protein). DLS studies, alongside with CD and UV investigations conducted on aqueous solutions of the derivatives under different concentration and temperature conditions, showed the formation of extensive molecular architectures with hydrodynamic mean diameters higher than 300 nm, with Thy-(Tyr-Tyr) forming at pH=7.5 particularly large and stable networks, involving multiple units, connected by H-bonding, aromatic and hydrophobic interactions. Finally, the findings of our study suggested that Thy-(Phe-Phe) and Thy-(Tyr-Tyr), very stable in human serum, were able to bind BSA protein altering its secondary structure

Synthesis and Biological Evaluation of a New Structural Simplified Analogue of cADPR, a Calcium-Mobilizing Secondary Messenger Firstly Isolated from Sea Urchin Eggs

Herein, we reported on the synthesis of cpIPP, which is a new structurally-reduced analogue of cyclic ADP-ribose (cADPR), a potent Ca2+-releasing secondary messenger that was firstly isolated from sea urchin eggs extracts. To obtain cpIPP the "northern" ribose of cADPR was replaced by a pentyl chain and the pyrophosphate moiety by a phophono-phosphate anhydride. The effect of the presence of the new phosphono-phosphate bridge on the intracellular Ca2+release induced by cpIPP was assessed in PC12 neuronal cells in comparison with the effect of the pyrophosphate bridge of the structurally related cyclic N1-butylinosine diphosphate analogue (cbIDP), which was previously synthesized in our laboratories, and with that of the linear precursor of cpIPP, which, unexpectedly, revealed to be the only one provided with Ca2+release properties

Design and Synthesis of a cADPR Mimic as a Novel Tool for Monitoring the Intracellular Ca2+ Concentration

Cyclic ADP-ribose (cADPR, 1, Figure 1) is a naturally occurring metabolite of NAD+ capable of mobilizing Ca2+ ions from intracellular stores. It was firstly isolated from sea urchin egg extract, but it was later established that it is also produced in many other mammalian cells, including pancreatic β-cells, T-lymphocytes, smooth and cardiac muscle cells, and cerebellar neurons, acting as a Ca2+-mobilizing agent. For this activity, cADPR has been classified as a second messenger that, by activating the ryanodine receptors of the sarcoplasmatic reticulum, is able to mobilize the calcium ions from intracellular stores. cADPR is involved in many physiological processes related to variation in the Ca2+ concentration, such as synaptic homeostasis in neurons as well as fertilization and cellular proliferation. This cyclic nucleotide, characterized by a very labile glycosidic bond at N1, is also rapidly hydrolysed in neutral aqueous solutions to inactive ADP-ribose. Matsuda and co-workers [1] were the first to synthesize new analogues of cADPR in which the adenine base is replaced by a hypoxanthine ring. This kind of modification produced the cyclic inosine diphosphate ribose (cIDPR), which proved to be stable in hydrolytic physiological conditions and showed significant Ca2+ mobilizing activity. Many modifications regarding the northern and southern ribose, as well as the purine base of cADPR, have been proposed so far. In our laboratories, we have synthesized several analogues of cIDPR [2–7]. In particular, the analogue with the northern ribose replaced by a pentyl chain (cpIDP) showed interesting Ca2+ mobilizing activity on the neuronal PC12 cell line [2]. Starting from these results, we report here the synthesis of the novel analogue 2, in which the “northern” ribose of cIDPR is replaced by a 2″,3″-dihydroxy pentyl chain. The effect of the presence of the diol moiety on the intracellular Ca2+ release will be assessed in due course

Nanogravimetric and Optical Characterizations of Thrombin Interaction with a Self-Assembled Thiolated Aptamer

Efficient biorecognition of thrombin (TB), a serine protease with crucial role in physiological and pathological blood coagulation, is a hot topic in medical diagnostics. In this work, we investigate the ability of synthetic thrombin aptamer (TBA), immobilized on a gold substrate, to bind thrombin by two different label-free techniques: the quartz crystal microbalance (QCM) and the spectroscopic ellipsometry (SE). By QCM characterization in the range from 20 to 110 nM, we demonstrate high specificity of TBA-TB interaction and determine affinity constant (Kd) of 17.7 ± 0.3 nM, system sensitivity of 0.42 ± 0.03 Hz nM-1, and limit of detection (LOD) of 240 ± 20 pM. The interaction between TBA and TB is also investigated by SE, an all-optical method, by quantifying the thickness increase of the TBA film assembled on gold substrate. AFM characterization of TBA and TB molecules deposited on flat silicon surface is also supplied

CD, UV, and In Silico Insights on the Effect of 1,3-Bis(1′-uracilyl)-2-propanone on Serum Albumin Structure

1,3-diaryl-2-propanone derivatives are synthetic compounds used as building blocks for the realization not only of antimicrobial drugs but also of new nanomaterials thanks to their ability to self-assemble in solution and interact with nucleopeptides. However, their ability to interact with proteins is a scarcely investigated theme considering the therapeutic importance that 1,3-diaryl-2-propanones could have in the modulation of protein-driven processes. Within this scope, we investigated the protein binding ability of 1,3-bis(1'-uracilyl)-2-propanone, which was previously synthesized in our laboratory utilizing a Dakin-West reaction and herein indicated as U2O, using bovine serum albumin (BSA) as the model protein. Through circular dichroism (CD) and UV spectroscopy, we demonstrated that the compound, but not the similar thymine derivative T2O, was able to alter the secondary structure of the serum albumin leading to significant consequences in terms of BSA structure with respect to the unbound protein (Δβ-turn + Δβ-sheet = +23.6%, Δα = -16.7%) as revealed in our CD binding studies. Moreover, molecular docking studies suggested that U2O is preferentially housed in the domain IIIB of the protein, and its affinity for the albumin is higher than that of the reference ligand HA 14-1 (HDOCK score (top 1-3 poses): -157.11 ± 1.38 (U2O); -129.80 ± 6.92 (HA 14-1); binding energy: -7.6 kcal/mol (U2O); -5.9 kcal/mol (HA 14-1)) and T2O (HDOCK score (top 1-3 poses): -149.93 ± 2.35; binding energy: -7.0 kcal/mol). Overall, the above findings suggest the ability of 1,3-bis(1'-uracilyl)-2-propanone to bind serum albumins and the observed reduction of the α-helix structure with the concomitant increase in the β-structure are consistent with a partial protein destabilization due to the interaction with U2O

Syntheses of cis-Zeatin and Its 9-(2-Deoxy-β-D-ribofuranosyl) Derivative : A Novel Synthetic Route to the Side Chain at C(6), and Cytokinin Activity

cis-Zeatin (3a) and its 9-(2-deoxy-β-D-ribofuranosyl) derivative (3c) have been synthesized from N-[(1,1-dimethylethoxy)carbonyl]glycine methyl ester (5) in 5 steps by adopting the "α-amino aldehyde/olefination" technology. The new cis-zeatin derivative (3c), its trans isomer (1c), and known trans-zeatin 9-β-D-riboside (1b) were tested for cytokinin activity in the stimulation of chlorophyll biosynthesis in etiolated cucumber cotyledons. The riboside 1b turned out to be the most active cytokinin among them, while the deoxyribosides 1c and 3c showed a marked decrease and a total loss, respectively, of cytokinin activity

Peptide Nucleic Acids as miRNA Target Protectors for the Treatment of Cystic Fibrosis

Cystic Fibrosis (CF) is one of the most common life shortening conditions in Caucasians. CF is caused by mutations in the CF Transmembrane Conductance Regulator (CFTR) gene which result in reduced or altered CFTR functionality. Several microRNAs (miRNAs) downregulate the expression of CFTR, thus causing or exacerbating the symptoms of CF. In this context, the design of anti-miRNA agents represents a valid functional tool, but its translation to the clinic might lead to unpredictable side effects because of the interference with the expression of other genes regulated by the same miRNAs. Herein, for the first time, is proposed the use of peptide nucleic acids (PNAs) to protect specific sequences in the 3'UTR (untranslated region) of the CFTR messenger RNA (mRNA) by action of miRNAs. Two PNAs (7 and 13 bases long) carrying the tetrapeptide Gly-SerP-SerP-Gly at their C-end, fully complementary to the 3'UTR sequence recognized by miR-509-3p, have been synthesized and the structural features of target PNA/RNA heteroduplexes have been investigated by spectroscopic and molecular dynamics studies. The co-transfection of the pLuc-CFTR-3´UTR vector with different combinations of PNAs, miR-509-3p, and controls in A549 cells demonstrated the ability of the longer PNA to rescue the luciferase activity by up to 70% of the control, thus supporting the use of suitable PNAs to counteract the reduction in the CFTR expression

PNA-based graphene oxide/porous silicon hybrid biosensor: towards a label-free optical assay for Brugada Syndrome

Peptide nucleic acid (PNA) is a synthetic DNA mimic that outperforms the properties of traditional oligonucleotides (ONs). On account of its outstanding features, such as remarkable binding affinity towards complementary DNA or RNA as well as high thermal and chemical stability, PNA has been proposed as a valuable alternative to the ON probe in gene-sensor design. In this study, a hybrid transducer made-up of graphene oxide (GO) nano-sheets covalently grafted onto a porous silicon (PSi) matrix has been investigated for the early detection of a genetic cardiac disorder, the Brugada syndrome (BS). A functionalization strategy towards the realization of a potential PNA-based device is described. A peptide nucleic acid (PNA), able to detect the SCN5A associated with the BS has been properly synthesized and used as a bioprobe for the realization of a proof-of-concept label-free optical PNA-biosensor. PSi reflectance and GO photoluminescence (PL) signals were simultaneously exploited for the monitoring of the device functionalization and response

Outstanding effects on antithrombin activity of modified TBA diastereomers containing an optically pure acyclic nucleotide analogue

Herein, we report optically pure modified acyclic nucleosides as ideal probes for aptamer modification. These new monomers offer unique advantages in exploring the role played in thrombin inhibition by a single residue modification at key positions of the TBA structure