Ultrasound responsive carbon monoxide releasing micelle

Recent advances in carbon monoxide-releasing nanomaterials

As an endogenous signaling molecule, carbon monoxide (CO) has emerged as an increasingly promising option regarding as gas therapy due to its positive pharmacological effects in various diseases. Owing to the gaseous nature and potential toxicity, it is particularly important to modulate the CO release dosages and targeted locations to elucidate the biological mechanisms of CO and facilitate its clinical applications. Based on these, diverse CO-releasing molecules (CORMs) have been developed for controlled release of CO in biological systems. However, practical applications of these CORMs are limited by several disadvantages including low stability, poor solubility, weak releasing controllability, random diffusion, and potential toxicity. In light of rapid developments and diverse advantages of nanomedicine, abundant nanomaterials releasing CO in controlled ways have been developed for therapeutic purposes across various diseases. Due to their nanoscale sizes, diversified compositions and modified surfaces, vast CO-releasing nanomaterials (CORNMs) have been constructed and exhibited controlled CO release in specific locations under various stimuli with better pharmacokinetics and pharmacodynamics. In this review, we present the recent progress in CORNMs according to their compositions. Following a concise introduction to CO therapy, CORMs and CORNMs, the representative research progress of CORNMs constructed from organic nanostructures, hybrid nanomaterials, inorganic nanomaterials, and nanocomposites is elaborated. The basic properties of these CORNMs, such as active components, CO releasing mechanisms, detection methods, and therapeutic applications, are discussed in detail and listed in a table. Finally, we explore and discuss the prospects and challenges associated with utilizing nanomaterials for biological CO release.

Carbon Monoxide as a Potential Therapeutic Agent: A Molecular Analysis of Its Safety Profiles

Carbon monoxide (CO) is endogenously produced in mammals, with blood concentrations in the high micromolar range in the hemoglobin-bound form. Further, CO has shown therapeutic effects in various animal models. Despite its reputation as a poisonous gas at high concentrations, we show that CO should have a wide enough safety margin for therapeutic applications. The analysis considers a large number of factors including levels of endogenous CO, its safety margin in comparison to commonly encountered biomolecules or drugs, anticipated enhanced safety profiles when delivered via a noninhalation mode, and the large amount of safety data from human clinical trials. It should be emphasized that having a wide enough safety margin for therapeutic use does not mean that it is benign or safe to the general public, even at low doses. We defer the latter to public health experts. Importantly, this Perspective is written for drug discovery professionals and not the general public.

Folate-conjugated organic CO prodrugs: Synthesis and CO release kinetic studies

Carbon monoxide (CO) is an endogenous produced molecule and has shown efficacy in animal models of inflammation, organ injury, colitis and cancer metastasis. Because of its gaseous nature, there is a need for developing efficient CO delivery approaches, especially those capable of targeted delivery. In this study, we aim to take advantage of a previously reported approach of enrichment-triggered prodrug activation to achieve targeted delivery by targeting the folate receptor. The general idea is to exploit folate receptor-mediated enrichment as a way to accelerate a biomolecular Diels-Alder reaction for prodrug activation. In doing so, we first need to find ways to tune the reaction kinetics in order to ensure minimal rection without enrichment and optimal activation upon enrichment. In this feasibility study, we synthesized two diene-dienophile pairs and studied their reaction kinetics and ability to target the folate receptor. We found that folate conjugation significantly affects the reaction kinetics of the original diene-dienophile pairs. Such information will be very useful in future designs of similar targeted approaches of CO delivery.

A Single-Component Dual Donor Enables Ultrasound-Triggered Co-release of Carbon Monoxide and Hydrogen Sulfide

The development of dual gasotransmitter donors can not only provide robust tools to investigate their subtle interplay under pathophysiological conditions but also optimize therapeutic efficacy. While conventional strategies are heavily dependent on multicomponent donors, we herein report an ultrasound-responsive water-soluble copolymer (PSHF) capable of releasing carbon monoxide (CO) and hydrogen sulfide (H2 S) based on single-component sulfur-substituted 3-hydroxyflavone (SHF) derivatives. Interestingly, sulfur substitution can not only greatly improve the ultrasound sensitivity but also enable the co-release of CO/H2 S under mild ultrasound irradiation. The co-release of CO/H2 S gasotransmitters exerts a bactericidal effect against Staphylococcus aureus and demonstrates anti-inflammatory activity in lipopolysaccharide-challenged macrophages. Moreover, the excellent tissue penetration of ultrasound irradiation enables the local release of CO/H2 S in the joints of septic arthritis rats, exhibiting superior therapeutic efficacy without the need for any antibiotics.

Ultrasound nanotheranostics: Toward precision medicine

Ultrasound (US) is a mechanical wave that can penetrate biological tissues and trigger complex bioeffects. The mechanisms of US in different diagnosis and treatment are different, and the functional application of commercial US is also expanding. In particular, recent developments in nanotechnology have led to a wider use of US in precision medicine. In this review, we focus on US in combination with versatile micro and nanoparticles (NPs)/nanovesicles for tumor theranostics. We first introduce US-assisted drug delivery as a stimulus-responsive approach that spatiotemporally regulates the deposit of nanomedicines in target tissues. Multiple functionalized NPs and their US-regulated drug-release curves are analyzed in detail. Moreover, as a typical representative of US therapy, sonodynamic antitumor strategy is attracting researchers' attention. The collaborative efficiency and mechanisms of US and various nano-sensitizers such as nano-porphyrins and organic/inorganic nanosized sensitizers are outlined in this paper. A series of physicochemical processes during ultrasonic cavitation and NPs activation are also discussed. Finally, the new applications of US and diagnostic NPs in tumor-monitoring and image-guided combined therapy are summarized. Diagnostic NPs contain substances with imaging properties that enhance US contrast and photoacoustic imaging. The development of such high-resolution, low-background US-based imaging methods has contributed to modern precision medicine. It is expected that the integration of non-invasive US and nanotechnology will lead to significant breakthroughs in future clinical applications.

Reassessing CORM-A1: redox chemistry and idiosyncratic CO-releasing characteristics of the widely used carbon monoxide donor

Redox activity and unreliable carbon monoxide production of CO donor, CORM-A1, presents new complications in its use for studying CO biology.

Therapeutic gas-releasing nanomedicines with controlled release: Advances and perspectives

Nanoparticle-based drug delivery has become one of the most popular approaches for maximising drug therapeutic potentials. With the notable improvements, a greater challenge hinges on the formulation of gasotransmitters with unique challenges that are not met in liquid and solid active ingredients. Gas molecules upon release from formulations for therapeutic purposes have not really been discussed extensively. Herein, we take a critical look at four key gasotransmitters, that is, carbon monoxide (CO), nitric oxide (NO), hydrogen sulphide (H2S) and sulphur dioxide (SO2), their possible modification into prodrugs known as gas-releasing molecules (GRMs), and their release from GRMs. Different nanosystems and their mediatory roles for efficient shuttling, targeting and release of these therapeutic gases are also reviewed extensively. This review thoroughly looks at the diverse ways in which these GRM prodrugs in delivery nanosystems are designed to respond to intrinsic and extrinsic stimuli for sustained release. In this review, we seek to provide a succinct summary for the development of therapeutic gases into potent prodrugs that can be adapted in nanomedicine for potential clinical use.

Controlled therapeutic delivery of CO from carbon monoxide-releasing molecules (CORMs)

Carbon monoxide (CO) has been regarded as a "silent killer" for its toxicity toward biological systems. However, a low concentration of endogenously produced CO has shown a number of therapeutic benefits such as anti-inflammatory, anti-proliferative, anti-apoptosis, and cytoprotective activities. Carbon monoxide-releasing molecules (CORMs) have been developed as alternatives to direct CO inhalation, which requires a specialized setting for strict dose control. CORMs are efficient CO donors, with central transition metals (such as ruthenium, iron, cobalt, and manganese) surrounded by CO as a ligand. CORMs can stably store and subsequently release their CO payload in the presence of certain triggers including solvent, light, temperature, and ligand substitution. However, CORMs require appropriate delivery strategies to improve short CO release half-life and target specificity. Herein, we highlighted the therapeutic potential of inhalation and CORMs-delivered CO. The applications of conjugate and nanocarrier systems for controlling CO release and improving therapeutic efficacy of CORMs are also described in detail. The review concludes with some of the hurdles that limit clinical translation of CORMs. Keeping in mind the tremendous potential and growing interest in CORMs, this review would be helpful for designing controlled CO release systems for clinical applications.

Activated charcoal dispersion of carbon monoxide prodrugs for oral delivery of CO in a pill

A novel orally bioavailable solid formulation to deliver a gaseous signaling molecule, carbon monoxide (CO), was developed by adsorbing oxalyl saccharin, a newly developed organic CO prodrug, in activated charcoal (AC). The resulting solid dispersion formulation addresses key developability issues of this CO prodrug. By taking advantage of the large surface area of AC, the paradoxical problem of low water solubility of the prodrug and the requirement of hydrolysis to release CO is resolved, and the need for an organic cosolvent is completely circumvented. The AC formulation also mitigates the adverse effect of low pH on the CO release yield, allowing steady CO release in simulated gastric and intestine fluids. This formulation allows encapsulation in normal and enteric-coated gel capsules, which enables controllable CO delivery to the upper or lower GI system. It also features an advantage of trapping CO prodrug and CO release product in the AC, therefore lowering systemic absorption of these chemicals. Through in-vivo pharmacokinetic studies in mice, the AC formulation showed better efficiency of delivering CO through oral administration compared to the prodrug dosed with an organic cosolvent. The AC formulation has also been applied to address similar developability issues of another cheletropic reaction-based CO prodrug. We envision the wide applicability of this formulation in facilitating the future development of CO-based therapeutics.

Ultrasound-Mediated Release of Gaseous Signaling Molecules for Biomedical Applications

Although nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂ S) have been considered as notorious gas pollutants for decades, they are considered as endogenous gaseous signaling molecules (GSMs), which have been widely recognized for their important signaling functions and prominent medical applications in human physiology. To achieve local delivery of GSMs to optimize therapeutic efficacy and reduce systemic side effects, stimuli-responsive nanocarriers have been successfully developed. Among them, ultrasound is considered as an attractive theranostic modality that can be used to track drug carriers, trigger drug release, and improve drug deposition, etc. In this minireview, we summarize recent achievements in designing ultrasound-responsive nanocarriers for the controlled delivery of GSMs and their biomedical applications. This emerging research direction enables the controlled delivery of GSMs to deep tissues, and the combination of ultrasound imaging techniques offers many possibilities for the fabrication of new theranostic platforms. This article is protected by copyright. All rights reserved.

The potentials of carbon monoxide-releasing molecules in cancer treatment: An outlook from ROS biology and medicine

Carbon monoxide (CO) is now well recognized a pivotal endogenous signaling molecule in mammalian lives. The proof-of-concept employing chemical carriers of exogenous CO as prodrugs for CO release, also known as CO-releasing molecules (CO-RMs), has been appreciated. The major advantage of CO-RMs is that they are able to deliver CO to the target sites in a controlled manner. There is an increasing body of experimental studies suggesting the therapeutic potentials of CO and CO-RMs in different cancer models. This review firstly presents a short but crucial view concerning the characteristics of CO and CO-RMs. Then, the anticancer activities of CO-RMs that target many cancer hallmarks, mainly proliferation, apoptosis, angiogenesis, and invasion and metastasis, are discussed. However, their anticancer activities are varying and cell-type specific. The aerobic metabolism of molecular oxygen inevitably generates various oxygen-containing reactive metabolites termed reactive oxygen species (ROS) which play important roles in both physiology and pathophysiology. Although ROS act as a double-edged sword in cancer, both sides of which may potentially have been exploited for therapeutic benefits. The main focus of the present review is thus to identify the possible signaling network by which CO-RMs can exert their anticancer actions, where ROS play the central role. Another important issue concerning the potential effect of CO-RMs on the aerobic glycolysis (the Warburg effect) which is a feature of cancer metabolic reprogramming is given before the conclusion with future prospects on the challenges of developing CO-RMs into clinically pharmaceutical candidates in cancer therapy.

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CO-RMs as pro-drugs for controlled CO delivery are potentially beneficial in cancer treatment.

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Anticancer activities of CO-RMs are varying and cell-type specific.

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Anti-proliferative, pro-apoptotic, and anti-angiogenic effects are major niches.

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ROS may play a central role in the molecular pathways underlying anticancer activities of CO-RMs.

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CO-RMs can act against Warburg effect, a feature of cancer metabolic reprogramming.