Multifunctional Ultrasound Contrast Agents for Imaging Guided Photothermal Therapy

Small molecules and conjugates as theranostic agents

Theranostics, the integration of therapy and diagnostics into a single entity for the purpose of monitoring disease progression and treatment response. Diagnostics involves identifying specific characteristics of a disease, while therapeutics refers to the treatment of the disease based on this identification. Advancements in medicinal chemistry and technology have led to the development of drug modalities that provide targeted therapeutic effects while also providing real-time updates on disease progression and treatment. The inclusion of imaging in therapy has significantly improved the prognosis of devastating diseases such as cancer and neurodegeneration. Currently, theranostic treatment approaches are based on nuclear medicine, while nanomedicine and a wide diversity of macromolecular systems such as gels, polymers, aptamers, and dendrimer-based agents are being developed for the purpose. Theranostic agents have significant roles to play in both early-stage drug development and clinical-stage therapeutic-containing drug candidates. This review will briefly outline the pros and cons of existing and evolving theranostic approaches before comprehensively discussing the role of small molecules and their conjugates.

Major Strategies for Spatial Control of Ultrasound-Driven Gene Expression to Enhance Therapeutic Specificity

A major challenge of gene therapy is to achieve highly specific transgene expression in tissues of interest with minimized off-target expression. Ultrasound in combination with microbubbles can transiently increase permeability of desired cells or tissues and thereby facilitate gene transfer. This kind of ultrasound-driven transgene expression has gained increasing attention due to its deep tissue penetration and high spatiotemporal resolution. However, successful genetic manipulation in vivo with ultrasound need to well optimize various aspects involved in this process. Ultrasound parameters, microbubble dose, and gene vectors need to be optimized for highly increased transgene expression in the cells of interest. Conversely, the potential off-target transgene expression and toxicities need to be reduced by modification of gene vectors and/or promoter sequence. This review will discuss some major strategies for enhanced specificity of the ultrasound-mediated gene transfer in vivo. Five major strategies will be discussed, including the integration of real-time imaging methods, local injection, targeted microbubbles loaded with nucleic acids, stealth nanocarriers, and cell-specific promoter. The advantages and limitations of each strategy were outlined, hoping to provide a guideline for researchers in achieving high specific ultrasound-driven gene expression.

New Degradable Semiconducting Polymers for Photoacoustic Imaging of λ-Carrageenan-Induced Arthritis Mouse Model

Semiconducting polymer has a high extinction coefficient and a long band absorption and can be used as a photoacoustic imaging contrast agent. However, nonbiodegradable semiconducting polymers may cause biosafety issues due to being retained in the body. Therefore, developing degradable semiconducting polymers is necessary for in vivo imaging. Herein, we developed three degradable semiconducting polymers with unique optical properties. We adjusted the optical properties of semiconducting polymers by designing the molecular structure of semiconducting polymers. Polymers with a donor-π-acceptor structure could easily improve the optical properties through adjusting the donor or acceptor units. Through adjusting the electron-donor and -acceptor units, three diketopyrrolopyrrole derivative polymers (DPPTz, DPPQu, and DPPWu) were synthesized and converted into nanosize particles. By introducing the degradable chemical groups in the main chain structure of semiconducting polymers, diketopyrrolopyrrole polymers could be degraded by ClO^-. Among these nanosize particles, DPPTz NPs and DPPQu NPs were used to achieve the in vivo photoacoustic imaging of λ-carrageenan-induced arthritis mouse model. This work provides a novel design idea for the designing of red-shifted semiconducting polymer with degradable properties.

Tumor-targeted/reduction-triggered composite multifunctional nanoparticles for breast cancer chemo-photothermal combinational therapy

Breast cancer has become the most commonly diagnosed cancer type in the world. A combination of chemotherapy and photothermal therapy (PTT) has emerged as a promising strategy for breast cancer therapy. However, the intricacy of precise delivery and the ability to initiate drug release in specific tumor sites remains a challenging puzzle. Therefore, to ensure that the therapeutic agents are synchronously delivered to the tumor site for their synergistic effect, a multifunctional nanoparticle system (PCRHNs) is developed, which is grafted onto the prussian blue nanoparticles (PB NPs) by reduction-responsive camptothecin (CPT) prodrug copolymer, and then modified with tumor-targeting peptide cyclo(Asp-d-Phe-Lys-Arg-Gly) (cRGD) and hyaluronic acid (HA). PCRHNs exhibited nano-sized structure with good monodispersity, high load efficiency of CPT, triggered CPT release in response to reduction environment, and excellent photothermal conversion under laser irradiation. Furthermore, PCRHNs can act as a photoacoustic imaging contrast agent-guided PTT. In vivo studies indicate that PCRHNs exhibited excellent biocompatibility, prolonged blood circulation, enhanced tumor accumulation, allow tumor-specific chemo-photothermal therapy to achieve synergistic antitumor effects with reduced systemic toxicity. Moreover, hyperthermia-induced upregulation of heat shock protein 70 in the tumor cells could be inhibited by CPT. Collectively, PCRHNs may be a promising therapeutic way for breast cancer therapy.

Advances in Ultrasound-Responsive Hydrogels for Biomedical Applications

Various intelligent hydrogels have been developed for biomedical applications because they can achieve multiple, variable, controllable and reversible changes in their shape and properties in a spatial and temporal manner,...

Photoechogenic Inflatable Nanohybrids for Upconversion-Mediated Sonotheranostics

Hybrid nanostructures are promising for ultrasound-triggered drug delivery and treatment, called sonotheranostics. Structures based on plasmonic nanoparticles for photothermal-induced microbubble inflation for ultrasound imaging exist. However, they have limited therapeutic applications because of short microbubble lifetimes and limited contrast. Photochemistry-based sonotheranostics is an attractive alternative, but building near-infrared (NIR)-responsive echogenic nanostructures for deep tissue applications is challenging because photolysis requires high-energy (UV-visible) photons. Here, we report a photochemistry-based echogenic nanoparticle for in situ NIR-controlled ultrasound imaging and ultrasound-mediated drug delivery. Our nanoparticle has an upconversion nanoparticle core and an organic shell carrying gas generator molecules and drugs. The core converts low-energy NIR photons into ultraviolet emission for photolysis of the gas generator. Carbon dioxide gases generated in the tumor-penetrated nanoparticle inflate into microbubbles for sonotheranostics. Using different NIR laser power allows dual-modal upconversion luminescence planar imaging and cross-sectional ultrasonography. Low-frequency (10 MHz) ultrasound stimulated microbubble collapse, releasing drugs deep inside the tumor through cavitation-induced transport. We believe that the photoechogenic inflatable hierarchical nanostructure approach introduced here can have broad applications for image-guided multimodal theranostics.

Enhancing Cancer Immunotherapeutic Efficacy with Sonotheranostic Strategies

Immunotherapy has revolutionized the modality for establishing a firm immune response and immunological memory. However, intrinsic limitations of conventional low responsive poor T cell infiltration and immune related adverse effects urge the coupling of cancer nanomedicines with immunotherapy for boosting antitumor response under ultrasound (US) sensitization to mimic dose-limiting toxicities for safe and effective therapy against advanced cancer. US is composed of high-frequency sound waves that mediate targeted spatiotemporal control over release and internalization of the drug. The unconventional US triggered immunogenic nanoengineered arena assists the limited immunogenic dose, limiting toxicities and efficacies. In this Review, we discuss current prospects of enhanced immunotherapy using nanomedicine under US. We highlight how nanotechnology designs and incorporates nanomedicines for the reprogramming of systematic immunity in the tumor microenvironment. We also emphasize the mechanical and biological potential of US, encompassing sonosensitizer activation for enhanced immunotherapeutic efficacies. Finally, the smartly converging combinational platform of US stimulated cancer nanomedicines for amending immunotherapy is summarized. This Review will widen scientists' ability to explore and understand the limiting factors for combating cancer in a precisely customized way.

Light: A Magical Tool for Controlled Drug Delivery

Light is a particularly appealing tool for on-demand drug delivery due to its noninvasive nature, ease of application and exquisite temporal and spatial control. Great progress has been achieved in the development of novel light-driven drug delivery strategies with both breadth and depth. Light-controlled drug delivery platforms can be generally categorized into three groups: photochemical, photothermal, and photoisomerization-mediated therapies. Various advanced materials, such as metal nanoparticles, metal sulfides and oxides, metal-organic frameworks, carbon nanomaterials, upconversion nanoparticles, semiconductor nanoparticles, stimuli-responsive micelles, polymer- and liposome-based nanoparticles have been applied for light-stimulated drug delivery. In view of the increasing interest in on-demand targeted drug delivery, we review the development of light-responsive systems with a focus on recent advances, key limitations, and future directions.

Ultrabright Fluorescent Polymeric Nanoparticles with a Stealth Pluronic Shell for Live Tracking in the Mouse Brain

Visualizing single organic nanoparticles (NPs) in vivo remains a challenge, which could greatly improve our understanding of the bottlenecks in the field of nanomedicine. To achieve high single-particle fluorescence brightness, we loaded polymer poly(methyl methacrylate)-sulfonate (PMMA-SO₃H) NPs with octadecyl rhodamine B together with a bulky hydrophobic counterion (perfluorinated tetraphenylborate) as a fluorophore insulator to prevent aggregation-caused quenching. To create NPs with stealth properties, we used the amphiphilic block copolymers pluronic F-127 and F-68. Fluorescence correlation spectroscopy and Förster resonance energy transfer (FRET) revealed that pluronics remained at the NP surface after dialysis (at one amphiphile per 5.5 nm²) and prevented NPs from nonspecific interactions with serum proteins and surfactants. In primary cultured neurons, pluronics stabilized the NPs, preventing their prompt aggregation and binding to neurons. By increasing dye loading to 20 wt % and optimizing particle size, we obtained 74 nm NPs showing 150-fold higher single-particle brightness with two-photon excitation than commercial Nile Red-loaded FluoSpheres of 39 nm hydrodynamic diameter. The obtained ultrabright pluronic-coated NPs enabled direct single-particle tracking in vessels of mice brains by two-photon intravital microscopy for at least 1 h, whereas noncoated NPs were rapidly eliminated from the circulation. Following brain injury or neuroinflammation, which can open the blood-brain barrier, extravasation of NPs was successfully monitored. Moreover, we demonstrated tracking of individual NPs from meningeal vessels until their uptake by meningeal macrophages. Thus, single NPs can be tracked in animals in real time in vivo in different brain compartments and their dynamics visualized with subcellular resolution.

Hydroxyapatite as a biomaterial - a gift that keeps on giving

The synthetic analogue to biogenic apatite, hydroxyapatite (HA) has a number of physicochemical properties that make it an attractive candidate for diagnosis, treatment of disease and augmentation of biological tissues. Here we describe some of the recent studies on HA, which may provide bases for a number of new medical applications. The content of this review is divided to different medical application modes utilizing HA, including tissue engineering, medical implants, controlled drug delivery, gene therapies, cancer therapies and bioimaging. A number of advantages of HA over other biomaterials emerge from this discourse, including (i) biocompatibility, (ii) bioactivity, (iii) relatively simple synthesis protocols for the fabrication of nanoparticles with specific sizes and shapes, (iv) smart response to environmental stimuli, (v) facile functionalization and surface modification through noncovalent interactions, and (vi) the capacity for being simultaneously loaded with a wide range of therapeutic agents and switched to bioimaging modalities for uses in theranostics. A special section is dedicated to analysis of the safety of particulate HA as a component of parenterally administrable medications. It is concluded that despite the fact that many benefits come with the usage of HA, its deficiencies and potential side effects must be addressed before the translation to the clinical domain is pursued. Although HA has been known in the biomaterials world as the exemplar of safety, this safety proves to be the function of size, morphology, surface ligands and other structural and compositional parameters defining the particles. For this reason, each HA, especially when it comes in a novel structural form, must be treated anew from the safety research angle before being allowed to enter the clinical stage.

N-Doped Carbon Quantum Dot (NCQD)-Deposited Carbon Capsules for Synergistic Fluorescence Imaging and Photothermal Therapy of Oral Cancer

Use of nanomaterials blessed with both therapeutic and diagnostic properties is a proficient strategy in the treatment of cancer in its early stage. In this context, our paper reports the synthesis of uniform size N-rich mesoporous carbon nanospheres of size 65-70 nm from pyrrole and aniline precursors using Triton-X as a structure-directing agent. Transmission electron microscopy reveals that these carbons spheres contain void spaces in which ultrasmall nitrogen-doped quantum dots (NCQD) are captured within the matrix. These mesoporous hollow NCQD captured carbon spheres (NCQD-HCS) show fluorescence quantum yield up to 14.6% under λ_ex = 340 nm. Interestingly, samples calcined at >800 °C clearly absorb in the wavelength range 700-1000 nm and shows light-to-heat conversion efficiency up to 52%. In vitro experiments in human oral cancer cells (FaDu) show that NCQD-HCS are internalized by the cells and induce a substantial thermal ablation effect in FaDu cells when exposed under a 980 nm near-infrared laser.

Polypyrrole-coated phase-change liquid perfluorocarbon nanoparticles for the visualized photothermal-chemotherapy of breast cancer

A theranostic nanoplatform (DTX/PFH@PPy-FA) for multi-modal imaging-guided photothermal-chemotherapy has been constructed. Lipid-perfluorohexane (PFH) nanodroplet loaded with docetaxel (DTX) was coated with a polypyrrole (PPy) shell. Then the folic acid (FA) molecule with active tumor-targeting function was modified on the surface of PPy shell. Due to the good photothermal conversion performance, PPy shell can raise the temperature under the near infrared laser irradiation, which not only produces photothermal effect to kill tumor cells, but also promotes liquid-gas phase change of PFH, and produces ultrasound imaging effect. The results of photothermal experiment and imaging experiment confirmed that the obtained DTX/PFH@PPy-FA possessed good photothermal, photoacoustic imaging and ultrasound imaging effects in vitro and in vivo. The results of in vitro cell experiments showed that DTX/PFH@PPy-FA had a active targeting ability to tumor cells, and its photothermal-chemotherapy synergistically inhibited the proliferation of tumor cells. In vivo study on 4T1-bearing BALB/c mice indicated that the photothermal-chemotherapy of DTX/PFH@PPy-FA not only effectively inhibited the growth of 4T1 breast cancer, but also inhibited lung metastasis. This multifunctional nanoparticle is expected to become a new nanoplatform for the visualized photothermal-chemotherapy of cancer. STATEMENT OF SIGNIFICANCE: In this work, we presented a multi-modal imaging-guided photothermal-chemotherapy theranostic nanoplatform (DTX/PFH@PPy-FA) for visualized treatment of breast cancer. The docetaxel (DTX) loaded perfluorohexane (PFH) nanodroplets (DTX/PFH@SPC) were firstly prepared and then coated with polypyrrole shell (PPy). Then, PEGylated folic acid was covalently modified to obtain the folate-targeted multifunctional nanoparticle (DTX/PFH@PPy-FA). Due to the good photothermal conversion performance, PPy shell can raise the temperature under the near infrared laser irradiation, which not only produces photothermal effect to kill tumor cells, but also promotes liquid-gas phase change of PFH, and produces good ultrasound imaging effect. The PPy shell also imparts photoacoustic imaging characteristics to the nanoparticles. Experimental results show that our prepared DTX/PFH@PPy-FA possesses folic acid-mediated tumor targeting ability, ultrasound and photoacoustic imaging, and photothermal-chemotherapy synergistic effect. This multi-functional nanoparticle is expected to become a new platform for the visualized photothermal-chemotherapy of breast cancer.

Low-intensity focused ultrasound (LIFU)-activated nanodroplets as a theranostic agent for noninvasive cancer molecular imaging and drug delivery

Theranostics is a new trend in the tumor research field, which involves the integration of diagnostic and therapeutic functions using imageable nanoparticles coupled with therapeutic drugs. Imaging-guided targeted delivery of therapeutics and diagnostics using nanocarriers hold great promise to minimize the side effects of conventional chemotherapy. Ultrasound microbubbles have been employed as theranostic agents over the last decade, which provide both real-time dynamic imaging for diagnosis and precise control for targeted tumor therapy. However, the intrinsic defects of microbubbles such as poor tissue penetration, short circulation time and instability hinder microbubble-based theranostic applications. In recent years, liquid-to-gas transitional perfluorocarbon nanoparticles have been developed as promising diagnostic and therapeutic nanoagents to solve the abovementioned problems. In this study, phase-changeable, folate-targeted perfluoropentane nanodroplets loaded with 10-hydroxycamptothecin (HCPT) and superparamagnetic Fe3O4 (denoted as FA-HCPT-Fe3O4-PFP NDs) are prepared and investigated for multimodal tumor imaging and targeted therapy. After intravenous administration into nude mice bearing SKOV3 ovarian cancer, FA-HCPT-Fe3O4-PFP NDs exhibit the ability to enhance MR and PA imaging. Furthermore, after the phase transition activated by low-intensity focused ultrasound (LIFU) sonication, FA-HCPT-Fe3O4-PFP NDs remarkably enhance US imaging at the tumor location. Meanwhile, the HCPT released from FA-HCPT-Fe3O4-PFP NDs during the liquid-to-gas transition provides a therapeutic effect on tumor cells with relatively low side effects to normal tissue. Therefore, the combination of LIFU and FA-HCPT-Fe3O4-PFPNDs presents an ideal modality for tumor-targeted theranostics.

Ultrasound Triggered Conversion of Porphyrin/Camptothecin-Fluoroxyuridine Triad Microbubbles into Nanoparticles Overcomes Multidrug Resistance in Colorectal Cancer

Multidrug resistance remains one of the main obstacles to efficient chemotherapy of colorectal cancer. Herein, an efficient combination therapeutic strategy is proposed based on porphyrin/camptothecin-floxuridine triad microbubbles (PCF-MBs) with high drug loading contents, which own highly stable co-delivery drug combinations and no premature release. The triad PCF-MBs can act not only as a contrast agent for ultrasound (US)/fluorescence bimodal imaging but also a multimodal therapeutic agent for synergistic chemo-photodynamic combination therapy. Upon local ultrasound exposure under the guidance of ultrasound imaging, in situ conversion of PCF-MBs into porphyrin/camptothecin-floxuridine nanoparticles (PCF-NPs) leads to high accumulation of chemo-drugs and photosensitizer in tumors due to the induced high permeability of the capillary wall and cell membrane temporarily via sonoporation effect, greatly reducing the risk of systemic exposure. Most importantly, it was found that the PCF-MB-mediated photodynamic therapy could significantly reduce the expression of adenosine-triphosphate (ATP)-binding cassette subfamily G member 2 (ABCG₂), which is responsible for the drug resistance in chemotherapy, resulting in a prominent intracellular camptothecin increase. In vivo experiments revealed that the PCF-MBs in combination with ultrasound and laser irradiation could achieve a 90% tumor inhibition rate of HT-29 cancer with no recurrence. Therefore, such triad PCF-MB-based combination therapeutic strategy shows great promise for overcoming drug resistance of colorectal cancer and other cancers.

Photoluminescent Cationic Carbon Dots as efficient Non-Viral Delivery of Plasmid SOX9 and Chondrogenesis of Fibroblasts

With the increasing demand for higher gene carrier performance, a multifunctional vector could immensely simplify gene delivery for disease treatment; nevertheless, the current non- viral vectors lack self-tracking ability. Here, a type of novel, dual-functional cationic carbon dots (CDs), produced through one-step, microwave-assisted pyrolysis of arginine and glucose, have been utilized as both a self-imaging agent and a non-viral gene vector for chondrogenesis from fibroblasts. The cationic CDs could condense the model gene plasmid SOX9 (pSOX9) to form ultra-small (10–30 nm) nanoparticles which possessed several favorable properties, including high solubility, tunable fluorescence, high yield, low cytotoxicity and outstanding biocompatibility. The MTT assay indicated that CDs/pSOX9 nanoparticles had little cytotoxicity against mouse embryonic fibroblasts (MEFs) compared to Lipofectamine2000 and PEI (25 kDa). Importantly, the CDs/pSOX9 nanoparticles with tunable fluorescence not only enabled the intracellular tracking of the nanoparticles, but also could successfully deliver the pSOX9 into MEFs with significantly high efficiency. Furthermore, the CDs/pSOX9 nanoparticles-mediated transfection of MEFs showed obvious chondrogenic differentiation. Altogether, these findings demonstrated that the CDs prepared in this study could serve as a paradigmatic example of the dual-functional reagent for both self-imaging and effective non-viral gene delivery.

Porphyrin-grafted Lipid Microbubbles for the Enhanced Efficacy of Photodynamic Therapy in Prostate Cancer through Ultrasound-controlled In Situ Accumulation

Photodynamic therapy (PDT) holds promise for focal therapy of prostate cancer (PCa). However, the therapeutic efficacy needs improvement, and further development of PDT for PCa has challenges, including uncertainty of photosensitizers (PSs) accumulation at the tumor site and difficulty in visualizing lesions using conventional ultrasound (US) imaging. We have developed novel porphyrin-grafted lipid (PGL) microbubbles (MBs; PGL-MBs) and propose a strategy to integrate PGL-MBs with US imaging to address these limitations and enhance PDT efficacy.

METHODS

PGL-MBs have two functions: imaging guidance by contrast-enhanced ultrasound (CEUS) and targeted delivery of PSs by ultrasound targeted microbubble destruction (UTMD). PGL-MBs were prepared and characterized before and after low-frequency US (LFUS) exposure. Then, in vitro studies validated the efficacy of PDT with PGL-MBs in human prostate cancer PC3 cells. PC3-xenografted nude mice were used to validate CEUS imaging, accumulation at the tumor site, and in vivo PDT efficacy.

RESULTS

PGL-MBs showed good contrast enhancement for US imaging and were converted into nanoparticles upon LFUS exposure. The resulting uniquely structured nanoparticles avoided porphyrin fluorescence quenching and efficiently accumulated at the tumor site through the sonoporation effect created with the assistance of US to achieve excellent PDT efficacy.

CONCLUSIONS

This is the first preclinical investigation of MBs applied in PDT for PCa. PGL-MBs possess favorable CEUS imaging effects to enhance the localization of tumors. PGL-MBs with LFUS control PS accumulation at the tumor site to achieve highly effective PDT of PCa. This strategy carries enormous clinical potential for PCa management.

Intrabilayer 64Cu Labeling of Photoactivatable, Doxorubicin-Loaded Stealth Liposomes

Doxorubicin (Dox)-loaded stealth liposomes (similar to those in clinical use) can incorporate small amounts of porphyrin-phospholipid (PoP) to enable chemophototherapy (CPT). PoP is also an intrinsic and intrabilayer ⁶⁴Cu chelator, although how radiolabeling impacts drug delivery has not yet been assessed. Here, we show that ⁶⁴Cu can radiolabel the stable bilayer of preformed Dox-loaded PoP liposomes with inclusion of 1% ethanol without inducing drug leakage. Dox-PoP liposomes labeled with intrabilayer copper behaved nearly identically to unlabeled ones in vitro and in vivo with respect to physical parameters, pharmacokinetics, and CPT efficacy. Positron emission tomography and near-infrared fluorescence imaging visualized orthotopic mammary tumors in mice with passive liposome accumulation following administration. A single CPT treatment with 665 nm light (200 J/cm²) strongly inhibited primary tumor growth. Liposomes accumulated in lung metastases, based on NIR imaging. These results establish the feasibility of CPT interventions guided by intrinsic multimodal imaging of Dox-loaded stealth PoP liposomes.

Targeted Soft Biodegradable Glycine/PEG/RGD-Modified Poly(methacrylic acid) Nanobubbles as Intelligent Theranostic Vehicles for Drug Delivery

The development of multifunctional ultrasound contrast agents has inspired considerable interest in the application of biomedical imaging and anticancer therapeutics. However, combining multiple components that can preferentially accumulate in tumors in a nanometer scale poses one of the major challenges in targeting drug delivery for theranostic application. Herein, reflux-precipitation polymerization, and N-(3-(dimethylamino)propyl)-N'-ethylcarbodiimide-meditated amidation reaction were introduced to effectively generate a new type of soft glycine/poly(ethylene glycol) (PEG)/RGD-modified poly(methacrylic acid) nanobubbles with a uniform morphology and desired particle size (less than 100 nm). Because of the enhanced biocompatibility resulting from the glycine modification, over 80% of the cells survived, even though the dosage of glycine-modified polymeric nanobubbles was up to 5 mg/mL. By loading doxorubicin as an anticancer drug and perfluorohexane as an ultrasound probe, the resulting glycine/PEG/RGD-modified nanobubbles showed remarkable cancer therapeutic efficacy and a high quality of ultrasonic imaging; thus, the ultrasonic signal exhibited a 1.47-fold enhancement at the tumor site after intravenous injection. By integrating diagnostic and therapeutic functions into a single nanobubble, the new type of theranostic nanobubbles offers a promising strategy to monitor the therapeutic effects, giving important insights into the ultrasound-traced and enhanced targeting drug delivery in biomedical applications.

Near-infrared light-activatable polymeric nanoformulations for combined therapy and imaging of cancer

Near infrared (NIR) light allows deep tissue penetration and high spatial resolution due to the reduced scattering of long-wavelength photons. NIR light-activatable polymer nanoparticles are widely exploited for enhanced cancer imaging (diagnosis) and therapy owing to their superior photostability, photothermal conversion efficiency (or high emission rate), and minimal toxicity to cells and tissues. This review surveys the most recent advances in the synthesis of different NIR-absorbing and emissive polymer nanoformulations, and their applications for cancer imaging, photothermal therapy, theranostics and combination therapy by delivering multiple small molecule chemotherapeutics. Photo-responsive drug delivery systems for NIR light-triggered drug release are also discussed with particular emphasis on their molecular designs and formulations as well as photo-reaction mechanisms. Finally, outlook and challenges are presented regarding potential clinical applications of NIR light-activatable nanoformulations.

Cell-borne 2D nanomaterials for efficient cancer targeting and photothermal therapy

Two of the challenges for clinical implementation of nano-therapeutic strategies are optimization of tumor targeting and clearance of the nanoagents in vivo. Herein, a cell-mediated therapy by transporting 2D Bi₂Se₃ nanosheets within macrophage vehicles is described. The Bi₂Se₃ nanosheets with excellent near-infrared photothermal performance exhibit high macrophage uptake and negligible cytotoxicity thus facilitating the fabrication of Bi₂Se₃-laden-macrophages. Compared with bare Bi₂Se₃, the Bi₂Se₃-laden-macrophages after intravenous injection show prolonged blood circulation and can overcome the hypoxia-associated drug delivery barrier to target the tumor efficiently and dramatically enhance the efficiency of photothermal cancer therapy. The Bi₂Se₃-laden-macrophages possess good biocompatibility as demonstrated by the biochemical and histological analyses and furthermore, most of the materials are excreted from the body within 25 days. Our findings reveal a desirable system for highly efficient near-infrared photothermal cancer therapy.

Progress in Nanotheranostics Based on Mesoporous Silica Nanomaterial Platforms

Theranostics based on nanoparticles (NPs) is a promising paradigm in nanomedicine. Mesoporous silica nanoparticle (MSN)-based systems offer unique characteristics to enable multimodal imaging or simultaneous diagnosis and therapy. They include large surface area and volume, tunable pore size, functionalizable surface, and acceptable biological safety. Hybridization with other NPs and chemical modification can further potentiate the multifunctionality of MSN-based systems toward translation. Here, we update the recent progress on MSN-based systems for theranostic purposes. We discuss various synthetic approaches used to construct the theranostic platforms either via intrinsic chemistry or extrinsic combination. These include defect generation in the silica structure, encapsulation of diagnostic NPs within silica, their assembly on the silica surface, and direct conjugation of dye chemicals. Collectively, in vitro and in vivo results demonstrate that multimodal imaging capacities can be integrated with the therapeutic functions of these MSN systems for therapy. With further improvement in bioimaging sensitivity and targeting specificity, the multifunctional MSN-based theranostic systems will find many clinical applications in the near future.

Recent advances in different modal imaging-guided photothermal therapy

Photothermal therapy (PTT) has recently attracted considerable attention owing to its controllable treatment process, high tumour eradication efficiency and minimal side effects on non-cancer cells. PTT can melt cancerous cells by localising tissue hyperthermia induced by internalised therapeutic agents with a high photothermal conversion efficiency under external laser irradiation. Numerous in vitro and in vivo studies have shown the significant potential of PTT to treat tumours in future practical applications. Unfortunately, the lack of visualisation towards agent delivery and internalisation, as well as imaging-guided comprehensive evaluation of therapeutic outcome, limits its further application. Developments in combined photothermal therapeutic nanoplatforms guided by different imaging modalities have compensated for the major drawback of PTT alone, proving PTT to be a promising technique in biomedical applications. In this review, we introduce recent developments in different imaging modalities including single-modal, dual-modal, triple-modal and even multi-modal imaging-guided PTT, together with imaging-guided multi-functional theranostic nanoplatforms.

Porphyrin-loaded nanoparticles for cancer theranostics

Porphyrins have been used as pioneering theranostic agents not only for the photodynamic therapy, sonodynamic therapy and radiotherapy of cancer, but also for diagnostic fluorescence imaging, magnetic resonance imaging and photoacoustic imaging. A variety of porphyrins have been developed but very few of them have actually been employed in clinical trials due to their poor selectivity to tumorous tissue and high accumulation rates in the skin. In addition, most porphyrin molecules are hydrophobic and form aggregates in aqueous media. Nevertheless, the use of nanoparticles as porphyrin carriers shows great promise to overcome these shortcomings. Encapsulating or attaching porphyrins to nanoparticles makes them more suitable for tissue delivery because we can create materials with a conveniently specific tissue lifetime, specific targeting, immune tolerance, and hydrophilicity as well as other characteristics through rational design. In addition, various functional components (e.g. for targeting, imaging or therapeutic functions) can be easily introduced into a single nanoparticle platform for cancer theranostics. This review presents the current state of knowledge on porphyrin-loaded nanoparticles for the interwined imaging and therapy of cancer. The future trends and limitations of prophyrin-loaded nanoparticles are also outlined.

Ultrasound-Induced Reactive Oxygen Species Mediated Therapy and Imaging Using a Fenton Reaction Activable Polymersome

Ultrasound techniques have been extensively employed for diagnostic purposes. Because of its features of low cost, easy access, and noninvasive real-time imaging, toward clinical practice it is highly anticipated to simply use diagnostic ultrasound to concurrently perform imaging and therapy. We report a H2O2-filled polymersome to display echogenic reflectivity and reactive oxygen species-mediated cancer therapy simply triggered by the microultrasound diagnostic system accompanied by MR imaging. Instead of filling common perfluorocarbons, the encapsulation of H2O2 in H2O2/Fe3O4-PLGA polymersome provides O2 as the echogenic source and (•)OH as the therapeutic element. On exposure to ultrasound, the polymersome can be easily disrupted to yield (•)OH through the Fenton reaction by reaction of H2O2 and Fe3O4. We showed that malignant tumors can be completely removed in a nonthermal process.

Microfluidic fabrication of stimuli-responsive microdroplets for acoustic and optical droplet vaporization

We developed a flow-focusing microfluidic assay for fabricating stimuli-responsive microdroplets (SRMs) for imaging and therapeutic applications.

Hyaluronic Acid Modified Hollow Prussian Blue Nanoparticles Loading 10-hydroxycamptothecin for Targeting Thermochemotherapy of Cancer

This paper reported the fabrication of a multifunctional nanoplatform by modifying hollow Prussian blue nanoparticles with hyaluronic acid grafting polyethylene glycol, followed by loading 10-hydroxycamptothecin for tumor-targeted thermochemotherapy. It was found that the surface modification of hollow Prussian blue nanoparticles with hyaluronic acid grafting polyethylene endowed a great colloidal stability, long blood circulation time and the capability for targeting Hela cells over-expressing the CD44 receptor. The obtained nanoagent exhibited efficient photothermal effect and a light triggered and stepwise release behavior of 10-hydroxycamptothecin due to the strong optical absorption in the near-infrared region. The investigations on the body weight change, histological injury and blood biochemical indexes showed that such nanoagent had excellent biocompatibility for medical application. Both in vitro and in vivo experiments proved that the combination of chemotherapy and photothermal therapy through the agent of hyaluronic acid modified Prussian blue nanoparticles loading 10-hydroxycamptothecin could significantly improve the therapeutic efficacy compared with either therapy alone because of a good synergetic effect.

(177)Lu-Labeled Cerasomes Encapsulating Indocyanine Green for Cancer Theranostics

This Article reported the fabrication of a robust theranostic cerasome encapsulating indocyanine green (ICG) by incorporating 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[carboxy(polyethylene glycol)2000]-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid monoamide (DSPE-PEG2000-DOTA), followed by chelating radioisotope of (177)Lu. Its applications in optical and nuclear imaging of tumor uptake and biodistribution, as well as photothermal killing of cancer cells, were investigated. It was found that the obtained cerasome could act efficiently as fluorescence contrast agent as well as nuclear imaging tracer. Encapsulating ICG into cerasome could protect ICG from degradation, aggregation, and fast elimination from body, resulting in remarkable improvement in near-infrared fluorescence imaging, photothermal stability, and in vivo pharmacokinetic profile. Both fluorescence and nuclear imaging showed that such agent could selectively accumulate in tumor site after intravenous injection of the cerasome agent into Lewis lung carcinoma tumor bearing mice, resulting in efficient photothermal ablation of tumor through a one-time NIR laser irradiation at the best time window. The ability to track the uptake of cerasomes on a whole body basis could provide researchers with an excellent tool for developing cerasome-based drug delivery agents, especially the strategy of labeling cerasomes with theranostic radionuclide (177)Lu, enabling the ability of the (177)Lu-labeled cerasomes for radionuclide cancer therapy and even the combined therapy.

Manganese (II) Chelate Functionalized Copper Sulfide Nanoparticles for Efficient Magnetic Resonance/Photoacoustic Dual-Modal Imaging Guided Photothermal Therapy

The integration of diagnostic and therapeutic functionalities into one nanoplatform shows great promise in cancer therapy. In this research, manganese (II) chelate functionalized copper sulfide nanoparticles were successfully prepared using a facile hydrothermal method. The obtained ultrasmall nanoparticles exhibit excellent photothermal effect and photoaoustic activity. Besides, the high loading content of Mn(II) chelates makes the nanoparticles attractive T₁ contrast agent in magnetic resonance imaging (MRI). In vivo photoacoustic imaging (PAI) results showed that the nanoparticles could be efficiently accumulated in tumor site in 24 h after systematic administration, which was further validated by MRI tests. The subsequent photothermal therapy of cancer in vivo was achieved without inducing any observed side effects. Therefore, the copper sulfide nanoparticles functionalized with Mn(II) chelate hold great promise as a theranostic nanomedicine for MR/PA dual-modal imaging guided photothermal therapy of cancer.

Magnetic Prussian blue nanoparticles for combined enzyme-responsive drug release and photothermal therapy

Multifunctional magnetic nanoparticles based on Fe₃O₄ nanocore and Prussian blue nanoshell for combined enzyme-responsive drug release and photothermal therapy.

Magnetic Prussian blue nanoparticles for targeted photothermal therapy under magnetic resonance imaging guidance

This paper reported a core-shell nanotheranostic agent by growing Prussian blue (PB) nanoshells of 3-6 nm around superparamagnetic Fe3O4 nanocores for targeted photothermal therapy of cancer under magnetic resonance imaging (MRI) guidance. Both in vitro and in vivo experiments proved that the Fe3O4@PB core-shell nanoparticles showed significant contrast enhancement for T2-weighted MRI with the relaxivity value of 58.9 mM(-1)·s(-1). Simultaneously, the composite nanoparticles exhibited a high photothermal effect under irradiation of a near-infrared laser due to the strong absorption of PB nanoshells, which led to more than 80% death of HeLa cells with only 0.016 mg·mL(-1) of the nanoparticles with the aid of the magnetic targeting effect. Using tumor-bearing nude mice as the model, the near-infrared laser light ablated the tumor effectively in the presence of the Fe3O4@PB nanoparticles and the tumor growth inhibition was evaluated to be 87.2%. Capabilities of MRI, magnetic targeting, and photothermal therapy were thus integrated into a single agent to allow efficient MRI-guided targeted photothermal therapy. Most importantly, both PB and Fe3O4 nanoparticles were already clinically approved drugs, so the Fe3O4@PB nanoparticles as a theranostic nanomedicine would be particularly promising for clinical applications in the human body due to the reliable biosafety.

Interplay Between Mechanochemistry and Sonochemistry

Ultrasonic irradiation-based mechanochemical strategies have recently been the subject of intensive investigation because of the advantages they offer. These include simplicity, energy savings and wide applicability. Traditional areas of sonoprocessing such as cleaning, efficient mixing and solid activation have been extended to both macromolecular and micro/nanostructures, some of which are biologically significant, ultrasound-responsive actuators and crystal design, among others. Unlike conventional mechanochemical protocols, which require little solvent usage if any at all, mechanical (and chemical) effects promoted by ultrasound are observed in a liquid medium. Tensile forces, which share similarities with solid mechanochemistry, are generated by virtue of nonlinear effects, notably cavitation, when high-amplitude waves propagate in a fluid. This work aims to provide insight into some recent developments in the multifaceted field of sono-mechanochemistry using various examples that illustrate the role of ultrasonic activation, which is capable of boosting hitherto sterile transformations and inventing new crafts in applied chemistry. After a preliminary discussion of acoustics, which is intended to provide a mechanistic background, we mainly focus on experimental developments, while we often mention emerging science and occasionally delve into theoretical models and force simulations.