Targeting of daunomycin using biotinylated immunoliposomes: Pharmacokinetics, tissue distribution andin vitropharmacological effects

To see or not to see: In vivo nanocarrier detection methods in the brain and their challenges

Nanoparticles have a great potential to significantly improve the delivery of therapeutics to the brain and may also be equipped with properties to investigate brain function. The brain, being a highly complex organ shielded by selective barriers, requires its own specialized detection system. However, a significant hurdle to achieve these goals is still the identification of individual nanoparticles within the brain with sufficient cellular, subcellular, and temporal resolution. This review aims to provide a comprehensive summary of the current knowledge on detection systems for tracking nanoparticles across the blood-brain barrier and within the brain. We discuss commonly employed in vivo and ex vivo nanoparticle identification and quantification methods, as well as various imaging modalities able to detect nanoparticles in the brain. Advantages and weaknesses of these modalities as well as the biological factors that must be considered when interpreting results obtained through nanotechnologies are summarized. Finally, we critically evaluate the prevailing limitations of existing technologies and explore potential solutions.

Overcoming the blood-brain barrier? - prediction of blood-brain permeability of hydrophobically modified polyethylenimine polyplexes for siRNA delivery into the brain with in vitro and in vivo models

The blood-brain barrier (BBB) is a highly selective biological barrier that represents a major bottleneck in the treatment of all types of central nervous system (CNS) disorders. Small interfering RNA (siRNA) offers in principle a promising therapeutic approach, e.g., for brain tumors, by downregulating brain tumor-related genes and inhibiting tumor growth via RNA interference. In an effort to develop efficient siRNA nanocarriers for crossing the BBB, we utilized polyethyleneimine (PEI) polymers hydrophobically modified with either stearic-acid (SA) or dodecylacrylamide (DAA) subunits and evaluated their suitability for delivering siRNA across the BBB in in vitro and in vivo BBB models depending on their structure. Physicochemical characteristics of siRNA-polymer complexes (polyplexes (PXs)), e.g., particle size and surface charge, were measured by dynamic light scattering and laser Doppler anemometry, whereas siRNA condensation ability of polymers and polyplex stability was evaluated by spectrophotometric methods. The composition of the biomolecule corona that absorbs on polyplexes upon encountering physiological fluids was investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and by a liquid chromatography-tandem mass spectrometry (LC-MS-MS) method. Cellular internalization abilities of PXs into brain endothelial cells (hCMEC/D3) was confirmed, and a BBB permeation assay using a human induced pluripotent stem cell (hiPSC)-derived BBB model revealed similar abilities to cross the BBB for all formulations under physiological conditions. However, biodistribution studies of radiolabeled PXs in mice were inconsistent with in vitro results as the detected amount of radiolabeled siRNA in the brain delivered with PEI PXs was higher compared to PEI-SA PXs. Taken together, PEI PXs were shown to be a suitable nanocarrier to deliver small amounts of siRNA across the BBB into the brain but more sophisticated human BBB models that better represent physiological conditions and biodistribution are required to provide highly predictive in vitro data for human CNS drug development in the future.

Lipid Nanoparticles Functionalized with Antibodies for Anticancer Drug Therapy

Nanotechnology takes the lead in providing new therapeutic options for cancer patients. In the last decades, lipid-based nanoparticles-solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), liposomes, and lipid-polymer hybrid nanoparticles-have received particular interest in anticancer drug delivery to solid tumors. To improve selectivity for target cells and, thus, therapeutic efficacy, lipid nanoparticles have been functionalized with antibodies that bind to receptors overexpressed in angiogenic endothelial cells or cancer cells. Most papers dealing with the preclinical results of antibody-conjugated nanoparticles claim low systemic toxicity and effective tumor inhibition, which have not been successfully translated into clinical use yet. This review aims to summarize the current "state-of-the-art" in anticancer drug delivery using antibody-functionalized lipid-based nanoparticles. It includes an update on promising candidates that entered clinical trials and some explanations for low translation success.

Distinct Binding Properties of Neutravidin and Streptavidin Proteins to Biotinylated Supported Lipid Bilayers: Implications for Sensor Functionalization

The exceptional strength and stability of noncovalent avidin-biotin binding is widely utilized as an effective bioconjugation strategy in various biosensing applications, and neutravidin and streptavidin proteins are two commonly used avidin analogues. It is often regarded that the biotin-binding abilities of neutravidin and streptavidin are similar, and hence their use is interchangeable; however, a deeper examination of how these two proteins attach to sensor surfaces is needed to develop reliable surface functionalization options. Herein, we conducted quartz crystal microbalance-dissipation (QCM-D) biosensing experiments to investigate neutravidin and streptavidin binding to biotinylated supported lipid bilayers (SLBs) in different pH conditions. While streptavidin binding to biotinylated lipid receptors was stable and robust across the tested pH conditions, neutravidin binding strongly depended on the solution pH and was greater with increasingly acidic pH conditions. These findings led us to propose a two-step mechanistic model, whereby streptavidin and neutravidin binding to biotinylated sensing interfaces first involves nonspecific protein adsorption that is mainly influenced by electrostatic interactions, followed by structural rearrangement of adsorbed proteins to specifically bind to biotin functional groups. Practically, our findings demonstrate that streptavidin is preferable to neutravidin for constructing SLB-based sensing platforms and can improve sensing performance for detecting antibody–antigen interactions.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.

Antibody-Targeted Liposomes for Enhanced Targeting of the Blood-Brain Barrier

The blood-brain barrier (BBB) hinders therapeutic delivery to the central nervous system (CNS), thereby impeding the development of therapies for brain injury and disease. Receptor-mediated transcytosis (RMT) systems are a promising way to shuttle a targeted therapeutic into the brain. Here, we developed and evaluated an RMT antibody-targeted liposomal system. A previously identified antibody, scFv46.1, that binds to the human and murine BBB and can pass through the murine BBB by transcytosis after intravenous injection was used to decorate the surface of liposomes. Using an in vitro BBB model, we demonstrated the cellular uptake of scFv46.1-modified liposomes (46.1-Lipo). Next, the biodistribution and brain uptake capacity of 46.1-targeted liposomes were assessed after intravenous administration. Our results showed that 46.1-Lipo can lead to increased brain accumulation through targeting of the brain vasculature. Initial rate pharmacokinetic experiments and biodistribution analyses indicated that 46.1-Lipo loaded with pralidoxime exhibited a 10-fold increase in brain accumulation compared with a mock-targeted liposomal group, and this increased accumulation was brain-specific. These studies indicate the potential of this 46.1-Lipo system as a synthetic vehicle for the targeted transport of therapeutic molecules into the CNS.

Photodynamic Priming Modulates Endothelial Cell-Cell Junction Phenotype for Light-activated Remote Control of Drug Delivery

The blood-brain barrier (BBB) remains a major obstacle for drug delivery to the central nervous system. In particular, the tight and adherens junctions that join the brain capillary endothelial cells limit the diffusion of various molecules from the bloodstream into the brain. Photodynamic priming (PDP) is a non-cytotoxic modality that involves light activation of photosensitizers to photochemically modulate nearby molecules without killing the cells. Here we investigate the effects of sub-lethal photochemistry on junction phenotype (i.e., continuous, punctate, or perpendicular), as well as the BBB permeability in a transwell model of human brain microvascular endothelial cells (HBMECs). We showed that PDP decreases the continuous junction architecture by ~20%, increases the perpendicular junction architecture by ~40%, and has minimal impact on cell morphology in HBMECs. Furthermore, transwell permeability assay revealed that PDP improves the HBMEC permeability to dextran or nanoliposomes by up to 30-fold for 6-9 days. These results suggest that PDP could safely reverse the mature brain endothelial junctions without killing the HBMECs. This study not only emphasizes the critical roles of PDP in the modulation junction phenotype, but also highlights the opportunity to further develop PDP-based combinations that opens the cerebrum endothelium for enhanced drug transporter across the BBB.

Advances in engineering of low molecular weight hydrogels for chemotherapeutic applications

Chemotherapy is the primary option for the treatment of cancer, inflammation, and infectious diseases. Conventional drug delivery poses solubility and bioavailability challenges, systemic toxicity, non-specific targeting, and poor accumulation of chemotherapeutic drugs at the desired site. Nanotechnology has led to the development of various nanomaterials that have decreased the toxicity and increased the accumulation of drugs at the target site. Systemic administration of nanomaterials causes burst release and non-specific targeting of chemotherapeutics, leading to off-target organ toxicity. Drug delivery based on low molecular weight hydrogels (LMWHs) provides a suitable alternative for drug delivery due to their ability to entrap chemotherapeutic drugs. Injectable and biodegradable LMWHs allow the administration of chemotherapeutics with minimal invasion, allow the sustained release of chemotherapeutic drugs for long periods, and reduce the challenges of immunogenicity and low drug entrapment efficiency. Herein, we summarize the advances in the engineering of LMWHs for controlled and prolonged delivery of chemotherapeutics for cancer, infectious diseases, and inflammatory disorders.

Brain Delivery of Nanomedicines: Trojan Horse Liposomes for Plasmid DNA Gene Therapy of the Brain

Non-viral gene therapy of the brain is enabled by the development of plasmid DNA brain delivery technology, which requires the engineering and manufacturing of nanomedicines that cross the blood-brain barrier (BBB). The development of such nanomedicines is a multi-faceted problem that requires progress at multiple levels. First, the type of nanocontainer, e.g., nanoparticle or liposome, which encapsulates the plasmid DNA, must be developed. Second, the type of molecular Trojan horse, e.g., peptide or receptor-specific monoclonal antibody (MAb), must be selected for incorporation on the surface of the nanomedicine, as this Trojan horse engages specific receptors expressed on the BBB, and the brain cell membrane, to trigger transport of the nanomedicine from blood into brain cells beyond the BBB. Third, the plasmid DNA must be engineered without bacterial elements, such as antibiotic resistance genes, to enable administration to humans; the plasmid DNA must also be engineered with tissue-specific gene promoters upstream of the therapeutic gene, to insure gene expression in the target organ with minimal off-target expression. Fourth, upstream manufacturing of the nanomedicine must be developed and scalable so as to meet market demand for the target disease, e.g., annual long-term treatment of 1,000 patients with an orphan disease, short term treatment of 10,000 patients with malignant glioma, or 100,000 patients with new onset Parkinson's disease. Fifth, downstream manufacturing problems, such as nanomedicine lyophilization, must be solved to ensure the nanomedicine has a commercially viable shelf-life for treatment of CNS disease in humans.

Functionalizing nanoparticles with cancer-targeting antibodies: A comparison of strategies

Standard cancer therapies sometimes fail to deliver chemotherapeutic drugs to tumor cells in a safe and effective manner. Nanotechnology takes the lead in providing new therapeutic options for cancer due to major potential for selective targeting and controlled drug release. Antibodies and antibody fragments are attracting much attention as a source of targeting ligands to bind specific receptors that are overexpressed on cancer cells. Therefore, researchers are devoting time and effort to develop targeting strategies based on nanoparticles functionalized with antibodies, which hold great promise to enhance therapeutic efficacy and circumvent severe side effects. Several methods have been described to immobilize antibodies on the surface of nanoparticles. However, selecting the most appropriate for each application is challenging but also imperative to preserve antigen binding ability and yield stable antibody-conjugated nanoparticles. From this perspective, we aim to provide considerable knowledge on the most widely used methods of functionalization that can be helpful for decision-making and design of conjugation protocols as well. This review summarizes adsorption, covalent conjugation (carbodiimide, maleimide and "click" chemistries) and biotin-avidin interaction, while discussing the advantages, limitations and relevant therapeutic approaches currently under investigation.

Functionalised Carbon Nanotubes Enhance Brain Delivery of Amyloid-Targeting Pittsburgh Compound B (PiB)-Derived Ligands

Alzheimer's disease (AD) is a neurodegenerative disorder characterised by brain accumulation of toxic protein aggregates, including extracellular amyloid beta (Aβ) plaques, inflammation, neuronal death and progressive cognitive dysfunction. Current diagnostic modalities, based on cognitive tests, fail to detect early AD onset, thus emphasising the need to develop improved methods for pre-symptomatic disease detection.

Building on the properties of the Pittsburgh Compound B (PiB), an Aβ-binding molecule suitable to use as positron emission tomography (PET) imaging agent, and aiming at using a more clinically available modality (like magnetic ressonance imaging, MRI), PiB derivatives have been conjugated to the macrocyclic chelator 1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane (DO3A) monoamide. However, these derivatives do not readily cross the highly selective blood-brain barrier (BBB). Taking advantage of the capacity of functionalised carbon nanotubes (f-CNTs) to cross biological barriers, including the BBB, this manuscript reports on the conjugation of two PiB derivative Gd³⁺ complexes - Gd(L₂) and Gd(L₃) - to multi-walled f-CNTs (f-MWNTs) and assessment of their in vivo biodistribution and brain uptake. It is shown that Gd(L₂) and Gd(L₃) can be efficiently loaded onto different f-MWNTs, with significant improvement in brain accumulation of the conjugates compared to the free metal complexes.

Overall, this study demonstrates that f-MWNTs have potential to be used as carriers in theranostic applications involving brain delivery of BBB impermeable compounds.

Qualitative and semiquantitative analysis of the protein coronas associated to different functionalized nanoparticles

AIM

The investigation on protein coronas (PCs) adsorbed onto nanoparticle (NP) surface is representing an open issue due to difficulties in detection and clear isolation of the adsorbed proteins. In this study, we investigated protocols able to isolate the compositions of PCs of three polymeric NPs.

MATERIALS & METHODS

Unfunctionalized NPs and two functionalized NPs were considered as proof-of-concept for the qualitative and semiquantitative analysis of both the corona levels (stably or weakly adsorbed coronas [SC/WC]) of these different nanocarriers.

RESULTS

The protocols applied were able to discriminate between the SC and WC. In particular, experimental results indicated that stably adsorbed coronas are prevalently composed by ApoE, while WC by albumin in all the NPs. Otherwise, some differences in WC could be correlated with surface functionalization.

CONCLUSION

This experimental approach allows characterizing the whole PCs, proposing a protocol for isolation of different types of proteins composing PCs.

Direct and enhanced delivery of nanoliposomes of anti schizophrenic agent to the brain through nasal route

The problem of inadequate oral bioavailability of Quetiapine Fumarate, a lipophilic drug used for schizophrenia, due to hepatic metabolism and repulsion by brain barrier was attempted in this study. Combination of two approaches, viz. Quetiapine inclusion into the liposomal carrier for better diffusion and administration through nasal route to avoid hepatic metabolism and barrier elimination was applied. Thin film hydration followed by sonication method was employed in liposome preparation and the formulation was optimized using 32 full factorial design. The number of sonication cycles (X1) of 2 min and 80% amplitude and molar ratio of constructional components such as cholesterol to egg phosphatidylcholine (X2) as independent variables and a % of entrapment efficiency (Y1) and cumulative in vitro drug release (Y2) at 6 h as dependent variables was selected. Batch F7 prepared by 2 cycles of sonication and 1:3 M ratio of cholesterol:egg phosphatidylcholine was optimized as a consequence of substantial entrapment efficiency of 75.63 ± 3.77%, and 99.92 ± 1.88% drug release and 32.33 ± 1.53% drug diffusion, which was optimum among all other batches at 6 h. Diffusion study was done for all the batches of liposomal formulation by using sheep nasal mucosa and good amount with better diffusion rate was measured which proved liposomal dispersion a virtuous delivery system for brain drug delivery through nasal route. Results of in vivo, ciliotoxicity and gamma scintigraphy studies on mice supported the above inference.

CNS Targeted Nanoparticle Drug Delivery

The idea of formulating brain permeable nanoparticles stems from the need to treat various neurological disorders like Parkinson's disease, Alzheimer's disease, schizophrenia, depression and brain tumors. Neuropeptides, antibiotics, anticancer drugs and many CNS active drugs cannot cross blood brain barrier (BBB). Studies have revealed that when these drugs are loaded on to nanoparticles they not only cross BBB, but also exhibit decreased side effects. The drug can be dissolved, dispersed, encapsulated inside the nanoparticle or attached on to surface of nanoparticles. In 1995, dalargin was the first drug to be delivered across blood brain barrier (BBB) using polysorbate 80 coated nanoparticles. The size of nanoparticles is usually between 10-1000nm. For crossing BBB it should be less than 300 nm.

Targeted Nanotherapies for the Treatment of Surgical Diseases

OBJECTIVE

To describe the components of targeted nanotherapeutics and to review their applications in the treatment of surgical diseases.

BACKGROUND

Targeted nanotherapeutic is a novel strategy for treating a variety of diseases and is an emerging technology that offers advantages over current treatment strategies. The nanoscale size, combined with the ability to surface functionalize the delivery vehicle to enable targeting and incorporate a therapeutic payload, provides a new and innovative therapeutic platform to treat surgical diseases that has yet to be fully realized in the surgical arena.

METHODS

A comprehensive literature review of nanotherapeutics, targeting strategies, and their utility in treating surgical diseases is performed.

RESULTS

Targeted nanotherapeutics have demonstrated safety and biocompatibility in treating surgical diseases. The ability to surface functionalize the nanoparticles affords a unique tailorability that enables targeting specificity and therapeutic payload delivery to treat a variety of surgical diseases. Moreover, the small size and targeting capabilities allow access to biological compartments, such as the blood-brain barrier, that have previously been difficult to treat.

CONCLUSIONS

Targeted nanotherapeutics represent a novel therapeutic platform and have great potential to impact the treatment of surgical diseases.

Non-viral liposome-mediated transfer of brain-derived neurotrophic factor across the blood-brain barrier

Brain-derived neurotrophic factor (BDNF) plays an important role in the repair of central nervous system injury, but cannot directly traverse the blood-brain barrier. Liposomes are a new type of non-viral vector, able to carry macromolecules across the blood-brain barrier and into the brain. Here, we investigate whether BDNF could be transported across the blood-brain barrier by tail-vein injection of liposomes conjugated to transferrin (Tf) and polyethylene glycol (PEG), and carrying BDNF modified with cytomegalovirus promoter (pCMV) or glial fibrillary acidic protein promoter (pGFAP) (Tf-pCMV-BDNF-PEG and Tf-pGFAP-BDNF-PEG, respectively). Both liposomes were able to traverse the blood-brain barrier, and BDNF was mainly expressed in the cerebral cortex. BDNF expression in the cerebral cortex was higher in the Tf-pGFAP-BDNF-PEG group than in the Tf-pCMV-BDNF-PEG group. This study demonstrates the successful construction of a non-virus targeted liposome, Tf-pGFAP-BDNF-PEG, which crosses the blood-brain barrier and is distributed in the cerebral cortex. Our work provides an experimental basis for BDNF-related targeted drug delivery in the brain.

Nanoparticles combined with growth factors: recent progress and applications

Increasing attention has been focused on the applications of nanoparticles combined with growth factors (NPs/GFs) due to the substantial functions of GFs in regenerative medicine and disease treatments.

Antibody-targeted biodegradable nanoparticles for cancer therapy

The use of nanotechnology has great potentials to revolutionize the future cancer diagnosis and therapy. In this context, various nanoparticles (NPs) have been developed for targeted delivery of diagnostic/therapeutic agents to the tumor sites, which thus result in greater efficacy and much less side effects. The targeting property of NPs is often achieved by functionalizing their surface with tumor-specific ligands, such as antibodies, peptides, small molecules and oligonucleotides. In this review, we will discuss recent progress in the multifunctional design of antibody-targeted NPs with a special focus on liposomal, polymeric and protein-based delivery systems.

Kinetics of functionalised carbon nanotube distribution in mouse brain after systemic injection: Spatial to ultra-structural analyses

Earlier studies proved the success of using chemically functionalised multi-walled carbon nanotubes (f-MWNTs) as nanocarriers to the brain. Little insight into the kinetics of brain distribution of f-MWNTs in vivo has been reported. This study employed a wide range of qualitative and quantitative techniques with the aim of shedding the light on f-MWNT's brain distribution following intravenous injection. γ-Scintigraphy quantified the uptake of studied radiolabelled f-MWNT in the whole brain parenchyma and capillaries while 3D-single photon emission computed tomography/computed tomography imaging and autoradiography illustrated spatial distribution within various brain regions. Raman and multiphoton luminescence together with transmission electron microscopy confirmed the presence of intact f-MWNT in mouse brain, in a label-free manner. The results evidenced the presence of f-MWNT in mice brain parenchyma, in addition to brain endothelium. Such information on the rate and extent of regional and cellular brain distribution is needed before further implementation into neurological therapeutics can be made.

Comparative study between simple and optimized liposomal dispersion of quetiapine fumarate for diffusion through nasal route

CONTEXT

Nasal route of drug administration is preferred more and more for the targeted delivery to the brain in current drug development scenario due to its ease of use, reliability, quick action, and lesser side effects. Those CNS drugs which have limited oral bioavailability due to pharmacokinetic consequences and brain barrier repulsion are getting onto this direction.

OBJECTIVE

Quetiapine fumarate, an analogous to above and an antischizophrenic agent, is tested for its diffusion property with and without lipophilic carrier through sheep nasal membrane. Being a BCS class II' and high permeable candidate, it tends to crossover easily, so made up in a simple dispersion.

MATERIALS AND METHODS

To improve its diffusion rate, it was embedded into liposomal dispersion, which has proven that it has advanced efficiency for diffusion. For this, both the formulations were checked and compared for their diffusion profile, as it is an essential property for bioavailability through nasal route. Comparison was made on the basis of % drug diffusion within 6 h, rate, mechanism, profile, and coefficient.

RESULTS

Liposomal dispersion has been proved superior with greater percentage diffusion of 32.61 ± 1.70 and very high permeability with a coefficient value of 4.1334 ± 0.7321 (× 10 (-) (5 )cm/s). Diffusion profile comparison bearing dissimilarity of 18 and similarity of 74 indicated that the diffusion profiles of liposomal dispersions and simple dispersion were similar but not identical.

CONCLUSION

Liposomal diffusion supremacy was further sustained by in vivo, ciliotoxicity, and gamma scintigraphy studies.

Nanomedicine in cancer therapy: challenges, opportunities, and clinical applications

Cancer is a leading cause of death worldwide. Currently available therapies are inadequate and spur demand for improved technologies. Rapid growth in nanotechnology towards the development of nanomedicine products holds great promise to improve therapeutic strategies against cancer. Nanomedicine products represent an opportunity to achieve sophisticated targeting strategies and multi-functionality. They can improve the pharmacokinetic and pharmacodynamic profiles of conventional therapeutics and may thus optimize the efficacy of existing anti-cancer compounds. In this review, we discuss state-of-the-art nanoparticles and targeted systems that have been investigated in clinical studies. We emphasize the challenges faced in using nanomedicine products and translating them from a preclinical level to the clinical setting. Additionally, we cover aspects of nanocarrier engineering that may open up new opportunities for nanomedicine products in the clinic.

Drug delivery nanoparticles in skin cancers

Nanotechnology involves the engineering of functional systems at nanoscale, thus being attractive for disciplines ranging from materials science to biomedicine. One of the most active research areas of the nanotechnology is nanomedicine, which applies nanotechnology to highly specific medical interventions for prevention, diagnosis, and treatment of diseases, including cancer disease. Over the past two decades, the rapid developments in nanotechnology have allowed the incorporation of multiple therapeutic, sensing, and targeting agents into nanoparticles, for detection, prevention, and treatment of cancer diseases. Nanoparticles offer many advantages as drug carrier systems since they can improve the solubility of poorly water-soluble drugs, modify pharmacokinetics, increase drug half-life by reducing immunogenicity, improve bioavailability, and diminish drug metabolism. They can also enable a tunable release of therapeutic compounds and the simultaneous delivery of two or more drugs for combination therapy. In this review, we discuss the recent advances in the use of different types of nanoparticles for systemic and topical drug delivery in the treatment of skin cancer. In particular, the progress in the treatment with nanocarriers of basal cell carcinoma, squamous cell carcinoma, and melanoma has been reported.

Liposomes for brain delivery

INTRODUCTION

Development of drug delivery systems for brain delivery is one of the most challenging research topics in pharmaceutical areas, mainly due to the presence of the blood-brain barrier (BBB), which separates the blood from the cerebral parenchyma thus limiting the brain uptake of the majority of therapeutic agents. Among the several carriers, which have been studied to overcome this problem, liposomes have gained increasing attention as promising strategies for brain-targeted drug delivery. The most advantageous features of liposomes are their ability to incorporate and deliver large amounts of drug and the possibility to decorate their surface with different ligands.

AREAS COVERED

The purpose of this review is to explore the different approaches studied to transport and deliver therapeutics and imaging agents to the brain by using liposomes. In the first part of the review, particular attention is paid to describe the anatomy of the BBB and different physiological transport mechanisms available for drug permeation. In the second part, the different strategies for the delivery of a drug to the brain using liposomes are reviewed for each transport mechanism.

EXPERT OPINION

Over the last decade, there have been significant developments concerning liposomal brain delivery systems conjugated with selected ligands with high specificity and low immunogenicity. An universally useful liposomal formulation for brain targeting does not exist but liposome design must be modulated by the appropriate choice of the specific homing device and transport mechanism.

Inspired by nature: fundamentals in nanotechnology design to overcome biological barriers

Synergy between nanotechnology and drug delivery has created a multitude of novel drug-delivery systems with great therapeutic potential. However, directing these systems across the biological barriers to the target site has proven difficult. Nanotechnology is looking for inspiration in natural systems that have evolved to overcome such barriers. Here, we review nature-inspired strategies and fundamental features common to successful drug-delivery systems across biological barriers.

Revolutionary impact of nanodrug delivery on neuroscience

Brain research is the most expanding interdisciplinary research that is using the state of the art techniques to overcome limitations in order to conduct more accurate and effective experiments. Drug delivery to the target site in the central nervous system (CNS) is one of the most difficult steps in neuroscience researches and therapies. Taking advantage of the nanoscale structure of neural cells (both neurons and glia); nanodrug delivery (second generation of biotechnological products) has a potential revolutionary impact into the basic understanding, visualization and therapeutic applications of neuroscience. Current review article firstly provides an overview of preparation and characterization, purification and separation, loading and delivering of nanodrugs. Different types of nanoparticle bioproducts and a number of methods for their fabrication and delivery systems including (carbon) nanotubes are explained. In the second part, neuroscience and nervous system drugs are deeply investigated. Different mechanisms in which nanoparticles enhance the uptake and clearance of molecules form cerebrospinal fluid (CSF) are discussed. The focus is on nanodrugs that are being used or have potential to improve neural researches, diagnosis and therapy of neurodegenerative disorders.

Can leptin-derived sequence-modified nanoparticles be suitable tools for brain delivery?

Aim: In order to increase the knowledge on the use of nanoparticles (NPs) in brain targeting, this article describes the conjugation of the sequence 12–32 (g21) of leptin to poly-lactide-co-glycolide NPs. The capability of these modified NPs to reach the brain was evaluated in rats after intravenous administration. Materials & Methods: The g21 was linked on the surface of NPs labeled with tetramethylrhodamine by means of the Avidin-Biotin technology. The g21-labeled NPs were injected into the tail vein of rats and, after animal sacrifice, the brain localization was evaluated by confocal microscopy, fluorescence microscopy and electron microscopy. Studies to evaluate the biodistribution of the g21-modified NPs in comparison to the unmodified NPs were also carried out. Moreover, to confirm the absence of any anorectic effect of g21 linked on the surface of NPs, appropriate studies were used to assess the rats. Results: After intravenous administration, the g21-modified NPs were able to cross the blood–brain barrier and to enter the brain parenchyma. The biodistribution studies of both unmodified and modified NPs pointed out an uptake at liver and spleen level, whereas only the g21-modified NPs showed brain localization. The food-intake experiments pointed out that the intravenous administration of g21 conjugated to the NP surface did not produce any anorectic effect in the rats. Conclusion: g21-modified NPs were able to cross the blood–brain barrier. These new modified NPs could be effectively considered as useful carrier systems for brain drug delivery.

Original submitted: 27/11/2010; Revised submitted: 09/03/2011

The Trojan Horse Liposome Technology for Nonviral Gene Transfer across the Blood-Brain Barrier

The application of blood-borne gene therapy protocols to the brain is limited by the presence of the blood-brain barrier (BBB). Viruses have been extensively used as gene delivery systems. However, their efficacy in brain is limited by the lack of transport across the BBB following intravenous (IV) administration. Recent progress in the “Trojan Horse Liposome” (THL) technology applied to transvascular non-viral gene therapy of the brain presents a promising solution to the trans-vascular brain gene delivery problem. THLs are comprised of immunoliposomes carrying nonviral gene expression plasmids. The tissue target specificity of the THL is provided by peptidomimetic monoclonal antibody (MAb) component of the THL, which binds to specific endogenous receptors located on both the BBB and on brain cellular membranes, for example, insulin receptor and transferrin receptor. These MAbs mediate (a) receptor-mediated transcytosis of the THL complex through the BBB, (b) endocytosis into brain cells and (c) transport to the brain cell nuclear compartment. The expression of the transgene in brain may be restricted using tissue/cell specific gene promoters. This manuscript presents an overview on the THL transport technology applied to brain disorders, including lysosomal storage disorders and Parkinson's disease.

Preparation and characterization of liposomal formulations of neurotensin-degrading enzyme inhibitors

Neurotensin-degrading enzyme (NTDE) inhibitors hold great potential for treating psychotic disorders. However, brain uptake of such compounds in vivo is generally low due to the presence of the blood-brain barrier. In this study, liposomal formulations of two NTDE inhibitors, named compound 1 (C1) and compound 2 (C2) were prepared. Association of these compounds with the liposomal bilayer, subsequent liposomal stability, and compound release in the presence of albumin was studied. Entrapment of the compounds in the liposomal bilayer showed the solubilizing properties of the liposomes. Size and polydispersity index of the compound-entrapped liposomes did not change over 1 month, showing colloidal stability of the liposomal drug formulations. The amount of compounds associated with the liposomes decreased within one day. After this, the association remained stable at 4°C. For C1, association remained stable at 37°C in HEPES buffered saline, and the compound was gradually released in the presence of bovine serum albumin. For C2, the release was rapid in both HBS and BSA at 37°C. In conclusion, the formulation of NTDE inhibitors C1 and C2 in liposomes has been demonstrated and holds promise to deliver NTDE inhibitors in vivo.

Novel and emerging strategies in drug delivery for overcoming the blood-brain barrier

Two decades of molecular research have revealed the presence of transporters and receptors expressed in the brain vascular endothelium that provide potential novel targets for the rational design of blood-brain barrier-penetrating drugs. In this review, we briefly introduce the reader to the molecular characteristics of the blood-brain barrier that make this one of the most important obstacles towards the development of efficacious CNS drugs. We highlight recent attempts to rationally target influx and bidirectional transport systems expressed on the brain endothelial cell and avoid the important obstacle presented in the form of efflux transporters. Many of these approaches are highly innovative and show promise for future human application. Some of these approaches, however, have revealed significant limitations and are critiqued in this review. Nonetheless, these combined efforts have left the field of CNS drug delivery better positioned for developing novel approaches towards the rational design of CNS-penetrating drugs.

In vivo methods to study uptake of nanoparticles into the brain

Several in vivo techniques have been developed to study and measure the uptake of CNS compounds into the brain. With these techniques, various parameters can be determined after drug administration, including the blood-to-brain influx constant (K_in), the permeability-surface area (PS) product, and the brain uptake index (BUI). These techniques have been mostly used for drugs that are expected to enter the brain via transmembrane diffusion or by carrier-mediated transcytosis. Drugs that have limitations in entering the brain via such pathways have been encapsulated in nanoparticles (based on lipids or synthetic polymers) to enhance brain uptake. Nanoparticles are different from CNS compounds in size, composition and uptake mechanisms. This has led to different methods and approaches to study brain uptake in vivo. Here we discuss the techniques generally used to measure nanoparticle uptake in addition to the techniques used for CNS compounds. Techniques include visualization methods, behavioral tests, and quantitative methods.

Targeted brain delivery of itraconazole via RVG29 anchored nanoparticles

The blood-brain barrier is a major barrier in the neurological diseases treatment and precludes the entry of drugs from blood to brain. Here, we developed 29-amino-acid peptide derived from rabies virus glycoprotein (RVG29) peptide conjugated itraconazole-loaded albumin nanoparticles (RVG29-ITZ-NPs). The RVG29 peptide was conjugated to the albumin NPs using biotin-binding streptavidin as crosslinker. The NPs were characterized in terms of particle size, zeta potential, drug loading and release behavior in vitro. Cellular uptake of RVG29-ITZ-NPs was investigated by flow cytometry. Pharmacokinetics and brain distribution of RVG29-ITZ-NPs were investigated after intravenous administration of NPs. The particle size of RVG29-ITZ-NPs was 89.3 ± 1.9 nm as determined by dynamic light scattering. The zeta potential of RVG29-ITZ-NPs was -33.1 ± 0.9 mV. RVG29-ITZ-NPs exhibited a sustained release profile within 24 h. In vitro cellular uptake studies demonstrated that RVG29 significantly facilitated the intracellular delivery of NPs. A significant (P < 0.05) accumulation of ITZ in brain was observed for RVG29-ITZ-NPs as compared with ITZ-NPs and cyclodextrin formulation of ITZ (ITZ-CD). These results suggested that RVG29-ITZ-NPs can be exploited as a potential therapeutic formulation for the intracranial fungal infection.

Nanotechnology applications for improved delivery of antiretroviral drugs to the brain

Human immunodeficiency virus (HIV) can gain access to the central nervous system during the early course of primary infection. Once in the brain compartment the virus actively replicates to form an independent viral reservoir, resulting in debilitating neurological complications, latent infection and drug resistance. Current antiretroviral drugs (ARVs) often fail to effectively reduce the HIV viral load in the brain. This, in part, is due to the poor transport of many ARVs, in particular protease inhibitors, across the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSBF). Studies have shown that nanocarriers including polymeric nanoparticles, liposomes, solid lipid nanoparticles (SLN) and micelles can increase the local drug concentration gradients, facilitate drug transport into the brain via endocytotic pathways and inhibit the ATP-binding cassette (ABC) transporters expressed at the barrier sites. By delivering ARVs with nanocarriers, significant increase in the drug bioavailability to the brain is expected to be achieved. Recent studies show that the specificity and efficiency of ARVs delivery can be further enhanced by using nanocarriers with specific brain targeting, cell penetrating ligands or ABC-transporters inhibitors. Future research should focus on achieving brain delivery of ARVs in a safe, efficient, and yet cost-effective manner.

Passive and active drug targeting: drug delivery to tumors as an example

The paradigm of using nanoparticulate pharmaceutical carriers has been well established over the past decade, both in pharmaceutical research and in the clinical setting. Drug carriers are expected to stay in the blood for long time, accumulate in pathological sites with affected and leaky vasculature (tumors, inflammations, and infarcted areas) via the enhanced permeability and retention (EPR) effect, and facilitate targeted delivery of specific ligand-modified drugs and drug carriers into poorly accessible areas. Among various approaches to specifically target drug-loaded carrier systems to required pathological sites in the body, two seem to be most advanced--passive (EPR effect-mediated) targeting, based on the longevity of the pharmaceutical carrier in the blood and its accumulation in pathological sites with compromised vasculature, and active targeting, based on the attachment of specific ligands to the surface of pharmaceutical carriers to recognize and bind pathological cells. Here, we will consider and discuss these two targeting approaches using tumor targeting as an example.

Nanotechnology for delivery of drugs to the brain for epilepsy

Epilepsy results from aberrant electrical activity that can affect either a focal area or the entire brain. In treating epilepsy with drugs, the aim is to decrease seizure frequency and severity while minimizing toxicity to the brain and other tissues. Antiepileptic drugs (AEDs) are usually administered by oral and intravenous routes, but these drug treatments are not always effective. Drug access to the brain is severely limited by a number of biological factors, particularly the blood-brain barrier, which impedes the ability of AEDs to enter and remain in the brain. To improve the efficacy of AEDs, new drug delivery strategies are being developed; these methods fall into the three main categories: drug modification, blood-brain barrier modification, and direct drug delivery. Recently, all three methods have been improved through the use of drug-loaded nanoparticles.

Endocytosis at the blood–brain barrier: From basic understanding to drug delivery strategies

The blood-brain barrier (BBB) protects the central nervous system (CNS) from potentially harmful xenobiotics and endogenous molecules. Anatomically, it comprises the brain microvasculature whose functionality is nevertheless influenced by associated astrocyte, pericyte and neuronal cells. The highly restrictive paracellular pathway within brain microvasculature restricts significant CNS penetration to only those drugs whose physicochemical properties afford ready penetration into hydrophobic cell membranes or are capable of exploiting endogenous active transport processes such as solute carriers or endocytosis pathways. Endocytosis at the BBB is an essential pathway by which the brain obtains its nutrients and affords communication with the periphery. The development of strategies to exploit these endocytic pathways for the purposes of drug delivery to the CNS is still an immature field although some impressive results have been documented with the targeting of particular receptors. This current article initially provides an overview of general endocytosis processes and pathways showing evidence of their functional existence within the BBB. Subsequent sections provide, in an entity-specific manner, comprehensive reviews on BBB transport investigations of endocytosis involving: transferrin and the targeting of the transferrin receptor; hormones; cytokines; cell penetrating peptides; microorganisms and toxins, and nanoparticles aimed at more effectively delivering drugs to the CNS.

Molecular imaging with nanoparticles: giant roles for dwarf actors

Molecular imaging, first developed to localise antigens in light microscopy, now encompasses all imaging modalities including those used in clinical care: optical imaging, nuclear medical imaging, ultrasound imaging, CT, MRI, and photoacoustic imaging. Molecular imaging always requires accumulation of contrast agent in the target site, often achieved most efficiently by steering nanoparticles containing contrast agent into the target. This entails accessing target molecules hidden behind tissue barriers, necessitating the use of targeting groups. For imaging modalities with low sensitivity, nanoparticles bearing multiple contrast groups provide signal amplification. The same nanoparticles can in principle deliver both contrast medium and drug, allowing monitoring of biodistribution and therapeutic activity simultaneously (theranostics). Nanoparticles with multiple bioadhesive sites for target recognition and binding will be larger than 20 nm diameter. They share functionalities with many subcellular organelles (ribosomes, proteasomes, ion channels, and transport vesicles) and are of similar sizes. The materials used to synthesise nanoparticles include natural proteins and polymers, artificial polymers, dendrimers, fullerenes and other carbon-based structures, lipid-water micelles, viral capsids, metals, metal oxides, and ceramics. Signal generators incorporated into nanoparticles include iron oxide, gadolinium, fluorine, iodine, bismuth, radionuclides, quantum dots, and metal nanoclusters. Diagnostic imaging applications, now appearing, include sentinal node localisation and stem cell tracking.

Design of targeted lipid nanocapsules by conjugation of whole antibodies and antibody Fab’ fragments

Immunonanocapsules were synthesized by conjugation to lipid nanocapsules (LNC) of whole OX26 monoclonal antibodies (OX26 MAb) directed against the transferrin receptor (TfR). The TfR is overexpressed on the cerebral endothelium and mediates the transcytosis mechanism. Fab' fragments, known for their reduced interaction with the reticuloendothelial system, were also conjugated to LNC. This coupling was facilitated by the incorporation of lipid PEG(2000) functionalized with reactive-sulfhydryl maleimide groups (DSPE-PEG(2000)-maleimide) into LNC shells by a post-insertion procedure, developed initially for liposome pegylation. An interfacial model using the dynamic rising drop technique helped determine the parameters influencing the DSPE-PEG(2000)-maleimide insertion and the quality of the anchorage. Heat was essential to promote both an important and stable adsorption of DSPE-PEG(2000)-maleimide onto LNC. OX26 MAb were thiolated to react with maleimide functions whereas thiol residues on Fab' fragments were used directly. The number of ligands per nanocapsule was adjusted according to their initial quantity in the coupling reaction mixture, with densities from 16 to183 whole antibodies and between 42 and 173 Fab' fragments per LNC. The specific association of immunonanocapsules to cells overexpressing TfR was thus demonstrated, suggesting their ability to deliver drugs to the brain.