Narrow Bandgap Schottky Heterojunction Sonosensitizer with High Electron-Hole Separation Boosted Sonodynamic Therapy in Bladder Cancer

Sonodynamic therapy (SDT) is applied to bladder cancer (BC) given its advantages of high depth of tissue penetration and nontoxicity due to the unique anatomical location of the bladder near the abdominal surface. However, low electron-hole separation efficiency and wide bandgap of sonosensitizers limit the effectiveness of SDT. This study aims to develop a TiO2-Ru-PEG Schottky heterojunction sonosensitizer with high electron-hole separation and narrow bandgap for SDT in BC. Density functional theory (DFT) calculations and experiments collectively demonstrate that the bandgap of TiO2-Ru-PEG is reduced due to the Schottky heterojunction with the characteristic of crystalline-amorphous interface formed by the deposition of ruthenium (Ru) within the shell layer of TiO2. Thanks to the enhancement of oxygen adsorption and the efficient separation of electron-hole pairs, TiO2-Ru-PEG promotes the generation of reactive oxygen species (ROS) under ultrasound (US) irradiation, resulting in cell cycle arrest and apoptosis of bladder tumor cells. The in vivo results prove that TiO2-Ru-PEG boosted the subcutaneous and orthotopic bladder tumor models while exhibiting good safety. This study adopts the ruthenium complex for optimizing sonosensitizers, contributing to the progress of SDT improvement strategies and presenting a paradigm for BC therapy.

Progress of Piezoelectric Semiconductor Nanomaterials in Sonodynamic Cancer Therapy

Sonodynamic therapy is an emerging noninvasive tumor treatment method that utilizes ultrasound to stimulate sonosensitizers to produce a large amount of reactive oxygen species, inducing tumor cell death. Though sonodynamic therapy has very promising prospects in cancer treatment, the application of early organic sonosensitizers has been limited in efficacy due to the high blood clearance-rate, poor water solubility, and low stability. Inorganic sonosensitizers have thus been developed, among which piezoelectric semiconductor materials have received increasing attention in sonodynamic therapy due to their piezoelectric properties and strong stability. In this review, we summarized the designs, principles, modification strategies, and applications of several commonly used piezoelectric materials in sonodynamic therapy and prospected the future clinical applications for piezoelectric semiconductor materials in sonodynamic therapy.

Sonosensitizer Nanoplatforms Augmented Sonodynamic Therapy-Sensitizing Shikonin-Induced Necroptosis Against Hepatocellular Carcinoma

Background

Apoptosis resistance of hepatocellular carcinoma (HCC) often leads to treatment failure. Nonetheless, overcoming the resistance of HCC to apoptosis by inducing necroptosis of tumor cells to bypass the apoptotic pathway may be a promising treatment strategy. Sonodynamic therapy (SDT) has broad prospects in disease treatment because of its noninvasive characteristic and spatiotemporal control. The combination of SDT and shikonin in the treatment of HCC is expected to be a new tumor treatment method that can overcome apoptosis resistance.

Methods

In this study, the antitumor effect was evaluated using normal liver cell line WRL68, HCC cell line HepG2 and HepG2 xenograft mouse models. Indocyanine green (ICG) was loaded on nanobubbles (NBs) to construct ICG-loaded nanobubbles (ICG-NBs). Combined sonosensitizer nanoplatforms with ultrasound (US) to achieve efficient SDT, the combination of SDT and shikonin in treating HCC can activate shikonin-induced necroptosis. As a result, tumor cells that produced apoptosis resistance were destroyed by necroptosis.

Results

The results indicated a successful preparation of ICG-NBs with a uniform particle size of 273.0 ± 118.9 nm spherical structures. ICG-NB-mediated SDT, in combination with shikonin treatment, inhibited the viability, invasion, and migration of tumor cells. SDT + shikonin treatment group caused a substantial increase in necroptotic cells. The increased degree of tumor necrosis and the upregulated expression of receptor-interacting protein 3 kinase were observed in vivo studies, which indicated that the antitumor effect was accompanied by enhanced necroptosis in the SDT + shikonin treatment group.

Conclusion

ICG-NB-mediated SDT combined with shikonin inhibits the growth of HCC by increasing the necroptosis of tumor cells. Therefore, this combination therapy is a promising treatment strategy against the specific cancer.

Porous Molybdenum Nitride Nanosphere as Carrier-Free and Efficient Nitric Oxide Donor for Synergistic Nitric Oxide and Chemo/Sonodynamic Therapy

Given its abundant physiological functions, nitric oxide (NO) has attracted much attention as a cancer therapy. The sensitive release and great supply capacity are significant indicators of NO donors and their performance. Here, a transition metal nitride (TMN) MoN@PEG is adopted as an efficient NO donor. The release process starts with H+-triggered denitrogen owing to the high electronegativity of the N atom and weak Mo-N bond. Then, these active NHx are oxidized by O2 and other reactive oxygen species (ROS) to form NO, endowing specific release to the tumor microenvironment (TME). With a porous nanosphere structure (80 nm), MoN@PEG does not require an extra carrier for NO delivery, contributing to ultrahigh atomic utilization for outstanding release ability (94.1 ± 5.6 μM). In addition, it can also serve as a peroxidase and sonosensitizer for anticancer treatment. To further improve the charge separation, MoN-Pt@PEG was prepared to enhance the sonodynamic therapy (SDT) effect. Accordingly, ultrasound (US) further promotes NO generation due to more ROS generation, facilitating in situ peroxynitrite (·ONOO-) generation with great cytotoxicity. At the same time, the nanostructure also degrades gradually, leading to high elimination (94.6%) via feces and urine within 14-day. The synergistic NO and chemo-/sono-dynamic therapy brings prominent antitumor efficiency and further activates the immune response to inhibit metastasis and recurrence. This work develops a family of NO donors that would further widen the application of NO therapy in other fields.

GSH-activated Porphyrin Sonosensitizer Prodrug for Fluorescence Imaging-guided Cancer Sonodynamic Therapy

Sonodynamic therapy (SDT), which uses ultrasound to trigger a sonosensitizer to generate reactive oxygen species (ROS), is a promising form of cancer therapy with outstanding tissue penetration depth. However, the sonosensitizer may inevitably spread to surrounding healthy tissue beyond the tumor, resulting in undesired side effects under an ultrasound stimulus. Herein, as glutathione (GSH) is overexpressed in the tumor microenvironment, a GSH-activatable sonosensitizer prodrug was designed by attaching a quencher to tetraphydroxy porphyrin for tumor therapy. The prodrug exhibited poor fluorescence and low ROS generation capacity under ultrasound irradiation but it can be activated by GSH to simultaneously switch on fluorescence emission and ROS generation in tumor site. Compared with the non-quenched sonosensitizer, the designed prodrug exhibited significantly higher tumor/healthy organ fluorescence ratios, due to the specific fluorescence and ROS activation by overexpressed GSH in the tumor. Finally, the prodrug exhibited efficient tumor growth inhibition under ultrasound irradiation, further demonstrating its promise as a GSH-activated sonosensitizer prodrug for highly effective cancer treatment.

Lattice Strain Engineering of Ti3C2 Narrows Band Gap for Realizing Extraordinary Sonocatalytic Bacterial Killing

The rapid development of sonodynamic therapy (SDT) provides a promising strategy for treating deep-seated multidrug-resistant (MDR) bacterial infection. However, the extreme scarcity of biologically functional and highly efficient sonosensitizers severely limits the further clinical practice of SDT. Herein, the lattice-strain-rich Ti3C2 (LS-Ti3C2) with greatly improved sonosensitizing effect is one-step synthesized using Ti3C2 and meso-tetra(4-carboxyphenyl)porphine (TCPP) by the solvothermal method for realizing extraordinary SDT. The intervention of TCPP causes all the Ti-O chemical bonds and most of the Ti-F chemical bonds on the surface layer of Ti3C2 to break down. The amino groups of TCPP are then recombined with these exposed Ti atoms to perturb the order of the Ti atoms, resulting in displacement of the Ti atoms and final lattice structural distortion of Ti3C2. The inherent lattice strain narrows the band gap of Ti3C2, which mainly facilitates the electron-hole pair separation and electron transfer under ultrasound irradiation, thereby resulting in US-mediated reactive oxygen species (ROS) production and the subsequent robust bactericidal capability (99.77 ± 0.16%) against methicillin-resistant Staphylococcus aureus (MRSA). Overall, this research offers a perspective into the development of Ti-familial sonosensitizers toward SDT practice.

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.

Covalent Organic Framework Nanocages with Enhanced Carrier Utilization and Cavitation Effect for Cancer Sonodynamic Therapy

Ultrasound (US)-triggered sonodynamic therapy (SDT) is an emerging method for treating cancer due to its non-invasive nature and high-depth tissue penetration ability. However, current sonosensitizers commonly have unsatisfactory quantum yields of free radicals. In this work, we have developed unique organic semiconductor π-conjugated covalent organic framework nanocages (COFNs) as highly efficient sonosensitizers to boost free radical (¹O₂ and ^•OH) production and cancer therapy. With the hollow and porous structure and band transport behavior, COFNs displayed remarkably improved SDT performance through enhanced electron utilization and cavitation effect, with a 1.8-fold increase in US pressure and a 64.8% increase in ¹O₂ production relative to the core-shell-structured COF under US irradiation. The in vitro and in vivo experimental results verified the elevated SDT performance, showing a high tumor suppression of 91.4% against refractory breast cancer in mice. This work provides a promising strategy to develop high-performance sonosensitizers for cancer therapy.

Piezoelectric Metal-Organic Frameworks Based Sonosensitizer for Enhanced Nanozyme Catalytic and Sonodynamic Therapies

The regulation of electrostatic electric fields through electrical stimulation is an efficient method to increase the catalytic activity of nanozymes and improve the therapeutic effect of nanozyme catalytic therapy. Piezoelectric materials, which are capable of generating a built-in electric field under ultrasound (US), not only improve the activity of nanozymes but also enable piezoelectric sonodynamic therapy (SDT). In this study, a sonosensitizer based on a Hf-based metal-organic framework (UIO-66) and Au nanoparticles (NPs) was produced. Under US irradiation, UIO-66 can generate a built-in electric field inside the materials, which promotes electron-hole separation and produces reactive oxygen species (ROS). The introduction of Au NPs facilitated the electron transfer, which inhibited the recombination of the electron-hole pairs and improved the piezoelectric properties of UIO-66. The value of the piezoelectric constant (d₃₃) increased from 71 to 122 pmV^-1 after the deposition of Au NPs. In addition, the intrinsic catalase and peroxidase activities of the Au NPs were increased 2-fold after the stimulation from the built-in electric field induced through US exposure. In vivo and in vitro experiments revealed that the proposed sonosensitizer can kill cancer cells and inhibit tumor growth in mice through the enhanced piezoelectric SDT and nanozyme catalytic therapy. The piezoelectric sensitizer proposed in this work proved to be an efficient candidate that can be used for multiple therapeutic modalities in tumor therapy.

Ultrasound Responsive Nanovaccine Armed with Engineered Cancer Cell Membrane and RNA to Prevent Foreseeable Metastasis

Cancer vaccine has been considered as a promising immunotherapy by inducing specific anti-tumor immune response. Rational vaccination at suitable time to efficiently present tumor associated antigen will boost tumor immunity and is badly needed. Here, a poly (lactic-co-glycolic acid) (PLGA)-based cancer vaccine of nanoscale is designed, in which engineered tumor cell membrane proteins, mRNAs, and sonosensitizer chlorin e6 (Ce6) are encapsulated at high efficiency. The nanosized vaccine can be efficiently delivered into antigen presentation cells (APCs) in lymph nodes after subcutaneous injection. In the APCs, the encapsulated cell membrane and RNA from engineered cells, which have disturbed splicing resembling the metastatic cells, provide neoantigens of metastatic cancer in advance. Moreover, the sonosensitizer Ce6 together with ultrasound irradiation promotes mRNA escape from endosome, and augments antigen presentation. Through 4T1 syngeneic mouse model, it has been proved that the proposed nanovaccine is efficient to elicit antitumor immunity and thus prevent cancer metastasis.

Application of sonodynamic technology and sonosensitizers in food sterilization: a review of developments, trends and challenges

Food safety and food waste have always been hot topics of discussion in recent years. However, the infection of human pathogenic bacteria and the waste of food resources caused by microbial-contaminated food remains common. Although traditional sterilization technology has been very mature, it causes changes in food flavor and excessive energy consumption to a certain extent. Moreover, the widespread bacterial resistance has also sounded a warning for researchers and finding a new alternative to antibiotics is urgently needed. The application of sonodynamic sterilization technology in medical treatment has aroused the interest of researchers. It provides ideas for new food sterilization technology. As a new non-thermal sterilization technology, sonodynamic sterilization technology has strong penetration, safety, less residue and by-products, and will less change the quality of the food itself. Therefore, sonodynamic sterilization technology has great potential applied in food sterilization technology. This review describes the concept of sonodynamic sterilization technology, the sterilization mechanism of sonodynamic sterilization and the inactivation mechanism of various pathogens, the classification and application of sonosensitizers, and the ultrasonic technology in sonodynamic sterilization in the application over the recent years. It provides a scientific reference for the application of sonodynamic sterilization technology in the field of food sterilization.

Piezotronic Effect-Augmented Cu2-xO-BaTiO3 Sonosensitizers for Multifunctional Cancer Dynamic Therapy

Ultrasound (US)-triggered sonodynamic therapy (SDT) based on semiconductor nanomaterials has attracted considerable attention for cancer therapy. However, most inorganic sonosensitizers suffer from low efficiency due to the rapid recombination of electron-hole pairs. Herein, the Cu_2-xO-BaTiO₃ piezoelectric heterostructure was fabricated as a sonosensitizer and chemodynamic agent, simultaneously, for improving reactive oxygen species (ROS) generation and cancer therapeutic outcome. Under US irradiation, the Cu_2-xO-BaTiO₃ heterojunction with a piezotronic effect exhibits high-performance singlet oxygen (¹O₂) and hydroxyl radical (•OH) generation to enhance SDT. Moreover, it possesses Fenton-like reaction activity to convert endogenous H₂O₂ into •OH for chemodynamic therapy (CDT). The integration of SDT and CDT substantially boosts ROS generation and cellular mitochondria damage, and the in vitro and in vivo results demonstrate high cytotoxicity and tumor inhibition on murine refractory breast cancer. This work realizes improvement in cancer therapy using piezoelectric heterostructures with piezotronic effects.

Two-Dimensional MXene-Originated In Situ Nanosonosensitizer Generation for Augmented and Synergistic Sonodynamic Tumor Nanotherapy

Despite the merits of high tissue-penetrating depth, no ionizing radiation, and low cost, sonodynamic therapy (SDT) still suffers from a low quantum yield of reactive oxygen species (ROS), limited delivery efficiency, and potential toxicity of sonosensitizers. Different from the direct delivery of sonosensitizers into tumor tissue for SDT, this work reports the fabrication of two-dimensional (2D) nanosonosensitizers/nanocatalysts (Ti₃C₂/CuO₂@BSA) for the in situ generation of nanosonosensitizers by responding to the tumor microenvironment, achieving the high-performance and synergistic sonodynamic/chemodynamic tumor therapy. CuO₂ nanoparticle integration on 2D Ti₃C₂ MXene achieved in situ H₂O₂ generation in an acidic tumor microenvironment for oxidizing Ti₃C₂ to produce TiO₂ nanosonosensitizers, accompanied by the enhanced separation of electrons (e^-) and holes (h⁺) by the carbon matrix after oxidation, further augmenting the SDT efficacy. Ultrasound irradiation during the sonodynamic process also enhanced the Cu-initiated Fenton-like reaction to produce more ROS for synergizing the sonodynamic tumor therapy. The experimental results confirm and demonstrate the synergistic therapeutic effects of chemodynamic and sonodynamic nanotherapy both in vitro and in vivo. The antitumor mechanisms of synergistic chemodynamic and sonodynamic therapies are associated with the upregulation of oxidative phosphorylation, ROS generation, and apoptosis as demonstrated by RNA sequencing. This work thus provides a distinct paradigm of 2D MXene-originated in situ nanosonosensitizer generation for augmented and synergistic sonodynamic tumor nanotherapy.

Tumor Microenvironment Triggered the In Situ Synthesis of an Excellent Sonosensitizer in Tumor for Sonodynamic Therapy

An ultrasound-triggered sonodynamic therapy has shown great promise for cancer therapy. However, its clinical applications are very limited because the traditional sonosensitizers tend to suffer from very poor efficiency combined with low retention in cancer cells and low tumor selectivity. Therefore, sonosensitizers with higher effectivity, higher tumor cell retention, and higher tumor cell specificity are highly required. Herein, we constructed a Ti2C(OH)X nanosheet, which was a poor sonosensitizer but had a long circulation in the blood system. However, it was very interesting to find that the tumor microenvironment could in situ turn Ti2C(OH)X nanosheet into a novel and excellent sonosensitizer with a nanofiber structure in tumors, exhibiting excellent ability to generate reactive oxygen species (ROS) under ultrasound. Moreover, the nanofiber structure made it very difficult to get out of cancer cells, highly enhancing the retention of the sonosensitizer in the tumor, thereby enabling it to effectively and selectively kill cancer cells in vivo. Our findings demonstrate that the strategy of the tumor microenvironment triggering the in situ synthesis of an effective sonosensitizer in tumor provided a promising means to simultaneously increase the efficiency, sonosensitizer retention in cancer cells, and cancer selectivity, thereby effectively killing cancer cells but causing little damage to healthy tissues via the sonodynamic therapy.

Ultrasound Triggers Hypericin Activation Leading to Multifaceted Anticancer Activity

The use of ultrasound (US) in combination with a responsive chemical agent (sonosensitizer) can selectively trigger the agent's anticancer activity in a process called sonodynamic therapy (SDT). SDT shares some properties with photodynamic therapy (PDT), which has been clinically approved, but sets itself apart because of its use of US rather than light to achieve better tissue penetration. SDT provides anticancer effects mainly via the sonosensitizer-mediated generation of reactive oxygen species (ROS), although the precise nature of the underpinning mechanism is still under debate. This work investigates the SDT anticancer activity of hypericin (Hyp) in vitro in two- (2D) and three-dimensional (3D) HT-29 colon cancer models, and uses PDT as a yardstick due to its well-known Hyp phototoxicity. The cancer cell uptake and cellular localization of Hyp were investigated first to determine the proper noncytotoxic concentration and incubation time of Hyp for SDT. Furthermore, ROS production, cell proliferation, and cell death were evaluated after Hyp was exposed to US. Since cancer relapse and transporter-mediated multidrug resistance (MDR) are important causes of cancer treatment failure, the US-mediated ability of Hyp to elicit immunogenic cell death (ICD) and overcome MDR was also investigated. SDT showed strong ROS-mediated anticancer activity 48 h after treatment in both the HT-29 models. Specific damage-associated molecular patterns that are consistent with ICD, such as calreticulin (CRT) exposure and high-mobility group box 1 protein (HMGB1) release, were observed after SDT with Hyp. Moreover, the expression of the ABC transporter, P-glycoprotein (P-gp), in HT-29/MDR cells was not able to hinder cancer cell responsiveness to SDT with Hyp. This work reveals, for the first time, the US responsiveness of Hyp with significant anticancer activity being displayed, making it a full-fledged sonosensitizer for the SDT of cancer.

An Urchin-Shaped Copper-Based Metalloporphyrin Nanosystem as a Sonosensitizer for Sonodynamic Therapy

Sonodynamic therapy (SDT), as a novel cancer therapy strategy, might be a promising approach due to the depth-penetration property in tissue. Sonosensitizers are the key element for efficient SDT. However, the development of sonosensitizers with strong sonosensitization efficacy is still a significant challenge. Herein, an urchin-shaped copper-based metalloporphyrin liposome nanosystem (FA–L–CuPP) is constructed and identified as an excellent sonosensitizer. Under ultrasound (US) irradiation, FA–L–CuPP can be highly excited to generate several reactive oxygen species (ROS), such as singlet oxygen (¹O₂) and free radicals (⋅OH). The molecular orbital distribution calculations reveal that a strong intramolecular charge transfer might occur in the CuPP complex under US irradiation, which could afford enough energy to the surrounding O₂ and H₂O to concert ¹O₂, O₂⁻ and ⋅OH. Working as “ammunitions”, the largely produced ROS can kill 4T1 tumor cells, effectively inhibiting tumor growth. This work provides an urchin-shaped nanosonosensitizer based on a copper complex, which might provide an idea to design a novel sonosensitizer for noninvasive and precise SDT antitumor applications.

Sonodynamic Effects of a Novel Ether-Group Modified Porphyrin Derivative Combined With Pulsed Low-Intensity Ultrasound on PC-9 Cells

Sonodynamic therapy (SDT) is a developing modality for cancer treatment based on the synergistic effect of ultrasound and chemical compounds which are known as sonosensitizers. The development of more efficient sonosensitizers has become an urgent issue in this field. In this study, a novel porphyrin derivative (BBTPP) mediated SDT was evaluated on PC-9 cells. Pulsed low-intensity ultrasound (PLIU) was used for its little thermal and mechanical damage. The accumulation of drugs in cells was evaluated through porphyrin fluorescence, and the cytotoxicity of BBTPP was evaluated using a cell counting kit-8 assay. The sonodynamic effect was investigated by Hoechst 33342/PI and Annexin V-FITC/PI double staining, which showed an apoptotic rate of 18.87% in the BBTPP-SDT group, as compared with 1.71%, 1.4%, 1.57%, 3.61%, 11.18% in the control, BBTPP, hematoporphyrin monomethyl ether (HMME), ultrasound, and HMME-SDT groups, respectively. The sono-toxic effect of BBTPP was significantly superior to HMME. Our results showed that BBTPP-SDT resulted in much higher intracellular reactive oxygen species (ROS) and lipid peroxidation levels which were evaluated by 2′,7′-dichlorodihydrofluorescein diacetate (H₂DCFDA) and Liperfluo assay, respectively. The expressions of Bax, Bcl-2, caspase-9, caspase-8, and cleaved caspase-3 proteins were evaluated to investigate the apoptotic mechanism of BBTPP-SDT. The results of this study showed that the combination of BBTPP and PLIU induced the generation of ROS, resulting in lipid peroxidation, and activated both the extrinsic and intrinsic apoptotic pathways of PC-9 cells. Our results also suggested that the ether group introduced in the side chain of porphyrin could enhance the sono-toxicity of porphyrin-based sensitizers under the sonication of PLIU. These results supported the possibility of BBTPP as a promising sonosensitizer, and an appropriate side chain could enhance the sono-sensitivity of porphyrins.

Facile Synthesis of a Cubic Porphyrin-Based Covalent Organic Framework for Combined Breast Cancer Therapy

A cubic porphyrin-based covalent organic framework (COF) named CTP with excellent hydrophilicity was prepared with a facile method for the first time. Different from the conventional methods for the synthesis of porphyrin-based COFs, this facile strategy has greatly shortened the reaction time under mild conditions. Linking the porphyrin monomer into the COF overcame its poor solubility and biocompatibility and also narrowed the band gap owing to the formation of the π-conjugation structure. The improved biocompatibility and narrowed band gap enabled CTP to be an excellent sonosensitizer with an enhanced sonodynamic effect. Moreover, CTP could also effectively realize photothermal conversion under external irradiation due to the extended conjugated structure. This work developed a novel synthesis method for COFs and employed a COF as a sonosensitizer for the first time, which not only provided a new strategy to improve the efficiency of organic sonosensitizers but also inspired us to design more functional COFs for versatile applications.

Safe and Targeted Sonodynamic Cancer Therapy Using Biocompatible Exosome-Based Nanosonosensitizers

Sonodynamic therapy (SDT), wherein sonosensitizers irradiated with ultrasound (US) produce cytotoxic reactive oxygen species (ROS), has garnered great attention as a promising alternative to photodynamic therapy owing to the significantly increased depth of tissue penetration. The development of nanocarriers that can selectively deposit sonosensitizers into tumor tissues without systemic toxicity is crucial to facilitate the translation of SDT to clinical use. In this study, exosomes, a class of naturally occurring nanoparticles, were utilized as nanocarriers for safe and cancer-targeted delivery of a sonosensitizer, indocyanine green (ICG). The exosomes were surface-engineered with an active cancer-targeting ligand, folic acid (FA), to increase the cancer specificity of the ICG-loaded exosomes (ExoICG). The FA-conjugated, ICG-loaded exosomes (FA-ExoICG) greatly improved aqueous stability and cellular uptake of ICG, resulting in significantly increased ROS generation in breast cancer cells. As a result, the FA-ExoICG demonstrated greater sonotoxicity against cancer cells than ExoICG and free ICG. The in vivo study revealed that compared to ExoICG, more FA-ExoICG accumulated in tumors, and their pharmacokinetic properties were superior. Notably, tumor growth in mice was significantly suppressed, without systemic toxicity, by a single intravenous injection of the FA-ExoICG and subsequent US irradiation. Therefore, this study demonstrated that active cancer-targeted FA-ExoICG could serve as effective nanosonosensitizers for safe and targeted cancer treatment.

Design and Challenges of Sonodynamic Therapy System for Cancer Theranostics: From Equipment to Sensitizers

As a novel noninvasive therapeutic modality combining low-intensity ultrasound and sonosensitizers, sonodynamic therapy (SDT) is promising for clinical translation due to its high tissue-penetrating capability to treat deeper lesions intractable by photodynamic therapy (PDT), which suffers from the major limitation of low tissue penetration depth of light. The effectiveness and feasibility of SDT are regarded to rely on not only the development of stable and flexible SDT apparatus, but also the screening of sonosensitizers with good specificity and safety. To give an outlook of the development of SDT equipment, the key technologies are discussed according to five aspects including ultrasonic dose settings, sonosensitizer screening, tumor positioning, temperature monitoring, and reactive oxygen species (ROS) detection. In addition, some state-of-the-art SDT multifunctional equipment integrating diagnosis and treatment for accurate SDT are introduced. Further, an overview of the development of sonosensitizers is provided from small molecular sensitizers to nano/microenhanced sensitizers. Several types of nanomaterial-augmented SDT are in discussion, including porphyrin-based nanomaterials, porphyrin-like nanomaterials, inorganic nanomaterials, and organic-inorganic hybrid nanomaterials with different strategies to improve SDT therapeutic efficacy. There is no doubt that the rapid development and clinical translation of sonodynamic therapy will be promoted by advanced equipment, smart nanomaterial-based sonosensitizer, and multidisciplinary collaboration.

Targeted sonodynamic destruction of glioblastoma cells using antibody-titanium dioxide nanoparticle conjugates

Aim: We present data on sonodynamic therapy (SDT) against glioblastoma cells utilizing titanium dioxide (TiO₂) nanoparticles conjugated to anti-EGFR antibody. Materials & methods: TiO₂ nanoparticles were bound to anti-EGFR antibody to form antibody-nanoparticle conjugates (ANCs), then characterized by x-ray photoelectron spectroscopy and transmission electron microscopy. Cells underwent ultrasound and assessment on viability, reactive oxygen species and apoptosis were performed. Results: X-ray photoelectron spectroscopy analysis revealed the formation of an ANC. Transmission electron microscopy showed internalization of the ANCs by glioblastoma cells. With SDT, cell viabilities were reduced in the presence of ANCs, reactive oxygen species production was formed, but minimal effect on apoptosis was seen. Conclusion: For the first time, an ANC can be used with SDT to kill glioblastoma cells.

Nanosonosensitizer-Augmented Sonodynamic Therapy Combined with Checkpoint Blockade for Cancer Immunotherapy

INTRODUCTION

Sonodynamic therapy (SDT) has good targeting and non-invasive advantages in the treatment of solid cancers, and checkpoint blockade immunotherapy is also a promising treatment to cure cancer. However, their antitumor effects are not sufficient due to some inherent factors. Some studies that combined SDT with immunotherapy or nanoparticles have managed to enhance its efficiency to treat cancers.

METHODS

In this work, an effective therapeutic strategy that can potentiate the antitumor efficacy of anti-PD-L1 antibody (aPD-L1) is developed by the use of cascade immuno-sonodynamic therapy (immuno-SDT). Titanium dioxide (TiO2), a nanostructured agent for SDT, sonosensitizer Chlorin e6 (Ce6), and immunological adjuvant CpG oligonucleotide (CpG ODN), are used to construct a multifunctional nanosonosensitizer (TiO2-Ce6-CpG). Then, we conducted in vitro and in vivo experiments to explore the antitumor effect of TiO2-Ce6-CpG under ultrasound (US) treatment.

RESULTS

The characterization tests showed that the nanosonosensitizers are polycrystalline structure with homogeneous sizes, resulting in a good drug loading efficiency. The innovative nanosonosensitizers (TiO2-Ce6-CpG) can not only effectively inhibit tumor growth but also stimulate the immune system to activate the adaptive immune responses, using the TiO2-Ce6 to augment SDT and the immune adjuvant CpG to enhance the immune response. After combined with the aPD-L1, the synergistic effect could not only efficiently inhibit the primary tumor growth but also lead to an inhibition of the non-irradiated pre-existing distant tumors by inducing a strong tumor-specific immune response.

CONCLUSION

In this study, we present an effective strategy for tumor treatment by combining nanosonosensitizer-augmented SDT and aPD-L1 checkpoint blockade. This work provides a promising strategy and offers a new vision for treating malignant tumors.

Synergistic Anticancer Strategy of Sonodynamic Therapy Combined with PI-103 Against Hepatocellular Carcinoma

Purpose

Sonodynamic therapy (SDT) is considered a promising therapeutic strategy for the effective elimination of cancer cells. However, developing novel sonosensitizers with potentially high SDT efficacy remains a considerable challenge. Herein, we utilized near-infrared dye IR820 nanobubbles (NBs) combined with a dual PI3K/mTOR inhibitor PI-103 for the SDT treatment of hepatocellular carcinoma (HCC) in vitro.

Methods

The generated reactive oxygen species (ROS) were quantified using 2,7-dichlorodihydrofluorescein diacetate to determine the feasibility of using IR820 NBs as a potential sonosensitizer. The inhibition effects of the synergistic therapy was examined using the cell counting Kit 8 assay and apoptosis assay. JC-1 staining was performed to study mitochondrial membrane depolarization, and the transwell assay was used for cell migration analysis.

Results

The particle size and zeta potential of IR820 NBs were 545.5±93.1 nm and −5.19±1.73 mV, respectively. ROS accumulation was observed after HepG2 cells were treated with IR820 NBs under ultrasound irradiation. The SDT combined with PI-103 group inhibited cell viability and migration more strongly than the other groups (P < 0.01). The apoptosis assay also demonstrated a relatively high anti-HCC efficacy with the synergistic therapy, while JC-1 staining showed a decrease in the mitochondrial membrane potential after the combined treatment.

Conclusion

The combination of SDT and PI-103 was very effective in suppressing HCC proliferation, which might help develop new minimally invasive cancer treatment strategies.

Exploiting Lipid and Polymer Nanocarriers to Improve the Anticancer Sonodynamic Activity of Chlorophyll

Sonodynamic therapy is an emerging approach that uses low-intensity ultrasound to activate a sonosensitizer agent triggering its cytotoxicity for selective cancer cell killing. Several molecules have been proposed as sonosensitizer agents, but most of these, as chlorophyll, are strongly hydrophobic with a low selectivity towards cancer tissues. Nanocarriers can help to deliver more efficiently the sonosensitizer agents in the target tumor site, increasing at the same time their sonodynamic effect, since nanosystems act as cavitation nuclei. Herein, we propose the incorporation of unmodified plant-extracted chlorophyll into nanocarriers with different composition and structure (i.e., liposomes, solid lipid nanoparticles and poly(lactic-co-glycolic acid) nanoparticles) to obtain aqueous formulations of this natural pigment. The nanocarriers have been deeply characterized and then incubated with human prostatic cancer cells (PC-3) and spheroids (DU-145) to assess the influence of the different formulations on the chlorophyll sonodynamic effect. The highest sonodynamic cytotoxicity was obtained with chlorophyll loaded into poly(lactic-co-glycolic acid) nanoparticles, showing promising results for future clinical investigations on sonodynamic therapy.

Development and characteristics of novel sonosensitive liposomes for vincristine bitartrate

The aim of drug delivery is to increase therapeutic efficacy. Externally triggered drug delivery systems enable site-specific and time-controlled drug release. To achieve this goal, our strategy was based on ultrasound-triggered release of an anticancer agent from sonosensitive liposomes (SL). To realize the ultrasound-triggered drug release, a lipophilic sonosensitizer, hematoporphyrin monomethyl ether (HMME) was incorporated into the lipid bilayer of liposomes. Once irradiated by the ultrasound in tumor tissues, the sonodynamic effect generated by HMME could lead to an efficient disruption of the lipid bilayer in the SL. After encapsulating vincristine bitartrate (VIN) as the model drug, the ultrasound-triggered lipid bilayer breakdown can trigger the instant release of VIN, enabling ultrasound-controlled chemotherapy with great specificity. In the in vitro and in vivo studies, by integrating tumor-specific targeting and stimuli-responsive controlled release into one system, VIN-loaded SL showed excellent antitumor efficacy. The SL could potentially produce viable clinical strategies for improved targeting efficiency of VIN for the treatment of related cancer. More importantly, this report provides an example of controlled release by means of a novel class of ultrasound triggering system.

Biodegradable Natural Product-Based Nanoparticles for Near-Infrared Fluorescence Imaging-Guided Sonodynamic Therapy

Natural products show high potential for clinical translation because of their specific biological activities and molecular structure diversities. Sonosensitizers that originate from natural products play a crucial role as anti-inflammatory and anticancer agents. Herein, hypocrellin-derivative nanoparticles (APHB NPs) were constructed for synchronous near-infrared fluorescence (NIR FL) imaging and sonodynamic therapy (SDT) for deep-seated tumors in vivo. The prepared APHB NPs exhibit excellent water solubility, FL in the NIR region, and effective reactive oxygen species generation under ultrasound stimulation. Furthermore, the APHB NPs show excellent biocompatibility, suitable biodegradation rate, and enhanced tumor accumulation. Therefore, the APHB NPs exhibit promising clinical potential as novel safe and precise NIR FL imaging and SDT agents for deep-seated tumor therapy.

Gold nanoparticle-induced sonosensitization enhances the antitumor activity of ultrasound in colon tumor-bearing mice

PURPOSE

As a noninvasive and nonionizing radiation, ultrasound can be focused remotely, transferring acoustic energy deep in the body, thereby addressing the penetration depth barrier of the light-based therapies. In cancer therapy, the effectiveness of ultrasound can be enhanced by utilizing nanomaterials that exhibit sonosensitizing properties called as nanosonosensitizers. The gold nanoparticle (AuNP) has been recently presented as a potent nanosonosensitizer with the potential to simultaneously enhance both the thermal and mechanical interactions of ultrasound with the tissue of the human body. Accordingly, this paper attempts to evaluate the in vivo antitumor efficiency of ultrasound in combination with AuNP.

METHODS

BALB/c mice-bearing CT26 colorectal tumor model was intraperitoneally injected with AuNPs and then subjected to ultrasound irradiation (1 MHz; 2 W/cm2 ; 10 min) for three sessions. Furthermore, [18 F]FDG (2-deoxy-2-[18 F]fluoro-d-glucose) positron-emission tomography (PET) imaging was performed and the radiomic features from different feature categorizes were extracted to quantify the tumors' phenotype.

RESULTS

The tumors were dramatically shrunk and the mice appeared healthy over 21 days of study span without the evidence of relapse. The animals treated with AuNP + ultrasound exhibited an obvious decline in tumor metabolic parameters such as standard uptake value (SUV), total lesion glycolysis (TLG), and metabolic tumor volume (MTV) compared to other treatment groups.

CONCLUSION

These findings support the use of AuNP as a potent sonosensitizing agent with the potential to use the thermal and mechanical effects of ultrasound so as to cause damage to the focused tumor site, resulting in an improved antitumor efficacy.

Enhanced selective sonosensitizing efficacy of ultrasound-based anticancer treatment by targeted gold nanoparticles

AIM

This study investigates cancer targeted gold nanoparticles as ultrasound sensitizers for the treatment of cancer.

METHODS

The ultrasound sensitizer activity of folate-PEG decorated gold nanoparticles (FA-PEG-GNP) has been studied on human cancer cell lines that overexpress folate receptors (KB and HCT-116) and another that does not (MCF7), at two ultrasound energy densities (8 × 10^-6 J cm^-2 and 8 × 10^-5 J cm^-2, for 5 min at 1.866 MHz).

RESULTS

FA-PEG-GNP selectively targeted KB and HCT-116 cells and a remarkable reduction in cancer cell growth was observed upon ultrasound exposure, along with significant reactive oxygen species generation and increase in necrotic cells.

CONCLUSION

The combined use of targeting capacity and the ultrasound sensitizing effect, make FA-PEG-GNP promising candidates for the site-specific cancer treatment.

Engineered porphyrin loaded core-shell nanoparticles for selective sonodynamic anticancer treatment

AIM

Porphyrin-loaded core-shell nanoparticles have been engineered for use as in vivo sonosensitizing systems, radio-tracers or magnetic resonance (MR) imaging agents, which may be suitable for the selective treatment of solid tumors and imaging analyses.

MATERIALS & METHODS

Polymethyl methacrylate nanoparticles (PMMANPs) have been either loaded with meso-tetrakis (4-sulphonatophenyl) porphyrin (TPPS) for sonodynamic anticancer treatment, with (64)Cu-TPPS for positron emission tomography biodistribution studies or with Mn(III)-TPPS for MR tumor accumulation evaluation.

RESULTS

PMMANPs are easily functionalized with negatively charged molecules and show favorable biodistribution. In vivo TPPS-PMMANPs have demonstrated shock wave responsiveness in a Mat B III syngeneic rat breast cancer model as measured by MR analyses of pre- and post-treatment tumor volumes.

CONCLUSION

TPPS-PMMANPs are a multimodal system which can efficiently induce in vivo sonodynamic anticancer activity.

Evaluation of the sonosensitizing activities of 5-aminolevulinic acid and Sn(IV) chlorin e6 in tumor-bearing chick embryos

BACKGROUND

Recently, 5-aminolevulinic acid (5-ALA), precursors of protoporphyrin IX (PpIX), and Sn(IV) chlorin e6 (SnCe6) have been proposed as possible sonosensitizers for sonodynamic therapy of cancer. Therefore, we evaluated the pharmacokinetic properties and sonosensitizing activities of 5-ALA and SnCe6 in vivo by using the EMT6/KU tumor-bearing chick embryos.

RESULTS

The concentration of PpIX in tumor and liver tissues and serum increased in a time-dependent manner after the i.v. administration of 5-ALA; PpIX concentrations reached their peak level after 5-7 h. The concentration of SnCe6 reached its maximum value in the tumor tissue and serum immediately after i.v. administration. The combined treatment of 5-ALA or SnCe6 with ultrasound irradiation showed a significant antitumor effect towards EMT6/KU solid tumors.

CONCLUSION

We evaluated the pharmacokinetic properties and sonosensitizing activities of 5-ALA and SnCe6 in a chick embryo model and found that 5-ALA might be more suitable as a sonosensitizer than SnCe6.

Sounding the death knell for microbes?

Over the past 5 years, several studies showed that ultrasound, which is sound with a frequency>20 kHz, is able to kill bacteria by activating molecules termed sonosensitizers (SS) to produce reactive oxygen species, which are toxic to microbes. It is our opinion that this work opens up the potential for the development of a novel form of ultrasound-mediated antimicrobial therapy. Termed sonodynamic antimicrobial chemotherapy (SACT), we define this therapy as a regime where a SS is selectively delivered to target microbial cells and activated by ultrasound to induce the death of those microbial cells. Here, we review recent work on SACT, current understanding of its mechanisms, and future prospects for SACT as a therapeutically viable antimicrobial regime.