Unveiling the enigma of the blood-brain barrier in glioblastoma: current advances from preclinical and clinical studies.

PURPOSE OF REVIEW: Glioblastoma (GBM), the most prevalent primary brain malignancy in adults, poses significant challenges in terms of treatment. Current therapeutic strategies for GBM patients involve maximal safe resection, followed by radiotherapy with concurrent and adjuvant temozolomide. However, despite this multimodal approach for GBM, the prognosis of GBM patients remains dismal because of their inherent primary and secondary resistances to treatments. RECENT FINDINGS: Several molecular and cellular mechanisms, including the presence of the blood-brain barrier (BBB), contribute to these resistances. The BBB, comprising multiple layers surrounding brain vessels, acts as a barrier limiting effective drug delivery to the brain. Invasive and noninvasive tools to deliver drugs and pharmaceutical formulations locally or systemically are continuously evolving to overcome the BBB in GBM toward improving drug bioavailability in the brain and reducing systemic toxicities. SUMMARY: Preliminary studies utilizing these approaches have demonstrated promising results in terms of safety and signals of efficacy during early-phase clinical trials. However, further work through additional clinical trials is necessary to evaluate the potential clinical benefits for GBM patients.

Development of Cationic Lipid LAH4-L1 siRNA Complexes for Focused Ultrasound Enhanced Tumor Uptake.

RNAi has considerable potential as a cancer therapeutic approach, but effective and efficient delivery of short interfering RNA (siRNA) to tumors remains a major hurdle. It remains a challenge to prepare a functional siRNA complex, target enough dose to the tumor, and stimulate its internalization into tumor cells and its release to the cytoplasm. Here, we show how these key barriers to siRNA delivery can be overcome with a complex─comprising siRNA, cationic lipids, and pH-responsive peptides─that is suited to tumor uptake enhancement via focused ultrasound (FUS). The complex provides effective nucleic acid encapsulation, nuclease protection, and endosomal escape such that gene silencing in cells is substantially more effective than that obtained with either equivalent lipoplexes or commercial reagents. In mice bearing MDA-MB-231 breast cancer xenografts, both lipid and ternary, lipid:peptide:siRNA complexes, prepared with near-infrared fluorescently labeled siRNA, accumulate in tumors following FUS treatments. Therefore, combining a well-designed lipid:peptide:siRNA complex with FUS tumor treatments is a promising route to achieve robust in vivo gene delivery.

Assessing Changes in Dielectric Properties Due to Nanomaterials Using a Two-Port Microwave System.

Detecting changes in the dielectric properties of tissues at microwave frequencies can offer simple and cost effective tools for cancer detection. These changes can be enhanced by the use of nanoparticles (NPs) that are characterised by both increased tumour uptake and high dielectric constant. This paper presents a two-port experimental setup to assess the impact of contrast enhancement on microwave signals. The study focuses on carbon nanotubes, as they have been previously shown to induce high microwave dielectric contrast. We investigate multiwall carbon nanotubes (MWNT) and their -OH functionalised version (MWNT-OH) dispersed in tissue phantoms as contrast enhancing NPs, as well as salt (NaCl) solutions as reference mixtures which can be easily dissolved inside water mixtures and thus induce dielectric contrast changes reliably. MWNT and MWNT-OH are characterised by atomic force microscopy, and their dielectric properties are measured when dispersed in 60% glycerol-water mixtures. Salt concentrations between 10 and 50 mg/mL in 60% glycerol mixtures are also studied as homogeneous samples known to affect the dielectric constant. Contrast enhancement is then evaluated using a simplified two-port microwave system to identify the impact on microwave signals with respect to dielectric contrast. Numerical simulations are also conducted to compare results with the experimental findings. Our results suggest that this approach can be used as a reliable method to screen and assess contrast enhancing materials with regards to a microwave system's ability to detect their impact on a target.

Focused ultrasound induced hyperthermia accelerates and increases the uptake of anti-HER-2 antibodies in a xenograft model.

Image guided drug delivery has gained significant attention during the last few years. Labelling nanoparticles or macromolecules and monitoring their fate in the body provides information that can be used to modulate their biodistribution and improve their pharmacokinetics. In this study we label antibodies and monitor their distribution in the tumours post intravenous injection. Using Focused Ultrasound (FUS, a non-invasive method of hyperthermia) we increase the tumour temperature to 42°C for a short period of time (3-5min) and we observe an increased accumulation of labelled antibody. Repetition of focused ultrasound induced hyperthermic treatment increased still further the accumulation of the antibodies in the tumour. This treatment also augmented the accumulation of other macromolecules non-specific to the tumour, such as IgG and albumin. These effects may be used to enhance the therapeutic efficiency of antibodies and/or targeted nanoparticles.

Thermosensitive, near-infrared-labeled nanoparticles for topotecan delivery to tumors.

Liposomal nanoparticles have proven to be versatile systems for drug delivery. However, the progress in clinic has been slower and less efficient than expected. This suggests a need for further development using carefully designed chemical components to improve usefulness under clinical conditions and maximize therapeutic effect. For cancer chemotherapy, PEGylated liposomes were the first nanomedicine to reach the market and have been used clinically for several years. Approaches toward targeted drug delivery using next generation "thermally triggered" nanoparticles are now in clinical trials. However, clinically tested thermosensitive liposomes (TSLs) lack the markers that allow tumor labeling and improved imaging for tissue specific applied hyperthermia. Here we describe the development of optically labeled TSLs for image guidance drug delivery and proof-of-concept results for their application in the treatment of murine xenograft tumors using the anticancer drug topotecan. These labeled TSLs also allow the simultaneous, real-time diagnostic imaging of nanoparticle biodistribution using a near-infrared (NIR; 750-950 nm) fluorophore coupled to a lipidic component of the lipid bilayer. When combined with multispectral fluorescence analysis, this allows for specific and high sensitivity tracking of the nanoparticles in vivo. The application of NIR fluorescence-labeled TSLs could have a transformative effect on future cancer chemotherapy.

Interface Engineering of Water-Dispersible Near-Infrared-Emitting CuInZnS/ZnSe/ZnS Quantum Dots.

We report the synthesis of near-infrared (IR)-emitting core/shell/shell quantum dots of CuInZnS/ZnSe/ZnS and their phase transfer to water. The intermediate ZnSe shell was added to inhibit the migration of ions from the standard ZnS shell into the emitting core, which often leads to a blue shift in the emission profile. By engineering the interface between the core and terminal shell layer, the optical properties can be controlled, and emission was maintained in the near-IR region, making the materials attractive for biological applications. In addition, the hydrodynamic diameter of the particle was controlled using amphiphilic polymers.

pH-triggered nanoparticle mediated delivery of siRNA to liver cells in vitro and in vivo.

Recently, we reported for the first time the development of pH-triggered nanoparticles for the functional delivery of small interfering RNA (siRNA) to liver for treatment of hepatitis B virus infections in vivo. Here, we report on systematic formulation and biophysical studies of three different pH-triggered nanoparticle formulations looking for ways to improve on the capabilities of our previous nanoparticle system. We demonstrate how pH-triggered, PEGylated siRNA nanoparticles stable with respect to aggregation in 80% serum can still release siRNA payload at pH 5.5 within 30 min. This capability allows functional delivery to cultured murine hepatocyte cells in vitro, despite a high degree of PEGylation (5 mol %). We also demonstrate that pH-triggered, PEGylated siRNA nanoparticles typically enter cells by clathrin-coated pit endocytosis, but functional delivery requires membrane fusion events (fusogenicity). Biodistribution studies indicate that >70% of our administered nanoparticles are found in liver hepatocytes, post intravenous administration. Pharmacodynamic experiments show siRNA delivery to murine liver effecting maximum knockdown 48 h post administration from a single dose, while control (nontriggered) nanoparticles require 96 h and two doses to demonstrate the same effect. We also describe an anti-hepatitis C virus (HCV) proof-of-concept experiment indicating the possibility of RNAi therapy for HCV infections using pH-triggered, PEGylated siRNA nanoparticles.

Enzyme-triggered PEGylated pDNA-nanoparticles for controlled release of pDNA in tumors.

Nanoparticle mediated functional delivery of plasmid DNA (pDNA) in vivo typically requires the formulation of pDNA-nanoparticles with a surface layer of stealth/biocompatibility polymer (usually poly(ethylene glycol) [PEG]). This PEG layer ensures the colloidal stability of pDNA-nanoparticles in biological fluids and minimizes nanoparticle interactions with the reticulo-endothelical system. Unfortunately, the presence of the PEG layer appears to contribute to a reduction in efficiency of functional delivery of pDNA once target cells are reached. For this reason, we have focused recent research efforts on "triggerable" nanoparticle systems. These are designed to be stable from the point of administration until a target site of interest is reached, then triggered for the controlled release of therapeutic agent payload(s) at the target site by changes in local endogenous conditions or through the application of some exogenous stimulus. Here, we describe investigations into the potential use of enzymes to trigger pDNA-mediated therapy through a process of enzyme-assisted nanoparticle triggerability. Our approach is to use PEG(2000)-peptidyl lipids with peptidyl moieties sensitive to tumor-localized elastase or matrix metalloproteinase-2 digestion, and from these prepare putative enzyme-triggered PEGylated pDNA-nanoparticles. Our results provide initial proof of concept in vitro. From these data, we propose that this concept should be applicable for functional delivery of therapeutic nucleic acids to tumor cells in vivo, although the mechanism for enzyme-assisted nanoparticle triggerability remains to be fully characterized.

Effect of Phase-Change Nanodroplets and Ultrasound on Blood-Brain Barrier Permeability In Vitro.

Phase-change nanodroplets (PCND;NDs) are emulsions with a perfluorocarbon (PFC) core that undergo acoustic vaporisation as a response to ultrasound (US). Nanodroplets change to microbubbles and cavitate while under the effect of US. This cavitation can apply forces on cell connections in biological barrier membranes, such as the blood-brain barrier (BBB), and trigger a transient and reversible increased permeability to molecules and matter. This study aims to present the preparation of lipid-based NDs and investigate their effects on the brain endothelial cell barrier in vitro. The NDs were prepared using the thin-film hydration method, followed by the PFC addition. They were characterised for size, cavitation (using a high-speed camera), and PFC encapsulation (using FTIR). The bEnd.3 (mouse brain endothelial) cells were seeded onto transwell inserts. Fluorescein with NDs and/or microbubbles were applied on the bEND3 cells and the effect of US on fluorescein permeability was measured. The Live/Dead assay was used to assess the BBB integrity after the treatments. Size and PFC content analysis indicated that the NDs were stable while stored. High-speed camera imaging confirmed that the NDs cavitate after US exposure of 0.12 MPa. The BBB cell model experiments revealed a 4-fold increase in cell membrane permeation after the combined application of US and NDs. The Live/Dead assay results indicated damage to the BBB membrane integrity, but this damage was less when compared to the one caused by microbubbles. This in vitro study shows that nanodroplets have the potential to cause BBB opening in a similar manner to microbubbles. Both cavitation agents caused damage on the endothelial cells. It appears that NDs cause less cell damage compared to microbubbles.

Characterising the chemical and physical properties of phase-change nanodroplets.

Phase-change nanodroplets have attracted increasing interest in recent years as ultrasound theranostic nanoparticles. They are smaller compared to microbubbles and they may distribute better in tissues (e.g. in tumours). They are composed of a stabilising shell and a perfluorocarbon core. Nanodroplets can vaporise into echogenic microbubbles forming cavitation nuclei when exposed to ultrasound. Their perfluorocarbon core phase-change is responsible for the acoustic droplet vaporisation. However, methods to quantify the perfluorocarbon core in nanodroplets are lacking. This is an important feature that can help explain nanodroplet phase change characteristics. In this study, we fabricated nanodroplets using lipids shell and perfluorocarbons. To assess the amount of perfluorocarbon in the core we used two methods, 19F NMR and FTIR. To assess the cavitation after vaporisation we used an ultrasound transducer (1.1 MHz) and a high-speed camera. The 19F NMR based method showed that the fluorine signal correlated accurately with the perfluorocarbon concentration. Using this correlation, we were able to quantify the perfluorocarbon core of nanodroplets. This method was used to assess the content of the perfluorocarbon of the nanodroplets in solutions over time. It was found that perfluoropentane nanodroplets lost their content faster and at higher ratio compared to perfluorohexane nanodroplets. The high-speed imaging indicates that the nanodroplets generate cavitation comparable to that from commercial contrast agent microbubbles. Nanodroplet characterisation should include perfluorocarbon concentration assessment as critical information for their development.

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.

Nanomaterials responding to microwaves: an emerging field for imaging and therapy.

In recent years, new microwave-based imaging, sensing and hyperthermia applications have emerged in the field of diagnostics and therapy. For diagnosis, this technology involves the application of low power microwaves, utilising contrast between the relative permittivity of tissues to identify pathologies. This contrast can be further enhanced through the implementation of nanomaterials. For therapy, this technology can be applied in tissues either through hyperthermia, which can help anti-cancer drug tumour penetration or as ablation to destroy malignant tissues. Nanomaterials can absorb electromagnetic radiation and can enhance the microwave hyperthermic effect. In this review we aim to introduce this area of renewed interest and provide insights into current developments in its technologies and companion nanoparticles, as well as presenting an overview of applications for diagnosis and therapy.

Image-guided thermosensitive liposomes for focused ultrasound enhanced co-delivery of carboplatin and SN-38 against triple negative breast cancer in mice.

Triggerable nanocarriers have the potential to significantly improve the therapeutic index of existing anticancer agents. They allow for highly localised delivery and release of therapeutic cargos, reducing off-target toxicity and increasing anti-tumour activity. Liposomes may be engineered to respond to an externally applied stimulus such as focused ultrasound (FUS). Here, we report the first co-delivery of SN-38 (irinotecan's super-active metabolite) and carboplatin, using an MRI-visible thermosensitive liposome (iTSL). MR contrast enhancement was achieved by the incorporation of a gadolinium lipid conjugate in the liposome bilayer along with a dye-labelled lipid for near infrared fluorescence bioimaging. The resulting iTSL were successfully loaded with SN-38 in the lipid bilayer and carboplatin in the aqueous core - allowing co-delivery of both. The iTSL demonstrated both thermosensitivity and MR-imageability. In addition, they showed effective local targeted co-delivery of carboplatin and SN-38 after triggered release with brief FUS treatments. A single dosage induced significant improvement of anti-tumour activity (over either the free drugs or the iTSL without FUS-activation) in triple negative breast cancer xenografts tumours in mice.

Calcium phosphate nanoparticles for potential application as enamel remineralising agent tested on hydroxyapatite discs.

Calcium phosphate exhibits excellent biocompatibility, and with particle size in the nanoscale, calcium phosphate nanoparticles (CPNPs) were explored to replace the hydroxyapatite lost in the nanoporous teeth due to dental erosion. CPNPs (2% w/v) colloidally stabilised by sodium citrate were synthesised via co-precipitation. They were characterised in terms of particle size, morphology, crystallinity, Ca/P ratio and calcium ion release. To ensure uniformity of the substrate, hydroxyapatite (HA) discs were examined as an alternative substrate model to enamel. They were eroded in acetate buffer (0.5 M; pH 4.0) at various timepoints (1, 5, 10, 30 min, and 2, 4 h), and their physical differences compared to enamel were assessed in terms of surface microhardness, surface roughness and step height. The remineralisation properties of the synthesised CPNPs on eroded HA discs at different pH levels were investigated. It was established that CPNPs were heterogeneously deposited on the HA discs at pH 9.2, whereas newly precipitated minerals from CPNPs were potentially formed at pH 6.2.

MR-labelled liposomes and focused ultrasound for spatiotemporally controlled drug release in triple negative breast cancers in mice.

Rationale: Image-guided, triggerable, drug delivery systems allow for precisely placed and highly localised anti-cancer treatment. They contain labels for spatial mapping and tissue uptake tracking, providing key location and timing information for the application of an external stimulus to trigger drug release. High Intensity Focused Ultrasound (HIFU or FUS) is a non-invasive approach for treating small tissue volumes and is particularly effective at inducing drug release from thermosensitive nanocarriers. Here, we present a novel MR-imageable thermosensitive liposome (iTSL) for drug delivery to triple-negative breast cancers (TNBC). Methods: A macrocyclic gadolinium-based Magnetic Resonance Imaging (MRI) contrast agent was covalently linked to a lipid. This was incorporated at 30 mol% into the lipid bilayer of a thermosensitive liposome that was also encapsulating doxorubicin. The resulting iTSL-DOX formulation was assessed for physical and chemical properties, storage stability, leakage of gadolinium or doxorubicin, and thermal- or FUS-induced drug release. Its effect on MRI relaxation time was tested in phantoms. Mice with tumours were used for studies to assess both tumour distribution and contrast enhancement over time. A lipid-conjugated near-infrared fluorescence (NIRF) probe was also included in the liposome to facilitate the real time monitoring of iTSL distribution and drug release in tumours by NIRF bioimaging. TNBC (MDA-MB-231) tumour-bearing mice were then used to demonstrate the efficacy at retarding tumour growth and increasing survival. Results: iTSL-DOX provided rapid FUS-induced drug release that was dependent on the acoustic power applied. It was otherwise found to be stable, with minimum leakage of drug and gadolinium into buffers or under challenging conditions. In contrast to the usually suggested longer FUS treatment we identified that brief (~3 min) FUS significantly enhanced iTSL-DOX uptake to a targeted tumour and triggered near-total release of encapsulated doxorubicin, causing significant growth inhibition in the TNBC mouse model. A distinct reduction in the tumours' average T1 relaxation times was attributed to the iTSL accumulation. Conclusions: We demonstrate that tracking iTSL in tumours using MRI assists the application of FUS for precise drug release and therapy.

Ultrasound mediated delivery of quantum dots from a proof of concept capsule endoscope to the gastrointestinal wall.

Biologic drugs, defined as therapeutic agents produced from or containing components of a living organism, are of growing importance to the pharmaceutical industry. Though oral delivery of medicine is convenient, biologics require invasive injections because of their poor bioavailability via oral routes. Delivery of biologics to the small intestine using electronic delivery with devices that are similar to capsule endoscopes is a promising means of overcoming this limitation and does not require reformulation of the therapeutic agent. The efficacy of such capsule devices for drug delivery could be further improved by increasing the permeability of the intestinal tract lining with an integrated ultrasound transducer to increase uptake. This paper describes a novel proof of concept capsule device capable of electronic application of focused ultrasound and delivery of therapeutic agents. Fluorescent markers, which were chosen as a model drug, were used to demonstrate in vivo delivery in the porcine small intestine with this capsule. We show that the fluorescent markers can penetrate the mucus layer of the small intestine at low acoustic powers when combining microbubbles with focused ultrasound during in vivo experiments using porcine models. This study illustrates how such a device could be potentially used for gastrointestinal drug delivery and the challenges to be overcome before focused ultrasound and microbubbles could be used with this device for the oral delivery of biologic therapeutics.

Bioresponsive small molecule polyamines as noncytotoxic alternative to polyethylenimine.

Nonviral gene therapy continues to require novel synthetic vectors to deliver therapeutic nucleic acids effectively and safely. The majority of synthetic nonviral vectors employed in clinical trials to date have been cationic liposomes; however, cationic polymers are attracting increasing attention. One of the few cationic polymers to enter clinical trials has been polyethylenimine (PEI); however, doubts remain over its cytotoxicity, and in addition it displays lower levels of transfection than viral systems. Herein, we report on the development of a series of small molecule analogues of PEI that are bioresponsive to the presence of pDNA, forming poly(disulfide)s that are capable of efficacious transfection with no associated toxicity. The most effective small molecule developed, a cyclic disulfide based upon a spermine backbone, is shown to form very well-defined polyplexes (100-200 nm in diameter) that mediate murine lung transfection in vivo to within an order of magnitude of in vivo jetPEI, and at the same time display a much improved cytotoxicity profile.

Exploiting disease-induced changes for targeted oral delivery of biologics and nanomedicines in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a chronic and progressive disorder with destructive inflammation in the gastrointestinal tract (GIT). Biologics have changed the management of IBD, but have serious limitations, which is associated with their systemic administration via injection. Oral administration is the most accepted route of drug administration. However, the physiological barriers of the GIT pose significant challenges for oral administration of biologics, making this route of administration currently unavailable. The status of tissue barriers to oral drug delivery is altered in IBD. This may bring more challenges, but also present opportunities for oral delivery of biologics. This article provides an overview of disease-induced alterations of GIT barriers in IBD and discusses challenges, opportunities and commonly-utilised strategies for oral delivery of complex therapeutics, including biologics and nanomedicines.

Emerging nanomaterials for dental treatments.

The emergence of nanomaterials for dental treatments is encouraged by the nanotopography of the tooth structure, together with the promising benefits of nanomedicine. The use of nanoparticles in dentistry, also termed as 'nanodentistry', has manifested in applications for remineralisation, antimicrobial activity, local anaesthesia, anti-inflammation, osteoconductivity and stem cell differentiation. Besides the applications on dental tissues, nanoparticles have been used to enhance the mechanical properties of dental composites, improving their bonding and anchorage and reducing friction. The small particle size allows for enhanced permeation into deeper lesions, and reduction in porosities of dental composites for higher mechanical strength. The large surface area to volume ratio allows for enhanced bioactivity such as bonding and integration, and more intense action towards microorganisms. Controlled release of encapsulated bioactive molecules such as drugs and growth factors enables them to be delivered more precisely, with site-targeted delivery for localised treatments. These properties have benefitted across multiple fields within dentistry, including periodontology and endodontics and reengineering of dental prosthetics and braces. This review summarises the current literature on the emerging field of nanomaterials for dental treatments.

Folate receptor targeted bimodal liposomes for tumor magnetic resonance imaging.

Folate-targeted bimodal paramagnetic and fluorescent liposomes were developed and showed enhanced accumulation in a folate receptor expressing tumor model. These bimodal liposomes were composed of both a paramagnetic and a fluorescent lipid, and utilized a PEG-lipid amphiphile for prolonged in vivo circulation. The particles were formulated to ensure a size distribution of approximately 100 nm with a low polydispersity index. IGROV-1 cells were used to induce tumors in nude Balb/c mice, and the folate-targeted liposomes were injected intravenously. Rapid accumulation of the folate-targeted liposomes within the tumor tissue compared to nontargeted liposomes was observed. Furthermore, folate-labeled liposomes showed a 4-fold increase in tumor T(1) signal intensity at just 2 h postinjection with similar results being obtained for the nontargeted liposomes only 24 h postinjection. In addition, the folate-targeted liposomes were injected at half the nontargeted liposome dose, further demonstrating their effectiveness. Histological analysis of sectioned tumor slices revealed distinct fluorescence patterns between the targeted and nontargeted systems, with a more localized and hyperintense fluorescence signal observed from tumor sections post-folate-targeted liposome injections. These results demonstrate the effectiveness of folate targeting for dynamic real-time solid tumor MRI and provide insight into kinetics of targeted and nontargeted nanoparticles to solid tumors.