Recent advances in diverse nanosystems for nitric oxide delivery in cancer therapy

Gas therapy has been proven to be a promising and advantageous treatment option for cancers. Studies have shown that nitric oxide (NO) is one of the smallest structurally significant gas molecules with great potential to suppress cancer. However, there is controversy and concern about its use as it exhibits the opposite physiological effects based on its levels in the tumor. Therefore, the anti-cancer mechanism of NO is the key to cancer treatment, and rationally designed NO delivery systems are crucial to the success of NO biomedical applications. This review summarizes the endogenous production of NO, its physiological mechanisms of action, the application of NO in cancer treatment, and nano-delivery systems for delivering NO donors. Moreover, it briefly reviews challenges in delivering NO from different nanoparticles and the issues associated with its combination treatment strategies. The advantages and challenges of various NO delivery platforms are recapitulated for possible transformation into clinical applications.

Photolytic or Oxidative Fragmentation of Trityl Diazeniumdiolate (O2N2CPh3-): Evidence for Both C-N and N-N Bond Cleavage

Exposure of [K(18-crown-6)(THF)₂][CPh₃] (THF = tetrahydrofuran; Ph = phenyl) to an atmosphere of nitric oxide (NO) cleanly generates [K(18-crown-6)][O₂N₂CPh₃] (1) in excellent yields. A subsequent reaction of [ZnCl₂(THF)₂] with 3 equiv of 1 affords the C-diazeniumdiolate complex [K(18-crown-6)][Zn(O₂N₂CPh₃)₃] (2). Both 1 and 2 were characterized by ¹H and ¹³C{¹H} NMR spectroscopy, and their structures were confirmed by X-ray crystallography. Photolysis of 2 using 371 nm light resulted in the formation of three trityl-containing products, namely, Ph₃CH, 9-phenylfluorene, and Ph₃CN(H)OCPh₃ (3). In addition, we detected nitrous oxide (N₂O), as well as small amounts of NO in the reaction mixture. In contrast, oxidation of 2 with 1.2 equiv of [Ag(MeCN)₄][PF₆] resulted in the formation of O(CPh₃)₂ as the major trityl-containing product; N₂O was also detected in the reaction mixture, but NO was not apparently formed in this case. The observation of these fragmentation products indicates that the [O₂N₂CPh₃]^- ligand is susceptible to both C-N bond and N-N bond cleavage. Moreover, the different product distributions suggest that [O₂N₂CPh₃]^- is susceptible to different modes of fragmentation.

Enhancing the therapeutic efficacy of nanoparticles for cancer treatment using versatile targeted strategies

Poor targeting of therapeutics leading to severe adverse effects on normal tissues is considered one of the obstacles in cancer therapy. To help overcome this, nanoscale drug delivery systems have provided an alternative avenue for improving the therapeutic potential of various agents and bioactive molecules through the enhanced permeability and retention (EPR) effect. Nanosystems with cancer-targeted ligands can achieve effective delivery to the tumor cells utilizing cell surface-specific receptors, the tumor vasculature and antigens with high accuracy and affinity. Additionally, stimuli-responsive nanoplatforms have also been considered as a promising and effective targeting strategy against tumors, as these nanoplatforms maintain their stealth feature under normal conditions, but upon homing in on cancerous lesions or their microenvironment, are responsive and release their cargoes. In this review, we comprehensively summarize the field of active targeting drug delivery systems and a number of stimuli-responsive release studies in the context of emerging nanoplatform development, and also discuss how this knowledge can contribute to further improvements in clinical practice.

Photoactivatable Nitric Oxide-Releasing Gold Nanocages for Enhanced Hyperthermia Treatment of Biofilm-Associated Infections

With the increasing clinical use of invasive medical devices, various healthcare-associated infections (HAIs) caused by bacterial biofilm colonization of biomedical devices have posed serious threats to patients. The formation of biofilms makes it much more difficult and costly to treat infections. Here, we report a nitric oxide (NO)-releasing gold nanocage (AuNC@NO) that is stimulated by near-infrared (NIR) irradiation to deliver NO and generate hyperthermia for biofilm elimination. AuNC@NO was prepared by immobilizing a temperature-responsive NO donor onto gold nanocages (AuNCs) through thiol-gold interactions. AuNC@NO possesses stable and excellent photothermal conversion efficiency, as well as the characteristics of slow NO release at physiological temperature and on-demand quick NO release under NIR irradiation. Based on these features, AuNC@NO exhibits enhanced in vitro bactericidal and antibiofilm efficacy compared with AuNCs, which could achieve 4 orders of magnitude bacterial reduction and 85.4% biofilm elimination under NIR irradiation. In addition, we constructed an implant biofilm infection model and a subcutaneous biofilm infection model to evaluate the anti-infective effect of AuNC@NO. The in vivo results indicated that after 5 min of 0.5 W cm^-2 NIR irradiation, NO release from AuNC@NO was significantly accelerated, which induced the dispersal of methicillin-resistant Staphylococcus aureus (MRSA) biofilms and synergized with photothermal therapy (PTT) to kill planktonic MRSA that had lost its biofilm protection. Meanwhile, the surrounding tissues showed little damage because of controlled photothermal temperature and toxicity. In view of the above-mentioned results, the AuNC@NO nanocomposite developed in this work reveals potential application prospects as a useful antibiofilm agent in the field of biofilm-associated infection treatment.

L-Arg-Rich Amphiphilic Dendritic Peptide as a Versatile NO Donor for NO/Photodynamic Synergistic Treatment of Bacterial Infections and Promoting Wound Healing

The development of alternative strategies for the efficient treatment of subcutaneous abscesses that do not require the massive use of antibiotics and surgical intervention is urgently needed. Herein, a novel synergistic antibacterial strategy based on photodynamic (PDT) and NO gas therapy is reported, in which, a PDT-driven NO controllable generation system (Ce6@Arg-ADP) is developed with l-Arg-rich amphiphilic dendritic peptide (Arg-ADP) as a carrier. This carrier not only displays superior bacterial association and biofilm penetration performance, but also acts as a versatile NO donor. Following efficient penetration into the interior of the biofilms, Ce6@Arg-ADP can rapidly produce massive NO via utilizing the H₂ O₂ generated during PDT to oxidize Arg-ADP to NO and l-citrulline, without affecting singlet oxygen (¹ O₂ ) production. The combination of ¹ O₂ and the reactive by-products of NO offers notable synergistic antibacterial and biofilm eradication effects. Importantly, following efficient elimination of all bacteria from the abscess site, Arg-ADP can further generate trace quantities of NO to facilitate the angiogenesis and epithelialization of the wound tissues, thereby notably promotes wound healing. Together, this study clearly suggests that Arg-ADP is a versatile NO donor, and the combination of PDT and NO represents a promising strategy for the efficient treatment of subcutaneous abscesses.

Structural control and biomedical applications of plasmonic hollow gold nanospheres: A mini review

Hollow gold nanospheres (HGNs) are core/shell structures with a dielectric material core, usually composed of solvent, and a gold metal shell. Such structures have two metal/dielectric interfaces to allow interaction between the gold metal with the interior and external dielectric environment. Upon illumination by light, HGNs exhibit unique surface plasmon resonance (SPR) properties compared to solid gold nanoparticles. Their SPR absorption/scattering can be tuned by changing their diameter, shell thicknesses, and surface morphologies. In addition to the low toxicity, easy functionalization, resistance to photobleaching, and sensitivity to changes in surrounding medium of gold, the enhanced surface-to-volume ratio and tunable SPR of HGNs make them highly attractive for different applications in the fields of sensing, therapy, and theranostics. In this article, we review recent progress on the synthesis and structural control of HGNs and applications of their SPR properties in biomedical sensing and theranostics. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > in vitro Nanoparticle-Based Sensing Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

ATP Suppression by pH-Activated Mitochondria-Targeted Delivery of Nitric Oxide Nanoplatform for Drug Resistance Reversal and Metastasis Inhibition

Mitochondria, which are important mediators for cancer initiation, growth, metastasis, and drug resistance, have been considered as a major target in cancer therapy. Herein, an acid-activated mitochondria-targeted drug nanocarrier is constructed for precise delivery of nitric oxide (NO) as an adenosine triphosphate (ATP) suppressor to amplify the therapeutic efficacy in cancer treatments. By combining α-cyclodextrin (α-CD) and acid-cleavable dimethylmaleic anhydride modified PEG conjugated mitochondria-targeting peptide, the nanocarrier shows prolonged blood circulation time and enhanced cellular uptake together with selectively restoring mitochondria-targeting capability under tumor extracellular pH (6.5). Such specific mitochondria-targeted delivery of NO proves crucial in inducing mitochondria dysfunction through facilitating mitochondrial membrane permeabilization and downregulating ATP level, which can inhibit P-glycoprotein-related bioactivities and formation of tumor-derived microvesicles to combat drug resistance and cancer metastasis. Therefore, this pioneering acid-activated mitochondria-targeted NO nanocarrier is supposed to be a malignant tumor opponent and may provide insights for diverse NO-relevant cancer treatments.

S-nitrosothiols loaded mini-sized Au@silica nanorod elicits collagen depletion and mitochondrial damage in solid tumor treatment

To a large extent, the dense extracellular matrix (ECM), which tightly connects tumor cells to arm the tumor into an intractable fortress, significantly decreases the nanoparticles delivery efficacy and overall performance in cancer treatments. Therefore, it is necessary to transform the dense stroma of solid tumors to loose state, which could realize deep penetration of nanomedicine and enhance cancer treatment effects. Here, we fabricated a protein-free collagen nanosweeper, triphenylphosphonium bromide (TPP) coated and S-nitrosothiols loaded mini-sized Au@silica nanorod (Au@SiO2-SNO/PEG/TPP, GSNP-TPP), to clear the transport barriers of nanoparticles as well as elevate enhanced permeability and retention (EPR) effect, thus alleviating the diffusion resistance and realizing further penetration of nanoparticles. Methods: By modifying the Au@silica with thermo-sensitive S-nitrosothiols, the carrier could release the nitric oxide (NO) due to the surface overheat as well as perform photothermal therapy (PTT) under near-infrared (NIR) laser irradiation. The level of collagen depletion was observed via western blotting and immunofluorescent staining. In addition, the dual-imaging and antitumor efficiency of GSNP-TPPs were evaluated with the HeLa tumor-bearing mouse model. Results: On one hand, the released NO could deplete collagen by activating matrix metalloproteinases (MMPs) to break collagen fibers, thus loosening the dense ECM to enhance the cellular internalization. On the other hand, with the mitochondrial-targeted effect of TPP, the diffusible NO in tumor might rapidly interact with superoxide anion (O2Ÿ-) to produce highly toxic and powerful reactive nitrogen species (RNS) -- peroxynitrite (ONOO-), which resulted in mitochondrial damage to induce cell apoptosis. With the unique properties of mini-sized gold nanorods, the formulated nanoparticles exhibited good computed tomography (CT) and multi-spectral optoacoustic tomography (MSOT) imaging effects in precisely locating and monitoring tumor. Moreover, the antitumor efficacy of GSNP-TPPs + laser group was further confirmed by ex-vivo histological analysis of tumor tissue. Conclusion: This work points out a strategy to overcome the obstacle standing in nanoparticles penetration, and opens the door of further exploitation of NO-related theranostic systems.

Dual Stimuli-Responsive Controlled Release Nanocarrier for Multidrug Resistance Cancer Therapy

Multidrug resistance of cancer cells is a major obstacle for cancer chemotherapy. Herein, we present a nanocarrier that can release chemotherapeutic agents to induce tumor cell death and generate NO under NIR to overcome multidrug resistance in cancer chemotherapy. Owing to the unique structure of the water channel in this controlled release system for chemotherapeutic agents, the nanocarrier surface is equipped with more active sites to graft NO donor molecules. The released NO performs very well in reversing multidrug resistance by inhibiting P-gp expression. Our findings provide new insight into multidrug resistance cancer therapy and controlled release nanocarriers for multiple drugs.

Near-infrared light switching nitric oxide nanoemitter for triple-combination therapy of multidrug resistant cancer

The multidrug resistance (MDR) of tumor cells often leads to the failure of chemotherapy against cancer. It is urgently needed to develop a safe and effective strategy of overcoming MDR for enhancing chemotherapy efficiency. In this work, one type of new folic acid-polyethylene glycol (FA-PEG) modified polydopamine nanoparticles (FAPPs) was synthesized for gas/chemo/photothermal triple-combination therapy of multidrug resistant cancer. The nanoparticles loaded nitric oxide (NO) donor act as a NO nanoemitter to generate NO via a NIR light irradiation switch, which has a great capacity of reversing MDR via inhibiting the overexpression of P-glycoprotein (P-gp) and cell respiration with the reduction of both the adenosine triphosphate (ATP) content and mitochondrial membrane potential (ΔΨ_m) in MDR tumor cells. Moreover, the amount of generated NO can be regulated by changing the action time of the nanoparticles. After that, the nanoparticles loaded chemotherapeutic agent (DOX) act as a photothermal-chemotherapy nanomedicine, which can release DOX with a high concentration in tumor cell for chemotherapy and simultaneously produce a large amount of heat for photothermal therapy under NIR irradiation. Finally, the gas/chemo/photothermal triple-combination therapy with the nanomedicines displays an excellent therapeutic efficacy in nude mice bearing MDR tumors. STATEMENT OF SIGNIFICANCE: The multidrug resistance (MDR) of tumor cells frequently leads to the failure of chemotherapy against cancer. It is urgently needed to develop a safe and effective strategy of overcoming MDR for enhancing chemotherapy efficiency. In this paper, a NIR light switching nitric oxide nanoemitter is successfully developed for gas/chemo/photothermal triple-combination therapy of multidrug resistant cancer. The controllably generated NO under NIR irradiation can effectively reverse multidrug resistance by inhibiting the overexpression of P-gp and cell respiration, significantly enhancing the chemotherapeutic agent concentration in tumor cells, and simultaneously a large amount of heat is produced for photothermal therapy.

Efficient Near Infrared Light Triggered Nitric Oxide Release Nanocomposites for Sensitizing Mild Photothermal Therapy

Mild photothermal therapy (PTT), as a new anticancer therapeutic strategy, faces big challenges of limited therapeutic accuracy and side-effects due to uneven heat distribution. Here, near infrared triggered nitric oxide (NO) release nanocomposites based on bismuth sulfide (Bi2S3) nanoparticles and bis-N-nitroso compounds (BNN) are constructed for NO-enhanced mild photothermal therapy. Upon 808 nm irradiation, the high photothermal conversion efficiency and on-demand NO release are realized simultaneously. Due to the unique properties of NO, enhanced antitumor efficacy of mild PTT based on BNN-Bi2S3 nanocomposites is achieved in vitro and in vivo. Mechanism studies reveal that the exogenous NO from BNN-Bi2S3 could not only impair the autophagic self-repairing ability of tumor cells in situ, but also diffuse to the surrounding cells to enhance the therapeutic effect. This work points out a strategy to overcome the difficulties in mild PTT, and has potentials for further exploitation of NO-sensitized synergistic cancer therapy.

Theranostic Mn-Porphyrin Metal-Organic Frameworks for Magnetic Resonance Imaging-Guided Nitric Oxide and Photothermal Synergistic Therapy

Chemotherapy remains restricted by its toxic adverse effects and resistance to drugs. The treatment of nitric oxide (NO) combined with imaging-guided physical therapy is a promising alternative for clinical applications. Herein, we report nanoscale metal-organic framework (NMOF) systems to integrate magnetic resonance (MR) imaging, spatiotemporally controllable NO delivery, and photothermal therapy (PTT) as a new means of cancer theranostics. As a proof of concept, the NMOFs are prepared with biocompatible Zr⁴⁺ ions and Mn-porphyrin as a bridging ligand. By inserting paramagnetic Mn ions into porphyrin rings, Mn-porphyrin renders the NMOFs strong T₁-weighted MR contrast capacity and high photothermal conversion for efficient PTT. S-Nitrosothiol (SNO) is conjugated to the surfaces of the NMOFs for heat-sensitive NO generation. Moreover, single near-infrared (NIR) light triggers the controllable NO release and PTT simultaneously for their efficient synergistic therapy with one-step operation. Upon intravenous injection, NMOF-SNO shows effective tumor accumulation as exposed by the MR images of the tumor-bearing mice. When exposed to the NIR laser, the tumors of mice injected with NMOF-SNO are completely inhibited, verifying the efficiency of NMOF-SNO. For the first time, Mn-porphyrin NMOFs are developed to be an effective theranostic system for MR imaging-guided controllable NO release and photothermal synergetic therapy under single NIR irradiation.

Macrophage-mediated delivery of light activated nitric oxide prodrugs with spatial, temporal and concentration control

Nitric oxide (NO) holds great promise as a treatment for cancer hypoxia, if its concentration and localization can be precisely controlled. Here, we report a "Trojan Horse" strategy to provide the necessary spatial, temporal, and dosage control of such drug-delivery therapies at targeted tissues. Described is a unique package consisting of (1) a manganese-nitrosyl complex, which is a photoactivated NO-releasing moiety (photoNORM), plus Nd3+-doped upconverting nanoparticles (Nd-UCNPs) incorporated into (2) biodegradable polymer microparticles that are taken up by (3) bone-marrow derived murine macrophages. Both the photoNORM [Mn(NO)dpaqNO2 ]BPh4(dpaqNO2 = 2-[N,N-bis(pyridin-2-yl-methyl)]-amino-N'-5-nitro-quinolin-8-yl-acetamido) and the Nd-UCNPs are activated by tissue-penetrating near-infrared (NIR) light at ∼800 nm. Thus, simultaneous therapeutic NO delivery and photoluminescence (PL) imaging can be achieved with a NIR diode laser source. The loaded microparticles are non-toxic to their macrophage hosts in the absence of light. The microparticle-carrying macrophages deeply penetrate into NIH-3T3/4T1 tumor spheroid models, and when the infiltrated spheroids are irradiated with NIR light, NO is released in quantifiable amounts while emission from the Nd-UCNPs provides images of microparticle location. Furthermore, varying the intensity of the NIR excitation allows photochemical control over NO release. Low doses reduce levels of hypoxia inducible factor 1 alpha (HIF-1α) in the tumor cells, while high doses are cytotoxic. The use of macrophages to carry microparticles with a NIR photo-activated theranostic payload into a tumor overcomes challenges often faced with therapeutic administration of NO and offers the potential of multiple treatment strategies with a single system.

Utilizing light-triggered plasmon-driven catalysis reactions as a template for molecular delivery and release

Due to the facile manipulation and non-invasive nature of light-triggered release, it is one of the most potent ways to selectively and remotely deliver a molecular target. Among the various carrier platforms, plasmonic nanoparticles possess advantages such as enhanced cellular uptake and easy loading of "cargo" molecules. Two general strategies are currently utilized to achieve light-induced molecule release from plasmonic nanoparticles. The first uses femtosecond laser pulses to directly break the bond between the nanoparticle and the loaded target. The other requires significant photo-thermal effects to weaken the interaction between the cargo molecules and nanoparticle-attached host molecules. Different from above mechanisms, herein, we introduce a new light-controlled molecular-release method by taking advantage of a plasmon-driven catalytic reaction at the particle surface. In this strategy, we link the target to a plasmon responsive molecule, 4-aminobenzenethiol (4-ABT), through the robust and simple EDC coupling reaction and subsequently load the complex onto the particles via the strong Au-thiol interaction. Upon continuous-wave (CW) laser illumination, the excited surface plasmon catalyzes the formation of 4,4'-dimercaptoazobenzenethiol (DMAB) and simultaneously releases the loaded molecules with high efficiency. This method does not require the use of high-power pulsed lasers, nor does it rely on photo-thermal effects. We believe that plasmon-driven release strategies open a new direction for the designing of next-generation light-triggered release processes.

Ultrafast Near-Infrared Light-triggered Intracellular Uncaging to Probe Cell Signaling

The possibility of regulating cell signaling with high spatial and temporal resolution within individual cells and complex cellular networks has important implications in biomedicine. In this report, we demonstrate a general strategy that uses near-infrared tissue-penetrating laser pulses to uncage biomolecules from plasmonic gold-coated liposomes, i.e. plasmonic liposomes, to activate cell signaling in a non-thermal, ultrafast and highly controllable fashion. Near-infrared picosecond laser pulse induces transient nanobubbles around plasmonic liposomes. The mechanical force generated from the collapse of nanobubbles rapidly ejects encapsulated compound within 0.1 ms. We showed that single pulse irradiation triggers the rapid intracellular uncaging of calcein from plasmonic liposomes inside endo-lysosomes. The uncaged calcein then evenly distributes over the entire cytosol and nucleus. Furthermore, we demonstrated the ability to trigger calcium signaling in both an immortalized cell line and primary dorsal root ganglion (DRG) neurons by intracellular uncaging of inositol triphosphate (IP3), an endogenous cell calcium signaling second messenger. Compared with other uncaging techniques, this ultrafast near-infrared light-driven molecular uncaging method is easily adaptable to deliver a wide range of bioactive molecules with an ultrafast optical switch, enabling new possibilities to investigate signaling pathways within individual cells and cellular networks.

From curiosity to applications. A personal perspective on inorganic photochemistry

Over the past several decades, the photochemistry and photophysics of transition metal compounds has blossomed from a relatively niche topic to a major research theme. Applications arising from the elucidation of the fundamental principles defining this field now range from probing the rates and mechanisms of small molecules with metalloproteins to light activated molecular machines. Offered here is a personal perspective of metal complex photochemistry drawn from this author's long involvement with this field. Several examples are described. Topics include characterizing key excited states and tuning these to modify chemical reactivity and/or photoluminescence properties, as well as using photoreactions as an entry to reactive intermediates relevant to homogeneous catalysts. This is followed by discussions of applying these concepts to developing precursors and precursor-antenna conjugates for the photochemical delivery of small molecule bioregulators to physiological targets.

trans- and cis-(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6): promising candidates for NO release in the NIR region

Efficient NO photodelivery from cis- and trans-(Cl,Cl)-[Ru^II(FT)Cl₂(NO)](PF₆) complexes upon two-photon excitation in the NIR region.