Cell-mediated drug delivery to the brain

Bio-Nano Toolbox for Precision Alzheimer's Disease Gene Therapy

Alzheimer's disease (AD) is the most burdensome aging-associated neurodegenerative disorder, and its treatment encounters numerous failures during drug development. Although there are newly approved in-market β-amyloid targeting antibody solutions, pathological heterogeneity among patient populations still challenges the treatment outcome. Emerging advances in gene therapies offer opportunities for more precise personalized medicine; while, major obstacles including the pathological heterogeneity among patient populations, the puzzled mechanism for druggable target development, and the precision delivery of functional therapeutic elements across the blood-brain barrier remain and limit the use of gene therapy for central neuronal diseases. Aiming for "precision delivery" challenges, nanomedicine provides versatile platforms that may overcome the targeted delivery challenges for AD gene therapy. In this perspective, to picture a toolbox for AD gene therapy strategy development, the most recent advances from benchtop to clinics are highlighted, possibly available gene therapy targets, tools, and delivery platforms are outlined, their challenges as well as rational design elements are addressed, and perspectives in this promising research field are discussed.

Novel Nano-Drug Delivery System for Brain Tumor Treatment

As the most dangerous tumors, brain tumors are usually treated with surgical removal, radiation therapy, and chemotherapy. However, due to the aggressive growth of gliomas and their resistance to conventional chemoradiotherapy, it is difficult to cure brain tumors by conventional means. In addition, the higher dose requirement of chemotherapeutic drugs caused by the blood-brain barrier (BBB) and the untargeted nature of the drug inevitably leads to low efficacy and systemic toxicity of chemotherapy. In recent years, nanodrug carriers have attracted extensive attention because of their superior drug transport capacity and easy-to-control properties. This review systematically summarizes the major strategies of novel nano-drug delivery systems for the treatment of brain tumors in recent years that cross the BBB and enhance brain targeting, and compares the advantages and disadvantages of several strategies.

Engineered strategies to enhance tumor penetration of drug-loaded nanoparticles

Nanocarriers have been widely employed in preclinical studies and clinical trials for the delivery of anticancer drugs. The most important causes of failure in clinical translation of nanocarriers is their inefficient accumulation and penetration which arises from special characteristics of tumor microenvironment such as insufficient blood supply, dense extracellular matrix, and elevated interstitial fluid pressure. Various strategies such as engineering extracellular matrix, optimizing the physicochemical properties of nanocarriers have been proposed to increase the depth of tumor penetration; however, these strategies have not been very successful so far. Novel strategies such as transformable nanocarriers, transcellular transport of peptide-modified nanocarriers, and bio-inspired carriers have recently been emerged as an advanced generation of drug carriers. In this study, the latest developments of nanocarrier-based drug delivery to solid tumor are presented with their possible limitations. Then, the prospects of advanced drug delivery systems are discussed in detail.

Cell-mediated targeting drugs delivery systems

Drug delivery systems have shown tremendous promise to improve the diagnostic and therapeutic effects of drugs due to their special property. Targeting tissue damage, tumors, or drugs with limited toxicity at the site of infection is the goal of successful pharmaceuticals. Targeted drug delivery has become significantly important in enhancing the pharmaceutical effects of drugs and reducing their side effects of therapeutics in the treatment of various disease conditions. Unfortunately, clinical translation of these targeted drug delivery system mechanisms faces many challenges. At present, only a few targeted drug delivery systems can achieve high targeting efficiency after intravenous injection, even though numerous surface markers and targeting approaches have been developed. Thus, cell-mediated drug-delivery targeting systems have received considerable attention for their enhanced therapeutic specificity and efficacy in the treatment of the disease. This review highlights the recent advances in the design of the different types of cells that have been explored for cell-mediated drug delivery and targeting mechanisms. A better understanding of cell biology orientation and a new generation of delivery strategies that utilize these endogenous approaches are expected to provide better solutions for specific site delivery and further facilitate clinical translation.

Macrophage-Laden Gold Nanoflowers Embedded with Ultrasmall Iron Oxide Nanoparticles for Enhanced Dual-Mode CT/MR Imaging of Tumors

The design of multimodal imaging nanoplatforms with improved tumor accumulation represents a major trend in the current development of precision nanomedicine. To this end, we report herein the preparation of macrophage (MA)-laden gold nanoflowers (NFs) embedded with ultrasmall iron oxide nanoparticles (USIO NPs) for enhanced dual-mode computed tomography (CT) and magnetic resonance (MR) imaging of tumors. In this work, generation 5 poly(amidoamine) (G5 PAMAM) dendrimer-stabilized gold (Au) NPs were conjugated with sodium citrate-stabilized USIO NPs to form hybrid seed particles for the subsequent growth of Au nanoflowers (NFs). Afterwards, the remaining terminal amines of dendrimers were acetylated to form the dendrimer-stabilized Fe₃O₄/Au NFs (for short, Fe₃O₄/Au DSNFs). The acquired Fe₃O₄/Au DSNFs possess an average size around 90 nm, display a high r₁ relaxivity (1.22 mM^-1 s^-1), and exhibit good colloidal stability and cytocompatibility. The created hybrid DSNFs can be loaded within MAs without producing any toxicity to the cells. Through the mediation of MAs with a tumor homing and immune evasion property, the Fe₃O₄/Au DSNFs can be delivered to tumors more efficiently than those without MAs after intravenous injection, thus significantly improving the MR/CT imaging performance of tumors. The developed MA-mediated delivery system may hold great promise for enhanced tumor delivery of other contrast agents or nanomedicines for precision cancer nanomedicine applications.

Construction and evaluation of red blood cells-based drug delivery system for chemo-photothermal therapy

In this study, a novel tumor-targeting drug delivery system (DDS) based on red blood cells (RBCs) were fabricated for combinational chemo-phototherapy against cancer. Cyclic peptide (cRGD) and indocyanine green (ICG) were applied to the surface of RBCs to increase the targeting and photothermal effect, respectively. Doxorubicin (DOX) as a model drug was loaded into RBCs by the hypotonic dialysis method. A series of tests have been carried out to evaluate the RBCs-based DDS and these tasks include physicochemical properties, cellular uptake, targeting ability, and combination therapeutic efficiency. As a result, the DOX was successfully loaded into RBCs and the drug loading amount was 0.84 ± 0.09 mg/mL. There was no significant change of particle size after surface modification of RBCs. The RBCs-based DDS could target to the surface of cancer cells, which delivery DOX to the lesions efficiently and accurately. Meanwhile, due to the combined treatment effect, the RBCs-based DDS can effectively inhibit tumor growth. The RBCs-based DDS constructed in this research may have promising applications in cancer therapy due to their highly synergistic efficient therapy and to investigate its possibility for tumor therapy.

Recent Progress in Magnetically Actuated Microrobots for Targeted Delivery of Therapeutic Agents

Therapeutic agents, such as drugs and cells, play an essential role in virtually every treatment of injury, illness, or disease. However, the conventional practices of drug delivery often result in undesirable side effects caused by drug overdose and off-target delivery. In the case of cell delivery, the survival rate of the transplanted cells is extremely low and difficulties with the administration route of cells remain a problem. Recently, magnetically actuated microrobots have started offering unique opportunities in targeted therapeutic delivery due to their tiny size and ability to access hard-to-reach lesions in a minimally invasive manner; considerable advances in this regard have been made over the past decade. Here, recent progress in magnetically actuated microrobots, developed for targeted drug/cell delivery, is presented, with a focus on their design features and mechanisms for controlled therapeutic release. Additionally, the practical challenges faced by the microrobots, and future research directions toward the swift bench-to-bedside translation of the microrobots are addressed.

T Cell-Mediated Transport of Polymer Nanoparticles across the Blood-Brain Barrier

Delivery of therapeutics to the central nervous system (CNS) is challenging due to the presence of the blood-brain barrier (BBB). Amongst various approaches that have been explored to facilitate drug delivery to the CNS, the use of cells that have the intrinsic ability to cross the BBB is relatively unexplored, yet very attractive. This paper presents a first proof-of-concept that demonstrates the feasibility of activated effector/memory CD4⁺ helper T cells (CD4⁺ T_EM cells) as carriers for the delivery of polymer nanoparticles across the BBB. This study shows that CD4⁺ T_EM cells can be decorated with poly(ethylene glycol)-modified polystyrene nanoparticles using thiol-maleimide coupling chemistry, resulting in the immobilization of ≈105 nanoparticles per cell as determined by confocal microscopy. The ability of these cells to serve as carriers to transport nanoparticles across the BBB is established in vitro and in vivo. Using in vitro BBB models, CD4⁺ T_EM cells are found to be able to transport nanoparticles across the BBB both under static conditions as well as under physiological flow. Finally, upon systemic administration, nanoparticle-modified T cells are shown to enter the brain parenchyma of mice, demonstrating the brain delivery potential of this T cell subset in allogeneic hosts.

T Cell Delivery of Nanoparticles-Bound Anti-CD20 Monoclonal Antibody: Successful B Cell Depletion in the Spinal Cord during Experimental Autoimmune Encephalomyelitis

We developed a nanotechnology based-cell mediated drug delivery system by loading myelin antigen-specific T cells with nanoparticles bound to anti-CD20 monoclonal antibody. Anti-CD20 antibody is a current treatment (ocrelizumab) for multiple sclerosis (MS), a chronic, inflammatory and autoimmune disease of the central nervous system (CNS). CD20-depletion has been associated with efficacy in active relapsing and progressive MS, but may not efficiently target inflammatory cells compartmentalized in the CNS. In our work, the intravenous transfer of T cells containing nanoparticle-anti-CD20 complex in mice causes B cell depletion in the spleen and in the brain, whereas the injection of anti-CD20 alone depletes B cells only in the spleen. Testing this system in Experimental Autoimmune Encephalomyelitis (EAE), animal model of MS, we found that spinal cord B cell depletion ameliorates the disease course and pathology. Graphical Abstract.

Non-Invasive Delivery of Therapeutics into the Brain: The Potential of Aptamers for Targeted Delivery

The blood-brain barrier (BBB) is a highly specialised network of blood vessels that effectively separates the brain environment from the circulatory system. While there are benefits, in terms of keeping pathogens from entering the brain, the BBB also complicates treatments of brain pathologies by preventing efficient delivery of macromolecular drugs to diseased brain tissue. Although current non-invasive strategies of therapeutics delivery into the brain, such as focused ultrasound and nanoparticle-mediated delivery have shown various levels of successes, they still come with risks and limitations. This review discusses the current approaches of therapeutic delivery into the brain, with a specific focus on non-invasive methods. It also discusses the potential for aptamers as alternative delivery systems and several reported aptamers with promising preliminary results.

Nanocarrier-based systems for targeted and site specific therapeutic delivery

Systemic drug delivery methods such as oral or parenteral administration of free drugs possess relatively low treatment efficiency and marked adverse side effects. The use of nanoparticles for drug delivery in most cases substantially enhances drug efficacy, improves pharmacokinetics and drug release and limits their side effects. However, further enhancement in drug efficacy and significant limitation of adverse side effects can be achieved by specific targeting of nanocarrier-based delivery systems especially in combination with local administration. The present review describes major advantages and limitations of organic and inorganic nanocarriers or living cell-based drug and nucleic acid delivery systems. Among these, different nanoparticles, supramolecular gels, therapeutic cells as living drug carriers etc. have emerged as a new frontier in modern medicine.

Nanotechnology-Based Strategies for siRNA Brain Delivery for Disease Therapy

Small interfering RNA (siRNA)-based gene silencing technology has demonstrated significant potential for treating brain-associated diseases. However, effective and safe systemic delivery of siRNA into the brain remains challenging because of biological barriers such as enzymatic degradation, short circulation lifetime, the blood-brain barrier (BBB), insufficient tissue penetration, cell endocytosis, and cytosolic transport. Nanotechnology offers intriguing potential for addressing these challenges in siRNA brain delivery in conjunction with chemical and biological modification strategies. In this review, we outline the challenges of systemic delivery of siRNA-based therapy for brain diseases, highlight recent advances in the development and engineering of siRNA nanomedicines for various brain diseases, and discuss our perspectives on this exciting research field for siRNA-based therapy towards more effective brain disease therapy.

Bio-inspired drug delivery systems: an emerging platform for targeted cancer therapy

Bio-inspired platforms directly derived from biological sources are becoming a rapidly emerging field in the development of future anticancer therapeutics. The various platforms discussed are bacteria-based, virus-inspired, cell-derived, nanostructured lipid nanoparticles, and biomacromolecular drug delivery systems.

Macrophage exosomes as natural nanocarriers for protein delivery to inflamed brain

Recent work has stimulated interest in the use of exosomes as nanocarriers for delivery of small drugs, RNAs, and proteins to the central nervous system (CNS). To overcome the blood-brain barrier (BBB), exosomes were modified with brain homing peptides that target brain endothelium but likely to increase immune response. Here for the first time we demonstrate that there is no need for such modification to penetrate the BBB in mammals. The naïve macrophage (Mϕ) exosomes can utilize, 1) on the one hand, the integrin lymphocyte function-associated antigen 1 (LFA-1) and intercellular adhesion molecule 1 (ICAM-1), and, 2) on the other hand, the carbohydrate-binding C-type lectin receptors, to interact with brain microvessel endothelial cells comprising the BBB. Notably, upregulation of ICAM-1, a common process in inflammation, promotes Mϕ exosomes uptake in the BBB cells. We further demonstrate in vivo that naïve Mϕ exosomes, after intravenous (IV) administration, cross the BBB and deliver a cargo protein, the brain derived neurotrophic factor (BDNF), to the brain. This delivery is enhanced in the presence of brain inflammation, a condition often present in CNS diseases. Taken together, the findings are of interest to basic science and possible use of Mϕ-derived exosomes as nanocarriers for brain delivery of therapeutic proteins to treat CNS diseases.