Metal-Organic Framework (MOF)-Based Ultrasound-Responsive Dual-Sonosensitizer Nanoplatform for Hypoxic Cancer Therapy

Resveratrol suppresses liver cancer progression by downregulating AKR1C3: targeting HCC with HSA nanomaterial as a carrier to enhance therapeutic efficacy

The enzyme AKR1C3 plays a crucial role in hormone and drug metabolism and is associated with abnormal expression in liver cancer, leading to tumor progression and poor prognosis. Nanoparticles modified with HSA can modulate the tumor microenvironment by enhancing photodynamic therapy to induce apoptosis in tumor cells and alleviate hypoxia. Therefore, exploring the potential regulatory mechanisms of resveratrol on AKR1C3 through the construction of HSA-RSV NPs carriers holds significant theoretical and clinical implications for the treatment of liver cancer. The aim of this study is to investigate the targeted regulation of AKR1C3 expression through the loading of resveratrol (RSV) on nanomaterials HSA-RSV NPs (Nanoparticles) in order to alleviate tumor hypoxia and inhibit the progression of hepatocellular carcinoma (HCC), and to explore its molecular mechanism. PubChem database and PharmMapper server were used to screen the target genes of RSV. HCC-related differentially expressed genes (DEGs) were analyzed through the GEO dataset, and relevant genes were retrieved from the GeneCards database, resulting in the intersection of the three to obtain candidate DEGs. GO and KEGG enrichment analyses were performed on the candidate DEGs to analyze the potential cellular functions and molecular signaling pathways affected by the main target genes. The cytohubba plugin was used to screen the top 10 target genes ranked by Degree and further intersected the results of LASSO and Random Forest (RF) to obtain hub genes. The expression analysis of hub genes and the prediction of malignant tumor prognosis were conducted. Furthermore, a pharmacophore model was constructed using PharmMapper. Molecular docking simulations were performed using AutoDockTools 1.5.6 software, and ROC curve analysis was performed to determine the core target. In vitro cell experiments were carried out by selecting appropriate HCC cell lines, treating HCC cells with different concentrations of RSV, or silencing or overexpressing AKR1C3 using lentivirus. CCK-8, clone formation, flow cytometry, scratch experiment, and Transwell were used to measure cancer cell viability, proliferation, migration, invasion, and apoptosis, respectively. Cellular oxygen consumption rate was analyzed using the Seahorse XF24 analyzer. HSA-RSV NPs were prepared, and their characterization and cytotoxicity were evaluated. The biological functional changes of HCC cells after treatment were detected. An HCC subcutaneous xenograft model was established in mice using HepG2 cell lines. HSA-RSV NPs were injected via the tail vein, with a control group set, to observe changes in tumor growth, tumor targeting of NPs, and biological safety. TUNEL, Ki67, and APC-hypoxia probe staining were performed on excised tumor tissue to detect tumor cell proliferation, apoptosis, and hypoxia. Lentivirus was used to silence or overexpress AKR1C3 simultaneously with the injection of HSA-RSV NPs via the tail vein to assess the impact of AKR1C3 on the regulation of HSA-RSV NPs in HCC progression. Bioinformatics analysis revealed that AKR1C3 is an important target gene involved in the regulation of HCC by RSV, which is associated with the prognosis of HCC patients and upregulated in expression. In vitro cell experiments showed that RSV significantly inhibits the respiratory metabolism of HCC cells, suppressing their proliferation, migration, and invasion and promoting apoptosis. Silencing AKR1C3 further enhances the toxicity of RSV towards HCC cells. The characterization and cytotoxicity experiments of nanomaterials demonstrated the successful construction of HSA-RSV NPs, which exhibited stronger inhibitory effects on HCC cells. In vivo, animal experiments further confirmed that targeted downregulation of AKR1C3 by HSA-RSV NPs suppresses the progression of HCC and tumor hypoxia while exhibiting tumor targeting and biological safety. Targeted downregulation of AKR1C3 by HSA-RSV NPs can alleviate HCC tumor hypoxia and inhibit the progression of HCC.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

pH-Responsive injectable self-healing hydrogels loading Au nanoparticles-decorated bimetallic organic frameworks for synergistic sonodynamic-chemodynamic-starvation-chemo therapy of cancer

A novel and efficient cancer therapy was developed using a smart hydrogel containing multifunctional bimetallic organic frameworks and anticancer drugs. The injectable self-healing hydrogel with pH-responsiveness was constructed through borate ester and imine bonds among dopamine-grafted sodium alginate (SADA), hydroxypropyl chitosan (HPCS) and 2-formylphenylboronic acid (2-FPBA). The Au nanoparticles-decorated Ti/Fe bimetallic organic framework tetragonal nanosheets (Au/TF-MOF TNS) were synthesized and incorporated into the hydrogel with the anticancer drugs doxorubicin (DOX). Upon intratumoral injection of nanocomposite hydrogel, the acidic tumor microenvironment triggered the cleavage of borate ester and imine bonds, causing the hydrogel to break down and accelerating the release of both Au/TF-MOF TNS and DOX. These Au/TF-MOF TNS functioned as nanozymes, producing hydroxyl radicals (·OH) for chemodynamic therapy (CDT), generating oxygen (O2) to support sonodynamic therapy (SDT), and depleting glucose for starvation therapy (ST). Additionally, the Au/TF-MOF TNS served as sonosensitizers, capable of converting O2 into singlet oxygen (1O2) upon ultrasound irradiation to achieve SDT. Therefore, this nanocomposite hydrogel system enabled synergistic sonodynamic-chemodynamic-starvation-chemo therapy (SDT-CDT-ST-CT) of cancer, presenting a promising platform for advanced cancer therapy strategies.

NIR-II-Absorbing NDI Polymer with Superior Penetration Depth for Enhanced Photothermal Therapy Efficiency of Hepatocellular Carcinoma

Introduction

Hepatocellular carcinomas (HCC) have a high morbidity and mortality rate, and is difficult to cure and prone to recurrence when it has already developed. Therefore, early detection and efficient treatment of HCC is necessary.

Methods

In this study, we synthesized a novel NDI polymer with uniform size, long-term stability, and high near-infrared two-zone (NIR-II) absorption efficiency, which can greatly enhance the effect of photothermal therapy (PTT) after intravenous injection into Huh-7-tumor bearing mice.

Results

The in vitro and in vivo studies showed that NDI polymer exhibited excellent NIR-guided PTT treatment, and the antitumor effect was approximately 88.5%, with obvious antimetastatic effects.

Conclusion

This study developed an NDI polymer-mediated integrated diagnostic and therapeutic modality for NIR-II fluorescence imaging and photothermal therapy.

Metal-organic frameworks as candidates for tumor sonodynamic therapy: Designable structures for targeted multifunctional transformation

Sonodynamic therapy (SDT), utilizing ultrasound (US) as the trigger, has gained popularity recently as a therapeutic approach with significant potential for treating various diseases. Metal-organic frameworks (MOFs), characterized by structural flexibility, are prominently emerging in the SDT realm as an innovative type of sonosensitizer, offering functional tunability and biocompatibility. However, due to the inherent limitations of MOFs, such as low reactivity to reactive oxygen species and challenges posed by the complex tumor microenvironment, MOF-based sonosensitizers with singular functions are unable to demonstrate the desired therapeutic efficacy and may pose risks of toxicity, limiting their biological applications to superficial tissues. MOFs generally possess distinctive crystalline structures and properties, and their controlled coordination environments provide a flexible platform for exploring structure-effect relationships and guiding the design and development of MOF-based nanomaterials to unlock their broader potential in biological fields. The primary focus of this paper is to summarize cases involving the modification of different MOF materials and the innovative strategies developed for various complex conditions. The paper outlines the diverse application areas of functionalized MOF-based sonosensitizers in tumor synergistic therapies, highlighting the extensive prospects of SDT. Additionally, challenges confronting SDT are briefly summarized to stimulate increased scientific interest in the practical application of MOFs and the successful clinical translation of SDT. Through these discussions, we strive to foster advancements that lead to early-stage clinical benefits for patients. STATEMENT OF SIGNIFICANCE: 1. An overview for the progresses in SDT explored from a novel and fundamental perspective. 2. Different modification strategies to improve the MOFs-mediated SDT efficacy are provided. 3. Guidelines for the design of multifunctional MOFs-based sonosensitizers are offered. 4. Powerful tumor ablation potential is reflected in SDT-led synergistic therapies. 5. Future challenges in the field of MOFs-based SDT in clinical translation are suggested.

Positron emission tomography guided synergistic treatment of melanoma using multifunctional zirconium-hematoporphyrin nanosonosensitizers

Sonodynamic therapy (SDT) has emerged as a useful approach for tumor treatment. However, its widespread application is impeded by poor pharmacokinetics of existing sonosensitizers. Here we developed a metal-organic nanoplatform, wherein a small-molecule sonosensitizer (hematoporphyrin monomethyl ether, HMME) was ingeniously coordinated with zirconium, resulting in a multifunctional nanosonosensitizer termed Zr-HMME. Through post-synthetic modifications involving PEGylation and tumor-targeting peptide (F3) linkage, a nanoplatform capable of homing on melanoma was produced, which could elicit robust immune responses to suppress tumor lung metastasis in the host organism. Importantly, after seamless incorporation of positron-emitting 89Zr into this nanosonosensitizer, positron emission tomography (PET) could be used to monitor its in vivo pharmacokinetics. PET imaging studies revealed that this nanoplatform exhibited potent tumor accumulation and strong in vivo stability. Using intrinsic fluorescence from HMME, a dual-modal diagnostic capability (fluorescence and PET) was confirmed for this nanosonosensitizer. In addition, the mechanisms of how this nanoplatform interacted with immune system were also investigated. The collective data proved that the coordination structure between small-molecule drug cargos and metals may enhance the functions of each other while mitigating their weaknesses. This straightforward approach can expand the potential applications of suitable drug molecules.

Time and Space Dual-Blockade Strategy for Highly Invasive Nature of Triple-Negative Breast Cancer in Enhanced Sonodynamic Therapy Based on Fe-MOF Nanoplatforms

Triple-negative breast cancer (TNBC), due to its high malignant degree and strong invasion ability, leads to poor prognosis and easy recurrence, so effectively curbing the invasion of TNBC is the key to obtaining the ideal therapeutic effect. Herein, a therapeutic strategy is developed that curbs high invasions of TNBC by inhibiting cell physiological activity and disrupting tumor cell structural function to achieve the time and space dual-blockade. The time blockade is caused by the breakthrough of the tumor-reducing blockade based on the ferroptosis process and the oxidation-toxic free radicals generated by enhanced sonodynamic therapy (SDT). Meanwhile, alkyl radicals from 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIPH) and 1O2 attacked the organelles of tumor cells under ultrasound (US), reducing the physiological activity of the cells. The attack of free radicals on the cytoskeleton, especially on the proteins of F-actin and its assembly pathway, achieves precise space blockade of TNBC. The damage to the cytoskeleton and the suppression of the repair process leads to a significant decline in the ability of tumor cells to metastasize and invade other organs. In summary, the FTM@AM nanoplatforms have a highly effective killing and invasion inhibition effect on invasive TNBC mediated by ultrasound, showcasing promising clinical transformation potential.

Advances in Nanomaterials for Immunotherapeutic Improvement of Cancer Chemotherapy

Immuno-stimulative effect of chemotherapy (ISECT) is recognized as a potential alternative to conventional immunotherapies, however, the clinical application is constrained by its inefficiency. Metronomic chemotherapy, though designed to overcome these limitations, offers inconsistent results, with effectiveness varying based on cancer types, stages, and patient-specific factors. In parallel, a wealth of preclinical nanomaterials holds considerable promise for ISECT improvement by modulating the cancer-immunity cycle. In the area of biomedical nanomaterials, current literature reviews mainly concentrate on a specific category of nanomaterials and nanotechnological perspectives, while two essential issues are still lacking, i.e., a comprehensive analysis addressing the causes for ISECT inefficiency and a thorough summary elaborating the nanomaterials for ISECT improvement. This review thus aims to fill these gaps and catalyze further development in this field. For the first time, this review comprehensively discusses the causes of ISECT inefficiency. It then meticulously categorizes six types of nanomaterials for improving ISECT. Subsequently, practical strategies are further proposed for addressing inefficient ISECT, along with a detailed discussion on exemplary nanomedicines. Finally, this review provides insights into the challenges and perspectives for improving chemo-immunotherapy by innovations in nanomaterials.

Metal-Organic Framework Nanomaterials as a Medicine for Catalytic Tumor Therapy: Recent Advances

Nanomaterials, with unique physical, chemical, and biocompatible properties, have attracted significant attention as an emerging active platform in cancer diagnosis and treatment. Amongst them, metal-organic framework (MOF) nanostructures are particularly promising as a nanomedicine due to their exceptional surface functionalities, adsorption properties, and organo-inorganic hybrid characteristics. Furthermore, when bioactive substances are integrated into the structure of MOFs, these materials can be used as anti-tumor agents with superior performance compared to traditional nanomaterials. In this review, we highlight the most recent advances in MOFs-based materials for tumor therapy, including their application in cancer treatment and the underlying mechanisms.

Ultrasound-Sensitive Intelligent Nanosystems: A Promising Strategy for the Treatment of Neurological Diseases

Neurological diseases are a major global health challenge, affecting hundreds of millions of people worldwide. Ultrasound therapy plays an irreplaceable role in the treatment of neurological diseases due to its noninvasive, highly focused, and strong tissue penetration capabilities. However, the complexity of brain and nervous system and the safety risks associated with prolonged exposure to ultrasound therapy severely limit the applicability of ultrasound therapy. Ultrasound-sensitive intelligent nanosystems (USINs) are a novel therapeutic strategy for neurological diseases that bring greater spatiotemporal controllability and improve safety to overcome these challenges. This review provides a detailed overview of therapeutic strategies and clinical advances of ultrasound in neurological diseases, focusing on the potential of USINs-based ultrasound in the treatment of neurological diseases. Based on the physical and chemical effects induced by ultrasound, rational design of USINs is a prerequisite for improving the efficacy of ultrasound therapy. Recent developments of ultrasound-sensitive nanocarriers and nanoagents are systemically reviewed. Finally, the challenges and developing prospects of USINs are discussed in depth, with a view to providing useful insights and guidance for efficient ultrasound treatment of neurological diseases.

Ultrasound-Triggered Azo Free Radicals for Cervical Cancer Immunotherapy

PD-1 blockade is a first-line treatment for recurrent/metastatic cervical cancer but benefits only a small number of patients due to low preexisting tumor immunogenicity. Using immunogenic cell death (ICD) inducers is a promising strategy for improving immunotherapy, but these compounds are limited by the hypoxic environment of solid tumors. To overcome this issue, the nanosensitizer AIBA@MSNs were designed based on sonodynamic therapy (SDT), which induces tumor cell death under hypoxic conditions through azo free radicals in a method of nonoxygen radicals. Mechanistically, the azo free radicals disrupt both the structure and function of tumor mitochondria by reversing the mitochondrial membrane potential and facilitating the collapse of electron transport chain complexes. More importantly, the AIBA@MSN-based SDT serves as an effective ICD inducer and improves the antitumor immune capacity. The combination of an AIBA@MSN-based SDT with a PD-1 blockade has the potential to improve response rates and provide protection against relapse. This study provides insights into the use of azo free radicals as a promising SDT strategy for cancer treatment and establishes a basic foundation for nonoxygen-dependent SDT-triggered immunotherapy in cervical cancer treatment.

Application of Nanomaterial-Based Sonodynamic Therapy in Tumor Therapy

Sonodynamic therapy (SDT) has attracted significant attention in recent years as it is an innovative approach to tumor treatment. It involves the utilization of sound waves or ultrasound (US) to activate acoustic sensitizers, enabling targeted drug release for precise tumor treatment. This review aims to provide a comprehensive overview of SDT, encompassing its underlying principles and therapeutic mechanisms, the applications of nanomaterials, and potential synergies with combination therapies. The review begins by introducing the fundamental principle of SDT and delving into the intricate mechanisms through which it facilitates tumor treatment. A detailed analysis is presented, outlining how SDT effectively destroys tumor cells by modulating drug release mechanisms. Subsequently, this review explores the diverse range of nanomaterials utilized in SDT applications and highlights their specific contributions to enhancing treatment outcomes. Furthermore, the potential to combine SDT with other therapeutic modalities such as photothermal therapy (PTT) and chemotherapy is discussed. These combined approaches aim to synergistically improve therapeutic efficacy while mitigating side effects. In conclusion, SDT emerges as a promising frontier in tumor treatment that offers personalized and effective treatment options with the potential to revolutionize patient care. As research progresses, SDT is poised to play a pivotal role in shaping the future landscape of oncology by providing patients with a broader spectrum of efficacious and tailored treatment options.

Photocatalytic manipulation of Ca2+ signaling for regulating cellular and animal behaviors via MOF-enabled H2O2 generation

The in situ generation of H2O2 in cells in response to external stimulation has exceptional advantages in modulating intracellular Ca2+ dynamics, including high controllability and biological safety, but has been rarely explored. Here, we develop photocatalyst-based metal-organic frameworks (DCSA-MOFs) to modulate Ca2+ responses in cells, multicellular spheroids, and organs. By virtue of the efficient photocatalytic oxygen reduction to H2O2 without sacrificial agents, photoexcited DCSA-MOFs can rapidly trigger Ca2+ outflow from the endoplasmic reticulum with single-cell precision in a repeatable and controllable manner, enabling the propagation of intercellular Ca2+ waves (ICW) over long distances in two-dimensional and three-dimensional cell cultures. After photoexcitation, ICWs induced by DCSA-MOFs can activate neural activities in the optical tectum of tadpoles and thighs of spinal frogs, eliciting the corresponding motor behaviors. Our study offers a versatile optical nongenetic modulation technique that enables remote, repeatable, and controlled manipulation of cellular and animal behaviors.

Mucus and Biofilm Penetrating Nanoplatform as an Ultrasound-Induced Free Radical Initiator for Targeted Treatment of Helicobacter pylori Infection

Helicobacter pylori (H. pylori) infection is closely associated with the development of various gastric diseases. The effectiveness of current clinical antibiotic therapy is hampered by the rise of drug-resistant strains and the formation of H. pylori biofilm. This paper reports a sonodynamic nanocomposite PtCu3-PDA@AIPH@Fucoidan (PPAF), which consists of dopamine-modified inorganic sonosensitizers PtCu3, alkyl radicals (R•) generator AIPH and fucoidan, can penetrate the mucus layer, target H. pylori, disrupt biofilms, and exhibit excellent bactericidal ability. In vitro experiments demonstrate that PPAF exhibits excellent acoustic kinetic properties, generating a significant amount of reactive oxygen species and oxygen-independent R• for sterilization under ultrasound stimulation. Simultaneously, the produced N2 can enhance the cavitation effect, aiding PPAF nanoparticles in penetrating the gastric mucus layer and disrupting biofilm integrity. This disruption allows more PPAF nanoparticles to bind to biofilm bacteria, facilitating the eradication of H. pylori. In vivo experiments demonstrate that ultrasound-stimulated PPAF exhibited significant antibacterial efficacy against H. pylori. Moreover, it effectively modulated the expression levels of inflammatory factors and maintained gastrointestinal microbiota stability when compared to the antibiotic treatment group. In summary, PPAF nanoparticles present a potential alternative to antibiotics, offering an effective and healthy option for treating H. pylori infection.

Tumor microenviroment-responsive self-assembly of barium titanate nanoparticles with enhanced piezoelectric catalysis capabilities for efficient tumor therapy

Catalytic therapy based on piezoelectric nanoparticles has become one of the effective strategies to eliminate tumors. However, it is still a challenge to improve the tumor delivery efficiency of piezoelectric nanoparticles, so that they can penetrate normal tissues while specifically aggregating at tumor sites and subsequently generating large amounts of reactive oxygen species (ROS) to achieve precise and efficient tumor clearance. In the present study, we successfully fabricated tumor microenvironment-responsive assembled barium titanate nanoparticles (tma-BTO NPs): in the neutral pH environment of normal tissues, tma-BTO NPs were monodisperse and possessed the ability to cross the intercellular space; whereas, the acidic environment of the tumor triggered the self-assembly of tma-BTO NPs to form submicron-scale aggregates, and deposited in the tumor microenvironment. The self-assembled tma-BTO NPs not only caused mechanical damage to tumor cells; more interestingly, they also exhibited enhanced piezoelectric catalytic efficiency and produced more ROS than monodisperse nanoparticles under ultrasonic excitation, attributed to the mutual extrusion of neighboring particles within the confined space of the assembly. tma-BTO NPs exhibited differential cytotoxicity against tumor cells and normal cells, and the stronger piezoelectric catalysis and mechanical damage induced by the assemblies resulted in significant apoptosis of mouse breast cancer cells (4T1); while there was little damage to mouse embryo osteoblast precursor cells (MC3T3-E1) under the same treatment conditions. Animal experiments confirmed that peritumoral injection of tma-BTO NPs combined with ultrasound therapy can effectively inhibit tumor progression non-invasively. The tumor microenvironment-responsive self-assembly strategy opens up new perspectives for future precise piezoelectric-catalyzed tumor therapy.

A "One Arrow Three Eagle" Strategy to Improve CM-272 Primed Bladder Cancer Immunotherapy

Immunotherapy using an immune-checkpoint blockade has significantly improved its therapeutic effects. CM-272, which is a novel epigenetic inhibitor of G9a, induces immunogenic cell death (ICD) for recovering the sensitivity to anti-PD-1 antibodies; however, the efficacy of CM-272 is greatly limited by promoting the transcription activity of HIF-1α to form a hypoxic environment. Here, a Fe3+ -based nanoscale metal-organic framework (MIL-53) is used to load CM-272 (ultra-high loading rate of 56.4%) for realizing an MIL-53@CM-272 nanoplatform. After entering bladder cancer cells, Fe3+ not only promotes the decomposition of H2 O2 into O2 for O2 -compensated sonodynamic therapy but reduces the high level of glutathione in the tumor microenvironment (TME) for enhancing reactive oxygen species, including ferroptosis and apoptosis. MIL-53 carriers can be degraded in response to the TME, accelerating the release of CM-272, which helps achieve the maximum effectiveness in an O2 -sufficient TME by attenuating drug resistance. Furthermore, MIL-53@CM-272 enhances dendritic cell maturation and synergistically combines it with an anti-programmed cell death protein 1 antibody during the study of immune-related pathways in the transcriptomes of bladder cancer cells using RNA-seq. This study presents the first instance of amalgamating nanomedicine with CM-272, inducing apoptosis, ferroptosis, and ICD to achieve the "one arrow three eagle" effect.

Ultrasound activated probe for disease imaging and therapy In-Vivo

Sonodynamic therapy (SDT) is the use of ultrasound (US) to excite sonosensitizers to produce reactive oxygen species (ROS) to induce tumor cell death, thereby achieving therapeutic purposes. Based on the strong tissue penetration ability of ultrasound, SDT can realize the treatment of deeper tumors, and it is targeted, can be specifically concentrated at the tumor site, and has little impact on surrounding normal tissues. It has broad clinical transformation prospects. Therefore, sonosensitizers are the key to SDT, and the exploration of sonosensitizers with excellent therapeutic performance has received great attention. We reviewed the development of ultrasound-inspired sound sensitizers for imaging and treatment. First, different types of sonosensitizers are introduced, the construction and performance of inorganic, organic and hybrid types of sonosensitizers are evaluated, followed by a review of different image-guided SDT, and finally the key problems and solutions in this field are discussed in detail.

Multifunctional nanoparticles for enhanced sonodynamic-chemodynamic immunotherapy with glutathione depletion

Aim: This study aimed to develop a sonodynamic-chemodynamic nanoparticle functioning on glutathione depletion in tumor immunotherapy. Materials & methods: The liposome-encapsulated 2,2-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH) and copper-cysteine nanoparticles, AIPH/Cu-Cys@Lipo, were synthesized with a one-pot method. 4T1 cells were injected into female BALB/c mice for modeling. Results: AIPH/Cu-Cys@Lipo was well synthesized. It generated alkyl radicals upon ultrasound stimulation. AIPH/Cu-Cys@Lipo promoted the generation of -OH via a Fenton-like reaction. Both in vitro and in vivo experiments verified that AIPH/Cu-Cys@Lipo significantly inhibited tumor development by decreasing mitochondrial membrane potential, activating CD4+ and CD8+ T cells and promoting the expression of IL-2 and TNF-α. Conclusion: AIPH/Cu-Cys@Lipo provides high-quality strategies for safe and effective tumor immunotherapy.

Platinum nanoparticle-anchored metal-organic complex nanospheres by a coordination-crystallization approach for enhanced sonodynamic therapy of tumors

The combination of noble metal nanoparticles with metal-organic complexes has attracted great attention for exploring new properties in biomedical application areas. So far, the preparation of noble metal nanoparticle-loaded metal-organic complexes often requires complex processes. Here, a simple coordination-crystallization approach was developed to prepare platinum nanoparticle-anchored metal-organic complexes (Pt-MOCs) by directly mixing disulfiram (DSF), chloroplatinic acid, and a reducing agent. The DSF and Pt ions first coordinate forming metal-organic complex nanospheres and then the Pt nanoparticles crystallized on the surface taking advantage of the coordination rate of the metal ions and organic ligand being greater than the reduction rate of the metal ions. The Pt-MOCs possess uniform and adjustable diameter (240-536 nm), and their surface potentials can also be modulated easily from -22 to +14 mV by adjusting the ratio of DSF and chloroplatinic acid. Phantom experiments show that the Pt-MOC nanospheres significantly improve the efficiency of singlet oxygen production after exposure to ultrasound irradiation. In vitro experiments show that the Pt-MOCs effectively produce reactive oxygen species and exhibit superior cytotoxicity for tumor cells under ultrasound irradiation compared to metal-organic complexes (MOCs) or Pt nanoparticles. Taken together, this work reports a coordination-crystallization approach to synthesize Pt-MOCs, which show excellent sonodynamic therapy for tumors.

Nanomaterials-based precision sonodynamic therapy enhancing immune checkpoint blockade: A promising strategy targeting solid tumor

Burgeoning is an evolution from conventional photodynamic therapy (PDT). Thus, sonodynamic therapy (SDT) regulated by nanoparticles (NPs) possesses multiple advantages, including stronger penetration ability, better biological safety, and not reactive oxygen species (ROS)-dependent tumor-killing effect. However, the limitation to tumor inhibition instead of shrinkage and the incapability of eliminating metastatic tumors hinder the clinical potential for SDT. Fortunately, immune checkpoint blockade (ICB) can revive immunological function and induce a long-term immune memory against tumor rechallenges. Hence, synergizing NPs-based SDT with ICB can provide a promising therapeutic outcome for solid tumors. Herein, we briefly reviewed the progress in NPs-based SDT and ICB therapy. We highlighted the synergistic anti-tumor mechanisms and summarized the representative preclinical trials on SDT-assisted immunotherapy. Compared to other reviews, we provided comprehensive and unique perspectives on the innovative sonosensitizers in each trial. Moreover, we also discussed the current challenges and future corresponding solutions.

Enhanced thrombolytic effect induced by acoustic cavitation generated from nitrogen-doped annealed nanodiamond particles

In biomedical research, ultrasonic cavitation, especially inertial cavitation (IC) has attracted extensive attentions due to its ability to induce mechanical, chemical and thermal effects. Like ultrasound contrast agent (UCA) microbubbles or droplets, acoustic cavitation can be effectively triggered beyond a certain pressure threshold through the interaction between ultrasound and nucleation particles, leading to an enhanced thrombolytic effect. As a newly developed nanocarbon material, nitrogen-doped annealed nanodiamond (N-AND) has shown promising catalytic performance. To further explore its effects on ultrasonic cavitation, N-AND was synthesized at the temperature of 1000 °C. After systematic material characterization, the potential of N-AND to induce enhanced IC activity was assessed for the first time by using passive cavitation detection (PCD). Based on experiments performed at varied material suspension concentration and cycle number, N-AND demonstrated a strong capability to generate significant cavitation characteristics, indicating the formation of stable bubbles from the surface of the materials. Furthermore, N-AND was applied in the in vitro thrombolysis experiments to verify its contribution to ultrasound thrombolysis. The influence of surface hydrophobicity on the cavitation potentials of ND and N-AND was innovatively discussed in combination with the theory of mote-induced nucleation. It is found that the cavitation stability of N-AND was better than that of the commercial UCA microbubbles. This study would provide better understanding of the potential of novel carbonous nanomaterials as cavitation nuclei and is expected to provide guidance for their future biomedical and industrial applications.

Recent Advances in Multifunctional Reticular Framework Nanoparticles: A Paradigm Shift in Materials Science Road to a Structured Future

Porous organic frameworks (POFs) have become a highly sought-after research domain that offers a promising avenue for developing cutting-edge nanostructured materials, both in their pristine state and when subjected to various chemical and structural modifications. Metal-organic frameworks, covalent organic frameworks, and hydrogen-bonded organic frameworks are examples of these emerging materials that have gained significant attention due to their unique properties, such as high crystallinity, intrinsic porosity, unique structural regularity, diverse functionality, design flexibility, and outstanding stability. This review provides an overview of the state-of-the-art research on base-stable POFs, emphasizing the distinct pros and cons of reticular framework nanoparticles compared to other types of nanocluster materials. Thereafter, the review highlights the unique opportunity to produce multifunctional tailoring nanoparticles to meet specific application requirements. It is recommended that this potential for creating customized nanoparticles should be the driving force behind future synthesis efforts to tap the full potential of this multifaceted material category.

Oxygen-defective zinc oxide nanoparticles as highly efficient and safe sonosensitizers for cancer therapy

Herein, an oxygen defect-modulated zinc oxide sonosensitizer is designed, which enhances the absorbance of ultrasound energy and suppresses the recombination of ultrasound-initiated electrons and holes to promote reactive oxygen species yield. It achieves a high tumor inhibition efficiency of 79.9%, which exhibits a potential application for sonodynamic cancer therapy.

Perfluoropentane/apatinib-encapsulated metal-organic framework nanoparticles enhanced the microwave ablation of hepatocellular carcinoma

Microwave ablation (MWA) is a promising minimally invasive therapy for hepatocellular carcinoma (HCC). However, the efficiency of MWA in treating HCC is evidently limited by the incomplete ablation of large tumors and tumors in high-risk locations. Here we designed an iron-based metal-organic framework nanomedicine (PFP-Apa-MOF) by loading perfluoropentane (PFP) and apatinib (Apa). After being absorbed by HCC, iron could induce ferroptosis. PFP could be activated into bubbles and act as an ultrasound agent for detecting the ablation margin. As an effective antiangiogenic drug, Apa could inhibit tumor residual growth after MWA. The high efficiency of PFP-Apa-MOF was fully demonstrated in vitro and in vivo. The results showed that MWA combined with PFP-Apa-MOF clearly enhanced the ablation efficiency, leading to apparent tumor inhibition, and increased tumor apoptosis and lipid peroxide. PFP-Apa-MOF could play a valuable role in enhancing MWA to achieve better therapeutic efficacy in HCC.

A Novel Platform of MOF for Sonodynamic Therapy Advanced Therapies

Metal-organic frameworks (MOFs) combined with sonodynamic therapy (SDT) have been introduced as a new and efficient treatment method. The critical advantage of SDT is its ability to penetrate deep tissues and concentrate energy on the tumor site to achieve a non-invasive or minimally invasive effect. Using a sonosensitizer to generate reactive oxygen species (ROS) under ultrasound is the primary SDT-related method of killing tumor cells. In the presence of a sonosensitizer, SDT exhibits a more lethal effect on tumors. The fast development of micro/nanotechnology has effectively improved the efficiency of SDT, and MOFs have been broadly evaluated in SDT due to their easy synthesis, easy surface functionalization, high porosity, and high biocompatibility. This article reviews the main mechanism of action of sonodynamic therapy in cancer treatment, and also reviews the applications of MOFs in recent years. The application of MOFs in sonodynamic therapy can effectively improve the targeting ability of SDT and the conversion ability of reactive oxygen species, thus improving their killing ability on cancer cells. This provides new ideas for the application of micro/nano particles in SDT and cancer therapy.

On-Demand Free Radical Release by Laser Irradiation for Photothermal-Thermodynamic Biofilm Inactivation and Tooth Whitening

Dental diseases associated with biofilm infections and tooth staining affect billions of people worldwide. In this study, we combine photothermal agents (MoS₂@BSA nanosheets, MB NSs), a thermolysis free-radical initiator (AIPH), and carbomer gel to develop laser-responsive hydrogel (MBA-CB Gel) for biofilm inactivating and tooth whitening. Under a physiological temperature without laser irradiation, MB NSs can eliminate free radicals generated from the slow decomposition of AIPH due to their antioxidative activity, thereby avoiding potential side effects. A cytotoxicity study indicates that MB NSs can protect mammalian cells from the free radicals released from AIPH without laser irradiation. Upon exposure to laser irradiation, MB NSs promote the rapid decomposition of AIPH to release free radicals by photothermal effect, suggesting their on-demand release ability of free radicals. In vitro experimental results show that the bacteria inactivation efficiency is 99.91% (3.01 log units) for planktonic Streptococcus mutans (S. mutans) and 99.98% (3.83 log units) for planktonic methicillin-resistant Staphylococcus aureus (MRSA) by the mixed solution of MB NSs and AIPH (MBA solution) under 808 nm laser irradiation (1.0 W/cm², 5 min). For S. mutans biofilms, an MBA solution can inactivate 99.97% (3.63 log units) of the bacteria under similar laser irradiation conditions. Moreover, MBA-CB Gel can whiten an indigo carmine-stained tooth under laser irradiation after 60 min of laser treatment, and the color difference (ΔE) in the teeth of the MBA-CB Gel treatment group was 10.9 times that of the control group. This study demonstrates the potential of MBA-CB Gel as a promising platform for biofilm inactivation and tooth whitening. It is worth noting that, since this study only used stained models of extracted teeth, the research results may not fully reflect the actual clinic situation. Future clinical research needs to further validate these findings.

Metal-organic framework decorated with glycyrrhetinic acid conjugated chitosan as a pH-responsive nanocarrier for targeted drug delivery

Stimulus-responsive nanomaterials have become a hot spot in controllable drug delivery systems researches owing to their spatiotemporal controllable properties based on the differences between tumor microenvironment and normal tissue. Herein, iron (III) carboxylate metal-organic framework nanoparticles coated with glycyrrhetinic acid-chitosan conjugate (MIL-101/GA-CS) were successfully fabricated and acted as the pH-responsive and target-selective system to deliver doxorubicin (DOX) for hepatocellular carcinoma (HCC) therapy. The prepared nanocarrier possess the advantages of uniform size, comparable drug loading efficiency (28.89 %), and superior pH-dependent controlled drug release (DOX release of 2.74 % and 89.18 % within 72 h at pH 7.4 and 5.5, respectively). In vitro cytotoxicity assays showed that the drug-loaded nanocarriers exhibited excellent inhibitory effects on HepG2 cells due to the sustained release of DOX, while the nanocarriers showed no significant toxicity. Furthermore, cell uptake experiments demonstrated that MIL-101-DOX/GA-CS could target HepG2 cells based on receptor-dependent internalization of glycyrrhetinic acid-receptors-mediated (GA-receptors). In vitro 3D hepatoma cell microspheres experiments showed that MIL-101-DOX/GA-CS had excellent penetration and tumor killing ability. Therefore, MIL-101-DOX/GA-CS nanoparticles have a prospective application in cancer therapy as a pH-responsive controlled drug delivery system.

Ultrasound nanomedicine and materdicine

The conventional microbubble-based ultrasound biomedicine clinically plays a vital role in providing the dynamic detection of macro and microvasculature and disease theranostics. However, the intrinsic limitation of particle size severely decreases the treatment effectiveness due to their vascular transport characteristics, which promotes the development and application of multifunctional ultrasound-responsive nanomaterials. Herein, we put forward a research field of "ultrasound nanomedicine and materdicine", referring to the interdiscipline of ultrasound, nanobiotechnology and materials, which seeks to produce specific biological effects for addressing the challenges faced and dilemma of conventional ultrasound medicine. We comprehensively summarize the state-of-the-art scientific advances in the latest progress in constructing ultrasound-based platforms and ultrasound-activated sonosensitizers, ranging from the synthesis strategies, biological functions to ultrasound-triggered therapeutic applications. Ultimately, the unresolved challenges and clinical-translation potentials of ultrasound nanomedicine and materdicine are discussed and prospected in this evolving field.

Metal-Organic Frameworks (MOF)-Assisted Sonodynamic Therapy in Anticancer Applications

Sonodynamic therapy (SDT) has emerged as a promising therapeutic modality for anticancer treatments and is becoming a cutting-edge interdisciplinary research field. This review starts with the latest developments of SDT and provides a brief comprehensive discussion on ultrasonic cavitation, sonodynamic effect, and sonosensitizers in order to popularize the basic principles and probable mechanisms of SDT. Then the recent progress of MOF-based sonosensitizers is overviewed, and the preparation methods and properties (e.g., morphology, structure, and size) of products are presented in a fundamental perspective. More importantly, many deep observations and understanding toward MOF-assisted SDT strategies were described in anticancer applications, aiming to highlight the advantages and improvements of MOF-augmented SDT and synergistic therapies. Last but not least, the review also pointed out the probable challenges and technological potential of MOF-assisted SDT for the future advance. In all, the discussions and summaries of MOF-based sonosensitizers and SDT strategies will promote the fast development of anticancer nanodrugs and biotechnologies.

Defect-Rich Ni-CoO@PEG Porous Hexagonal Nanosheets: Multi-enzyme and Ultrasound Catalysis for Synergistic Anticancer Treatment

Given the similarity with photocatalysis, sonodynamic therapy (SDT) can be defined as ultrasonic (US) catalysis. Encouraged by the principles of photocatalysis and defect chemistry, defect-rich nickel (Ni)-doped cobaltous oxide (Ni-CoO@PEG) porous hexagonal nanosheets have been synthesized as a sonosensitizer. The doping of Ni decreases the band gap that is testified by density functional theory to increase the US-generated charges. Under US irradiation, Ni-CoO@PEG nanosheets produce ¹O₂ as an active species that is determined by dissolved O₂ and electrons. Moreover, the doping also brings abundant oxygen vacancies (O_V) that not only are in favor of efficient separation of electron-hole but also enhance the interaction toward O₂, boosting ¹O₂ generation. In addition, Ni-CoO@PEG shows robust mimic catalase (CAT) and peroxidase characterization to effectively improve the intratumor O₂ content and oxidation stress. What is more, the nanosheets also possess glucose oxidase activity that can consume glucose to elevate the H₂O₂/acid level and to block the intracellular energy supply. The tandem nanozyme behaviors would further regulate the tumor microenvironment for assisting anticancer treatment. It is noted that Ni-CoO@PEG reveals a novel half-metallic feature endowing great magnetism and magnetic resonance imaging capacity. The above synergistic treatments exhibit outstanding anticancer performance that also evokes antitumor immunity to suppress metastasis and recurrence, efficiently.

Multifunctional nanoparticle for cancer therapy

Cancer is a complex disease associated with a combination of abnormal physiological process and exhibiting dysfunctions in multiple systems. To provide effective treatment and diagnosis for cancer, current treatment strategies simultaneously focus on various tumor targets. Based on the rapid development of nanotechnology, nanocarriers have been shown to exhibit excellent potential for cancer therapy. Compared with nanoparticles with single functions, multifunctional nanoparticles are believed to be more aggressive and potent in the context of tumor targeting. However, the development of multifunctional nanoparticles is not simply an upgraded version of the original function, but involves a sophisticated system with a proper backbone, optimized modification sites, simple preparation method, and efficient function integration. Despite this, many well-designed multifunctional nanoparticles with promising therapeutic potential have emerged recently. Here, to give a detailed understanding and analyzation of the currently developed multifunctional nanoparticles, their platform structures with organic or inorganic backbones were systemically generalized. We emphasized on the functionalization and modification strategies, which provide additional functions to the nanoparticle. We also discussed the application combination strategies that were involved in the development of nanoformulations with functional crosstalk. This review thus provides an overview of the construction strategies and application advances of multifunctional nanoparticles.

Nanoengineered sonosensitive platelets for synergistically augmented sonodynamic tumor therapy by glutamine deprivation and cascading thrombosis

Ultrasound (US)-activated sonodynamic therapy (SDT) stands for a distinct antitumor modality because of its attractive characteristics including intriguing noninvasiveness, desirable safety, and high tissue penetration depth, which, unfortunately, suffers from compromised therapeutic efficacy due to cancer cell-inherent adaptive mechanisms, such as glutathione (GSH) neutralization response to reactive oxygen species (ROS), and glutamine addictive properties of tumors. In this work, we developed a biological sonosensitive platelet (PLT) pharmacytes for favoring US/GSH-responsive combinational therapeutic of glutamine deprivation and augmented SDT. The amino acid transporter SLC6A14 blockade agent α-methyl-_DL-tryptophan (α-MT)-loaded and MnO₂-coated porphyrinic metal-organic framework (MOF) nanoparticles were encapsulated in the PLTs through the physical adsorption of electrostatic attraction and the intrinsic endocytosis of PLTs. When the sonosensitive PLT pharmacytes reached tumor sites through their natural tendencies to TME, US stimulated the PLTs-loaded porphyrinic MOF to generate ROS, resulting in morphological changes of the PLTs and the release of nanoparticles. Subsequently, intracellular high concentration of GSH and extracellular spatio-temporal controlled US irradiation programmatically triggered the release of α-MT, which enabled the synergistically amplified SDT by inducing amino acid starvation, inhibiting mTOR, and mediating ferroptosis. In addition, US stimulation achieved the targeted activation of PLTs at tumor vascular site, which evolved from circulating PLTs to dendritic PLTs, effectively blocking the blood supply of tumors through thrombus formation, and revealing the encouraging potential to facilitate tumor therapeutics.

Ultrasound-Activatable Phase-Shift Nanoparticle as a Targeting Antibacterial Agent for Efficient Eradication of Pseudomonas aeruginosa Biofilms

Biofilms are physical barriers composed of extracellular polymeric substances (EPS) that enable planktonic bacteria to resist host responses and antibacterial treatments, complicating efforts to clear bacteria such as Pseudomonas aeruginosa (P. aeruginosa) and thereby contributing to persistently chronic infections. As such, it is critical to develop a robust antimicrobial strategy capable of effectively eradicating P. aeruginosa biofilms and to further address aggressive clinical infection. In this study, ultrasound-activatable targeted nanoparticles were designed by using poly(lactic-co-glycolic acid) (PLGA) nanoparticles to encapsulate phase-transformable perfluoropentane (PFP) and the antibiotic meropenem via a double emulsion approach, followed by conjugation with anti-P. aeruginosa antibodies. In this strategy, ultrasound exposure can trigger PFP to produce microbubbles, inducing ultrasonic cavitation effects that can disrupt EPS components and allow nanoparticles to release meropenem to kill P. aeruginosa directly and accelerate the associated wound healing. These nanoparticles eradicated biofilms effectively and cleared bacteria in vitro as well as exhibited potent anti-infective activity in vivo. In summary, this study demonstrates the efficacy of a sonobactericidal strategy as a means of effectively and reliably eliminating biofilms.

Hypoxia-Nitric Oxide Axis and the Associated Damage Molecular Pattern in Cutaneous Melanoma

Hypoxia was intensively studied in cancer during the last few decades, being considered a characteristic of the tumor microenvironment. The aim of the study was to evaluate the capacity of tumor cells to adapt to the stress generated by limited oxygen tissue in cutaneous melanoma. We developed a case-control prospective study that included 52 patients with cutaneous melanoma and 35 healthy subjects. We focused on identifying and monitoring hypoxia, the dynamic of nitric oxide (NO) serum metabolites and posttranslational metabolic disorders induced by NO signaling according to the clinical, biological and tumoral characteristics of the melanoma patients. Our study showed high levels of hypoxia-inducible factor-1a (HIF-1a) and hypoxia-inducible factor-2a (HIF-2a) in the melanoma patients. Hypoxia-inducible factors (HIFs) control the capacity of tumor cells to adapt to low levels of oxygen. Hypoxia regulated the nitric oxide synthase (NOS) expression and activity. In the cutaneous melanoma patients, disorders in NO metabolism were detected. The serum levels of the NO metabolites were significantly higher in the melanoma patients. NO signaling influenced the tumor microenvironment by modulating tumoral proliferation and sustaining immune suppression. Maintaining NO homeostasis in the hypoxic tumoral microenvironment could be considered a future therapeutic target in cutaneous melanoma.

Curcumin- and resveratrol-co-loaded nanoparticles in synergistic treatment of hepatocellular carcinoma

BACKGROUND

Currently, systemic therapies for patients with advanced-stage hepatocellular carcinoma (HCC) rely mainly on systemic drugs. However, traditional systemic drugs have a high rate of serious adverse events, and the curative effects of some potential anticancer drugs, such as curcumin (CUR) and resveratrol (RSV), are less apparent due to their poor bioavailability. Therefore, it is urgent to develop a highly effective therapy to improve patient prognosis. Herein, an injectable HCC-targeted nanoparticle (NP) was designed to deliver CUR and RSV to hepatoma cells.

RESULTS

The molecular self-assembled NPs showed higher tumour retention through the enhanced permeability and retention (EPR) effect of the NPs and surface modification with the HCC-specific peptide moiety SP94 to effectively treat HCC. These HCC-targeted NPs led to a significant reduction in the drug dosage, delayed the rate of drug release and improved the bioavailability of the encapsulated drugs. The drug concentrations in the vicinity of the tumour increased, and a good therapeutic effect was observed without obvious side effects.

CONCLUSIONS

These SP94-mediated NPs allowed large amounts of antitumor drugs to accumulate in tumours, providing a novel strategy for innovative HCC therapy. This nanoplatform also offers an idea for exploring other potential chemotherapeutics.

Free-Radical Cascade Generated by AIPH/Fe3O4-Coloaded Nanoparticles Enhances MRI-Guided Chemo/Thermodynamic Hypoxic Tumor Therapy

Free radicals, including reactive oxygen species (ROS), play a critical role in determining cell's fate. When the level of free radicals is increased to a fatal value, it causes cancer cells to undergo senescence or cell death. Strategies that target this mechanism offer promising therapies against cancer. However, efficient and sustainable systems that generate free radicals, especially oxygen-independent systems, remain deficient. Herein, functionalized PLGA-based nanocomposites that efficiently co-deliver magnetic nanoparticles and 2,2'-azobis[2-(2-imidazolin-2-yl) propane]-dihydrochloride (AIPH) were fabricated to achieve photothermal-induced thermodynamic therapy combined with macrophage polarization strategies; this therapy targets hypoxic tumors through the generation of an oxygen-independent free-radical cascade. These hybrid NPs can accumulate in the tumor microenvironment, and the encapsulated MNPs not only serve as contrast agents for enhanced magnetic resonance imaging but also exhibit the expected photothermal conversion and trigger the decomposition of AIPH to generate free radicals, thus causing cancer cell death. More importantly, the cell debris from apoptotic or necrotic cancer cells carries nondegraded MNPs, which can be endocytosed by recruited TAMs. MNPs can further induce TAMs to polarize to the M1 subtype to subsequently generate ROS. This study provides an alternative method for the generation of an oxygen-independent free-radical cascade for tumor co-therapy guided by magnetic resonance imaging PTT/TDT.

Ultrasound-activated nanomaterials for sonodynamic cancer theranostics

Despite intensive efforts to develop diagnostic and therapeutic tools, the successful treatment of cancer is still hampered by the obscure boundary between cancerous cells and normal cells, recurrence of the cancer, and the development of drug resistance during chemotherapy. In recent years, sonodynamic therapy (SDT), employing therapeutic ultrasound with sonosensitizers, has attracted attention as a potentially promising approach for cancer therapy. This review describes the current understanding of the mechanisms and the preclinical and clinical efficacy of SDT-based applications in tumors, providing an insight into the therapeutic potential offered by SDT. The limitations and future directions of this emerging treatment are also discussed.