Ultrasound-responsive highly biocompatible nanodroplets loaded with doxorubicin for tumor imaging and treatment in vivo

Programmable ultrasound imaging guided theranostic nanodroplet destruction for precision therapy of breast cancer

Ultrasound-stimulated contrast agents have gained significant attention in the field of tumor treatment as drug delivery systems. However, their limited drug-loading efficiency and the issue of bulky, imprecise release have resulted in inadequate drug concentrations at targeted tissues. Herein, we developed a highly efficient approach for doxorubicin (DOX) precise release at tumor site and real-time feedback via an integrated strategy of "programmable ultrasonic imaging guided accurate nanodroplet destruction for drug release" (PND). We synthesized DOX-loaded nanodroplets (DOX-NDs) with improved loading efficiency (15 %) and smaller size (mean particle size: 358 nm). These DOX-NDs exhibited lower ultrasound activation thresholds (2.46 MPa). By utilizing a single diagnostic transducer for both ultrasound stimulation and imaging guidance, we successfully vaporized the DOX-NDs and released the drug at the tumor site in 4 T1 tumor-bearing mice. Remarkably, the PND group achieved similar tumor remission effects with less than half the dose of DOX required in conventional treatment. Furthermore, the ultrasound-mediated vaporization of DOX-NDs induced tumor cell apoptosis with minimal damage to surrounding normal tissues. In summary, our PND strategy offers a precise and programmable approach for drug delivery and therapy, combining ultrasound imaging guidance. This approach shows great potential in enhancing tumor treatment efficacy while minimizing harm to healthy tissues.

Ultrasound-responsive microbubbles and nanodroplets: A pathway to targeted drug delivery

Ultrasound-responsive agents have shown great potential as targeted drug delivery agents, effectively augmenting cell permeability and facilitating drug absorption. This review focuses on two specific agents, microbubbles and nanodroplets, and provides a sequential overview of their drug delivery process. Particular emphasis is given to the mechanical response of the agents under ultrasound, and the subsequent physical and biological effects on the cells. Finally, the state-of-the-art in their pre-clinical and clinical implementation are discussed. Throughout the review, major challenges that need to be overcome in order to accelerate their clinical translation are highlighted.

ROS regulation in gliomas: implications for treatment strategies

Gliomas are one of the most common primary malignant tumours of the central nervous system (CNS), of which glioblastomas (GBMs) are the most common and destructive type. The glioma tumour microenvironment (TME) has unique characteristics, such as hypoxia, the blood-brain barrier (BBB), reactive oxygen species (ROS) and tumour neovascularization. Therefore, the traditional treatment effect is limited. As cellular oxidative metabolites, ROS not only promote the occurrence and development of gliomas but also affect immune cells in the immune microenvironment. In contrast, either too high or too low ROS levels are detrimental to the survival of glioma cells, which indicates the threshold of ROS. Therefore, an in-depth understanding of the mechanisms of ROS production and scavenging, the threshold of ROS, and the role of ROS in the glioma TME can provide new methods and strategies for glioma treatment. Current methods to increase ROS include photodynamic therapy (PDT), sonodynamic therapy (SDT), and chemodynamic therapy (CDT), etc., and methods to eliminate ROS include the ingestion of antioxidants. Increasing/scavenging ROS is potentially applicable treatment, and further studies will help to provide more effective strategies for glioma treatment.

Piezoelectric enhanced sulfur doped graphdiyne nanozymes for synergistic ferroptosis-apoptosis anticancer therapy

Graphdiyne has excellent potential due to its enzymatic properties. Metal-free sulfur-doped Graphdiyne (S-GDY) has piezoelectric characteristics, and ultrasonic excitation of S-GDY enhances peroxidase activity. It can turn hydrogen peroxide into toxic hydroxyl radicals and induce apoptosis in 4T1 cells. More importantly, the ultrasound (US) enhanced nanozyme induced 4T1 cell ferroptosis by promoting an imbalanced redox reaction due to glutathione depletion and glutathione peroxidase 4 inactivation. S-GDY exhibited enhanced nanozyme activity in vitro and in vivo that may directly trigger apoptosis-ferroptosis for effective tumor therapy. Altogether, this study was expected to provide new insights into the design of piezoelectric catalytic nanozyme and expand their application in the catalytic therapy of tumors.

Stimuli-responsive nanocarrier delivery systems for Pt-based antitumor complexes: a review

Platinum-based anticancer drugs play a crucial role in the clinical treatment of various cancers. However, the application of platinum-based drugs is heavily restricted by their severe toxicity and drug resistance/cross resistance. Various drug delivery systems have been developed to overcome these limitations of platinum-based chemotherapy. Stimuli-responsive nanocarrier drug delivery systems as one of the most promising strategies attract more attention. And huge progress in stimuli-responsive nanocarrier delivery systems of platinum-based drugs has been made. In these systems, a variety of triggers including endogenous and extracorporeal stimuli have been employed. Endogenous stimuli mainly include pH-, thermo-, enzyme- and redox-responsive nanocarriers. Extracorporeal stimuli include light-, magnetic field- and ultrasound responsive nanocarriers. In this review, we present the recent advances in stimuli-responsive drug delivery systems with different nanocarriers for improving the efficacy and reducing the side effects of platinum-based anticancer drugs.

Ultrasound Molecular Imaging and Its Applications in Cancer Diagnosis and Therapy

Ultrasound imaging is regarded as a highly sensitive imaging modality used in routine clinical examinations. Over the last several decades, ultrasound contrast agents have been widely applied in ultrasound molecular cancer imaging to improve the detection, characterization, and quantification of tumors. To date, a few new potential preclinical and clinical applications regarding ultrasound molecular cancer imaging are being investigated. This review presents an overview of the various kinds of ultrasound contrast agents employed in ultrasound molecular imaging and advanced imaging techniques using these contrast agents. Additionally, we discuss the recent enormous development of ultrasound contrast agents in the relevant preclinical and clinical applications, highlight the recent challenges which need to be overcome to accelerate the clinical translation, and discuss the future perspective of ultrasound molecular cancer imaging using various contrast agents. As a highly promising and valuable tumor-specific imaging technique, it is believed that ultrasound molecular imaging will pave an accurate and efficient way for cancer diagnosis.

Slow-Flow Ultrasound Localization Microscopy Using Recondensation of Perfluoropentane Nanodroplets

Ultrasound localization microscopy (ULM) is an emerging, super-resolution imaging technique for detailed mapping of the microvascular structure and flow velocity via subwavelength localization and tracking of microbubbles. Because microbubbles rely on blood flow for movement throughout the vascular space, acquisition times can be long in the smallest, low-flow microvessels. In addition, detection of microbubbles in low-flow regions can be difficult because of minimal separation of microbubble signal from tissue. Nanoscale, phase-change contrast agents (PCCAs) have emerged as a switchable, intermittent or persisting contrast agent for ULM via acoustic droplet vaporization (ADV). Here, the focus is on characterizing the spatiotemporal contrast properties of less volatile perfluoropentane (PFP) PCCAs. The results indicate that at physiological temperature, nanoscale PFP PCCAs with diameters less than 100 nm disappear within microseconds after ADV with high-frequency ultrasound (16 MHz, 5- to 6-MPa peak negative pressure) and that nanoscale PFP PCCAs have an inherent deactivation mechanism via immediate recondensation after ADV. This "blinking" on-and-off contrast signal allowed separation of flow in an in vitro flow phantom, regardless of flow conditions, although with a need for some replenishment at very low flow conditions to maintain count rate. This blinking behavior allows for rapid spatial mapping in areas of low or no flow with ULM, but limits velocity tracking because there is no stable bubble formation with nanoscale PFP PCCAs.

Phase-shift nanodroplets as an emerging sonoresponsive nanomaterial for imaging and drug delivery applications

Nanodroplets - emerging phase-changing sonoresponsive materials - have attracted substantial attention in biomedical applications for both tumour imaging and therapeutic purposes due to their unique response to ultrasound. As ultrasound is applied at different frequencies and powers, nanodroplets have been shown to cavitate by the process of acoustic droplet vapourisation (ADV), causing the development of mechanical forces which promote sonoporation through cellular membranes. This allows drugs to be delivered efficiently into deeper tissues where tumours are located. Recent reviews on nanodroplets are mostly focused on the mechanism of cavitation and their applications in biomedical fields. However, the chemistry of the nanodroplet components has not been discussed or reviewed yet. In this review, the commonly used materials and preparation methods of nanodroplets are summarised. More importantly, this review provides examples of variable chemistry components in nanodroplets which link them to their efficiency as ultrasound-multimodal imaging agents to image and monitor drug delivery. Finally, the drawbacks of current research, future development, and future direction of nanodroplets are discussed.

Ultrasound-Enabled Therapeutic Delivery and Regenerative Medicine: Physical and Biological Perspectives

The role of ultrasound in medicine and biological sciences is expanding rapidly beyond its use in conventional diagnostic imaging. Numerous studies have reported the effects of ultrasound on cellular and tissue physiology. Advances in instrumentation and electronics have enabled successful in vivo applications of therapeutic ultrasound. Despite path breaking advances in understanding the biophysical and biological mechanisms at both microscopic and macroscopic scales, there remain substantial gaps. With the progression of research in this area, it is important to take stock of the current understanding of the field and to highlight important areas for future work. We present herein key developments in the biological applications of ultrasound especially in the context of nanoparticle delivery, drug delivery, and regenerative medicine. We conclude with a brief perspective on the current promise, limitations, and future directions for interfacing ultrasound technology with biological systems, which could provide guidance for future investigations in this interdisciplinary area.

Acoustic Nanodrops for Biomedical Applications

Acoustic nanodrops are designed to vaporize into ultrasound-responsive microbubbles, which presents certain challenges nonexistent for conventional nano-emulsions. The requirements of biocompatibility, vaporizability and colloidal stability has focused research on perfluorocarbons (PFCs). Shorter PFCs yield better vaporizability via their lower critical temperature, but they also dissolve more easily owing to their higher vapor pressure and solubility. Thus, acoustic nanodrops have required a tradeoff between vaporizability and colloidal stability in vivo. The recent advent of vaporizable endoskeletal droplets, which are both stable and vaporizable, may have solved this problem. The purpose of this review is to justify this premise by pointing out the beneficial properties of acoustic nanodrops, providing an analysis of vaporization and dissolution mechanisms, and reviewing current biomedical applications.

Engineered bovine serum albumin-based nanoparticles with pH-sensitivity for doxorubicin delivery and controlled release

In this work, we prepared a stimuli-responsive system for drug delivery and controlled release by engineering the bovine serum albumin (BSA). The doxorubicin (DOX)-loaded BSA nanoparticles (NPs) were conveniently prepared using desolvation method, followed by crosslinking through Schiff base bonds, leading to pH-sensitive DOX-loaded system (DOXs@BSA NPs). The resulted DOXs@BSA NPs showed high drug loading capacity (21.4%), and the particle size was about 130 nm with narrow polydispersity and high negative surface charge (-20.5 mV). The pH-sensitivity of DOXs@BSA NPs was evidenced by the size changes and charge reversal after incubation at different pH values. The DOXs@BSA NPs showed high serum stability which indicated the prolonged circulation time. The in vitro drug release experiment showed that the release of DOX was obviously accelerated by acidity because of disassembly of NPs induced by cleavage of Schiff base bonds. The drug release mechanism was thoroughly studied using a semi-empirical model, further confirming the pH played an important role in drug controlled release process. The results of cytotoxicity assay revealed that DOXs@BSA NPs exhibited much higher toxic effects for tumor cells in comparison to the free DOX control. Collectively, these results demonstrated that DOXs@BSA NPs might be potential application for drug delivery and controlled release in cancer chemotherapy. Moreover, this work also showed that preparation of stimuli-responsive drug delivery system by engineering the commercial biomaterials could be a promising method to develop multi-functional nanomedicine.