Gold nanorods for target selective SPECT/CT imaging and photothermal therapy in vivo

Gold Nanorods-Based Photothermal Therapy: Interactions Between Biostructure, Nanomaterial, and Near-Infrared Irradiation

Gold nanorods (AuNRs) are ideal inorganic nanophotothermal agents with unique characteristics, including local surface plasmon resonance effects, easy scale preparation and functional modification, and good biocompatibility. This review summarizes several recent advances in AuNRs-based photothermal therapy (PTT) research. Functionalized AuNRs photothermal agents have optimized biocompatibility and targeting properties. The multifunctional AuNRs nanoplatform composite structure meets the requirements for synergistic effects of PTT, photoacoustic imaging, and other therapeutic methods. Photothermal therapy with AuNRs (AuNRs-PTT) is widely used to treat tumors and inflammatory diseases; its tumor-targeting, tumor metastasis inhibition, and photothermal tumor ablation abilities have remarkable curative effects. An in-depth study of AuNRs in living systems and the interactions between biological structure, nanomaterial, and near-infrared irradiation could lay the foundation for further clinical research and the broad application of AuNRs in PTT.

Evaluation of Brain Nuclear Medicine Imaging Tracers in a Murine Model of Sepsis-Associated Encephalopathy

Purpose

The purpose of this study was to evaluate a set of widely used nuclear medicine imaging agents as possible methods to study the early effects of systemic inflammation on the living brain in a mouse model of sepsis-associated encephalopathy (SAE). The lipopolysaccharide (LPS)-induced murine systemic inflammation model was selected as a model of SAE.

Procedures

C57BL/6 mice were used. A multimodal imaging protocol was carried out on each animal 4 h following the intravenous administration of LPS using the following tracers: [^99mTc][2,2-dimethyl-3-[(3E)-3-oxidoiminobutan-2-yl]azanidylpropyl]-[(3E)-3-hydroxyiminobutan-2-yl]azanide ([^99mTc]HMPAO) and ethyl-7-[¹²⁵I]iodo-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate ([¹²⁵I]iomazenil) to measure brain perfusion and neuronal damage, respectively; 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) to measure cerebral glucose uptake. We assessed microglia activity on another group of mice using 2-[6-chloro-2-(4-[¹²⁵I]iodophenyl)-imidazo[1,2-a]pyridin-3-yl]-N-ethyl-N-methyl-acetamide ([¹²⁵I]CLINME). Radiotracer uptakes were measured in different brain regions and correlated. Microglia activity was also assessed using immunohistochemistry. Brain glutathione levels were measured to investigate oxidative stress.

Results

Significantly reduced perfusion values and significantly enhanced [¹⁸F]FDG and [¹²⁵I]CLINME uptake was measured in the LPS-treated group. Following perfusion compensation, enhanced [¹²⁵I]iomazenil uptake was measured in the LPS-treated group’s hippocampus and cerebellum. In this group, both [¹⁸F]FDG and [¹²⁵I]iomazenil uptake showed highly negative correlation to perfusion measured with ([^99mTc]HMPAO uptake in all brain regions. No significant differences were detected in brain glutathione levels between the groups. The CD45 and P2Y12 double-labeling immunohistochemistry showed widespread microglia activation in the LPS-treated group.

Conclusions

Our results suggest that [¹²⁵I]CLINME and [^99mTc]HMPAO SPECT can be used to detect microglia activation and brain hypoperfusion, respectively, in the early phase (4 h post injection) of systemic inflammation. We suspect that the enhancement of [¹⁸F]FDG and [¹²⁵I]iomazenil uptake in the LPS-treated group does not necessarily reflect neural hypermetabolism and the lack of neuronal damage. They are most likely caused by processes emerging during neuroinflammation, e.g., microglia activation and/or immune cell infiltration.

Electronic supplementary material

The online version of this article (10.1007/s11307-018-1201-3) contains supplementary material, which is available to authorized users.

Contemporary Polymer-Based Nanoparticle Systems for Photothermal Therapy

Current approaches for the treatment of cancer, such as chemotherapy, radiotherapy, immunotherapy, and surgery, are limited by various factors, such as inadvertent necrosis of healthy cells, immunological destruction, or secondary cancer development. Hyperthermic therapy is a promising strategy intended to mitigate many of the shortcomings associated with traditional therapeutic approaches. However, to utilize this approach effectively, it must be targeted to specific tumor sites to prevent adverse side effects. In this regard, photothermal therapy, using intravenously-administered nanoparticle materials capable of eliciting hyperthermic effects in combination with the precise application of light in the near-infrared spectrum, has shown promise. Many different materials have been proposed, including various inorganic materials such as Au, Ag, and Germanium, and C-based materials. Unfortunately, these materials are limited by concerns about accumulation and potential cytotoxicity. Polymer-based nanoparticle systems have been investigated to overcome limitations associated with traditional inorganic nanoparticle systems. Some of the materials that have been investigated for this purpose include polypyrrole, poly-(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), polydopamine, and polyaniline. The purpose of this review is to summarize these contemporary polymer-based nanoparticle technologies to acquire an understanding of their current applications and explore the potential for future improvements.

Nd3+ sensitized core-shell-shell nanocomposites loaded with IR806 dye for photothermal therapy and up-conversion luminescence imaging by a single wavelength NIR light irradiation

To perform photothermal therapy (PTT) and luminescence imaging by a single wavelength NIR light irradiation, we have designed and prepared a novel nanocomposite incorporating the IR806 photothermal sensitizers (PTS) into the core-shell-shell NaYF₄:Yb,Er@ NaYF₄:Yb@NaYF₄:Yb,Nd up-conversion nanoparticles (UCNPs). Irradiation with the 793 nm near-infrared (NIR) laser, the Nd³⁺ ions in the UCNPs were sensitized to up-convert energy via Yb³⁺ to the Er³⁺ ions to emit visible light at 540 nm and 654 nm, as well as to down-convert energy to the Yb³⁺ ions to emit NIR light at 980 nm. For luminescence imaging, the 793 nm NIR radiation is more suitable to use for deeper-tissue penetration and to reduce overheating problem due to water absorption as compared to 980 nm radiation. Additionally, the same 793 nm NIR radiation could also excite the IR806 dye for effective PTT. Surface modifications of the UCNPs with mesoporous silica (mSiO₂) and polyallylamine (PAH) allow stable loading of IR806 dye and further derivatization with polyethylene glycol-folic acid (PEG-FA) for tumor targeting. Preliminary in vitro studies demonstrated that the final UCNP@mSiO₂/IR806@PAH-PEG-FA nanocomposites (UCNC-FAs) could be uptaken by the MDA-MB-231 cancer cells and were “dark” viable, and when irradiated with the 793 nm laser, the MDA-MB-231 cell viability was effectively reduced. This indicated that the UCNC-FAs nanocomposites could be potentially useful for targeted photothermal therapy and up-conversion luminescence imaging by a single wavelength NIR light irradiation.

Biocompatible Chitosan Oligosaccharide Modified Gold Nanorods as Highly Effective Photothermal Agents for Ablation of Breast Cancer Cells

Photothermal therapy (PTT) using biocompatible nanomaterials have recently attracted much attention as a novel candidate technique for cancer therapy. In this work we report the performance of newly synthesized multidentate chitosan oligosaccharide modified gold nanorods (AuNRs-LA-COS) as novel agents for PTT of cancer cells due to their excellent biocompatibility, photothermal stability, and high absorption in the near-infrared (NIR) region. The AuNRs-LA-COS exhibit a strong NIR absorption peak at 838 nm with a mean length of 26 ± 3.1 nm and diameter of 6.8 ± 1.7 nm, respectively. The temperature of AuNRs-LA-COS rapidly reached 52.6 °C for 5 min of NIR laser irradiation at 2 W/cm². The AuNRs-LA-COS had very low cytotoxicity and exhibited high efficiency for the ablation of breast cancer cells in vitro. The tumor-bearing mice were completely ablated without tumor recurrence after photothermal treatment with AuNRs-LA-COS (25 µg/mL) under laser irradiation. In summary, this study demonstrated that AuNRs-LA-COS with laser irradiation as novel agents pave an alternative way for breast cancer therapy and hold great promise for clinical trials in the near future.

Structure-Inherent Targeting of Near-Infrared Fluorophores for Image-Guided Surgery

Although various clinical imaging modalities have been developed to visualize internal body structures and detect abnormal tissues prior to surgical procedures, most medical imaging modalities do not provide disease-specific images in real-time. Optical imaging can provide the surgeon with real-time visualization of the surgical field for intraoperative image-guided surgery. Imaging in the near-infrared (NIR) window (650-900 nm), also known as the "therapeutic window" has high potential by offering low absorbance and scattering in tissues resulting in minimized background autofluorescence. Clinically, optical fluorescence imaging with the targeted contrast agents provides opportunities for significant advances in intraoperative image-guided surgery. There are only two clinically available NIR fluorophores, indocyanine green (ICG) and methylene blue (MB), that support the image-guided surgery. However, neither of them perform in vivo by providing optimum specificity and stability for targeted image guidance. Therefore, it is of paramount importance to develop targeted NIR fluorophores for unmet clinical needs. Using the right combination of an NIR fluorescence imaging system and a targeted fluorophore, the desired target tissues can be imaged to provide real-time fluorescence guidance without changing the field-of-view during surgery. Thus, in a clinical discipline, the development of NIR fluorophores for 'structure-inherent targeting' is an unmet need for early phase diagnostics with accurate targeting.

Positron emission tomography and nanotechnology: A dynamic duo for cancer theranostics

Development of novel imaging probes for cancer diagnosis is critical for early disease detection and management. The past two decades have witnessed a surge in the development and evolution of radiolabeled nanoparticles as a new frontier in personalized cancer nanomedicine. The dynamic synergism of positron emission tomography (PET) and nanotechnology combines the sensitivity and quantitative nature of PET with the multifunctionality and tunability of nanomaterials, which can help overcome certain key challenges in the field. In this review, we discuss the recent advances in radionanomedicine, exemplifying the ability to tailor the physicochemical properties of nanomaterials to achieve optimal in vivo pharmacokinetics and targeted molecular imaging in living subjects. Innovations in development of facile and robust radiolabeling strategies and biomedical applications of such radionanoprobes in cancer theranostics are highlighted. Imminent issues in clinical translation of radiolabeled nanomaterials are also discussed, with emphasis on multidisciplinary efforts needed to quickly move these promising agents from bench to bedside.

Visualization of Macrophage Recruitment to Inflammation Lesions using Highly Sensitive and Stable Radionuclide-Embedded Gold Nanoparticles as a Nuclear Bio-Imaging Platform

Reliable and sensitive imaging tools are required to track macrophage migration and provide a better understating of their biological roles in various diseases. Here, we demonstrate the possibility of radioactive iodide-embedded gold nanoparticles (RIe-AuNPs) as a cell tracker for nuclear medicine imaging. To demonstrate this utility, we monitored macrophage migration to carrageenan-induced sites of acute inflammation in living subjects and visualized the effects of anti-inflammatory agents on this process. Macrophage labeling with RIe-AuNPs did not alter their biological functions such as cell proliferation, phenotype marker expression, or phagocytic activity. In vivo imaging with positron-emission tomography revealed the migration of labeled macrophages to carrageenan-induced inflammation lesions 3 h after transfer, with highest recruitment at 6 h and a slight decline of radioactive signal at 24 h; these findings were highly consistent with the data of a bio-distribution study. Treatment with dexamethasone (an anti-inflammation drug) or GSK5182 (an ERRγ inverse agonist) hindered macrophage recruitment to the inflamed sites. Our findings suggest that a cell tracking strategy utilizing RIe-AuNPs will likely be highly useful in research related to macrophage-related disease and cell-based therapies.

Polydopamine Nanoparticles as a Versatile Molecular Loading Platform to Enable Imaging-guided Cancer Combination Therapy

Cancer combination therapy to treat tumors with different therapeutic approaches can efficiently improve treatment efficacy and reduce side effects. Herein, we develop a theranostic nano-platform based on polydopamine (PDA) nanoparticles, which then are exploited as a versatile carrier to allow simultaneous loading of indocyanine green (ICG), doxorubicin (DOX) and manganese ions (PDA-ICG-PEG/DOX(Mn)), to enable imaging-guided chemo & photothermal cancer therapy. In this system, ICG acts as a photothermal agent, which shows red-shifted near-infrared (NIR) absorbance and enhanced photostability compared with free ICG. DOX, a model chemotherapy drug, is then loaded onto the surface of PDA-ICG-PEG with high efficiency. With Mn²⁺ ions intrinsically chelated, PDA-ICG-PEG/DOX(Mn) is able to offer contrast under T1-weighted magnetic resonance (MR) imaging. In a mouse tumor model, the MR imaging-guided combined chemo- & photothermal therapy achieves a remarkable synergistic therapeutic effect compared with the respective single treatment modality. This work demonstrates that PDA nanoparticles could serve as a versatile molecular loading platform for MR imaging guided combined chemo- & photothermal therapy with minimal side effects, showing great potential for cancer theranostics.

Using Rose's metal alloy as a pinhole collimator material in preclinical small-animal imaging: a Monte Carlo evaluation

PURPOSE

Pinhole collimation is the most common method of high-resolution preclinical single photon emission computed tomography imaging. The collimators are usually constructed from dense materials with high atomic numbers, such as gold and platinum, which are expensive and not always flexible in the fabrication step. In this work, the authors have investigated the properties of a fusible alloy called Rose's metal and its potential in pinhole preclinical imaging. When compared to current standard pinhole materials such as gold and platinum, Rose's metal has a lower density and a relatively low effective atomic number. However, it is inexpensive, has a low melting point, and does not contract when solidifying. Once cast, the piece can be machined with high precision. The aim of this study was to evaluate the imaging properties for Rose's metal and compare them with those of standard materials.

METHODS

After validating their Monte Carlo code by comparing its results with published data and the results from analytical calculations, they investigated different pinhole geometries by varying the collimator material, acceptance angle, aperture diameter, and photon incident angle. The penetration-to-scatter and penetration-to-total component ratios, sensitivity, and the spatial resolution were determined for gold, tungsten, and Rose's metal for two radionuclides, (99)Tc(m) and (125)I.

RESULTS

The Rose's metal pinhole-imaging simulations show higher penetration/total and scatter/total ratios. For example, the penetration/total is 50% for gold and 75% for Rose's metal when simulating (99)Tc(m) with a 0.3 mm aperture diameter and a 60° acceptance angle. However, the degradation in spatial resolution remained below 10% relative to the spatial resolution for gold for acceptance angles below 40° and aperture diameters larger than 0.5 mm.

CONCLUSIONS

Extra penetration and scatter associated with Rose's metal contribute to degradation in the spatial resolution, but this degradation is not always substantial. The most important factor besides the collimator material was the acceptance angle. This should be kept to a minimum to prevent unnecessary scatter and penetration. For (125)I, the difference in spatial resolution between gold and Rose's metal is very small, 2.2% in the worst-case scenario. Based on these results, the authors conclude that Rose's metal is an alternative to standard materials not only for low-energy photon imaging but also for medium-energy applications that require low-cost, flexible pinhole configurations and designs, and that can tolerate a degraded spatial resolution.

Gold Nanotheranostics: Proof-of-Concept or Clinical Tool?

Nanoparticles have been making their way in biomedical applications and personalized medicine, allowing for the coupling of diagnostics and therapeutics into a single nanomaterial—nanotheranostics. Gold nanoparticles, in particular, have unique features that make them excellent nanomaterials for theranostics, enabling the integration of targeting, imaging and therapeutics in a single platform, with proven applicability in the management of heterogeneous diseases, such as cancer. In this review, we focus on gold nanoparticle-based theranostics at the lab bench, through pre-clinical and clinical stages. With few products facing clinical trials, much remains to be done to effectively assess the real benefits of nanotheranostics at the clinical level. Hence, we also discuss the efforts currently being made to translate nanotheranostics into the market, as well as their commercial impact.

Design of a platform technology for systemic delivery of siRNA to tumours using rolling circle transcription

For therapeutic applications of siRNA, there are technical challenges with respect to targeted and systemic delivery. We here report a new siRNA carrier, RNAtr NPs, in a way that multiple tandem copies of RNA hairpins as a result of rolling circle transcription (RCT) can be readily adapted in tumour-targeted and systemic siRNA delivery. RNAtr NPs provide a means of condensing large amounts of multimeric RNA transcripts into the compact nanoparticles, especially without the aid of polycationic agents, and thus reduce the risk of immunogenicity and cytotoxicity by avoiding the use of synthetic polycationic reagents. This strategy allows the design of a platform technology for systemic delivery of siRNA to tumour sites, because RCT reaction, which enzymatically generates RNA polymers in multiple copy numbers at low cost, can lead to directly accessible routes to targeted and systemic delivery. Therefore, RNAtr NPs suggest great potentials as the siRNA therapeutics for cancer treatment.

RNA interference has provided a promising tool to suppress the expression of specific genes associated with human diseases. Here, the authors present a platform technology for the systemic delivery of siRNA to tumour sites using rolling circle transcription.

Imaging intracellular and systemic in vivo gold nanoparticles to enhance radiotherapy

Nanoparticles offer alternative options in cancer therapy both as drug delivery carriers and as direct therapeutic agents for cancer cell inactivation. More recently, gold nanoparticles (AuNPs) have emerged as promising radiosensitizers achieving significantly elevated radiation dose enhancement factors when irradiated with both kilo-electron-volt and mega-electron-volt X-rays. Use of AuNPs in radiobiology is now being intensely driven by the desire to achieve precise energy deposition in tumours. As a consequence, there is a growing demand for efficient and simple techniques for detection, imaging and characterization of AuNPs in both biological and tumour samples. Spatially accurate imaging on the nanoscale poses a serious challenge requiring high- or super-resolution imaging techniques. In this mini review, we discuss the challenges in using AuNPs as radiosensitizers as well as various current and novel imaging techniques designed to validate the uptake, distribution and localization in mammalian cells. In our own work, we have used multiphoton excited plasmon resonance imaging to map the AuNP intracellular distribution. The benefits and limitations of this approach will also be discussed in some detail. In some cases, the same “excitation” mechanism as is used in an imaging modality can be harnessed to make it also a part of therapy modality (e.g. phototherapy)—such examples are discussed in passing as extensions to the imaging modality concerned.

Cancer immunotherapy: nanodelivery approaches for immune cell targeting and tracking

Cancer is one of the most common diseases afflicting people globally. New therapeutic approaches are needed due to the complexity of cancer as a disease. Many current treatments are very toxic and have modest efficacy at best. Increased understanding of tumor biology and immunology has allowed the development of specific immunotherapies with minimal toxicity. It is important to highlight the performance of monoclonal antibodies, immune adjuvants, vaccines and cell-based treatments. Although these approaches have shown varying degrees of clinical efficacy, they illustrate the potential to develop new strategies. Targeted immunotherapy is being explored to overcome the heterogeneity of malignant cells and the immune suppression induced by both the tumor and its microenvironment. Nanodelivery strategies seek to minimize systemic exposure to target therapy to malignant tissue and cells. Intracellular penetration has been examined through the use of functionalized particulates. These nano-particulate associated medicines are being developed for use in imaging, diagnostics and cancer targeting. Although nano-particulates are inherently complex medicines, the ability to confer, at least in principle, different types of functionality allows for the plausible consideration these nanodelivery strategies can be exploited for use as combination medicines. The development of targeted nanodelivery systems in which therapeutic and imaging agents are merged into a single platform is an attractive strategy. Currently, several nanoplatform-based formulations, such as polymeric nanoparticles, micelles, liposomes and dendrimers are in preclinical and clinical stages of development. Herein, nanodelivery strategies presently investigated for cancer immunotherapy, cancer targeting mechanisms and nanocarrier functionalization methods will be described. We also intend to discuss the emerging nano-based approaches suitable to be used as imaging techniques and as cancer treatment options.

Advanced tracers in PET imaging of cardiovascular disease

Cardiovascular disease is the leading cause of death worldwide. Molecular imaging with targeted tracers by positron emission tomography (PET) allows for the noninvasive detection and characterization of biological changes at the molecular level, leading to earlier disease detection, objective monitoring of therapies, and better prognostication of cardiovascular diseases progression. Here we review, the current role of PET in cardiovascular disease, with emphasize on tracers developed for PET imaging of cardiovascular diseases.

Recent advances in superparamagnetic iron oxide nanoparticles for cellular imaging and targeted therapy research

Advances of nanotechnology have led to the development of nanomaterials with both potential diagnostic and therapeutic applications. Among them, superparamagnetic iron oxide (SPIO) nanoparticles have received particular attention. Over the past decade, various SPIOs with unique physicochemical and biological properties have been designed by modifying the particle structure, size and coating. This article reviews the recent advances in preparing SPIOs with novel properties, the way these physicochemical properties of SPIOs influence their interaction with cells, and the development of SPIOs in liver and lymph nodes magnetic resonance imaging (MRI) contrast. Cellular uptake of SPIO can be exploited in a variety of potential clinical applications, including stem cell and inflammation cell tracking and intra-cellular drug delivery to cancerous cells which offers higher intra-cellular concentration. When SPIOs are used as carrier vehicle, additional advantages can be achieved including magnetic targeting and hyperthermia options, as well as monitoring with MRI. Other potential applications of SPIO include magnetofection and gene delivery, targeted retention of labeled stem cells, sentinel lymph nodes mapping, and magnetic force targeting and cell orientation for tissue engineering.

Research perspectives: gold nanoparticles in cancer theranostics

High recurrence rates after surgical resection remain a formidable challenge in many cancers. Although chemo- and/or radiotherapy are often applied following surgery to prevent tumor relapse, these treatments are generally accompanied by serious side effects and challenges in their delivery that limit their effectiveness. Gold nanoparticles (AuNPs), which possess unique physicochemical properties, have the potential to enhance the efficacy of these conventional treatment modalities. In this review, we briefly describe the current state of AuNP research in the area of cancer theranostics. Recent studies have investigated AuNPs' use as photothermal converters, drug carriers, radiosensitizers, and imaging probes in a wide range of applications for cancer diagnosis and therapy. AuNPs have promise in minimally invasive thermal ablation therapy, diagnostic imaging, intraoperative tumor margin delineation, and multimodal anticancer therapy. The successful translation of AuNPs into the clinic will have significant impact on the care of cancer patients using image-guided, minimally invasive approaches.

Design considerations for targeted optical contrast agents

Optical fluorescence imaging with the right combination of imaging modality and targeted contrast agents offers tremendous improvement in intraoperative imaging and clinical output (i.e., image-guided cancer surgery). Therefore, it is of paramount importance to gain an in-depth knowledge in the design of targeted contrast agents to meet clinical requirements. Currently, there are several clinically approved contrast agents available; however, none perform optimally in vivo by providing optimum sensitivity, stability, specificity, and safety for target imaging, diagnosis, and therapy. In this review, we discuss basic design considerations for targeted contrast agents in terms of optical and physicochemical properties, biological and physiological interactions, and biodistribution and targeting.