Aptamer Nanoconstructs Crossing Human Blood-Brain Barrier Discovered via Microphysiological System-Based SELEX Technology.

Blood-brain barrier (BBB) remains one of the critical challenges in developing neurological therapeutics. Short single-stranded DNA/RNA nucleotides forming a three-dimensional structure, called aptamers, have received increasing attention as BBB shuttles for efficient brain drug delivery owing to their practical advantages over Trojan horse antibodies or peptides. Aptamers are typically obtained by combinatorial chemical technology, termed Systemic Evolution of Ligands by EXponential Enrichment (SELEX), against purified targets, living cells, or animal models. However, identifying reliable BBB-penetrating aptamers that perform efficiently under human physiological conditions has been challenging because of the poor physiological relevance in the conventional SELEX process. Here, we report a human BBB shuttle aptamer (hBS) identified using a human microphysiological system (MPS)-based SELEX (MPS-SELEX) method. A two-channel MPS lined with human brain microvascular endothelial cells (BMECs) interfaced with astrocytes and pericytes, recapitulating high-level barrier function of in vivo BBB, was exploited as a screening platform. The MPS-SELEX procedure enabled robust function-based screening of the hBS candidates, which was not achievable in traditional in vitro BBB models. The identified aptamer (hBS01) through five-round of MPS-SELEX exhibited high capability to transport protein cargoes across the human BBB via clathrin-mediated endocytosis and enhanced uptake efficiency in BMECs and brain cells. The enhanced targeting specificity of hBS01 was further validated both in vitro and in vivo, confirming its powerful brain accumulation efficiency. These findings demonstrate that MPS-SELEX has potential in the discovery of aptamers with high target specificity that can be widely utilized to boost the development of drug delivery strategies.

A novel therapeutic strategy of multimodal nanoconjugates for state-of-the-art brain tumor phototherapy.

BACKGROUND: The outcome of phototherapy, including photothermal therapy (PTT) and photodynamic therapy (PDT) for glioblastoma multiforme (GBM), is disappointing due to insufficient photoconversion efficiency and low targeting rate. The development of phototherapeutic agents that target GBM and generate high heat and potent ROS is important to overcome the weak anti-tumor effect. RESULTS: In this study, nanoconjugates composed of gold nanoparticles (AuNPs) and photosensitizers (PSs) were prepared by disulfide conjugation between Chlorin e6 (Ce6) and glutathione coated-AuNP. The maximum heat dissipation of the nanoconjugate was 64.5 ± 4.5 °C. Moreover, the proximate conjugation of Ce6 on the AuNP surface resulted in plasmonic crossover between Ce6 and AuNP. This improves the intrinsic ROS generating capability of Ce6 by 1.6-fold compared to that of unmodified-Ce6. This process is called generation of metal-enhanced reactive oxygen species (MERos). PEGylated-lactoferrin (Lf-PEG) was incorporated onto the AuNP surface for both oral absorption and GBM targeting of the nanoconjugate (denoted as Ce6-AuNP-Lf). In this study, we explored the mechanism by which Ce6-AuNP-Lf interacts with LfR at the intestinal and blood brain barrier (BBB) and penetrates these barriers with high efficiency. In the orthotopic GBM mice model, the oral bioavailability and GBM targeting amount of Ce6-AuNP-Lf significantly improved to 7.3 ± 1.2% and 11.8 ± 2.1 µg/kg, respectively. The order of laser irradiation, such as applying PDT first and then PTT, was significant for the treatment outcome due to the plasmonic advantages provided by AuNPs to enhance ROS generation capability. As a result, GBM-phototherapy after oral administration of Ce6-AuNP-Lf exhibited an outstanding anti-tumor effect due to GBM targeting and enhanced photoconversion efficiency. CONCLUSIONS: The designed nanoconjugates greatly improved ROS generation by plasmonic crossover between AuNPs and Ce6, enabling sufficient PDT for GBM as well as PTT. In addition, efficient GBM targeting through oral administration was possible by conjugating Lf to the nanoconjugate. These results suggest that Ce6-AuNP-Lf is a potent GBM phototherapeutic nanoconjugate that can be orally administered.

Recent advances with liposomes as drug carriers for treatment of neurodegenerative diseases.

A major challenge in treating neurogenerative diseases is delivering drugs across the blood-brain barrier (BBB). In this review, we summarized the development of liposome-based drug delivery system with enhanced BBB penetration for efficient brain drug delivery. We focused on the liposome-based therapeutics targeting Alzheimer's disease and Parkinson's disease because they are most common types of adult chronic neurodegenerative disorders. A variety of liposome with surface modification of BBB-targeting ligands have been created to cross the BBB via transcytosis to the therapeutic efficacy of Alzheimer's disease and Parkinson's disease drugs. Recent advances in liposome are providing alternatives to overcome BBB for more efficient therapeutic strategy. To improve the BBB penetration of liposomes, we need to completely understand the pathophysiological changes at the BBB.

Engineering Human Brain Organoids: From Basic Research to Tissue Regeneration.

BACKGROUND: Brain organoids are self-organized from human pluripotent stem cells and developed into various brain region following the developmental process of brain. Brain organoids provide promising approach for studying brain development process and neurological diseases and for tissue regeneration. METHODS: In this review, we summarized the development of brain organoids technology, potential applications focusing on disease modeling for regeneration medicine, and multidisciplinary approaches to overcome current limitations of the technology. RESULTS: Generations of brain organoids are categorized into two major classes by depending on the patterning method. In order to guide the differentiation into specific brain region, the extrinsic factors such as growth factors, small molecules, and biomaterials are actively studied. For better modelling of diseases with brain organoids and clinical application for tissue regeneration, improvement of the brain organoid maturation is one of the most important steps. CONCLUSION: Brain organoids have potential to develop into an innovative platform for pharmacological studies and tissue engineering. However, they are not identical replicas of their in vivo counterpart and there are still a lot of limitations to move forward to clinical applications.