Eradication of Pathogenic Bacteria by Remote Delivery of Nitric Oxide via Light-Triggering of Nitrosyl-Containing Materials

Photo-triggered NO release of nitrosyl complexes bearing first-row transition metals and therapeutic applications

In biological systems, nitric oxide (NO) is a crucial signaling molecule that regulates a wide range of physiological and pathological processes. Given the significance of NO, there has been considerable interest in delivering NO exogenously, particularly through light as a non-invasive therapeutic approach. However, due to the high reactivity and instability of NO under physiological conditions, directly delivering NO to targeted sites remains challenging. In recent decades, photo-responsive transition metal-nitrosyl complexes, especially based on first-row transition metals such as Mn, Fe, and Co, have emerged as efficient NO donors, offering higher delivery efficiency and quantum yields than heavy metal-nitrosyl complexes under light exposure. This review provides a comprehensive overview of current knowledge and recent developments in the field of photolabile first-row transition metal-nitrosyl complexes, focusing on the structural and electronic properties, photoreactivity, photodissociation mechanisms, and potential therapeutic applications. By consolidating the key features of photoactive nitrosyl complexes, the review offers deeper insights and highlights the potential of first-row transition metal-nitrosyl complexes as versatile tools for photo-triggered NO delivery.

Nitric oxide-releasing molecules at the interface of inorganic chemistry and biology: a concise overview

The useful aspects of nitric oxide (NO) are nowadays widely known. Due to the need for this molecule in the maintenance of homeostasis, NO-releasing compounds are tested every year to optimize its levels in a patient suffering from low NO production. This manuscript is an update of some important historical concerns about nitrosyl complexes having the ability to act as NO-releasing compounds under the influence of different chemically modified environments. At present, the search for efficient and less harmful NO-releasing molecules at desirable targets and concentrations has gained considerable momentum in nitrosyl chemistry. Iron, ruthenium, and manganese nitrosyls have been investigated elitely to disentangle their electronic transition (excitation) under visible light to act as NO donors without harming the healthy cells of a target. There is much evidence supporting the increase of NO lability if amino acids are used as complexing ligands, the design of a reduction center close to an NO grouping, and the development of porphyrin system-based nitrosyl complexes. From the overall survey, it may be concluded that the desirable properties of such scaffolds need to be evaluated further to complement the biological milieu.

Nitric Oxide-Releasing Macromolecular Scaffolds for Antibacterial Applications

Exogenous nitric oxide (NO) represents an attractive antibacterial agent because of its ability to both disperse and directly kill bacterial biofilms while avoiding resistance. Due to the challenges associated with administering gaseous NO, NO-releasing macromolecular scaffolds are developed to facilitate NO delivery. This progress report describes the rational design and application of NO-releasing macromolecular scaffolds as antibacterial therapeutics. Special consideration is given to the role of the physicochemical properties of the NO storage vehicles on antibacterial or anti-biofilm activity.

Ru(ii) polypyridyl complexes as photocages for bioactive compounds containing nitriles and aromatic heterocycles

Photocaging allows for precise spatiotemporal control over the release of biologically active compounds with light. Most photocaged molecules employ organic photolabile protecting groups; however, biologically active compounds often contain functionalities such as nitriles and aromatic heterocycles that cannot be caged with organic groups. Despite their prevalence, only a few studies have reported successful caging of nitriles and aromatic heterocycles. Recently, Ru(ii)-based photocaging has emerged as a powerful method for the release of bioactive molecules containing these functional groups, in many cases providing high levels of spatial and temporal control over biological activity. This Feature Article discusses recent developments in applying Ru(ii)-based photocaging towards biological problems. Our groups designed and synthesized Ru(ii)-based platforms for the photoinduced delivery of cysteine protease and cytochrome P450 inhibitors in order to achieve selective control over enzyme inhibition. We also reported Ru(ii) photocaging groups derived from higher-denticity ancillary ligands that possess photophysical and photochemical properties distinct from more traditional Ru(ii)-based caging groups. In addition, for the first time, we are able to rapidly synthesize and screen Ru(ii) polypyridyl complexes that elicit desired properties by solid-phase synthesis. Finally, our work also defined steric and orbital mixing effects that are important factors in controlling photoinduced ligand exchange.

Remote-controlled delivery of CO via photoactive CO-releasing materials on a fiber optical device

Although carbon monoxide (CO) delivery materials (CORMAs) have been generated, remote-controlled delivery with light-activated CORMAs at a local site has not been achieved. In this work, a fiber optic-based CO delivery system is described in which the photoactive and water insoluble CO releasing molecule (CORM) manganese(i) tricarbonyl [(OC)3Mn(μ3-SR)]4 (R = nPr, 1) has been non-covalently embedded into poly(l-lactide-co-d/l-lactide) and poly(methyl methacrylate) non-woven fabrics via the electrospinning technique. SEM images of the hybrid materials show a porous fiber morphology for both polymer supports. The polylactide non-woven fabric was attached to a fiber optical device. In combination with a laser irradiation source, remote-controlled and light-triggered CO release at 405 nm excitation wavelength was achieved. The device enabled a high flexibility of the spatially and timely defined application of CO with the biocompatible hybrid fabric in aqueous media. The rates of liberated CO were adjusted with the light intensity of the laser. CO release was confirmed via ATR-IR spectroscopy, a portable electrochemical CO sensor and a heterogeneous myoglobin assay.

Lysozyme and DNA binding affinity of Pd(ii) and Pt(ii) complexes bearing charged N,N-pyridylbenzimidazole bidentate ligands

The 2-pyridylbenzimidazole Pt(ii) complex functionalized with triphenylphosphonium interacts covalently with lysozyme via the loss of labile ligands and the departure of the TPP⁺ part.

IClick cycloaddition reaction of light-triggered manganese(i) carbonyl complexes

For a binuclear blue-light-induced CO-releasing manganese(i) tricarbonyl complex bearing bidentate ligand, the effect of the ancillary ligand on the dark stability and photolysis process was studied.

Eradication of HT-29 colorectal adenocarcinoma cells by controlled photorelease of CO from a CO-releasing polymer (photoCORP-1) triggered by visible light through an optical fiber-based device

The gaseous signaling molecule carbon monoxide (CO) has recently been recognized for its wide range of physiological activity as well as its antineoplastic properties. However, site-specific delivery of this noxious gas presents a major challenge in hospital settings. In this work, a visible light-sensitive CO-releasing molecule (photoCORM) derived from manganese(I) and 2-(quinolyl)benzothiazole (qbt) namely, [Mn(CO)₃(qbt)(4-vpy)](CF₃SO₃) (1), has been co-polymerized within a gas-permeable HEMA/EGDMA hydrogel. The resulting photoactive CO-releasing polymer (photoCORP-1) incorporates 1 such that neither the carbonyl complex nor its photoproduct(s) exits the polymer at any time. The material can be triggered to photorelease CO remotely by low-power broadband visible light (<1mWcm^-2) with the aid of fiber optics technology. The CO photorelease rates of photoCORP-1 (determined by spectrophotometry) can be modulated by both the concentration of 1 in the hydrogel and the intensity of the light. A CO-delivery device has been assembled to deliver CO to a suspension of human colorectal adenocarcinoma cells (HT-29) under the control of visible light and the extent of CO-induced apoptotic death of the cancer cells has been determined via Annexin V/Propidium iodide stain and flow cytometry. This photoactive CO-releasing polymer could find use in delivering controlled doses of CO to cellular targets such as malignant tissues in remote parts of the body.

Change in the structure and function of lectin by photodissociation of NO

We have shown here that the structure and sugar-binding activity of lectin can be changed by the photodissociation of NO.

Paulo T, de França Lopes LG, Sousa EHS. A biphosphinic ruthenium complex with potent anti-bacterial and anti-cancer activity

Photorelease of CO and moderate binding to DNA did not seem to be essential features for potent biological activities.

Sustained Nitric Oxide-Releasing Nanoparticles Interfere with Methicillin-Resistant Staphylococcus aureus Adhesion and Biofilm Formation in a Rat Central Venous Catheter Model

Staphylococcus aureus is frequently isolated in the setting of infections of indwelling medical devices, which are mediated by the microbe's ability to form biofilms on a variety of surfaces. Biofilm-embedded bacteria are more resistant to antimicrobial agents than their planktonic counterparts and often cause chronic infections and sepsis, particularly in patients with prolonged hospitalizations. In this study, we demonstrate that sustained nitric oxide-releasing nanoparticles (NO-np) interfere with S. aureus adhesion and prevent biofilm formation on a rat central venous catheter (CVC) model of infection. Confocal and scanning electron microscopy showed that NO-np-treated staphylococcal biofilms displayed considerably reduced thicknesses and bacterial numbers compared to those of control biofilms in vitro and in vivo, respectively. Although both phenotypes, planktonic and biofilm-associated staphylococci, of multiple clinical strains were susceptible to NO-np, bacteria within biofilms were more resistant to killing than their planktonic counterparts. Furthermore, chitosan, a biopolymer found in the exoskeleton of crustaceans and structurally integrated into the nanoparticles, seems to add considerable antimicrobial activity to the technology. Our findings suggest promising development and translational potential of NO-np for use as a prophylactic or therapeutic against bacterial biofilms on CVCs and other medical devices.

A bactericidal calix[4]arene-based nanoconstruct with amplified NO photorelease

A hydrophobic N-dodecyl-3-(trifluoromethyl)-4-nitrobenzenamine has been synthesized as a suitable NO photodonor and encapsulated in a nanocontainer based on a polycationic calix[4]arene derivative, leading to a supramolecular micellar-like nanoassembly ca. 45 nm in diameter. Visible light excitation of this nanoconstruct triggers NO generation with an efficiency remarkably higher than that observed for the free NO photoreleaser. This amplified NO release results in considerable antibacterial activity against Staphylococcus aureus (ATCC 6538) and Pseudomonas aeruginosa (ATCC 9027) as representative Gram positive and Gram negative bacteria, respectively.

Sustained Nitric Oxide-Releasing Nanoparticles Induce Cell Death in Candida albicans Yeast and Hyphal Cells, Preventing Biofilm Formation In Vitro and in a Rodent Central Venous Catheter Model

Candida albicansis a leading nosocomial pathogen. Today, candidal biofilms are a significant cause of catheter infections, and such infections are becoming increasingly responsible for the failure of medical-implanted devices.C. albicansforms biofilms in which fungal cells are encased in an autoproduced extracellular polysaccharide matrix. Consequently, the enclosed fungi are protected from antimicrobial agents and host cells, providing a unique niche conducive to robust microbial growth and a harbor for recurring infections. Here we demonstrate that a recently developed platform comprised of nanoparticles that release therapeutic levels of nitric oxide (NO-np) inhibits candidal biofilm formation, destroys the extracellular polysaccharide matrices of mature fungal biofilms, and hinders biofilm development on surface biomaterials such as the lumen of catheters. We found NO-np to decrease both the metabolic activity of biofilms and the cell viability ofC. albicansin vitroandin vivo Furthermore, flow cytometric analysis found NO-np to induce apoptosis in biofilm yeast cellsin vitro Moreover, NO-np behave synergistically when used in combination with established antifungal drug therapies. Here we propose NO-np as a novel treatment modality, especially in combination with standard antifungals, for the prevention and/or remediation of fungal biofilms on central venous catheters and other medical devices.

Solid-phase synthesis as a platform for the discovery of new ruthenium complexes for efficient release of photocaged ligands with visible light

Ruthenium-based photocaging groups have important applications as biological tools and show great potential as therapeutics. A method was developed to rapidly synthesize, screen, and identify ruthenium-based caging groups that release nitriles upon irradiation with visible light. A diverse library of tetra- and pentadentate ligands was synthesized on polystyrene resin. Ruthenium complexes of the general formula [Ru(L)(MeCN)n](m+) (n = 1-3, m = 1-2) were generated from these ligands on solid phase and then cleaved from resin for photochemical analysis. Data indicate a wide range of spectral tuning and reactivity with visible light. Three complexes that showed strong absorbance in the visible range were synthesized by solution phase for comparison. Photochemical behavior of solution- and solid-phase complexes was in good agreement, confirming that the library approach is useful in identifying candidates with desired photoreactivity in short order, avoiding time-consuming chromatography and compound purification.

Light-triggered nitric oxide delivery to malignant sites and infection

The discovery of nitric oxide (NO) as a signalling molecule in various physiological and pathological pathways has spurred research in the design of exogenous NO donors as drugs. In recent years, metal nitrosyls (NO complexes of metals) have been investigated as NO-donating agents. Results from our laboratory during the past few years have demonstrated that metal nitrosyls derived from designed ligands can deliver NO under the total control of light of various frequencies. Careful incorporation of these photoactive nitrosyls into polymer matrices has afforded a set of nitrosyl-polymer composites that can be used to make such NO delivery site-specific. The composite materials have shown excellent antineoplastic and antimicrobial actions in several in vitro experiments. This review highlights our key results in the context of recent developments in this area of NO donors that deliver NO on demand.

Nitric oxide donors for cardiovascular implant applications

In an era of increased cardiovascular disease burden in the ageing population, there is great demand for devices that come in to contact with the blood such as heart valves, stents, and bypass grafts that offer life saving treatments. Nitric oxide (NO) elution from healthy endothelial tissue that lines the vessels maintains haemostasis throughout the vasculature. Surgical devices that release NO are desirable treatment options and N-diazeniumdiolates and S-nitrosothiols are recognized as preferred donor molecules. There is a keen interest to investigate newer methods by which NO donors can be retained within biomaterials so that their release and kinetic profiles can be optimized. A range of polymeric scaffolds incorporating microparticles and nanomaterials are presenting solutions to current challenges, and have been investigated in a range of clinical applications. This review outlines the application of NO donors for cardiovascular therapy using biomaterials that release NO locally to prevent thrombosis and intimal hyperplasia (IH) and enhance endothelialization in the fabrication of next generation cardiovascular device technology.

Nitric oxide (NO)-induced death of gram-negative bacteria from a light-controlled NO-releasing platform

A NO-delivery platform has been fabricated from polydimethylsiloxane (PDMS) and Pluronic(®) F127 gel that contains the light-sensitive NO donor, [Mn(PaPy(3))(NO)]ClO(4). The material was assembled layer-by-layer. First, a thin PDMS membrane was cast. It was then layered with cold 25% (w/v) Pluronic(®) F127 gel mixed with [Mn(PaPy(3))(NO)]ClO(4). Finally, it was covered with a thick layer (nearly impermeable to NO) of PDMS (=polydimethoxysiloxane) to allow release of NO only from the thinner side upon exposure to light. Light-induced NO release from this layered material has been confirmed via NO-specific electrode and by a modified soft Griess-agar assay. Incorporation of ca. 8 mg/g of [Mn(PaPy(3))(NO)]ClO(4) in the Pluronic gel layer affords a material that drastically reduces the microbial loads of Acinetobacter baumannii and Pseudomonas aeruginosa via the antibiotic effects of the photoreleased NO. Application of this flexible layered NO-donating composite as bandage material has been proposed.

Wireless platform for controlled nitric oxide releasing optical fibers for mediating biological response to implanted devices

Despite the documented potential to leverage nitric oxide generation to improve in vivo performance of implanted devices, a key limitation to current NO releasing materials tested thus far is that there has not been a means to modulate the level of NO release after it has been initiated. We report the fabrication of a wireless platform that uses light to release NO from a polymethylmethacrylate (PMMA) optical fiber coated with an S-nitroso-N-acetylpenicillamine derivatized polydimethylsiloxane (SNAP-PDMS). We demonstrate that a VAOL-5GSBY4 LED (λ(dominant)=460 nm) can be used as a dynamic trigger to vary the level of NO released from 500 μm diameter coated PMMA. The ability to generate programmable sequences of NO flux from the surface of these coated fibers offers precise spatial and temporal control over NO release and provides a platform to begin the systematic study of in vivo physiological response to implanted devices. NO surface fluxes up to 3.88 ± 0.57 × 10(-10)mol cm(-2)min(-1) were achieved with -100 μm thick coatings on the fibers and NO flux was pulsed, ramped and held steady using the wireless platform developed. We demonstrate the NO release is linearly proportional to the drive current applied to the LED (and therefore level of light produced from the LED). This system allow the surface flux of NO from the fibers to be continuously changed, providing a means to determine the level and duration of NO needed to mediate physiological response to blood contacting and subcutaneous implants and will ultimately lead to the intelligent design of NO releasing materials tailored to specific patterns of NO release needed to achieve reliable in vivo performance for intravascular and subcutaneous sensors and potentially for a wide variety of other implanted biomedical devices.

Nitric oxide release: part II. Therapeutic applications

A wide range of nitric oxide (NO)-releasing materials has emerged as potential therapeutics that exploit NO's vast biological roles. Macromolecular NO-releasing scaffolds are particularly promising due to their ability to store and deliver larger NO payloads in a more controlled and effective manner compared to low molecular weight NO donors. While a variety of scaffolds (e.g., particles, dendrimers, and polymers/films) have been cleverly designed, the ultimate clinical utility of most NO-releasing macromolecules remains unrealized. Although not wholly predictive of clinical success, in vitro and in vivo investigations have enabled a preliminary evaluation of the therapeutic potential of such materials. In this tutorial review, we review the application of macromolecular NO therapies for cardiovascular disease, cancer, bacterial infections, and wound healing.

Polymer-Based Nitric Oxide Therapies: Recent Insights for Biomedical Applications

Since the discovery of nitric oxide (NO) in the 1980s, this cellular messenger has been shown to participate in diverse biological processes such as cardiovascular homeostasis, immune response, wound healing, bone metabolism, and neurotransmission. Its beneficial effects have prompted increased research in the past two decades, with a focus on the development of materials that can locally release NO. However, significant limitations arise when applying these materials to biomedical applications. This Feature Article focuses on the development of NO-releasing and NO-generating polymeric materials (2006-2011) with emphasis on recent in vivo applications. Results are compared and discussed in terms of NO dose, release kinetics, and biological effects, in order to provide a foundation to design and evaluate new NO therapies.

The In Vitro and In Vivo Antitumour Activities of Nitrosyl Ruthenium Amine Complexes

Ruthenium compounds of the type trans-[Ru(NO)(NH3)4(L)]X3, L = N-heterocyclic ligands, P(OEt)3, SO32–, X = BF4– or PF6–, or [Ru(NO)Hedta], were tested for antitumour activity in vitro against murine melanoma and human tumour cells. The ruthenium complexes induced DNA fragmentation and morphological alterations suggestive of necrotic tumour cell death. The calculated IC50 values were lower than 100 μM. Complexes for which L = isn or imN were partially effective in vivo in a syngeneic model of murine melanoma B16F10, increasing animal survival. In addition, the same ruthenium complexes effectively inhibited angiogenesis of HUVEC cells in vitro. The results suggest that these nitrosyl complexes are a promising platform to be explored for the development of novel antitumour agents.

Synthesis, characterization, and light-controlled antibiotic application of a composite material derived from polyurethane and silica xerogel with embedded photoactive manganese nitrosyl

The synthesis of a light-sensitive polyurethane-based composite material (PUX-NO) is described. In its polyurethane medium, PUX-NO contains entrapped silica xerogel particles in which a photoactive manganese nitrosyl has been incorporated. Green flexible films of PUX-NO readily release nitric oxide (NO) only when exposed to low power (mW) visible light. Incorporation of the nitrosyl in the xerogel not only retains the nitrosyl (NO donor) within the composite material but also provides the right extent of hydration. Pre-swelled films of PUX-NO have water content close to 30 Wt % and such films can be stored for months under slightly moist condition without loss in NO-delivering capacity. The NO-releasing parameters of the film have been determined. The NO-releasing capacity of PUX-NO films can be conveniently altered by changing the amount of the nitrosyl as well as the thickness of the films. Patches of PUX-NO film have been successfully employed to reduce drastically bacterial loads of both gram-positive and gram-negative bacteria including methicillin-resistant Staphylococcus aureus and Acinetobacter baumannii under the total control of light. Effective control of infections by these bacterial pathogens via delivery of proper doses of NO only to the sites of infection appears feasible with PUX-NO films.

Photoactive ruthenium nitrosyls as NO donors: how to sensitize them toward visible light

Nitric oxide (NO) can induce apoptosis (programmed cell death) at micromolar or higher doses. Although cell death via NO-induced apoptosis has been studied quite extensively, the targeted delivery of such doses of NO to infected or malignant tissues has not been achieved. The primary obstacle is indiscriminate NO release from typical systemic donors such as glycerin trinitrate: once administered, the drug travels throughout the body, and NO is released through a variety of enzymatic, redox, and pH-dependent pathways. Photosensitive NO donors have the ability to surmount this difficulty through the use of light as a localized stimulus for NO delivery. The potential of the method has prompted synthetic research efforts toward new NO donors for use as photopharmaceuticals in the treatment of infections and malignancies. Over the past few years, we have designed and synthesized several metal nitrosyls (NO complexes of metals) that rapidly release NO when exposed to low-power (milliwatt or greater) light of various wavelengths. Among them, the ruthenium nitrosyls exhibit exceptional stability in biological media. However, typical ruthenium nitrosyls release NO upon exposure to UV light, which is hardly suitable for phototherapy. By following a few novel synthetic strategies, we have overcome this problem and synthesized a variety of ruthenium nitrosyls that strongly absorb light in the 400-600-nm range and rapidly release NO under such illumination. In this Account, we describe our progress in designing photoactive ruthenium nitrosyls as visible-light-sensitive NO donors. Our research has shown that alteration of the ligands, in terms of (i) donor atoms, (ii) extent of conjugation, and (iii) substituents on the ligand frames, sensitizes the final ruthenium nitrosyls toward visible light in a predictable fashion. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations provide guidance in this "smart design" of ligands. We have also demonstrated that direct attachment of dye molecules as light-harvesting antennas also sensitize ruthenium nitrosyls to visible light, and TDDFT calculations provide insight into the mechanisms of sensitization by this technique. The fluorescence of the dye ligands makes these NO donors "trackable" within cellular matrices. Selected ruthenium nitrosyls have been used to deliver NO to cellular targets to induce apoptosis. Our open-design strategies allow the isolation of a variety of these ruthenium nitrosyls, depending on the choices of the ligand frames and dyes. These designed nitrosyls will thus be valuable in the future endeavor of synthesizing novel pharmaceuticals for phototherapy.

Designed iron carbonyls as carbon monoxide (CO) releasing molecules: rapid CO release and delivery to myoglobin in aqueous buffer, and vasorelaxation of mouse aorta

The physiological roles of CO in neurotransmission, vasorelaxation, and cytoprotective activities have raised interest in the design and syntheses of CO-releasing materials (CORMs) that could be employed to modulate such biological pathways. Three iron-based CORMs, namely, [(PaPy(3))Fe(CO)](ClO(4)) (1), [(SBPy(3))Fe(CO)](BF(4))(2) (2), and [(Tpmen)Fe(CO)](ClO(4))(2) (3), derived from designed polypyridyl ligands have been synthesized and characterized by spectroscopy and X-ray crystallography. In these three Fe(II) carbonyls, the CO is trans to a carboxamido-N (in 1), an imine-N (in 2), and a tertiary amine-N (in 3), respectively. This structural feature has been correlated to the strength of the Fe-CO bond. The CO-releasing properties of all three carbonyls have been studied in various solvents under different experimental conditions. Rapid release of CO is observed with 2 and 3 upon dissolution in both aqueous and nonaqueous media in the presence and absence of dioxygen. With 1, CO release is observed only under aerobic conditions, and the final product is an oxo-bridged diiron species while with 2 and 3, the solvent bound [(L)Fe(CO)](2+) (where L = SBPy(3) or Tpmen) results upon loss of CO under both aerobic and anaerobic conditions. The apparent rates of CO loss by these CORMs are comparable to other CORMs such as [Ru(glycine)(CO)(3)Cl] reported recently. Facile delivery of CO to reduced myoglobin has been observed with both 2 and 3. In tissue bath experiments, 2 and 3 exhibit rapid vasorelaxation of mouse aorta muscle rings. Although the relaxation effect is not inhibited by the soluble guanylate cyclase inhibitor ODQ, significant inhibition is observed with the BK(Ca) channel blocker iberiotoxin.

A highly divergent approach for synthesis of metal-binding peptide libraries

A highly divergent approach for the synthesis of metal-binding peptides is described. This approach builds pyridine-based chelators in a stepwise fashion on resin and provides rapid access to a diverse array of metal-binding peptides in minimal synthetic steps.