Nanoparticle-assisted ultrasound: A special focus on sonodynamic therapy against cancer

Molecular Imaging and Non-molecular Imaging of Atherosclerotic Plaque Thrombosis

Thrombosis in the context of atherosclerosis typically results in life-threatening consequences, including acute coronary events and ischemic stroke. As such, early detection and treatment of thrombosis in atherosclerosis patients is essential. Clinical diagnosis of thrombosis in these patients is typically based upon a combination of imaging approaches. However, conventional imaging modalities primarily focus on assessing the anatomical structure and physiological function, severely constraining their ability to detect early thrombus formation or the processes underlying such pathology. Recently, however, novel molecular and non-molecular imaging strategies have been developed to assess thrombus composition and activity at the molecular and cellular levels more accurately. These approaches have been successfully used to markedly reduce rates of atherothrombotic events in patients suffering from acute coronary syndrome (ACS) by facilitating simultaneous diagnosis and personalized treatment of thrombosis. Moreover, these modalities allow monitoring of plaque condition for preventing plaque rupture and associated adverse cardiovascular events in such patients. Sustained developments in molecular and non-molecular imaging technologies have enabled the increasingly specific and sensitive diagnosis of atherothrombosis in animal studies and clinical settings, making these technologies invaluable to patients' health in the future. In the present review, we discuss current progress regarding the non-molecular and molecular imaging of thrombosis in different animal studies and atherosclerotic patients.

The promising shadow of microbubble over medical sciences: from fighting wide scope of prevalence disease to cancer eradication

Microbubbles are typically 0.5-10 μm in size. Their size tends to make it easier for medication delivery mechanisms to navigate the body by allowing them to be swallowed more easily. The gas included in the microbubble is surrounded by a membrane that may consist of biocompatible biopolymers, polymers, surfactants, proteins, lipids, or a combination thereof. One of the most effective implementation techniques for tiny bubbles is to apply them as a drug carrier that has the potential to activate ultrasound (US); this allows the drug to be released by US. Microbubbles are often designed to preserve and secure medicines or substances before they have reached a certain area of concern and, finally, US is used to disintegrate microbubbles, triggering site-specific leakage/release of biologically active drugs. They have excellent therapeutic potential in a wide range of common diseases. In this article, we discussed microbubbles and their advantageous medicinal uses in the treatment of certain prevalent disorders, including Parkinson's disease, Alzheimer's disease, cardiovascular disease, diabetic condition, renal defects, and finally, their use in the treatment of various forms of cancer as well as their incorporation with nanoparticles. Using microbubble technology as a novel carrier, the ability to prevent and eradicate prevalent diseases has strengthened the promise of effective care to improve patient well-being and life expectancy.

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.

Transformable Nanosensitizer with Tumor Microenvironment-Activated Sonodynamic Process and Calcium Release for Enhanced Cancer Immunotherapy

Despite the promise of sonodynamic processes in cancer therapy, existing sonosensitizers often fail to regulate the generation of reactive oxygen species (ROS) against tumors, potentially leading to off-target toxicity to normal tissues. We report a transformable core-shell nanosonosensitizer (TiO₂ @CaP) that reinvigorates ROS generation and dissolves its CaP shell to release Ca²⁺ in an acidic tumor microenvironment (TME) under ultrasound activation. Thus, TiO₂ @CaP acts as a smart nanosonosensitizer that specifically induces mitochondrial dysfunction via overloading intracellular Ca²⁺ ions to synergize with the sonodynamic process in the TME. TiO₂ @CaP substantially enhances immunogenic cell death, resulting in enhanced T-cell recruitment and infiltration into the immunogenic cold tumor (4T1). In conjunction with checkpoint blockade therapy (anti-PD 1), TiO₂ @CaP-mediated sonodynamic therapy elicits systemic antitumor immunity, leading to regression of non-treated distant tumors and inhibition of lung metastasis. This work paves the way to development of "smart" TME-activatable sonosensitizers with temporospatial control over antitumor responses.

Nanomaterials to Fight Cancer: An Overview on Their Multifunctional Exploitability

In recent years the worldwide research community has highlighted innumerable benefits of nanomaterials in cancer detection and therapy. Nevertheless, the development of cancer nanomedicines and other bionanotechnology requires a huge amount of considerations about the interactions of nanomaterials and biological systems, since long-term effects are not yet fully known. Open issues remain the determination of the nanoparticles distributions patterns and the internalization rate into the tumor while avoiding their accumulation in internal organs or other healthy tissues. The purpose of this work is to provide a standard overview of the most recent advances in nanomaterials to fight cancer and to collect trends and future directions to follow according to some critical aspects still present in this field. Complementary to the very recent review of Wolfram and Ferrari which discusses and classifies successful clinically-approved cancer nanodrugs as well as promising candidates in the pipeline, this work embraces part of their proposed classification system based on the exploitation of multifunctionality and extends the review to peer-reviewed journal articles published in the last 3 years identified through international databases.

Conferring Ti-Based MOFs with Defects for Enhanced Sonodynamic Cancer Therapy

The development of highly efficient, multifunctional, and biocompatible sonosensitizer is still a priority for current sonodynamic therapy (SDT). Herein, a defect-rich Ti-based metal-organic framework (MOF) (D-MOF(Ti)) with greatly improved sonosensitizing effect is simply constructed and used for enhanced SDT. Compared with the commonly used sonosensitizer TiO₂ , D-MOF(Ti) results in a superior reactive oxygen species (ROS) yield under ultrasound (US) irradiation due to its narrow bandgap, which principally improves the US-triggered electron-hole separation. Meanwhile, due to the existence of Ti³⁺ ions, D-MOF(Ti) also exhibits a high level of Fenton-like activity to enable chemodynamic therapy. Particularly, US as the excitation source of SDT can simultaneously enhance the Fenton-like reaction to achieve remarkably synergistic outcomes for oncotherapy. More importantly, D-MOF(Ti) can be degraded and metabolized out of the body after completion of its therapeutic functions without off-target toxicity. Overall, this work identifies a novel Ti-familial sonosensitizer harboring great potential for synergistic sonodynamic and chemodynamic cancer therapy.

Comprehensive Evaluation of the Toxicity and Biosafety of Plasma Polymerized Nanoparticles

The rapid growth of nanoparticle-based therapeutics has underpinned significant developments in nanomedicine, which aim to overcome the limitations imposed by conventional therapies. Establishing the safety of new nanoparticle formulations is the first important step on the pathway to clinical translation. We have recently shown that plasma-polymerized nanoparticles (PPNs) are highly efficient nanocarriers and a viable, cost-effective alternative to conventional chemically synthesized nanoparticles. Here, we present the first comprehensive toxicity and biosafety study of PPNs using both established in vitro cell models and in vivo models. Overall, we show that PPNs were extremely well tolerated by all the cell types tested, significantly outperforming commercially available lipid-based nanoparticles (lipofectamine) used at the manufacturer’s recommended dosage. Supporting the in vitro data, the systemic toxicity of PPNs was negligible in BALB/c mice following acute and repeated tail-vein intravenous injections. PPNs were remarkably well tolerated in mice without any evidence of behavioral changes, weight loss, significant changes to the hematological profile, or signs of histological damage in tissues. PPNs were tolerated at extremely high doses without animal mortality observed at 6000 mg/kg and 48,000 mg/kg for acute and repeated-injection regimens, respectively. Our findings demonstrate the safety of PPNs in biological systems, adding to their future potential in biomedical applications.

Recent advances in mechanical force-assisted transdermal delivery of macromolecular drugs

The transdermal delivery of macromolecular drugs has become one of the focused topics in pharmaceutical research since it enables highly specific and effective delivery, while avoiding the pain and needle phobia associated with injection, or incidences like drug degradation and low bioavailability of oral administration. However, the passive absorption of macromolecular drugs via skin is highly restricted by the stratum corneum owing to high molecular weight. Therefore, various strategies have been extensively developed and conducted to facilitate the transdermal delivery of macromolecular drugs, among which, mechanical force-assisted techniques occupy dominant positions. Such techniques include ultrasound, needle-free jet injection, temporary pressure and microneedles. In this review, we focus on recent transdermal enhancing strategies utilizing mechanical force, and summarize their mechanisms, advantages, limitations and clinical applications respectively.

Ultrasound-Responsive Nanocarriers in Cancer Treatment: A Review

The safe and effective delivery of anticancer agents to diseased tissues is one of the significant challenges in cancer therapy. Conventional anticancer agents are generally cytotoxins with poor pharmacokinetics and bioavailability. Nanocarriers are nanosized particles designed for the selectivity of anticancer drugs and gene transport to tumors. They are small enough to extravasate into solid tumors, where they slowly release their therapeutic load by passive leakage or biodegradation. Using smart nanocarriers, the rate of release of the entrapped therapeutic(s) can be increased, and greater exposure of the tumor cells to the therapeutics can be achieved when the nanocarriers are exposed to certain internally (enzymes, pH, and temperature) or externally (light, magnetic field, and ultrasound) applied stimuli that trigger the release of their load in a safe and controlled manner, spatially and temporally. This review gives a comprehensive overview of recent research findings on the different types of stimuli-responsive nanocarriers and their application in cancer treatment with a particular focus on ultrasound.

Sonoporation: Underlying Mechanisms and Applications in Cellular Regulation

Ultrasound combined with microbubble-mediated sonoporation has been applied to enhance drug or gene intracellular delivery. Sonoporation leads to the formation of openings in the cell membrane, triggered by ultrasound-mediated oscillations and destruction of microbubbles. Multiple mechanisms are involved in the occurrence of sonoporation, including ultrasonic parameters, microbubbles size, and the distance of microbubbles to cells. Recent advances are beginning to extend applications through the assistance of contrast agents, which allow ultrasound to connect directly to cellular functions such as gene expression, cellular apoptosis, differentiation, and even epigenetic reprogramming. In this review, we summarize the current state of the art concerning microbubble‐cell interactions and sonoporation effects leading to cellular functions.

The anti-biofilm capability of nano-emodin-mediated sonodynamic therapy on multi-species biofilms produced by burn wound bacterial strains

BACKGROUND

Management of burn wound infections (BWIs) is difficult due to the emergence of multidrug-resistant microorganisms. This study aimed to explore the anti-biofilm efficacy of sonodynamic therapy (SDT) using nano-emodin (N-EMO) against multi-species bacterial biofilms containing Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii.

METHODS

Following synthesis and confirmation of N-EMO as a sonosensitizer, the anti-biofilm efficacy of SDT against multi-species bacterial biofilms was determined using minimum inhibitory concentrations (MIC), minimum biofilm inhibitory concentration (MBIC), and minimal biofilm eradication concentration (MBEC) of N-EMO. The reduction of multi-species bacterial biofilms was then evaluated following the treatments using Log reduction and crystal violet (CV) assays. In addition, the expression profiling of abaI, agrA, and lasI genes using SDT with sub-MIC, sub-MBIC, and sub-MBEC of N-EMO was assessed.

RESULTS

Successful synthesis of N-EMO was confirmed through several characterization tests. As the results demonstrated, the MIC value of N-EMO for the multi-species bacterial suspension was 0.15 × 10^-4 g/L, as well as, the MBEC value of N-EMO was 2.5 × 10^-4 g/L, approximately 4-fold higher than that of MBIC (0.62 × 10^-4 g/L). According to the CV assay, there were 57.8 %, 71.0 %, and 81.5 % reduction in the biofilm of multi-species bacterial growth following SDT using 1/128 MBEC, 1/16 MBIC, and 1/2 MIC of N-EMO, respectively. Log reductions analysis demonstrated that 1/2 MIC of N-EMO was more potent in inhibiting the biofilm growth of multi-species test bacteria by 5.725 ± 0.12 (99.9993 %). In this study, N-EMO-mediated SDT could obviously downregulate the gene expression of virulence factors (P < 0.05). The gene expression of lasI, agrA, and abaI were downregulated about 2.5-, 3.6-, and 5.5-fold; and 3.0-, 5.2-, and 7.4-fold following SDT with sub-MBIC and sub-MBEC of N-EMO, respectively.

CONCLUSION

These results highlight the potential of N-EMO-mediated SDT in inhibition of biofilm formation, degradation of formed biofilms, and reduction of virulence factor associated with biofilms of multi-species bacterial biofilms in BWIs.

Engineering oxygen-deficient ZrO2-x nanoplatform as therapy-activated "immunogenic cell death (ICD)" inducer to synergize photothermal-augmented sonodynamic tumor elimination in NIR-II biological window

Nano-zirconia, as an amphoteric semiconductor, has been industrially exploited in photocatalytic reactions and as piezoelectric sensors. However, its biomedical applications, especially in antitumor therapeutics, have been seldom investigated to date. Here, oxygen-deficient zirconia (ZrO_2-x)-based nanoplatform with surface PEGylation and cyclic-Arg-Gly-Asp (cRGD) peptide functionalization (ZrO_2-x@PEG/cRGD, abbreviated as ZPR) was rationally designed and established for the first time, which was utilized as therapy-activated "immunogenic cell death (ICD)" inducer to boost photothermal-augmented sonodynamic tumor elimination in NIR-II biological window. As-synthesized ZPR nanoparticles (NPs) exhibited intense optical absorbance in the wavelength range of 900-1100 nm, which endowed ZPR NPs with a photothermal conversion efficiency as high as 45.8% for photothermal therapy (PTT). Moreover, owing to the abundant surface oxygen defects, ZPR NPs can serve as a category of high-performance nano-sonosensitizer based on the strengthened separation of electron (e^-)/hole (h⁺) pairs from the energy band under external ultrasound (US) activation. More importantly, cytotoxic reactive oxygen species (ROS) generated from sonodynamic therapy (SDT) can effectively induce immunogenic cell death (ICD), which is regarded to be significant to boost systemic anti-tumor immunity for rendering a complete tumor eradication post-treatment. In vivo experiments on tumor xenografts demonstrated the high therapeutic efficacy upon photothermal-augmented sonodynamic therapy, with the aid of photoacoustic (PA) imaging navigation. Remarkably, the level of inflammatory cytokines, including type I interferon (IFN), tumor necrosis factor α (TNF-α) as well as interleukin (IL-6) were systemically upgraded after NIR-II/US irradiation, verifying the promotion of immunogenicity. Taken together, this study delivers useful insights for extending the applications of zirconia as promising translational medicine for tumor theranostics in the near future.

Triggered Drug Release From Liposomes: Exploiting the Outer and Inner Tumor Environment

Since more than 40 years liposomes have being extensively studied for their potential as carriers of anticancer drugs. The basic principle behind their use for cancer treatment consists on the idea that they can take advantage of the leaky vasculature and poor lymphatic drainage present at the tumor tissue, passively accumulating in this region. Aiming to further improve their efficacy, different strategies have been employed such as PEGlation, which enables longer circulation times, or the attachment of ligands to liposomal surface for active targeting of cancer cells. A great challenge for drug delivery to cancer treatment now, is the possibility to trigger release from nanosystems at the tumor site, providing efficacious levels of drug in the tumor. Different strategies have been proposed to exploit the outer and inner tumor environment for triggering drug release from liposomes and are the focus of this review.

Cascaded amplification of intracellular oxidative stress and reversion of multidrug resistance by nitric oxide prodrug based-supramolecular hydrogel for synergistic cancer chemotherapy

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Supramolecular hydrogel was facilely developed by self-assembly of NO prodrug conjugated hydrogelator sequence.

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The locoregionally sustained NO release from the hydrogel could be triggered by intracellular over-expressed GSH/GST.

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NO could effectively reverse the P-gp mediated MDR effect and facilitate the intracellular accumulation of DOX.

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This type of stimuli-sensitive NO delivery platform holds great potential for combating drug-resistance cancer.

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.

Hierarchical responsive micelle facilitates intratumoral penetration by acid-activated positive charge surface and size contraction

Integrating these features of acid-activated positively charged surface and size contraction into single nanoparticle would be an effective strategy for enhancing cellular uptake, intratumoral penetration and accumulation. Here, hierarchical responsive micelle (HVDMs) was developed via RAFT reaction as multifunctional polymer-drug conjugate for maximizing penetration and therapeutic effect against MCF-7 tumor by combining positively charged surface with size contraction: surface zeta-potential reversal (-2 to +12 mV) by protonation of PHEME and size contraction (~81-~41 nm) by simultaneous hydrophobic/hydrophilic conversion (pH ≈ 6.7); the disintegration of hydrazone bond between hydrophobic PVB and DOX triggered drug release (pH ≈ 5.0). The in vitro structural stabilization, cellular uptake and anti-proliferative efficiency were significantly higher than other control groups (CVDMs and HSDMs) at pH 6.7. The markedly increased penetration depth, cellular internalization and anti-tumor efficiency were confirmed in 3D MCSs spheroids at pH 6.7, and the ex vivo DOX fluorescence images further verified obvious penetration and accumulation in internal region of solid tumor. The antitumor effect in vivo demonstrated that HVDMs accelerated tumor atrophy, induced intratumoral cells apoptosis and alleviated system toxicity.

Penetration and preferential binding of charged nanoparticles to mixed lipid monolayers: interplay of lipid packing and charge density

Designing of nanoparticles (NPs) for biomedical applications or mitigating their cytotoxic effects requires microscopic understanding of their interactions with cell membranes. Such insight is best obtained by studying model biomembranes which, however, need to replicate actual cell membranes, especially their compositional heterogeneity and charge. In this work we have investigated the role of lipid charge density and packing of phase separated Langmuir monolayers in the penetration and phase specificity of charged quantum dot (QD) binding. Using an ordered and anionic charged lipid in combination with uncharged but variable stiffness lipids we demonstrate how the subtle interplay of zwitterionic lipid packing and anionic lipid charge density can affect cationic nanoparticle penetration and phase specific binding. Under identical subphase pH, the membrane with higher anionic charge density displays higher NP penetration. We also observe coalescence of charged lipid rafts floating amidst a more fluidic zwitterionic lipid matrix due to the phase specificity of QD binding. Our results suggest effective strategies which can be used to design NPs for diverse biomedical applications as well as to devise remedial actions against their harmful cytotoxic effects especially against respiratory diseases.

Ultrasound-triggered delivery of paclitaxel encapsulated in an emulsion at low acoustic pressures

We investigated the in vitro ultrasound-triggered delivery of paclitaxel, a well known anti-cancerous drug, encapsulated in an emulsion and in the presence of CT26 tumor cells. The emulsion was made of nanodroplets, whose volume comprised 95% perfluoro-octyl bromide and 5% tributyl O-acetylcitrate, in which paclitaxel was solubilized. These nanodroplets, prepared using a high-pressure microfluidizer, were stabilized by a tailor-made and recently patented biocompatible fluorinated surfactant. The delivery investigations were performed at 37 °C using a high intensity focused ultrasound transducer at a frequency of 1.1 MHz. The ultrasonic pulse was made of 275 sinusoidal periods and the pulse repetition frequency was 200 Hz with a duty cycle of 5%. The measured viabilities of CT26 cells showed that paclitaxel delivery was achievable for peak-to-peak pressures of 0.4 and 3.5 MPa, without having to vaporize the perfluorocarbon part of the droplet or to induce inertial cavitation.

Effect of ultrasonic frequency and power on the sonodynamic therapy activity of cationic Zn(II) phthalocyanines

We report on the sonodynamic activity of cationic phthalocyanines (Pcs) and the effect of the variation of two parameters: ultrasound frequency and power (Par I (1 MHz, 1 W cm^-2), Par II (1 MHz, 2 W cm^-2), Par III (3 MHz, 1 W cm^-2) and Par IV (3 MHz, 2 W cm^-2)) on the efficiency of their reactive oxygen species generation and cancer eradication in vitro thereof. Where Par stands for the various combinations of these parameters. Four Pcs were investigated with substituents bearing diethylamine, ortho- and para-pyridine and morpholine groups. Overall, the para-pyridine and morpholine Pcs showed substantial sono-activity in the various ultrasound parameters with Par I and IV generally showing better singlet oxygen and hydroxyl radicals generation confirmed by electron paramagnetic resonance spectroscopy. In some cases, very high hydroxyl radicals' generation was observed at Par II. Furthermore, the fragmentation of the Pcs after Par II treatments was confirmed using UV-vis and magnetic circular dichroism spectroscopy. The reactive species generation efficacy decreased at Par III for all samples. Ultrasound assisted cytotoxicity of the Pcs was confirmed in vitro using the human (Michigan Cancer Foundation-7) breast cancer cell line.

Applications of Micro/Nanotechnology in Ultrasound-based Drug Delivery and Therapy for Tumor

Ultrasound has been broadly used in biomedicine for both tumor diagnosis as well as therapy. The applications of recent developments in micro/nanotechnology promote the development of ultrasound-based biomedicine, especially in the field of ultrasound-based drug delivery and tumor therapy. Ultrasound can activate nano-sized drug delivery systems by different mechanisms for ultrasound- triggered on-demand drug release targeted only at the tumor sites. Ultrasound Targeted Microbubble Destruction (UTMD) technology can not only increase the permeability of vasculature and cell membrane via sonoporation effect but also achieve in situ conversion of microbubbles into nanoparticles to promote cellular uptake and therapeutic efficacy. Furthermore, High Intensity Focused Ultrasound (HIFU), or Sonodynamic Therapy (SDT), is considered to be one of the most promising and representative non-invasive treatment for cancer. However, their application in the treatment process is still limited due to their critical treatment efficiency issues. Fortunately, recently developed micro/nanotechnology offer an opportunity to solve these problems, thus improving the therapeutic effect of cancer. This review summarizes and discusses the recent developments in the design of micro- and nano- materials for ultrasound-based biomedicine applications.

Reactive Oxygen Species-Regulating Strategies Based on Nanomaterials for Disease Treatment

Reactive oxygen species (ROS) play an essential role in physiological and pathological processes. Studies on the regulation of ROS for disease treatments have caused wide concern, mainly involving the topics in ROS-regulating therapy such as antioxidant therapy triggered by ROS scavengers and ROS-induced toxic therapy mediated by ROS-elevation agents. Benefiting from the remarkable advances of nanotechnology, a large number of nanomaterials with the ROS-regulating ability are developed to seek new and effective ROS-related nanotherapeutic modalities or nanomedicines. Although considerable achievements have been made in ROS-based nanomedicines for disease treatments, some fundamental but key questions such as the rational design principle for ROS-related nanomaterials are held in low regard. Here, the design principle can serve as the initial framework for scientists and technicians to design and optimize the ROS-regulating nanomedicines, thereby minimizing the gap of nanomedicines for biomedical application during the design stage. Herein, an overview of the current progress of ROS-associated nanomedicines in disease treatments is summarized. And then, by particularly addressing these known strategies in ROS-associated therapy, several fundamental and key principles for the design of ROS-associated nanomedicines are presented. Finally, future perspectives are also discussed in depth for the development of ROS-associated nanomedicines.

Interaction of Genetically Encoded Photosensitizers with Scintillating Nanoparticles for X-ray Activated Photodynamic Therapy

Photodynamic therapy (PDT) applications are limited by the low penetration of UV-visible light into biological tissues. Considering X-rays as an alternative to excite photosensitizers (PS) in a deeper tumor, an intermediate particle able to convert the X-ray energy into visible light (scintillating nanoparticle, ScNP) is necessary. Moreover, accumulation of PS in the target cells is also required. Genetically encoded proteins could be used as a photosensitizer, allowing the exclusive expression of PS inside the tumor cells. Here, the interaction of eGFP, KillerOrange, and KillerRed proteins with LaF₃:Tb³⁺ ScNP was investigated, for the first time, in terms of its physicochemical and energy transfer properties. The protein structure, stability, and function were evaluated upon adverse physiological conditions and X-ray irradiation. Optimal parameters for energy transfer from ScNP to the proteins were investigated, paving the way for the use of genetically encoded photosensitizers for applications in X-ray activated photodynamic therapy.

External and Internal Stimuli-Responsive Metallic Nanotherapeutics for Enhanced Anticancer Therapy

Therapeutic, diagnostic, and imaging approaches based on nanotechnology offer distinct advantages in cancer treatment. Various nanotherapeutics have been presented as potential alternatives to traditional anticancer therapies such as chemotherapy, radiotherapy, and surgical intervention. Notably, the advantage of nanotherapeutics is mainly attributable to their accumulation and targeting ability toward cancer cells, multiple drug-carrying abilities, combined therapies, and imaging approaches. To date, numerous nanoparticle formulations have been developed for anticancer therapy and among them, metallic nanotherapeutics reportedly demonstrate promising cancer therapeutic and diagnostic efficiencies owing to their dense surface functionalization ability, uniform size distribution, and shape-dependent optical responses, easy and cost-effective synthesis procedure, and multiple anti-cancer effects. Metallic nanotherapeutics can remodel the tumor microenvironment by changing unfavorable therapeutic conditions into therapeutically accessible ones with the help of different stimuli, including light, heat, ultrasound, an alternative magnetic field, redox, and reactive oxygen species. The combination of metallic nanotherapeutics with both external and internal stimuli can be used to trigger the on-demand release of therapeutic molecules, augmenting the therapeutic efficacies of anticancer therapies such as photothermal therapy, photodynamic therapy, magnetic hyperthermia, sonodynamic therapy, chemodynamic therapy, and immunotherapy. In this review, we have summarized the role of different metallic nanotherapeutics in anti-cancer therapy, as well as their combinational effects with multiple stimuli for enhanced anticancer therapy.

K. PK, Lee J, Kim CH, You DG, Park JH. Recent advances in nanomaterial-based augmented sonodynamic therapy of cancer

This review focuses on recent advances in augmented sonodynamic therapy (SDT) using engineered nanomaterials, and the mechanism of SDT for discussing future perspectives.

Sonodynamic therapy in combination with photodynamic therapy shows enhanced long-term cure of brain tumor

This article presents the construction of a multimodality platform that can be used for efficient destruction of brain tumor by a combination of photodynamic and sonodynamic therapy. For in vivo studies, U87 patient-derived xenograft tumors were implanted subcutaneously in SCID mice. For the first time, it has been shown that the cell-death mechanism by both treatment modalities follows two different pathways. For example, exposing the U87 cells after 24 h incubation with HPPH [3-(1'-hexyloxy)ethyl-3-devinyl-pyropheophorbide-a) by ultrasound participate in an electron-transfer process with the surrounding biological substrates to form radicals and radical ions (Type I reaction); whereas in photodynamic therapy, the tumor destruction is mainly caused by highly reactive singlet oxygen (Type II reaction). The combination of photodynamic therapy and sonodynamic therapy both in vitro and in vivo have shown an improved cell kill/tumor response, that could be attributed to an additive and/or synergetic effect(s). Our results also indicate that the delivery of the HPPH to tumors can further be enhanced by using cationic polyacrylamide nanoparticles as a delivery vehicle. Exposing the nano-formulation with ultrasound also triggered the release of photosensitizer. The combination of photodynamic therapy and sonodynamic therapy strongly affects tumor vasculature as determined by dynamic contrast enhanced imaging using HSA-Gd(III)DTPA.

Biomimetic Amorphous Titania Nanoparticles as Ultrasound Responding Agents to Improve Cavitation and ROS Production for Sonodynamic Therapy

Conventional therapies to treat cancer often exhibit low specificity, reducing the efficiency of the treatment and promoting strong side effects. To overcome these drawbacks, new ways to fight cancer cells have been developed so far focusing on nanosystems. Different action mechanisms to fight cancer cells have been explored using nanomaterials, being their remote activation one of the most promising. Photo- and sonodynamic therapies are relatively new approaches that emerged following this idea. These therapies are based on the ability of specific agents to generate highly cytotoxic reactive oxygen species (ROS) by external stimulation with light or ultrasounds (US), respectively. Crystalline (TiO2) and amorphous titania (a-TiO2) nanoparticles (NPs) present a set of very interesting characteristics, such as their photo-reactivity, photo stability, and effective bactericidal properties. Their production is inexpensive and easily scalable; they are reusable and demonstrated already to be nontoxic. Therefore, these NPs have been increasingly studied as promising photo- or sonosensitizers to be applied in photodynamic/sonodynamic therapies in the future. However, they suffer from poor colloidal stability in aqueous and biological relevant media. Therefore, various organic and polymer-based coatings have been proposed. In this work, the role of a-TiO2 based NPs synthesized through a novel, room-temperature, base-catalyzed, sol-gel protocol in the generation of ROS and as an enhancer of acoustic inertial cavitation was evaluated under ultrasound irradiation. A novel biomimetic coating based on double lipidic bilayer, self-assembled on the a-TiO2-propylamine NPs, is proposed to better stabilize them in water media. The obtained results show that the biomimetic a-TiO2-propylamine NPs are promising candidates to be US responding agents, since an improvement of the cavitation effect occurs in presence of the developed NPs. Further studies will show their efficacy against cancer cells.

Recent advances in bioelectronics chemistry

Research in bioelectronics is highly interdisciplinary, with many new developments being based on techniques from across the physical and life sciences. Advances in our understanding of the fundamental chemistry underlying the materials used in bioelectronic applications have been a crucial component of many recent discoveries. In this review, we highlight ways in which a chemistry-oriented perspective may facilitate novel and deep insights into both the fundamental scientific understanding and the design of materials, which can in turn tune the functionality and biocompatibility of bioelectronic devices. We provide an in-depth examination of several developments in the field, organized by the chemical properties of the materials. We conclude by surveying how some of the latest major topics of chemical research may be further integrated with bioelectronics.

Recent advances in bioelectronics chemistry

Research in bioelectronics is highly interdisciplinary, with many new developments being based on techniques from across the physical and life sciences. Advances in our understanding of the fundamental chemistry underlying the materials used in bioelectronic applications have been a crucial component of many recent discoveries. In this review, we highlight ways in which a chemistry-oriented perspective may facilitate novel and deep insights into both the fundamental scientific understanding and the design of materials, which can in turn tune the functionality and biocompatibility of bioelectronic devices. We provide an in-depth examination of several developments in the field, organized by the chemical properties of the materials. We conclude by surveying how some of the latest major topics of chemical research may be further integrated with bioelectronics.

Enhanced Radiosensitization for Cancer Treatment with Gold Nanoparticles through Sonoporation

We demonstrate the megavoltage (MV) radiosensitization of a human liver cancer line by combining gold-nanoparticle-encapsulated microbubbles (AuMBs) with ultrasound. Microbubbles-mediated sonoporation was administered for 5 min, at 2 h prior to applying radiotherapy. The intracellular concentration of gold nanoparticles (AuNPs) increased with the inertial cavitation of AuMBs in a dose-dependent manner. A higher inertial cavitation dose was also associated with more DNA damage, higher levels of apoptosis markers, and inferior cell surviving fractions after MV X-ray irradiation. The dose-modifying ratio in a clonogenic assay was 1.56 ± 0.45 for a 10% surviving fraction. In a xenograft mouse model, combining vascular endothelial growth factor receptor 2 (VEGFR2)-targeted AuMBs with sonoporation significantly delayed tumor regrowth. A strategy involving the spatially and temporally controlled release of AuNPs followed by clinically utilized MV irradiation shows promising results that make it worthy of further translational investigations.

Recent Advances in Nanomaterial-Assisted Combinational Sonodynamic Cancer Therapy

Ultrasound (US)-triggered sonodynamic therapy (SDT), as a promising noninvasive therapeutic modality, has received ever-increasing attention in recent years. Its specialized chemical agents, named sonosensitizers, are activated by low-intensity US to produce lethal reactive oxygen species (ROS) for oncotherapy. Compared with phototherapeutic strategies, SDT provides many noteworthy opportunities and benefits, such as deeper penetration depth, absence of phototoxicity, and fewer side effects. Nevertheless, previous studies have also demonstrated its intrinsic limitations. Thanks to the facile engineering nature of nanotechnology, numerous novel nanoplatforms are being applied in this emerging field to tackle these intrinsic barriers and achieve continuous innovations. In particular, the combination of SDT with other treatment strategies has demonstrated a superior efficacy in improving anticancer activity relative to that of monotherapies alone. Therefore, it is necessary to summarize the nanomaterial-assisted combinational sonodynamic cancer therapy applications. Herein, the design principles in achieving synergistic therapeutic effects based on nanomaterial engineering methods are highlighted. The ultimate goals are to stimulate the design of better-quality combined sonodynamic treatment schemes and provide innovative ideas for the perspectives of SDT in promoting its future transformation to clinical application.

Remotely Activated Nanoparticles for Anticancer Therapy

Cancer has nowadays become one of the leading causes of death worldwide. Conventional anticancer approaches are associated with different limitations. Therefore, innovative methodologies are being investigated, and several researchers propose the use of remotely activated nanoparticles to trigger cancer cell death. The idea is to conjugate two different components, i.e., an external physical input and nanoparticles. Both are given in a harmless dose that once combined together act synergistically to therapeutically treat the cell or tissue of interest, thus also limiting the negative outcomes for the surrounding tissues. Tuning both the properties of the nanomaterial and the involved triggering stimulus, it is possible furthermore to achieve not only a therapeutic effect, but also a powerful platform for imaging at the same time, obtaining a nano-theranostic application. In the present review, we highlight the role of nanoparticles as therapeutic or theranostic tools, thus excluding the cases where a molecular drug is activated. We thus present many examples where the highly cytotoxic power only derives from the active interaction between different physical inputs and nanoparticles. We perform a special focus on mechanical waves responding nanoparticles, in which remotely activated nanoparticles directly become therapeutic agents without the need of the administration of chemotherapeutics or sonosensitizing drugs.

The investigation of the parameters affecting the ZnO nanoparticle cytotoxicity behaviour: a tutorial review

In the last 30 years the research about zinc oxide nanoparticles (ZnO NPs) and their related toxicity has shown a boom. ZnO NPs show cytotoxicity for both prokaryotic and eukaryotic cells and many studies demonstrated their selective toxicity towards cancer cells. However, with the increasing number of publications, it is observed an increase in the discrepancies obtained between the various results. Soon the scientific community understood that the ZnO NC toxicity behaviour is affected by many factors, related not only to the ZnO NPs themselves, but also to the experimental conditions used. Many recent reviews discussed these parameters by reporting experimental evidence and tried to assess the general statements about the ZnO NP cytotoxicity. This information is extremely useful for the evaluation of which type of ZnO NPs is more or less suitable for a specific study or application. However, despite that, a deep comprehension of the ZnO NP behaviour in relation to the different experimental conditions is still lacking. Actually, a full understanding of the reasons behind the NP behaviour is essential to better assess their biological activity and in particular their therapeutic application, avoiding undesired effects both in the experimental and clinical contexts. This tutorial review aims to be an experimental and practical guide for scientists that faced with the use of ZnO NPs for biomedical applications and, in particular, for their therapeutic purposes. The driving idea is to not simply summarize the results reported in the literature, but to provide instruments for a deep comprehension of the mechanisms affecting the ZnO NP cytotoxicity and behavior. This review also aims to point out the critical experimental parameters to be considered when working with these NPs, as well as the main related risks and limitations that scientists have to face.

Perfluoropolyether Nanoemulsion Encapsulating Chlorin e6 for Sonodynamic and Photodynamic Therapy of Hypoxic Tumor

Sonodynamic therapy (SDT) has emerged as an important modality for cancer treatment. SDT utilizes ultrasound excitation, which overcomes the limitations of light penetration in deep tumors, as encountered by photodynamic therapy (PDT) which uses optical excitations. A comparative study of these modalities using the same sensitizer drug can provide an assessment of their effects. However, the efficiency of SDT and PDT is low in a hypoxic tumor environment, which limits their applications. In this study, we report a hierarchical nanoformulation which contains a Food and Drug Administration (FDA) approved sensitizer chlorin, e6, and a uniquely stable high loading capacity oxygen carrier, perfluoropolyether. This oxygen carrier possesses no measurable cytotoxicity. It delivers oxygen to overcome hypoxia, and at the same time, boosts the efficiency of both SDT and PDT. Moreover, we comparatively analyzed the efficiency of SDT and PDT for tumor treatment throughout the depth of the tissue. Our study demonstrates that the strengths of PDT and SDT could be combined into a single multifunctional nanoplatform, which works well in the hypoxia environment and overcomes the limitations of each modality. The combination of deep tissue penetration by ultrasound and high spatial activation by light for selective treatment of single cells will significantly enhance the scope for therapeutic applications.

Cavitation-Inducible Mesoporous Silica-Titania Nanoparticles for Cancer Sonotheranostics

Sonodynamic therapy has received increasing attention for cancer treatments as an alternative to photodynamic therapy. However, its clinical applications have been limited by the lack of a sonosensitizer that is capable of producing sufficient amounts of reactive oxygen species (ROS) in response to ultrasound (US) exposure. Herein, PEGylated mesoporous silica-titania nanoparticles (P-MSTNs) are prepared and used as US-responsive nanocarriers for cancer sonotheranostics. Perfluorohexane (PFH), which is chosen as the gas precursor, is physically encapsulated into P-MSTNs using the oil-in-water emulsion method. Owing to the vaporization of the gas precursor, PFH@P-MSTNs (137 nm in diameter) exhibit a strong photoacoustic signal in vivo for at least 6 h. Compared to P-MSTNs, PFH@P-MSTNs generate significantly higher amounts of ROS due to the nanobubble-induced cavitation in the presence of US. When systemically administered to tumor-bearing mice, PFH@P-MSTNs effectively accumulate in the tumor site due to the passive targeting mechanism. Consequently, PFH@P-MSTNs show much higher antitumor efficacy than P-MSTNs due to the enhanced cavitation-mediated ROS generation in response to US exposure. It is considered that PFH@P-MSTNs may hold significant potential for cancer sonotheranostics.

Leveraging re-chargeable nanobubbles on amine-functionalized ZnO nanocrystals for sustained ultrasound cavitation towards echographic imaging

Nanoparticles able to promote inertial cavitation when exposed to focused ultrasound have recently gained much attention due to their vast range of possible applications in the biomedical field, such as enhancing drug penetration in tumor or supporting ultrasound contrast imaging. Due to their nanometric size, these contrast agents could penetrate through the endothelial cells of the vasculature to target tissues, thus enabling higher imaging resolutions than commercial gas-filled microbubbles. Herein, Zinc Oxide NanoCrystals (ZnO NCs), opportunely functionalized with amino-propyl groups, are developed as novel nanoscale contrast agents that are able, for the first time, to induce a repeatedly and over-time sustained inertial cavitation as well as ultrasound contrast imaging. The mechanism behind this phenomenon is investigated, revealing that re-adsorption of air gas nanobubbles on the nanocrystal surface is the key factor for this re-chargeable cavitation. Moreover, inertial cavitation and significant echographic signals are obtained at physiologically relevant ultrasound conditions (MI < 1.9), showing great potential for low side-effects in in-vivo applications of the novel nanoscale agent from diagnostic imaging to gas-generating theranostic nanoplatforms and to drug delivery.

Phototherapy and Sonotherapy of Melanoma Cancer Cells Using Nanoparticles of Selenium-Polyethylene Glycol-Curcumin as a Dual-Mode Sensitizer

Background:

As an alternative form of cancer therapy, photothermal therapy (PTT) and sonodynamic therapy (SDT) using nanomaterials are in development. Nanomaterials can act as energy absorber as well as anti-cancer agent.

Objective:

In this study, the effects of laser and ultrasound irradiation with Se-PEG-Cur nanoparticles were investigated on melanoma cancer.

Material and Methods:

In this experimental study, nanoparticles of selenium-polyethylene glycol-curcumin (Se-PEG-Cur) were synthesized, and their UV-vis absorption, particle size, zeta potential and photothermal conversion efficiency were determined. Se-PEG-Cur was then introduced as a novel 808-nm laser light absorbing agent as well as ultrasound (US) wave for treatment of C540 (B16/F10) cancer cells. Also, ROS generation in C540 (B16/F10) cancer cells was measured upon PTT and SDT using Se-PEG-Cur.

Results:

Mean size, zeta potential and photothermal conversion efficiency of Se-PEG-Cur were obtained as ~300 nm, 42.7 mV and 16.7%, respectively. Cell viability upon irradiation of the laser light or US waves with 100 µg mL^-1 Se-PEG-Cur were decreased to 33.9 and 22.9%, respectively.

Conclusion:

Intracellular ROS detection indicated that dual PTT and SDT in the presence of Se-PEG-Cur induced the highest ROS production. Se-PEG-Cur was therefore introduced as an absorbing agent of both laser light and US waves for cancer treatment.

Recent Advances in Nanocarrier-Assisted Therapeutics Delivery Systems

Nanotechnologies have attracted increasing attention in their application in medicine, especially in the development of new drug delivery systems. With the help of nano-sized carriers, drugs can reach specific diseased areas, prolonging therapeutic efficacy while decreasing undesired side-effects. In addition, recent nanotechnological advances, such as surface stabilization and stimuli-responsive functionalization have also significantly improved the targeting capacity and therapeutic efficacy of the nanocarrier assisted drug delivery system. In this review, we evaluate recent advances in the development of different nanocarriers and their applications in therapeutics delivery.

A mitochondria-targeted anticancer nanoplatform with deep penetration for enhanced synergistic sonodynamic and starvation therapy

Sonodynamic therapy (SDT), as an emerging technique, gives rise to reactive oxygen species (ROS)-induced apoptosis of tumor cells. However, nonselective enrichment and unsatisfactory penetration depth of sonosensitizers in tumor tissues limit its application. In this study, we synthesized core/shell (glucose oxidase (GOx) in the core/hematoporphyrin monomethyl ether (HMME) and IR780 in the shell) structured polylactic-co-glycolic acid (PLGA) nanoparticles (NPs) with deep tumor penetration and mitochondrial targeting capability for synergistic sonodynamic and starvation therapy. After passing through the endothelial space of tumor vasculatures, by virtue of IR780, these NPs can selectively accumulate towards cancer cells/sites, especially in mitochondria and diffuse into deep tumour centres. Upon ultrasound (US) exposure, the overproduced ROS cause tumor cell apoptosis. Sonodynamic effects can be amplified by mitochondrial targeting because mitochondria are susceptible to ROS. GOx blocks glucose (energy) supply, further suppressing the growth of malignant tumors. This synergistic therapy exhibited a superb response to treatment (4.7-fold lower tumor growth in volume than the control group). In addition, these NPs also serve as excellent photoacoustic (PA)/fluorescent (FL) imaging contrast agents to simultaneously monitor and guide cancer therapy. This study paves a promising way to achieve an ideal strategy for cancer therapy.

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.

Two-Dimensional Theranostic Nanomaterials in Cancer Treatment: State of the Art and Perspectives

As the combination of therapies enhances the performance of biocompatible materials in cancer treatment, theranostic therapies are attracting increasing attention rather than individual approaches. In this review, we describe a variety of two-dimensional (2D) theranostic nanomaterials and their efficacy in ablating tumors. Though many literature reports are available to demonstrate the potential application of 2D nanomaterials, we have reviewed here cancer-treating therapies based on such multifunctional nanomaterials abstracting the content from literature works which explain both the in vitro and in vivo level of applications. In addition, we have included a discussion about the future direction of 2D nanomaterials in the field of theranostic cancer treatment.

Recent Progresses in Cancer Nanotherapeutics Design Using Artemisinins as Free Radical Precursors

Artemisinin and its derivatives (ARTs) are sort of important antimalarials, which exhibit a wide range of biological activities including anticancer effect. To solve the issues regarding poor solubility and limited bioavailability of ARTs, nanoformulation of ARTs has thus emerged as a promising strategy for cancer treatment. A common consideration on nanoARTs design lies on ARTs' delivery and controlled release, where ARTs are commonly regarded as hydrophobic drugs. Based on the mechanism that ARTs' activation relies on ferrous ions (Fe2+) or Fe2+-bonded complexes, new designs to enhance ARTs' activation have thus attracted great interests for advanced cancer nanotherapy. Among these developments, the design of a nanoparticle that can accelerate ARTs' activation has become the major consideration, where ARTs have been regarded as radical precursors. This review mainly focused on the most recent developments of ARTs nanotherapeutics on the basis of advanced drug activation. The basic principles in those designs will be summarized, and a few excellent cases will be also discussed in detail.

Zinc Oxide Nanocrystals and High-Energy Shock Waves: A New Synergy for the Treatment of Cancer Cells

In the last years, different nanotools have been developed to fight cancer cells. They could be administered alone, exploiting their intrinsic toxicity, or remotely activated to achieve cell death. In the latter case, ultrasound (US) has been recently proposed to stimulate some nanomaterials because of the US outstanding property of deep tissue penetration and the possibility of focusing. In this study, for the first time, we report on the highly efficient killing capability of amino-propyl functionalized ZnO nanocrystals (ZnO NCs) in synergy with high-energy ultrasound shock waves (SW) for the treatment of cancer cells. The cytotoxicity and internalization of ZnO NCs were evaluated in cervical adenocarcinoma KB cells, as well as the safety of the SW treatment alone. Then, the remarkably high cytotoxic combination of ZnO NCs and SW was demonstrated, comparing the effect of multiple (3 times/day) SW treatments toward a single one, highlighting that multiple treatments are necessary to achieve efficient cell death. At last, preliminary tests to understand the mechanism of the observed synergistic effect were carried out, correlating the nanomaterial surface chemistry to the specific type of stimulus used. The obtained results can thus pave the way for a novel nanomedicine treatment, based on the synergistic effect of nanocrystals combined with highly intense mechanical pressure waves, offering high efficiency, deep and focused tissue penetration, and a reduction of side effects on healthy cells.

Annealing-modulated nanoscintillators for nonconventional X-ray activation of comprehensive photodynamic effects in deep cancer theranostics

Photodynamic therapy (PDT), which involves the generation of reactive oxygen species (ROS) through interactions of a photosensitizer (PS) with light and oxygen, has been applied in oncology. Over the years, PDT techniques have been developed for the treatment of deep-seated cancers. However, (1) the tissue penetration limitation of excitation photon, (2) suppressed efficiency of PS due to multiple energy transfers, and (3) insufficient oxygen source in hypoxic tumor microenvironment still constitute major challenges facing the clinical application of PDT for achieving effective treatment. We present herein a PS-independent, ionizing radiation-induced PDT agent composed of yttrium oxide nanoscintillators core and silica shell (Y₂O₃:Eu@SiO₂) with an annealing process. Our results revealed that annealed Y₂O₃:Eu@SiO₂ could directly induce comprehensive photodynamic effects under X-ray irradiation without the presence of PS molecules. The crystallinity of Y₂O₃:Eu@SiO₂ was demonstrated to enable the generation of electron-hole (e^--h⁺) pairs in Y₂O₃ under ionizing irradiation, giving rise to the formation of ROS including superoxide, hydroxyl radical and singlet oxygen. In particular, combining Y₂O₃:Eu@SiO₂ with fractionated radiation therapy increased radio-resistant tumor cell damage. Furthermore, photoacoustic imaging of tumors showed re-distribution of oxygen saturation (_SO₂) and reoxygenation of the hypoxia region. The results of this study support applicability of the integration of fractionated radiation therapy with Y₂O₃:Eu@SiO₂, achieving synchronously in-depth and oxygen-insensitive X-ray PDT. Furthermore, we demonstrate Y₂O₃:Eu@SiO₂ exhibited radioluminescence (RL) under X-ray irradiation and observed the virtually linear correlation between X-ray-induced radioluminescence (X-RL) and the Y₂O₃:Eu@SiO₂ concentration in vivo. With the pronounced X-RL for in-vivo imaging and dosimetry, it possesses significant potential for utilization as a precision theranostics producing highly efficient X-ray PDT for deep-seated tumors.