Synthesis of 3'- and 5'-nitrooxy pyrimidine nucleoside nitrate esters: "nitric oxide donor" agents for evaluation as anticancer and antiviral agents

Chemical Strategies Toward Prodrugs and Fluorescent Probes for Gasotransmitters

Three gaseous molecules are widely accepted as important gasotransmitters in mammalian cells, namely NO, CO and H2S. Due to the pharmacological effects observed in preclinical studies, these three gasotransmitters represent promising drug candidates for clinical translation. Fluorescent probes of the gasotransmitters are also in high demand; however, the mechanisms of actions or the roles played by gasotransmitters under both physiological and pathological conditions remain to be answered. In order to bring these challenges to the attention of both chemists and biologists working in this field, we herein summarize the chemical strategies used for the design of both probes and prodrugs of these three gasotransmitters.

Syntheses and high selective cytotoxicity of dehydroabietylamine C-ring nitration derivatives

To find more effective anticancer agents, a series of novel dehydroabietylamine (DA) derivatives were synthesized, focusing on C-ring nitro modifications and C-18 imide introduction. Their cytotoxic activities against human tumor cell line HeLa (cervix), MCF-7 (breast), A549 (lung), HepG2 (liver), and nonmalignant cell line HUVEC (umbilical vein) in vitro were screened. The C-18 imide heterocyclic compounds 1, 2, and C-ring 14-nitro substituted 14 exhibited moderate to good cytotoxic activities and significant selectivity towards malignant cell lines. More importantly, they were significantly less cytotoxic to nonmalignant cells (HUVEC) than the parent compound and positive control doxorubicin hydrochloride (DOX). Meantime the mechanism of cytotoxicity of DA derivatives was studied. Annexin V-FITC/PI double-staining analysis suggested that cytotoxicity of compounds 2 and 14 was associated with early apoptosis induction. The interaction between compounds and DNA (herring sperm DNA) was studied using absorption spectral analysis and ethidium bromide (EB) fluorescence displacement experiments, the results exhibited that the binding of the compound to DNA was in the intercalative mode. The structure-activity relationship discussion implied that introduction of the nitro-group, especially the 14-nitro group, can significantly improve the cytotoxicity of dehydroabietylimide compounds. The relatively high cytotoxicity and significant high selectivity of compounds 2 and 14 indicated that they were particularly noteworthy. NO released amounts indicated that the amounts of NO released by the compounds bearing nitro-group were quite well associated positive correlation with their cytotoxic activity, which provide a new strategy for structure design of DA anticancer agents in the future.

NO in Viral Infections: Role and Development of Antiviral Therapies

Nitric oxide is a ubiquitous signaling radical that influences critical body functions. Its importance in the cardiovascular system and the innate immune response to bacterial and viral infections has been extensively investigated. The overproduction of NO is an early component of viral infections, including those affecting the respiratory tract. The production of high levels of NO is due to the overexpression of NO biosynthesis by inducible NO synthase (iNOS), which is involved in viral clearance. The development of NO-based antiviral therapies, particularly gaseous NO inhalation and NO-donors, has proven to be an excellent antiviral therapeutic strategy. The aim of this review is to systematically examine the multiple research studies that have been carried out to elucidate the role of NO in viral infections and to comprehensively describe the NO-based antiviral strategies that have been developed thus far. Particular attention has been paid to the potential mechanisms of NO and its clinical use in the prevention and therapy of COVID-19.

Nitric Oxide Releasing Delivery Platforms: Design, Detection, Biomedical Applications, and Future Possibilities

Gasotransmitters belong to the subfamily of endogenous gaseous signaling molecules, which find a wide range of biomedical applications. Among the various gasotransmitters, nitric oxide (NO) has an enormous effect on the cardiovascular system. Apart from this, NO showed a pivotal role in neurological, respiratory, and immunological systems. Moreover, the paradoxical concentration-dependent activities make this gaseous signaling molecule more interesting. The gaseous NO has negligible stability in physiological conditions (37 °C, pH 7.4), which restricts their potential therapeutic applications. To overcome this issue, various NO delivering carriers were reported so far. Unfortunately, most of these NO donors have low stability, short half-life, or low NO payload. Herein, we review the synthesis of NO delivering motifs, development of macromolecular NO donors, their advantages/disadvantages, and biological applications. Various NO detection analytical techniques are discussed briefly, and finally, a viewpoint about the design of polymeric NO donors with improved physicochemical characteristics is predicted.

Nitric oxide and viral infection: Recent developments in antiviral therapies and platforms

Nitric oxide (NO) is a gasotransmitter of great significance to developing the innate immune response to many bacterial and viral infections, while also modulating vascular physiology. The generation of NO from the upregulation of endogenous nitric oxide synthases serves as an efficacious method for inhibiting viral replication in host defense and warrants investigation for the development of antiviral therapeutics. With increased incidence of global pandemics concerning several respiratory-based viral infections, it is necessary to develop broad therapeutic platforms for inhibiting viral replication and enabling more efficient host clearance, as well as to fabricate new materials for deterring viral transmission from medical devices. Recent developments in creating stabilized NO donor compounds and their incorporation into macromolecular scaffolds and polymeric substrates has created a new paradigm for developing NO-based therapeutics for long-term NO release in applications for bactericidal and blood-contacting surfaces. Despite this abundance of research, there has been little consideration of NO-releasing scaffolds and substrates for reducing passive transmission of viral infections or for treating several respiratory viral infections. The aim of this review is to highlight the recent advances in developing gaseous NO, NO prodrugs, and NO donor compounds for antiviral therapies; discuss the limitations of NO as an antiviral agent; and outline future prospects for guiding materials design of a next generation of NO-releasing antiviral platforms.

Recent Advances in Berberine Inspired Anticancer Approaches: From Drug Combination to Novel Formulation Technology and Derivatization

Berberine is multifunctional natural product with potential to treat diverse pathological conditions. Its broad-spectrum anticancer effect through direct effect on cancer cell growth and metastasis have been established both in vitro and in vivo. The cellular targets that account to the anticancer effect of berberine are incredibly large and range from kinases (protein kinase B (Akt), mitogen activated protein kinases (MAPKs), cell cycle checkpoint kinases, etc.) and transcription factors to genes and protein regulators of cell survival, motility and death. The direct effect of berberine in cancer cells is however relatively weak and occur at moderate concentration range (10–100 µM) in most cancer cells. The poor pharmacokinetics profile resulting from poor absorption, efflux by permeability-glycoprotein (P-gc) and extensive metabolism in intestinal and hepatic cells are other dimensions of berberine’s limitation as anticancer agent. This communication addresses the research efforts during the last two decades that were devoted to enhancing the anticancer potential of berberine. Strategies highlighted include using berberine in combination with other chemotherapeutic agents either to reduce toxic side effects or enhance their anticancer effects; the various novel formulation approaches which by order of magnitude improved the pharmacokinetics of berberine; and semisynthetic approaches that enhanced potency by up to 100-fold.

Nitro-Group-Containing Drugs

The nitro group is considered to be a versatile and unique functional group in medicinal chemistry. Despite a long history of use in therapeutics, the nitro group has toxicity issues and is often categorized as a structural alert or a toxicophore, and evidence related to drugs containing nitro groups is rather contradictory. In general, drugs containing nitro groups have been extensively associated with mutagenicity and genotoxicity. In this context, efforts toward the structure-mutagenicity or structure-genotoxicity relationships have been undertaken. The current Perspective covers various aspects of agents that contain nitro groups, their bioreductive activation mechanisms, their toxicities, and approaches to combat their toxicity issues. In addition, recent advances in the field of anticancer, antitubercular and antiparasitic agents containing nitro groups, along with a patent survey on hypoxia-activated prodrugs containing nitro groups, are also covered.

Incorporation of nitric oxide donor into 1,3-dioxyxanthones leads to synergistic anticancer activity

Fifty 1,3-dioxyxanthone nitrates (4a ∼ i-n, n = 1-6) were designed and synthesized based on molecular similarity strategy. Incorporation of nitrate into 1,3-dioxyxanthones with electron-donating groups at 6-8 position brought about synergistic anticancer effect. Among them, compound 4g-4 was confirmed the most active agent against HepG-2 cells growth with an IC₅₀ of 0.33 ± 0.06 μM. It dose-dependently increased intramolecular NO levels. This activity was attenuated by either NO scavenger PTIO or mitochondrial aldehyde dehydrogenase (mtADH) inhibitor PCDA. Apoptosis analysis indicated different contributions of early/late apoptosis and necrosis to cell death for different dose of 4g-4. 4g-4 arrested more cells on S phase. Results from Western Blot implied that 4g-4 regulated p53/MDM2 to promote cancer cell apoptosis. All the evidences support that 4g-4 is a promising anti-cancer agent.

Nitric Oxide Donor-Based Cancer Therapy: Advances and Prospects

The increasing understanding of the role of nitric oxide (NO) in cancer biology has generated significant progress in the use of NO donor-based therapy to fight cancer. These advances strongly suggest the potential adoption of NO donor-based therapy in clinical practice, and this has been supported by several clinical studies in the past decade. In this review, we first highlight several types of important NO donors, including recently developed NO donors bearing a dinitroazetidine skeleton, represented by RRx-001, with potential utility in cancer therapy. Special emphasis is then given to the combination of NO donor(s) with other therapies to achieve synergy and to the hybridization of NO donor(s) with an anticancer drug/agent/fragment to enhance the activity or specificity or to reduce toxicity. In addition, we briefly describe inducible NO synthase gene therapy and nanotechnology, which have recently entered the field of NO donor therapy.

TET1-Mediated Oxidation of 5-Formylcytosine (5fC) to 5-Carboxycytosine (5caC) in RNA

It was recently revealed that 5-methylcytosine (5mC) in mRNA, similar to its behavior in DNA, can be oxidized to produce 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC), implying the potential regulatory roles of this post-transcriptional RNA modification. In this study, we demonstrate the in vitro oxidation of 5fC to 5-carboxycytidine (5caC) by the catalytic domain of mammalian ten-eleven translocation enzyme (TET1) in different RNA contexts. We observed that this oxidation process has very low sequence dependence and can take place in single-stranded, double-stranded, or hairpin forms of RNA sequences, although the overall conversion yields are low.

Vibrational spectra (experimental and theoretical), molecular structure, natural bond orbital, HOMO-LUMO energy, Mulliken charge and thermodynamic analysis of N'-hydroxy-pyrimidine-2-carboximidamide by DFT approach

The FT-IR, FT-Raman, (1)H, (13)C NMR and UV-Visible spectral measurements of N'-hydroxy-pyrimidine-2-carboximidamide (HPCI) and complete analysis of the observed spectra have been proposed. DFT calculation has been performed and the structural parameters of the compound was determined from the optimized geometry with 6-311+G(d,p) basis set and giving energies, harmonic vibrational frequencies and force constants. The results of the optimized molecular structure are presented and compared with the experimental. The geometric parameters, harmonic vibrational frequencies and chemical shifts were compared with the experimental data of the molecule. The title compound, C5H6N4O, is approximately planar, with an angle of 11.04 (15)°. The crystal structure is also stabilized by intermolecular N-H⋯O, N-H⋯N, O-H⋯N, C-H⋯O hydrogen bond and offset π-π stacking interactions. The influences of hydroxy and carboximidamide groups on the skeletal modes and proton chemical shifts have been investigated. Moreover, we have not only simulated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) but also determined the transition state and band gap. The kinetic, thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intermolecular electronic interactions and their stabilization energy. The thermodynamic properties like entropies and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized structure.

Effect of protonation and hydrogen bonding on 2, 4, 6-substituted pyrimidine and its salt complex-experimental and theoretical evidence

Quantum molecular simulations of chemical systems can provide detailed information that is often inaccessible to direct experimental measurement. Pyrimidine is an interesting π-electron heterocyclic aromatic system which acts as the building block of many nucleic acid bases. The hydrogen bonds associated with the 2, 4, and 6-substituted pyrimidine and its hydrogen sulfate anion are considered for this current work. The experimental and computational evidence for the strength of these intra and intermolecular hydrogen are determined using vibrational spectra and quantum chemical calculations. Thus the effect of hydrogen bonding on the title compound is studied using its geometrical parameters, interaction energies, and vibrational spectra. Aromaticity and charge transfer studies have been performed to ascertain the aromatic behavior of the molecule. The PES scan studies have been done by varying the bond length to ascertain the protonation process of the compound. The IR spectral red shift (∼100 cm⁻¹), blue shift (∼97 cm⁻¹) and broadening of the polar stretching peaks shows the inter and intramolecular hydrogen bonding strength. Bond length alternation of proton donors along with the enormous interaction energies (∼0.5-150 kJ mol⁻¹) between the lone pair and proton donors provides clear evidence for this hydrogen bonding. The charge transfer due to the methyl substitutions which enhances the possibility of hydrogen bonding has been discussed. The main scope of this work is to study the protonation and hydrogen bonding associated with charge transfer which has great effect on the 2-amino-4, 6-dimethyl pyrimidinium hydrogen sulfate (ADHS) molecule.

Licofelone-nitric oxide donors as anticancer agents

Five licofelone ([2,2-dimethyl-6-(4-chlorophenyl)-7-phenyl-2,3-dihydro-1H-pyrrolizin-5-yl]acetic acid) nitric oxide donor conjugates were developed by a parallel synthesis approach. The biological screening revealed that compounds with a propyl (6b), butyl (6c), or octyl (6d) chain between licofelone and the nitric oxide donor exhibited high antiproliferative potency at MCF-7 and MDA-MB-231 breast cancer as well as at HT-29 colon cancer cells. Moreover, 6b-d possessed at least 2-fold higher cytotoxicity at MDA-MB-231 cells than the parent compound licofelone although they showed less inhibitory activity at COX-1 and COX-2. A correlation between COX inhibition and growth inhibitory properties is not visible. However, the high levels of nitric oxide production of the compounds may result in their high cytotoxic activity.

Synthesis, characterization, antiamoebic activity and cytotoxicity of new pyrazolo[3, 4-d]pyrimidine-6-one derivatives

A new series of pyrazolo[3,4-d]pyrimidine-6-one derivatives (2a-2j) were prepared by using the Biginelli multicomponent cyclocondensation of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (1a), different aromatic aldehydes, and urea with a catalytic amount of HCl at reflux temperature. These compounds were characterized by IR, (1)H NMR, (13)C NMR, and Mass spectral data. In vitro antiamoebic activity was performed against HM1:IMSS strain of Entamoeba histolytica. The results showed that the compounds 2b, 2i, and 2j with IC(50) values of 0.37 µM, 0.04 µM, and 0.06 µM, respectively, exhibited better antiamoebic activity than the standard drug metronidazole (IC(50) = 1.33 µM). The toxicological studies of these compounds on human breast cancer MCF-7 cell line showed that the compounds 2b, 2i, and 2j exhibited >80% viability at the concentration range of 1.56-50 µM.

Synthesis and evaluation of the biological activities of some 3-{[5-(6-methyl-4-aryl-2-oxo-1,2,3,4-tetrahydropyrimidin-5-yl)-1,3,4-oxadiazol-2-yl]-imino}-1,3-dihydro-2H-indol-2-one derivatives

Reaction of ethyl-6-methyl-2-oxo-4-aryl-1,2,3,4-tetrahydropyrimidin-5-carboxylates (1a-i) with hydrazine hydrate yielded 6-methyl-2-oxo-4-aryl-1,2,3,4-tetrahydropyrimidin-5-carbohydrazides (2a-i). These products, on reaction with cyanogen bromide, gave 5-(5-amino-1,3,4-oxadiazol-2-yl)-6-methyl-4-aryl-3,4-dihydropyrimidin-2 (1H)-ones (3a-i). The resultant aminooxadiazolylpyrimidinones were condensed with isatin to obtain various 3-{[5-(6-methyl-4-aryl-2-oxo-1,2,3,4-tetrahydropyrimidin-5-yl)-1,3,4-oxadiazol-2-yl]-imino}-1,3-dihydro-2H-indol-2-ones (4a-i). These products were characterized by IR, 1H NMR, mass spectra and elemental analysis. Products (4a-i) revealed promising antibacterial, antifungal and antioxidant activity.

Synthesis of oligonucleotides with 3'-terminal 5-(3-acylamidopropargyl)-3'-amino-2',3'-dideoxyuridine residues and their reactivity in single-nucleotide steps of chemical replication

Oligonucleotides with a 3'-terminal 5-alkynyl-3'-amino-2',3'-dideoxyuridine residue were prepared, starting from 2'-deoxyuridine. The optimized route employs a 2',3'-dideoxy-3'-trifluoroacetamido-5-iodouridine 5'-phosphoramidite as building block for DNA synthesis and involves on-support Sonogashira coupling with N-tritylpropargylamine to generate oligonucleotides. The amino group of the propargylamine side chain was acylated to accelerate primer extension reactions involving the 3'-amino group. Three acyl groups were identified that decrease the half-life for DNA-templated extension steps with 7-azabenzotriazole esters of 2'-deoxynucleotides. The residue of 4-pyrenylbutyric acid was found to accelerate primer extension reactions and to render them more selective than those of the control primer. With this substituent, primer extension is also faster than previously measured for three-strand systems involving template, aminoprimer, and a downstream-binding helper oligonucleotide. Fast-reacting primers might become useful for genotyping single nucleotides.

Chemical and cytotoxic constituents from the leaves of Cinnamomum kotoense

Three new butanolides, kotomolide A (1), isokotomolide A (2), and kotomolide B (3), and a new secobutanolide, secokotomolide A (4), along with 21 known compounds were isolated from the leaves of Cinnamomum kotoense. Their structures were determined by spectroscopic analyses. Compound 4 was found to induce significant cell death in the human HeLa cell line. Apoptotic-related DNA damage can be positively related to the dose of compound 4. The DNA damage was measured by the percentage of subG1 (24 h after the treatment of compound 4) as determined by cell cycle analysis and TUNEL assay. Treatment with 4 significantly increased intracellular H2O2 and/or peroxide, nitric oxide (NO) at 1, 3, and 24 h. Our results also showed that compound 4 induced (a) noticeable reduction of mitochondrial transmembrane potential (DeltaPsi(m)), (b) activation of caspase 3/7, and (c) up-regulation of the p53 expression. Compound 4-induced DNA damage was found to markedly decrease when the cells were pretreated with an intracellular glutathione supplement (glutathione ethyl ester). These results suggest that an increase of H2O2 and/or peroxide by compound 4 is the initial apoptotic event. The intracellular GSH depletion is a critical event in compound 4-induced apoptosis in HeLa cells.

Actinodaphnine induces apoptosis through increased nitric oxide, reactive oxygen species and down-regulation of NF-kappaB signaling in human hepatoma Mahlavu cells

Actinodaphnine, extracted from Cinnamomum insularimontanum (Lauraceae), possesses cytotoxicity in some cancers, but the mechanism by which actinodaphnine induces apoptosis in human hepatoma cells remains poorly understood. In this study, we investigated the mechanisms of apoptosis induced by actinodaphnine in human hepatoma Mahlavu cells. Treatment with actinodaphnine dose-dependently induced apoptosis in Mahlavu cells that correlated with increased intracellular nitric oxide (NO) and reactive oxygen species (ROS), disruptive mitochondrial transmembrane potential (DeltaPsi(m)), and activation of caspase 3/7. Our data also demonstrated that actinodaphnine down-regulated activity of nuclear factor kappaB (NF-kappaB). The apoptotic response to actinodaphnine was markedly decreased in Mahlavu cells pretreated with dexsamethasone, a NO inhibitor, N-acetylcysteine (NAC), an antioxidant, and Boc-Asp(OMe)-fmk, a broad caspases inhibitor. These results suggested that actinodaphnine-induced apoptosis is initially mediated through the NO and/or ROS increase and caspases-dependent pathway. In conclusion, our results indicate that an increase of ROS and/or NO is the initial essential event that results in the decrease of DeltaPsi(m) and the activation of caspases that commits the cells to the apoptotic pathway in actinodaphnine-treated hepatoma Mahlavu cells.

Radiosynthesis, in vitro cellular uptake and in vivo biodistribution of 3′-O-(3-benzenesulfonylfuroxan-4-yl)-5-[125I]iodo-2′-deoxyuridine, a nucleoside-based nitric oxide donor

INTRODUCTION

3'-O-(3-Benzenesulfonylfuroxan-4-yl)-5-iodo-2'-deoxyuridine (1) is a cytotoxic nitric oxide (NO) donor-nucleoside dual action prodrug designed to exploit both NO and an antimetabolite nucleoside for cancer therapy.

METHODS

1 was radiolabeled by radioiodide exchange and purified by HPLC in 16% overall radiochemical yield. The specific activity of [(125)I]1 was 31.8 microCi/mug (680 MBq/microM). Protein binding, deiodination, cellular uptake and incorporation of 1 into cellular nucleic acids were measured by standard methods, and its in vivo biodistribution was determined in Balb/c mice bearing implanted EMT-6 tumors following intravenous injection.

RESULTS

[(125)I]1 degraded rapidly during the in vitro tests, thus impeding unequivocal assessment but indicating that it was only weakly protein bound and that it was resistant to deiodination under test conditions. Uptake of [(125)I]1 by murine tumor cells (KBALB and KBALB-STK) in vitro was low (approximately 17 fmol/microg protein over 2 h) with only approximately 0.3% (0.04-0.06 fmol/microg protein) of total uptake present in the DNA fraction. In the murine tumor model, liver, kidney, intestine and tumor showed the greatest uptake, with liver, intestine and blood all containing >5 injected dose per gram of tissue (%ID/g) during the 15-min to 2-h postinjection period. Maximum tissue/blood level ratios were 3.6 (2 h) for tumor and 6.4 (24 h) for liver. Low uptake in thyroid and stomach was indicative of minimal in vivo deiodination.

CONCLUSIONS

[(125)I]1 undergoes only minimal deoiodination under both in vitro and in vivo conditions. Under conditions of the in vitro NO release assay, 1 reacts to produce a single, major, unstable adduct that decomposes upon workup. Protein binding of [(125)I]1 could not be assessed because of similar chemical reaction with albumin. Incorporation of radioactivity into the cellular nucleic acid fraction was low, and in vivo distribution of [(125)I]1 was consistent with nonspecific reactivity towards tissue nucleophiles. The chemical reactivity of [(125)I]1 mitigates against its use as a NO donor and as a tracer for this class of compounds.

Biochemical and pharmacokinetic evaluation of a novel pyrimidine nucleoside nitric oxide donor as a potential anticancer/antiviral agent

The objective of this study was to determine the physiochemical, biochemical and pharmacokinetic properties of 5-iodo-3'-O-nitro-2'-deoxyuridine (INUdR), a novel prodrug releasing both nitric oxide (NO) and 5-iodo-2'-deoxyuridine. The INUdR partition coefficient (log P=1.12) was determined by both the shake-flask method and by calculation using Interactive Analysis Log P Program. In vitro binding of INUdR to bovine serum albumin (BSA) was estimated using an ultrafiltration method to be 65 to 77%, depending on the INUdR concentration. INUdR was stable in phosphate buffer (pH 7.4) and in water, at both ambient temperature and at 37 degrees C. INUdR was resistant to phosphorolysis when incubated with thymidine phosphorylase. Plasma, L-cysteine and glutathione catalyzed release of NO from INUdR, as determined using the Griess reaction. In all three systems, the release of NO by INUdR was equal to or greater than that of the reference drug isosorbide dinitrate. The pharmacokinetics of INUdR following single intravenous bolus and oral doses of INUdR (40 mg/kg) to male Sprague-Dawley rats were characterized by a short elimination half-life (T(1/2) 0.27 h), a large steady-state volume of distribution (V(ss) 0.89 l/kg) and high oral bioavailability (F=0.95). In conclusion, INUdR lipophilicity, shelf-stability, and resistance towards catabolic breakdown by thymidine phosphorylase, together with its non-spontaneous, yet considerable NO release, constitute favorable characteristics of a potential anticancer/antiviral agent.