Nanosensitizers for sonodynamic therapy for glioblastoma multiforme: current progress and future perspectives

Glioblastoma multiforme(GBM) is the most common primary malignant brain tumor, and it is associated with poor prognosis. Its characteristics of being highly invasive and undergoing heterogeneous genetic mutation, as well as the presence of the blood–brain barrier(BBB), have reduced the efficacy of GBM treatment. The emergence of a novel therapeutic method, namely, sonodynamic therapy(SDT), provides a promising strategy for eradicating tumors via activated sonosensitizers coupled with low-intensity ultrasound. SDT can provide tumor killing effects for deep-seated tumors, such as brain tumors. However, conventional sonosensitizers cannot effectively reach the tumor region and kill additional tumor cells, especially brain tumor cells. Efforts should be made to develop a method to help therapeutic agents pass through the BBB and accumulate in brain tumors. With the development of novel multifunctional nanosensitizers and newly emerging combination strategies, the killing ability and selectivity of SDT have greatly improved and are accompanied with fewer side effects. In this review, we systematically summarize the findings of previous studies on SDT for GBM, with a focus on recent developments and promising directions for future research.

Research progress on reactive oxygen species production mechanisms in tumor sonodynamic therapy

In recent years,because of the growing desire to improve the noninvasiveness and safety of tumor treatments,sonodynamic therapy has gradually become a popular research topic.However,due to the complexity of the therapeutic process,the relevant mechanisms have not yet been fully elucidated.One of the widely accepted possibilities involves the effect of reactive oxygen species.In this review,the mechanism of reactive oxygen species production by sonodynamic therapy(SDT)and ways to enhance the sonodynamic production of reactive oxygen species are reviewed.Then,the clinical application and limitations of SDT are discussed.In conclusion,current research on sonodynamic therapy should focus on the development of sonosensitizers that efficiently produce active oxygen,exhibit biological safety,and promote the clinical transformation of sonodynamic therapy.

Recent advances of sonodynamic therapy in cancer treatment

Sonodynamic therapy(SDT) is an emerging approach that involves a combination of low-intensity ultrasound and specialized chemical agents known as sonosensitizers. Ultrasound can penetrate deeply into tissues and can be focused into a small region of a tumor to activate a sonosensitizer which offers the possibility of non-invasively eradicating solid tumors in a site-directed manner.In this article, we critically reviewed the currently accepted mechanisms of sonodynamic action and summarized the classification of sonosensitizers. At the same time, the breath of evidence from SDT-based studies suggests that SDT is promising for cancer treatment.

Induction of the apoptosis of cancer cell by sonodynamic therapy:a review

Ultrasound can be used not only in examination, but also in therapy, especially in the therapy of cancer. Sonodynamic therapy is an experimental cancer therapy method which uses ultrasound to enhance the cytotoxic effects of agents known as sonosensitizers. It has been tested in vitro and in vivo. The ultrasound could penetrate the tissue and cell under some of conditions which directly changes cell membrane permeability, thereby allowing the delivery of exogenous molecules into the cells in some degree. Ultrasound could inhibit the proliferation or induce the apoptosis of cancer cells in vitro or in vivo. Recent researches indicated low-frequency and low-intensity ultrasound could induce cell apoptosis, which could be strengthened by sonodynamic sensitivity, microbubbles, chemotherapeutic drugs and so on. Most kinds of ultrasound suppressed the proliferation of cancer cells through inducing the apoptosis of cancer cells. The mechanism of apoptosis is not clear. In this review, we will focus on and discuss the mechanisms of the induction of cancer cell apoptosis by ultrasound.

Nanotechnology assisted photo-and sonodynamic therapy for overcoming drug resistance

Drug resistance is considered the most important reason for the clinical failure of cancer chemotherapy.Circumventing drug resistance and improving the efficacy of anticancer agents remains a major challenge.Over the past several decades,photodynamic therapy(PDT)and sonodynamic therapy(SDT)have attracted substantial attention for their efficacy in cancer treatment,and have been combined with chemotherapy to overcome drug resistance.However,simultaneously delivering sensitizers and chemotherapy drugs to same tumor cell remains challenging,thus greatly limiting this combinational therapy.The rapid development of nanotechnology provides a new approach to solve this problem.Nano-based drug delivery systems can not only improve the targeted delivery of agents but also co-deliver multiple drug components in single nanoparticles to achieve optimal synergistic effects.In this review,we briefly summarize the mechanisms of drug resistance,discuss the advantages and disadvantages of PDT and SDT in reversing drug resistance,and describe state-of-the-art research using nano-mediated PDT and SDT to solve these refractory problems.This review also highlights the clinical translational potential for this combinational therapy.

Metal-based inorganic nanocrystals for biological sonodynamic therapy applications:recent progress and perspectives

With the fast development of technology for the treatment of tumor and bacteria,photo-therapeutic strate-gies emerge as a kind of highly effective and common treatment,but the low tissue penetration depth of light limits their development.Sonodynamic therapy(SDT),as an efficient and non-invasive treatment,attracts more people's attention due to the inherent property of high tissue penetration.The soft tissue penetration depth of ultrasound(US)can even reach more than 10 cm,which has great advantage over that of light.Therefore,many sonosensitizers are studied and applied to SDT-based therapy.Metal-based inorganic nanocrystals are able to generate more reactive oxygen species(ROS)due to the special composition and band structure.The representative achievements and the specific functions of the nanocrystals sonosensitizers are summarized in this work,and the relationship of structure/composition-SDT performance and the internally regulated composite is revealed.Syner-gistic effects of SDT in combination with other therapeutic modalities are mainly highlighted.At the same time,the critical and potential issues and future perspectives are addressed.

Porphyrin-based metal-organic framework nanocrystals for combination of immune and sonodynamic therapy

Immune therapy based on programmed death-ligand 1(PD-L1)is widely used to treat human tumors.The current strategies to improve immune checkpoint blockade therapy fail in rescuing increased expression of PD-L1 in tumor issues.Here,we for the first time synthesized the metal-organic framework(MOF)nanocrystals of rare-earth element dysprosium(Dy)coordinated with tetrakis(4-carboxyphenyl)porphyrin(TCPP),which show well-defined two-dimensional morphologies.The MOF nanocrystals of Dy-TCPP could apparently reduce PD-L1 expression in tumor cells both in vitro and in vivo,and therefore display effective tumor treatment through immune therapy without any immune checkpoint inhibitor drugs.Considering the sensitivity of TCPP ligand toward ultrasound,the prepared Dy-TCPP can also realize sonodynamic therapy(SDT)besides immune therapy.In addition,the Dy-TCPP nanocrystals can efficiently obtain T_(2)-weight magnetic resonance imaging(MRI)of tumor sites.Our study provides the Dy-TCPP nanocrystals as promising diagnostic MRI-guided platforms for the combined treatment on tumors with SDT and immune therapy.Moreover,this strategy succeeds in reducing the elevated expression of PD-L1 in tumor cells,which might serve as a novel avenue for tumor immunotherapy in future.

Evoking robust immunogenic cell death by synergistic sonodynamic therapy and glucose depletion using Au clusters/single atoms modified TiO_(2)nanosheets

Facilitated by reactive oxygen species(ROS)-involved therapies,tumor cells undergo immunogenic cell death(ICD)to stimulate long-term immunity response.However,it is hard to trigger abundant and large-scale ICD for satisfactory cancer immunotherapy.Herein,a multifunctional sonosensitizer that consists of Au single atoms and clusters anchored on TiO_(2)nanosheets(named Au_(S/C)-TiO_(2))is reported for augmented sonodynamic therapy(SDT)and glucose depletion,which ultimately induce robust ICD due to the improved ROS generation and strong endoplasmic reticulum(ER)stress.The synergy effect between Au cluster/single atom with TiO_(2)nanosheets intensifies apoptosis and ICD pathways to inhibit 80%of tumor cells through in vivo analyses.Furthermore,immune cells in vivo analyses verify the effectiveness of Au_(S/C)-TiO_(2)sonosensitizer towards the induction of antitumor immunity.This study thus reveals that simultaneous presence of ROS generation and strong ER stress can efficiently evoke a strong ICD-mediated immune response.

Newly developed gas-assisted sonodynamic therapy in cancer treatment

Sonodynamic therapy(SDT) is an emerging noninvasive treatment modality that utilizes lowfrequency and low-intensity ultrasound(US) to trigger sensitizers to kill tumor cells with reactive oxygen species(ROS).Although SDT has attracted much attention for its properties including high tumor specificity and deep tissue penetration,its anticancer efficacy is still far from satisfactory.As a result,new strategies such as gas-assisted therapy have been proposed to further promote the effectiveness of SDT.In this review,the mechanisms of SDT and gas-assisted SDT are first summarized.Then,the applications of gas-assisted SDT for cancer therapy are introduced and categorized by gas types.Next,therapeutic systems for SDT that can realize real-time imaging are further presented.Finally,the challenges and perspectives of gas-assisted SDT for future clinical applications are discussed.

Ultrasound-active ReCORM-AIEgen for gas and sonodynamic therapy of mycobacterium biofilms

Bacterial infection is the leading cause of many severe inflammation diseases. The development of novel and effective therapeutic approaches to counter bacterial infections, especially for drug-resistant bacteria, is essential. Herein, we have successfully developed an ultrasound-active tricarbonyl rhenium(Ⅰ) complex with tetraphenylethylene(TPE) modification(RePyTPE) for CO gas therapy and sonodynamic therapy of bacterial infections. RePy-TPE produced reactive oxygen species and released CO under ultrasound irradiation. In addition, RePy-TPE showed aggregation-induced emission in water due to the introduction of TPE, which enhanced the yield of ^(1)O_(2) generation in a biological aqueous solution. The produced ^(1)O_(2) and released CO killed mycobacterium smegmatis(M. smegmatis) and Escherichia coli(E. coli), as shown by bacterial membrane damage and biofilm elimination. Furthermore, ultrasound-active RePy-TPE perturbed the purine metabolism of the bacteria, which disturbed the biosynthesis of DNA and energy metabolism, eventually reducing the vitality of bacteria. This article provides a novel strategy for the development of ultrasound-active metal-based antibiotics.

RNA sequencing-based optimization of biological lipid droplets for sonodynamic therapy to reverse tumor hypoxia and elicit robust immune response

Mitochondria-targeted sonodynamic therapy(SDT)is a promising strategy to inhibit tumor growth and activate the anti-tumor immune responses.Identifying the mechanisms underlying mitochondria-targeted SDT,further optimizing its efficacy,developing novel sonosensitizer carriers with good biocompatibility pose major challenges to the clinical practice of SDT.In this study,we investigated the mechanisms of mitochondria-targeted SDT and demonstrated that it suppressed the mitochondrial electron transport chain(ETC)in pancreatic cancer cells through RNA-sequencing analysis.Based on these findings,we constructed the functional lipid droplets(LDs)(CPI-613/IR780@LDs),which combined mitochondria-targeted SDT with the tricarboxylic acid(TCA)cycle inhibitor CPI-613.CPI-613/IR780@LDs synergistically inhibited the TCA cycle and the ETC of mitochondrial aerobic respiration to reduce oxygen consumption and increase reactive oxygen species(ROS)generation at the tumor site,thus enhancing the efficacy of SDT in hypoxic pancreatic cancer.Moreover,the combination of mitochondria-targeted SDT and anti-PD-1 antibody exhibited excellent tumor inhibition and activated anti-tumor immune responses by increasing tumorinfiltrating CD8+T cells and reducing regulatory T cells,synergistically arresting the growth of both primary and metastatic pancreatic tumors.Meanwhile,lipid droplets are cell-derived biological carriers with natural mitochondrial targeting ability and can achieve efficient hydrophobic drug loading through active phagocytosis.Therefore,the functional lipid droplet-based SDT combined with anti-PD-1 antibody holds great potential in the clinical treatment of hypoxic pancreatic cancer.

Modulation of reactive oxygen species to enhance sonodynamic therapy

Reactive oxygen species(ROS),involving in many biological reactions,play an important role in disease treatment.Among the various ROS-based therapeutic modalities,sonodynamic therapy(SDT)stands out with its unique advantages.In turn,the SDT efficacy is mainly dependent on the ROS levels in the disease microenvironment.Therefore,in recent years,researchers have extensively investigated SDT with high ROS generation capacity.In this review,we focus on effective strategies to improve the therapeutic ef-ficiency of SDT by modulating ROS,overview the basic mechanisms of ROS generation by sonosensitizers,highlight the rational design of sonosensitizers,and summarize strategies to improve the SDT efficacy by modulating disease microenvironment.In addition,multiple ROS synergistic treatment modalities and the prospect of SDT are discussed.We believe that the understanding and exploration of SDT enhancement strategies will facilitate the clinical translation of SDT.

Recent advances in nanomaterials for sonodynamic therapy

Sonodynamic therapy(SDT),as a novel non-invasive strategy for eliminating tumor,has the advantages of deeper tissue penetration,fewer side effects,and better patient compliance,compared with photodynamic therapy(PDT).In SDT,ultrasound was used to activate sonosensitizer to produce cytotoxic reactive oxygen species(ROS),induce the collapse of vacuoles in solution,and bring about irreversible damage to cancer cells.In recent years,much effort has been devoted to developing highly efficient sonosensitizers which can efficiently generate ROS.However,the traditional organic sonosensitizers,such as porphyrins,hypericin,and curcumins,suffer from complex synthesis,poor water solubility,and low tumor targeting efficacy which limit the benefits of SDT.In contrast,inorganic sonosensitizers show good in vivo stability,controllable physicochemical properties,ease of achieving multifunctionality,and high tumor targeting,which greatly expanded their application in SDT.In this review,we systematically summarize the nanomaterials which act as the carrier of molecular sonosensitizers,and directly produce ROS under ultrasound.Moreover,the prospects of inorganic nanomaterials for SDT application are also discussed.

Sonodynamic therapy with immune modulatable two-dimensional coordination nanosheets for enhanced anti-tumor immunotherapy

Ultrasound with deep penetration depth and high security could be adopted in sonodynamic therapy(SDT)by activating sonosensitizers to generate cytotoxic reactive oxygen species(ROS).Herein,two-dimensional(2D)coordination nanosheets composed of Zn^(2+)and Tetrakis(4-carboxyphenyl)porphyrin(TCPP)are fabricated.While exhibiting greatly enhanced ultrasoundtriggered ROS generation useful for noninvasive SDT,such Zn-TCPP 2D nanosheets show high loading capacity of oligodeoxynudeotides such as cytosine—phosphorothioate-guanine(CpG),which is a potent toll like receptor 9(TLR9)agonist useful in activating immune responses.Highly effective SD T of primary tumors could release tumor-associated antigens,which working together with Zn-TCPP/CpG adjuvant nanosheets could function like whole-tumor-cell vaccines and trigger tumor-specific immune responses.Interestingly,ultrasound itself could strengthen anti-tumor immune responses by improving the tumor-infiltration of T cells and limiting regulatory T cells in the tumor microenvironment.Thus,SDT using Zn-TCPP/CpG nanosheets after destruction of primary tumors could induce potent antitumor immune responses to inhibit distant abscopal tumors without direct SD T treatment.Moreover,SDT with Zn-TCPP/CpG could trigger strong immunological memory effects to inhibit cancer recurrence after elimination of primary tumors.Therefore,the 2D coordination nanosheet may be a promising platform to deliver potent SDT-triggered immunotherapy for highly effective cancer treatment.

On-demand assembly of polymeric nanoparticles for longer-blood-circulation and disassembly in tumor for boosting sonodynamic therapy

Sonodynamic therapy (SDT) is one of the promising strategies for tumor therapy, but its application is usually hindered by fast clearance in blood-circulation, abnormal tumor microenvironment, and inefficient generation of reactive oxygen species. To solve these problems, we proposed an on-demand assembly-disassembly strategy, where the assembly is favorable for longer-blood-circulation and then the disassembly in tumor is favorable for boosting SDT. Hematoporphyrin monomethyl ether (HMME) as the model of organic sonosensitizers were conjugated with hyaluronic acid (HA). Then HA-HMME was mixed with catalase (CAT) and assembled into polymeric nanoparticles (CAT@HA-HMME NPs) with size of ~80 nm. CAT@HA-HMME NPs exhibit good biocompatibility and a longer blood half-time (t1/2 = 4.17 h) which is obviously longer than that (~0.82 h) of HMME molecules. After HA receptor-mediated endocytosis of cancer cells, CAT@HA-HMME NPs can be cleaved by endogenous hyaluronidase, resulting in the on-demand disassembly in tumor to release HA-HMME molecules and CAT. The CAT catalyzes the endogenous H_(2)O_(2) into O_(2) to relieve the hypoxic microenvironment, and the released HA-HMME exhibits a higher ROS generation ability, greatly boosting SDT for the inhibition of tumor growth. Therefore, the on-demand assembly-disassembly strategy may provide some insight in the design and development of nanoagents for tumor therapy.

Titanium carbide nanosheets with defect structure for photothermal-enhanced sonodynamic therapy

Sonodynamic therapy(SDT)has attracted widespread interest in biomedicine,owing to its novel and noninvasive therapeutic method triggered by ultrasound(US).Herein,the Ti_(3)C_(2) MXene nanosheets(Ti_(3)C_(2) NSs)are developed as good sonosensitizers via a two-step method of chemical exfoliation and high-temperature treatment.With the high-temperature treatment,the oxygen defect of Ti_(3)C_(2) MXene nanosheets(H-Ti_(3)C_(2) NSs)is greatly increased.Therefore,the electron(e^(-))and hole(h^(+))generated by US can be separated faster due to the improved degree of oxidation,and then the recombination of e^(-)-h^(+)can be prevented with the abundant oxygen defect under US irradiation,which induced the sonodynamic efficiency greatly to improve around 3.7-fold compared with Ti_(3)C_(2) NSs without high-temperature treatment.After PEGylation,the H-Ti_(3)C_(2)-PEG NSs show good stability and biocompatibility.In vitro studies exhibit that the inherent property of mild photothermal effect can promote the endocytosis of H-Ti_(3)C_(2)-PEG NSs,which can improve the SDT efficacy.In vivo studies further display that the increased blood supply by the mild photothermal effect can significantly relieve hypoxia in the tumor microenvironment,showing photothermal therapy(PTT)enhanced SDT.Most importantly,the H-Ti_(3)C_(2)-PEG NSs can be biodegraded and excreted out of the body,showing no significant long-term toxicity.Our work develops the defective H-Ti_(3)C_(2) NSs as high-efficiency and safe sonosensitizers for photothermal-enhanced SDT of cancer,extending the biomedical application of MXene-based nanoplatforms.

A multifunctional nanoparticle system combines sonodynamic therapy and chemotherapy to treat hepatocellular carcinoma

Hepatocellular carcinoma （HCC） is one of the most common and deadly malignancies worldwide. To date, the survival of patients with HCC has not improved because of the insensitivity of HCC to conventional treatments. Sonodynamic therapy （SDT） is a promising new approach that shows remarkable potential in the treatment of HCC. Here, we designed a simple, biocompatible, and multifunctional nanosystem that combines SDT and chemotherapy to treat HCC. This nanosystem, called HPDF nanoparticles, had a core-shell structure in which hematoporphyrin （HP） was complexed with doxorubicin （DOX） to form the hydrophobic core and the surface was coated with Pluronic F68 to form the hydrophilic shell. In HCC cells, HPDF nanoparticles in combination with ultrasonic irradiation （1.0 MHz, 1.5 W/cm2, 30 s） exhibited potent cytotoxicity, resulting from the synergistic effects of a large amount of reactive oxygen species generated from HP and DOX-induced DNA damage. Notabl~ HPDF nanoparticles in combination with ultrasonic irradiation significantly reversed drug resistance in Nanog-positive cancer stem cells （CSCs） in HCC. In nude mice bearing HCC tumors, HPDF nanoparticles efficiently accumulated in the tumors and reached the maximum levels within 6-8 h, post intravenous injection. HPDF nanoparticles, in combination with ultrasonic irradiation （1.0 MHz, 3 W/cm2, 5 min）, suppressed tumor growth, angiogenesis, and collagen deposition, considerably. In summary, our results show that HPDF nanoparticles can effectively combine SDT and chemotherapy to inhibit HCC growth and progression through multiple mechanisms in both cellular and animal models.

Cancer-macrophage hybrid membrane-camouflaged photochlor for enhanced sonodynamic therapy against triple-negative breast cancer

Sonodynamic therapy(SDT)has aroused considerable momentum in cancer therapy due to its abilities of deep penetration,low toxicity,and noninvasion,while insufficient tumor accumulation of sonosensitizers is a major obstacle for SDT effect.Here,we developed a 4T1 cancer cell-macrophage hybrid membrane(HM)-camouflaged sonosensitizer nanoplatform by encapsulating photochlor(HPPH)-loaded albumin nanoparticles(PHNPs).The experimental results proved that the HM-coated biomimetic NPs(PHNPs@HM)could express the characteristic membrane proteins of both cancer cells and macrophages,remarkedly enhancing the effective targeting and endocytosis to 4T1 cells through homologous adhesion recognition and immune escaping.Meanwhile,as a novel sonosensitizer,HPPH could generate amount of reactive oxygen species(ROS)under ultrasound(US)irradiation and exhibit obvious SDT efficiency to inhibit 4T1 tumor growth through ROS-induced cell apoptosis.This study provides a novel and multifunctional biomimetic sonosensitizer system to enhance SDT efficiency.

Versatile nanocomposite augments high-intensity focused ultrasound for high-efficacy sonodynamic therapy of glioma

High-intensity focused ultrasound(HIFU),with inherent advantages of improved ultrasonic depth and low off-target damage,holds the promising capability for glioma treatment,but the relatively long therapeutic time and potential physical complications may hamper its clinical application.Herein,a bovine serum albumin(BSA)-based nanoplatform with in situ growth of MnO_(2) was synthesized,and Protoporphyrin IX(PpIX)was further anchored to obtain a versatile PpIX@MnO_(2)@BSA nanoplatform(denoted as BMP).By employing HIFU as the exogenous irradiation source,a high-efficacy sonodynamic therapy(SDT)is developed,in which the excited BMP enables the production of tumoricidal reactive oxygen species(ROS).The inherent tumor microenvironment(TME)-responsive property of MnO_(2) endows BMP with specific T1-weighted magnetic resonance imaging(MRI)by releasing Mn2+,and the simultaneously generated O_(2) facilitates hypoxia alleviation as well as ^(1)O_(2) generation.Compared with HIFU therapy alone,suppression of glioma growth and improved survival benefits are achieved through the designed TMEresponsive nanocomposite under HIFU exposure.The high-efficacy SDT strategy combining BMP and HIFU demonstrated favorable TME-responsive T1-weighted MRI,hypoxic environment alleviation,and anti-tumor capability,providing a perspective paradigm for MRI-guided glioma treatment.

Integrating Au and ZnO nanoparticles onto graphene nanosheet for enhanced sonodynamic therapy

Sonodynamic therapy has attracted widespread attention for cancer treatment because of its noninvasiveness and high tissuepenetration ability.Generally,ultrasound irradiation of sonosensitizers produces separated electrons(e−)and holes(h+),which inhibits cancer by producing reactive oxygen species(ROS).However,the separated electrons(e−)and holes(h+)could easily recombine,lowering the yield of ROS and hindering the application of sonodynamic therapy(SDT).Herein,we present a highly efficient sonosensitizer system for enhanced sonodynamic therapy built on reduced graphene oxide(rGO)nanosheets,bridged ZnO and Au nanoparticles,coated with polyvinyl pyrrolidone(PVP).The ultrasound irradiation activates ZnO nanoparticles to generate separated electron–hole(e−–h+)pairs,and the rGO nanosheets facilitate electron transfer from ZnO to Au nanoparticles because of the narrow band gap of rGO,which could efficiently restrain the recombination of the e−–h+pairs,thereby significantly augmenting the production of ROS to kill cancer cells,such as U373MG,HeLa,and CT26 cells.Moreover,rGO nanosheets integrated with Au nanoparticles could catalyze the endogenous decomposition of H_(2)O_(2) into O_(2),which can alleviate hypoxic tumor microenvironment(TME).Therefore,the rational design of Au-rGO-ZnO@PVP nanomaterials can not only improve the efficiency of sonodynamic therapy,but also mitigate the hypoxic tumor microenvironment,which would provide a new perspective in the development of efficient sonosensitizers.