Antisense drug delivery through the blood-brain barrier

Strategic nanocarriers to control neurodegenerative disorders: Concept, challenges, and future perspective

Various neurodegenerative diseases (parkinson, huntington, alzheimer, and amyotrophic lateral sclerosis) are becoming serious global health challenges. Despite various treatment options, successful delivery and effective outcomes have been challenged with several physiological-anatomical barriers, formulation related issues, post-administration hurdles, regulatory constraints, physical hurdles, environmental issues, and safety concern. In the present review, we addressed a brief understanding of pathological and normal condition of blood brain barrier (BBB), rational for brain delivery using nanocarriers, major challenges, advantages of nanomedicine, critical aspects of nanomedicine to translate from bed to clinics, and strategic approaches for improved delivery across BBB. The review addressed various mechanistic perspective for delivery of drug loaded nanocarriers across BBB. Moreover, several reports have been published wherein phytomedicine, exosomes, magnetic nanopartilces, functionalized nanocarriers, cationic nanopartilces, and nano-phytomedicine were investigated for remarkable improvement in neurological disorders. These findings are informative for healthcare professionals, researchers, and scientists working in the domains. The successful application and convincing outcomes of nanomedicines were envisaged with clinical trials conducted on various drugs intended to control neurological disorders (NDs). Conclusively, the review addressed comprehensive findings on various aspects of drug loaded nanocarrier delivery across BBB, considerable risks, potential therapeutic benefits, clinical trial based outcomes, and recent advances followed by future perspectives.

Gold nanoparticles: emerging paradigm for targeted drug delivery system

The application of nanotechnology in medicine, known as nanomedicine, has introduced a plethora of nanoparticles of variable chemistry and design considerations for cancer diagnosis and treatment. One of the most important field is the design and development of pharmaceutical drugs, based on targeted drug delivery system (TDDS). Being inspired by physio-chemical properties of nanoparticles, TDDS are designed to safely reach their targets and specifically release their cargo at the site of disease for enhanced therapeutic effects, thereby increasing the drug tissue bioavailability. Nanoparticles have the advantage of targeting cancer by simply being accumulated and entrapped in cancer cells. However, even after rapid growth of nanotechnology in nanomedicine, designing an effective targeted drug delivery system is still a challenging task. In this review, we reveal the recent advances in drug delivery approach with a particular focus on gold nanoparticles. We seek to expound on how these nanomaterials communicate in the complex environment to reach the target site, and how to design the effective TDDS for complex environments and simultaneously monitor the toxicity on the basis of designing such delivery complexes. Hence, this review will shed light on the research, opportunities and challenges for engineering nanomaterials with cancer biology and medicine to develop effective TDDS for treatment of cancer.

Nanoparticles in the treatment and diagnosis of neurological disorders: untamed dragon with fire power to heal

The incidence of neurological diseases of unknown etiology is increasing, including well-studied diseases such as Alzhiemer's, Parkinson's, and multiple sclerosis. The blood-brain barrier provides protection for the brain but also hinders the treatment and diagnosis of these neurological diseases, because the drugs must cross the blood-brain barrier to reach the lesions. Thus, attention has turned to developing novel and effective delivery systems that are capable of carrying drug and that provide good bioavailability in the brain. Nanoneurotechnology, particularly application of nanoparticles in drug delivery, has provided promising answers to some of these issues in recent years. Here we review the recent advances in the understanding of several common forms of neurological diseases and particularly the applications of nanoparticles to treat and diagnose them. In addition, we discuss the integration of bioinformatics and modern genomic approaches in the development of nanoparticles.

FROM THE CLINICAL EDITOR

In this review paper, applications of nanotechnology-based diagnostic methods and therapeutic modalities are discussed addressing a variety of neurological disorders, with special attention to blood-brain barrier delivery methods. These novel nanomedicine approaches are expected to revolutionize several aspects of clinical neurology.

The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides

Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.

Site-specific administration of antisense oligonucleotides using biodegradable polymer microspheres provides sustained delivery and improved subcellular biodistribution in the neostriatum of the rat brain

Antisense oligonucleotides (ODNs) are being increasingly used in the central nervous system as biological tools, as drug-target validation agents and as potential therapeutic agents. Although the local delivery of naked ODNs to the brain can result in the desired biological effects, the duration of efficacy is relatively short lived due to the combined effects of rapid ODN degradation and elimination half-lives in vivo. In this study, we have examined the use of biodegradable polymer microspheres as a site-specific delivery system for targeting ODNs to the neostriatum of the rat brain. Model phosphorothioate backbone-modified ODNs were entrapped within poly(D,L-lactide-co-glycolide) (PLAGA) microspheres using a double emulsion-deposition method and the formulations characterised in terms of particle size, surface morphology, percent encapsulation efficiency, ODN loading and in vitro release profiles. For in vivo evaluation, PLAGA microspheres containing fluorescently-labelled ODNs were stereo-taxically administered to the neostriatum of the rat brain and biodistribution of ODNs monitored after 48 h. Administration of free fluorescently-labelled ODNs to the neostriatum resulted in a punctate cellular distribution of ODNs after 24 h with little or no ODN remaining in the neostriatum after 48 h. In comparison, fluorescently-labelled ODNs delivered using polymer microspheres were intensely visible in cells after 48 h post-administration and the fluorescence appeared to be diffuse covering both cytosolic and nuclear regions. Dual-label immunohistochemical analyses suggested that ODNs were mainly distributed to neuronal cells. These data indicate that site-specific administration of ODNs using biodegradable polymer microspheres will not only provide sustained delivery of nucleic acids but can also improve the cellular distribution of ODNs to brain cells. Sustained or controlled-release biodegradable polymer formulations, therefore, represent an attractive strategy for improved local delivery of ODNs to the CNS.

Synthetic hydrogels as carriers in antisense therapy: preliminary evaluation of an oligodeoxynucleotide covalent conjugate with a copolymer of 1-vinyl-2-pyrrolidinone and 2-hydroxyethyl methacrylate

A major challenge of the antisense therapeutic strategies is the development of improved systems for the delivery of antisense oligodeoxynucleotides (AS ODNs) in order to enhance the cellular uptake, to assure a better efficiency in reaching the target tissue, and to provide sustained delivery over longer periods of time. Because the current methods for delivery (liposomes and cationic polymers) present some disadvantages, the attention was directed toward the use of neutral polymers as carriers for the AS ODNs. Based on our previous work on synthetic hydrogels for vitreous substitution, we developed a poly[1-vinyl-2-pyrrolidinone-co-(2-hydroxyethyl methacrylate)] hydrogel as a potential carrier for AS ODNs. We have previously demonstrated that such hydrogels are not cytotoxic, and they may have growth-promoting effects on cultured fibroblasts. This copolymer also has the advantage of being injectable. In this study, a specific AS ODN was synthesized and then covalently bound to the copolymer via carbodiimide coupling method. The resulting conjugate was subjected to in vitro release experiments over 46 days in the presence of bovine vitreous humor. Compared with the control (no enzyme present), a significant amount of covalently bound ODN was released from the ODN-hydrogel conjugate, suggesting the possibility of using such systems for the sustained delivery of AS ODNs.

An Antibody-Avidin Fusion Protein Specific for the Transferrin Receptor Serves as a Delivery Vehicle for Effective Brain Targeting: Initial Applications in Anti-HIV Antisense Drug Delivery to the Brain

In the present study a novel Ab-avidin fusion protein has been constructed to deliver biotinylated compounds across the blood brain barrier. This fusion molecule consists of an Ab specific for the transferrin receptor genetically fused to avidin. The Ab-avidin fusion protein (anti-TfR IgG3-CH3-Av) expressed in murine myeloma cells was correctly assembled and secreted and showed both Ab- and avidin-related activities. In animal models, it showed much longer serum half-life than the chemical conjugate between OX-26 and avidin. Most importantly, this fusion protein demonstrated superior [3H]biotin uptake into brain parenchyma in comparison with the chemical conjugate. We also delivered a biotinylated 18-mer antisense peptide-nucleic acid specific for the rev gene of HIV-1 to the brain. Brain uptake of the HIV antisense drug was increased at least 15-fold when it was bound to the anti-TfR IgG3-CH3-Av, suggesting its potential use in neurologic AIDS. This novel Ab fusion protein should have general utility as a universal vehicle to effectively deliver biotinylated compounds across the blood-brain barrier for diagnosis and/or therapy of a broad range of CNS disorders such as infectious diseases, brain tumors as well as Parkinson’s and Huntington’s diseases.

Drug delivery of antisense molecules to the brain for treatment of Alzheimer's disease and cerebral AIDS

Antisense oligonucleotides (ODNs) and peptide nucleic acids (PNAs) are potential therapeutics for eradication of malignancies, viral infections, and other pathologies. However, ODNs and PNAs in general are unable to cross cellular membranes and blood-tissue barriers, such as the blood-brain barrier (BBB), which is only permeable to lipophilic molecules of molecular weight <600 Da. Cellular delivery systems based on conjugates of streptavidin (SA) and the OX26 monoclonal antibody directed to the transferrin receptor may be employed as a universal carrier for the transport of mono-biotinylated peptides, ODNs, or PNAs. 3'-Biotinylation of phosphodiester (PO)-ODN produces complete protection of ODN against serum and cellular 3'-exonucleases, facilitating the conjugation to avidin-based delivery systems and maintaining the activation of RNase H. These delivery systems markedly increased the cellular uptake and antisense efficacy of 3'-biotinylated ODNs in models of Alzheimer's disease and HIV-AIDS. In vivo brain delivery studies demonstrated that 3'-protected PO-ODNs and PO-phosphorothioate(PS)-ODN hybrids containing a single PO linkage are subjected to endonuclease degradation in vivo. On the contrary PS-ODNs, which were also protected at 3'-terminus by biotinylation, are metabolically stable in vivo and resistant to exo/endonuclease degradation. However, because of the strong binding of these oligomers to plasma protein, PS-ODNs are poorly transported into the brain through the BBB by the OX26-SA delivery vector following intravenous administration. PNAs are also resistant to exo/endonuclease and protease degradation, and these molecules biotinylated at the amino terminal group were transported into the brain by the OX26-SA delivery system with brain uptake levels comparable to that of morphine. Using the rev gene of HIV as a model target, RNase protection assays and cell-free translation arrest showed that the PNA-OX26-SA conjugate maintained active recognition and inactivation of target mRNA, respectively. The overall experimental evidence suggests that PNA-OX26-SA conjugates represent optimal antisense molecules for drug delivery to the brain.

Development of targeted delivery systems for nucleic acid drugs

Our increased understanding of disease pathogenesis is the basis for developing novel nucleic acid drugs. The main challenge encountered in this development is how to maintain therapeutically meaningful concentrations of the drugs in the vicinity of their targets for the desired periods. The intrinsic difficulty arises from the fact that nucleic acid drugs are not readily transported across membranes. Hence, their delivery and transport characteristics at the whole body, organ and cellular levels need to be thoroughly examined. Liposomes and receptor-mediated polycation systems are promising carriers for their delivery in vivo. There are many barriers to be overcome for successful antisense and gene therapies. Along with other factors, disposition, stability against nucleases, binding to cell surface receptor and internalization, and intracellular trafficking affect the in vivo delivery and efficacy of nucleic acid drugs. This review article discusses the delivery and transport of these compounds.

Targeted radiotherapy using Auger electron emitters

Auger-emitting radionuclides have potential for the therapy of cancer due to their high level of cytotoxicity and short-range biological effectiveness. Biological effects are critically dependent on the sub-cellular (and sub-nuclear) localization of Auger emitters. Mathematical modelling studies suggest that there are theoretical advantages in the use of radionuclides with short half-lives (such as 123I) in preference to those (such as 125I) with long half-lives. In addition, heterogeneity of radionuclide uptake is predicted to be a serious limitation on the ultimate therapeutic effect of targeted Auger therapy. Possible methods of targeting include the use of analogues of DNA precursors such as iodo-deoxyuridine and molecules which bind DNA such as steroid hormones or growth factors. A longer term possibility may be the use of molecules such as oligonucleotides which can discriminate at the level of DNA sequence. It seems likely that the optimal clinical role of targeted Auger therapy will be as one component of a multi-modality therapeutic strategy for the treatment of selected malignant diseases.

Peptide nucleic acid characterization by MALDI-TOF mass spectrometry

Peptide nucleic acids (PNAs) are a new class of DNA mimics in which the regular nucleobases of adenine, thymine, cytosine, and guanine are connected via a peptide-like backbone. PNA molecules retain the same Watson-Crick base pairing as regular oligonucleotides, with the added benefits of greater specificity and resistance to enzymatic digestion. While the use of PNAs has grown rapidly because of their potential applications in biotechnology, little work has been done on developing analytical procedures for characterizing them. We have found matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry to be an effective tool for PNA analysis. PNA molecules survive the MALDI process intact and are easily ionized with almost no multiply-charged species. These features allow mixtures to be easily characterized. Traditional protein matrices (e.g., sinapinic acid,2,5-dihydroxybenzoic acid, alpha-cyano-4-hydroxycinnamic acid) were found to be superior to DNA matrices (e.g., trihydroxy-acetophenone, 3-hydroxypicolinic acid, picolinic acid). In addition, the new DNA matrix 6-aza-2-thiothymine worked well. The ability of MALDI-TOF-MS to ascertain PNA purity and sequence information at low picomole levels will be important as greater quality control of PNA synthesis is needed (e.g., when PNAs are used as antisense or antigene drugs).