Polymer nanocarriers protecting active enzyme cargo against proteolysis

Smart nanocarriers for enzyme-activated prodrug therapy

Exogenous enzyme-activated prodrug therapy (EPT) is a potential cancer treatment strategy that delivers non-human enzymes into or on the surface of the cell and subsequently converts a non-toxic prodrug into an active cytotoxic substance at a specific location and time. The development of several pharmacological pairs based on EPT has been the focus of anticancer research for more than three decades. Numerous of these pharmacological pairs have progressed to clinical trials, and a few have achieved application in specific cancer therapies. The current review highlights the potential of enzyme-activated prodrug therapy as a promising anticancer treatment. Different microbial, plant, or viral enzymes and their corresponding prodrugs that advanced to clinical trials have been listed. Additionally, we discuss new trends in the field of enzyme-activated prodrug nanocarriers, including nanobubbles combined with ultrasound (NB/US), mesoscopic-sized polyion complex vesicles (PICsomes), nanoparticles, and extracellular vesicles (EVs), with special emphasis on smart stimuli-triggered drug release, hybrid nanocarriers, and the main application of nanotechnology in improving prodrugs.

Challenges of enzyme therapy: Why two players are better than one

Enzyme-based therapy has garnered significant attention for its current applications in various diseases. Despite the notable advantages associated with the use of enzymes as therapeutic agents, that could have high selectivity, affinity, and specificity for the target, their application faces challenges linked to physico-chemical and pharmacological properties. These limitations can be addressed through the encapsulation of enzymes in nanoplatforms as a comprehensive solution to mitigate their degradation, loss of activity, off-target accumulation, and immunogenicity, thus enhancing bioavailability, therapeutic efficacy, and circulation time, thereby reducing the number of administrations, and ameliorating patient compliance. The exploration of novel nanomedicine-based enzyme therapeutics for the treatment of challenging diseases stands as a paramount goal in the contemporary scientific landscape, but even then it is often not enough. Combining an enzyme with another therapeutic (e.g., a small molecule, another enzyme or protein, a monoclonal antibody, or a nucleic acid) within a single nanocarrier provides innovative multidrug-integrated therapy and ensures that both the actives arrive at the target site and exert their therapeutic effect, leading to synergistic action and superior therapeutic efficacy. Moreover, this strategic approach could be extended to gene therapy, a field that nowadays has gained increasing attention, as enzymes acting at genomic level and nucleic acids may be combined for synergistic therapy. This multicomponent therapeutic approach opens opportunities for promising future developments. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Polymer-based drug delivery systems under investigation for enzyme replacement and other therapies of lysosomal storage disorders

Lysosomes play a central role in cellular homeostasis and alterations in this compartment associate with many diseases. The most studied example is that of lysosomal storage disorders (LSDs), a group of 60 + maladies due to genetic mutations affecting lysosomal components, mostly enzymes. This leads to aberrant intracellular storage of macromolecules, altering normal cell function and causing multiorgan syndromes, often fatal within the first years of life. Several treatment modalities are available for a dozen LSDs, mostly consisting of enzyme replacement therapy (ERT) strategies. Yet, poor biodistribution to main targets such as the central nervous system, musculoskeletal tissue, and others, as well as generation of blocking antibodies and adverse effects hinder effective LSD treatment. Drug delivery systems are being studied to surmount these obstacles, including polymeric constructs and nanoparticles that constitute the focus of this article. We provide an overview of the formulations being tested, the diseases they aim to treat, and the results observed from respective in vitro and in vivo studies. We also discuss the advantages and disadvantages of these strategies, the remaining gaps of knowledge regarding their performance, and important items to consider for their clinical translation. Overall, polymeric nanoconstructs hold considerable promise to advance treatment for LSDs.

The possibility of angiogenesis inhibition in cutaneous melanoma by bevacizumab-loaded lipid-chitosan nanoparticles

Cutaneous malignant melanoma is fastest-growing cancer in white populations with a large majority of dermal cancer death. The activity of vascular endothelial growth factors (VEGFs) results in the signaling of a variety of downstream intracellular pathways that ultimately leads to cell activation, proliferation, migration, and angiogenesis. VEGF inhibitors such as bevacizumab are widely used in chemotherapy with systemic administration, which in many cases is associated with a variety of side effects. Here, we designed and synthesized a lipid-polymer nanoparticle for local administration of bevacizumab. Drug release, dermal absorption, and the effects of synthesized nanoparticles containing bevacizumab on cell proliferation and in vitro and in vivo angiogenesis were investigated. Encapsulating bevacizumab in the synthesized nanoparticles resulted in a significant increase in its dermal absorption compared to free bevacizumab. Also, the suppressor effects of bevacizumab encapsulated in the synthesized nanoparticle on cell proliferation and angiogenesis were significantly more than those of free bevacizumab. Our findings indicate the remarkable effects of lipid-polymer nanoparticles in dermal absorption and in maintaining bevacizumab bioactivity, suggesting therapeutic benefits of local bevacizumab administration for angiogenesis-related disorders such as cutaneous melanoma. Chitosan nanoparticles containing bevacizumab antibody were synthesized by ion exchange method, and finally, these nanoparticles were coated with lipid (Lip-Chi-Bev NPs). In this study, the effect of synthesized nanoparticles on dermal absorption of bevacizumab was evaluated and its potential in inhibiting angiogenesis was evaluated by in vitro and in vivo models.

ROS-responsive EPO nanoparticles ameliorate ionizing radiation-induced hematopoietic injury

Stimulus-responsive polymer materials have attracted much attention as drug carriers because of the ability to deliver drugs to the active site. Reactive oxygen species (ROS) play crucial roles in cellular signaling and regulation of oxygen homeostasis. However, ROS are present in abnormally high levels in many pathological environments. Based on the above points, three-arm poly(lactic-co-glycolic acid)-PO-poly(ethylene glycol) (3s-PLGA-PO-PEG or simply PP) was synthesized by using peroxalate esters (PO) as hydrogen peroxide-responsive linkages. PP was used to deliver promote hematopoietic recovery drugs erythropoietin (EPO) and EPO nanoparticles (EPO NPs) were prepared. We established a hematopoietic system injury model by ionizing radiation (IR) and unexpectedly found the good therapeutic effect of blank PP. Moreover, the administration of EPO NPs obviously decreased IR-induced ROS in bone marrow cells (BMCs) and reconstituted hematopoietic stem cells in BMCs. This study reveals a novel ROS-responsive polymer material that could be employed to remove excess ROS in the lesion and promote the efficacy of drug therapy.

Formulation and Efficacy of Catalase-Loaded Nanoparticles for the Treatment of Neonatal Hypoxic-Ischemic Encephalopathy

Neonatal hypoxic-ischemic encephalopathy is the leading cause of permanent brain injury in term newborns and currently has no cure. Catalase, an antioxidant enzyme, is a promising therapeutic due to its ability to scavenge toxic reactive oxygen species and improve tissue oxygen status. However, upon in vivo administration, catalase is subject to a short half-life, rapid proteolytic degradation, immunogenicity, and an inability to penetrate the brain. Polymeric nanoparticles can improve pharmacokinetic properties of therapeutic cargo, although encapsulation of large proteins has been challenging. In this paper, we investigated hydrophobic ion pairing as a technique for increasing the hydrophobicity of catalase and driving its subsequent loading into a poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticle. We found improved formation of catalase-hydrophobic ion complexes with dextran sulfate (DS) compared to sodium dodecyl sulfate (SDS) or taurocholic acid (TA). Molecular dynamics simulations in a model system demonstrated retention of native protein structure after complexation with DS, but not SDS or TA. Using DS-catalase complexes, we developed catalase-loaded PLGA-PEG nanoparticles and evaluated their efficacy in the Vannucci model of unilateral hypoxic-ischemic brain injury in postnatal day 10 rats. Catalase-loaded nanoparticles retained enzymatic activity for at least 24 h in serum-like conditions, distributed through injured brain tissue, and delivered a significant neuroprotective effect compared to saline and blank nanoparticle controls. These results encourage further investigation of catalase and PLGA-PEG nanoparticle-mediated drug delivery for the treatment of neonatal brain injury.

Enzymatic protection and biocompatibility screening of enzyme-loaded polymeric nanoparticles for neurotherapeutic applications

Polymeric nanoparticles provide a non-invasive strategy for enhancing the delivery of labile hydrophilic enzymatic cargo for neurological disease applications. One of the most common polymeric materials, poly(lactic-co-glycolic acid) (PLGA) copolymerized with poly(ethylene glycol) (PEG) is widely studied due to its biocompatible and biodegradable nature. Although PLGA-PEG nanoparticles are generally known to be non-toxic and protect enzymatic cargo from degradative proteases, different formulation parameters including surfactant, organic solvent, sonication times, and formulation method can all impact the final nanoparticle characteristics. We show that 30s sonication double emulsion (DE)-formulated nanoparticles achieved the highest enzymatic activity and provided the greatest enzymatic activity protection in degradative conditions, while nanoprecipitation (NPPT)-formulated nanoparticles exhibited no protection compared to free catalase. However, the same DE nanoparticles also caused significant toxicity on excitotoxicity-induced brain tissue slices, but not on healthy or neuroinflammation-induced tissue. We narrowed the culprit of toxicity to specifically sonication of PLGA-PEG polymer with dichloromethane (DCM) as the organic solvent, independent of surfactant type. We also discovered that toxicity was oxidative stress-dependent, but that increased toxicity was not enacted through increasing oxidative stress. Furthermore, no PEG degradation or aldehyde, alcohol, or carboxylic acid functional groups were detected after sonication. We identified that inclusion of free PEG along with PLGA-PEG polymer during the emulsification phases or replacing DCM with trichloromethane (chloroform) produced biocompatible polymeric nanoparticle formulations that still provided enzymatic protection. This work encourages thorough screening of nanoparticle toxicity and cargo-protective capabilities for the development of enzyme-loaded polymeric nanoparticles for the treatment of disease.

Targeting drug delivery in the vascular system: Focus on endothelium

The bloodstream is the main transporting pathway for drug delivery systems (DDS) from the site of administration to the intended site of action. In many cases, components of the vascular system represent therapeutic targets. Endothelial cells, which line the luminal surface of the vasculature, play a tripartite role of the key target, barrier, or victim of nanomedicines in the bloodstream. Circulating DDS may accumulate in the vascular areas of interest and in off-target areas via mechanisms bypassing specific molecular recognition, but using ligands of specific vascular determinant molecules enables a degree of precision, efficacy, and specificity of delivery unattainable by non-affinity DDS. Three decades of research efforts have focused on specific vascular targeting, which have yielded a multitude of DDS, many of which are currently undergoing a translational phase of development for biomedical applications, including interventions in the cardiovascular, pulmonary, and central nervous systems, regulation of endothelial functions, host defense, and permeation of vascular barriers. We discuss the design of endothelial-targeted nanocarriers, factors underlying their interactions with cells and tissues, and describe examples of their investigational use in models of acute vascular inflammation with an eye on translational challenges.

Biomimetic Nanotechnology toward Personalized Vaccines

While traditional approaches for disease management in the era of modern medicine have saved countless lives and enhanced patient well-being, it is clear that there is significant room to improve upon the current status quo. For infectious diseases, the steady rise of antibiotic resistance has resulted in super pathogens that do not respond to most approved drugs. In the field of cancer treatment, the idea of a cure-all silver bullet has long been abandoned. As a result of the challenges facing current treatment and prevention paradigms in the clinic, there is an increasing push for personalized therapeutics, where plans for medical care are established on a patient-by-patient basis. Along these lines, vaccines, both against bacteria and tumors, are a clinical modality that could benefit significantly from personalization. Effective vaccination strategies could help to address many challenging disease conditions, but current vaccines are limited by factors such as a lack of potency and antigenic breadth. Recently, researchers have turned toward the use of biomimetic nanotechnology as a means of addressing these hurdles. Recent progress in the development of biomimetic nanovaccines for antibacterial and anticancer applications is discussed, with an emphasis on their potential for personalized medicine.

Nanotherapeutic modulation of excitotoxicity and oxidative stress in acute brain injury

Excitotoxicity is a primary pathological process that occurs during stroke, traumatic brain injury (TBI), and global brain ischemia such as perinatal asphyxia. Excitotoxicity is triggered by an overabundance of excitatory neurotransmitters within the synapse, causing a detrimental cascade of excessive sodium and calcium influx, generation of reactive oxygen species, mitochondrial damage, and ultimately cell death. There are multiple potential points of intervention to combat excitotoxicity and downstream oxidative stress, yet there are currently no therapeutics clinically approved for this specific purpose. For a therapeutic to be effective against excitotoxicity, the therapeutic must accumulate at the disease site at the appropriate concentration at the right time. Nanotechnology can provide benefits for therapeutic delivery, including overcoming physiological obstacles such as the blood-brain barrier, protect cargo from degradation, and provide controlled release of a drug. This review evaluates the use of nano-based therapeutics to combat excitotoxicity in stroke, TBI, and hypoxia-ischemia with an emphasis on mitigating oxidative stress, and consideration of the path forward toward clinical translation.

Influence of PEG coating on the biodistribution and tumor accumulation of pH-sensitive liposomes

Liposomes are lipid vesicles widely used as nanocarriers in targeted drug delivery systems for therapeutic and/or diagnostic purposes. A strategy to prolong the blood circulation time of the liposomes includes the addition of a hydrophilic polymer polyethylene glycol (PEG) moiety onto the surface of the vesicle. Several studies claim that liposome PEGylation by a single chain length or a combination of PEG with different chain lengths may alter the liposomes' pharmacokinetic properties. Therefore, the purpose of this study was to evaluate the influence of PEG on the biodistribution of pH-sensitive liposomes in a tumor-bearing animal model. Three liposomal formulations (PEGylated or not) were prepared and validated to have a similar mean diameter, monodisperse distribution, and neutral zeta potential. The pharmacokinetic properties of each liposome were evaluated in healthy animals, while the biodistribution and scintigraphic images were evaluated in tumor-bearing mice. High tumor-to-muscle ratios were not statistically different between the PEGylated and non-PEGylated liposomes. While PEGylation is a well-established strategy for increasing the blood circulation of nanostructures, in our study, the use of polymer coating did not result in a better in vivo profile. Further studies must be carried out to confirm the feasibility of the non-PEGylated pH-sensitive liposomes for tumor treatment.

Click Nucleic Acid Mediated Loading of Prodrug Activating Enzymes in PEG-PLGA Nanoparticles for Combination Chemotherapy

The simultaneous delivery of multiple therapeutics to a single site has shown promise for cancer targeting and treatment. However, because of the inherent differences in charge and size between drugs and biomolecules, new approaches are required for colocalization of unlike components in one delivery vehicle. In this work, we demonstrate that triblock copolymers containing click nucleic acids (CNAs) can be used to simultaneously load a prodrug enzyme (cytosine deaminase, CodA) and a chemotherapy drug (doxorubicin, DOX) in a single polymer nanoparticle. CNAs are synthetic analogs of DNA comprised of a thiolene backbone and nucleotide bases that can hybridize to complementary strands of DNA. In this study, CodA was appended with complementary DNA sequences and fluorescent dyes to allow its encapsulation in PEG-CNA-PLGA nanoparticles. The DNA-modified CodA was found to retain its enzyme activity for converting prodrug 5-fluorocytosine (5-FC) to active 5-fluorouracil (5-FU) using a modified fluorescent assay. The DNA-conjugated CodA was then loaded into the PEG-CNA-PLGA nanoparticles and tested for cell cytotoxicity in the presence of the 5-FC prodrug. To study the effect of coloading DOX and CodA within a single nanoparticle, cell toxicity assays were run to compare dually loaded nanoparticles with nanoparticles loaded only with either DOX or CodA. We show that the highest level of cell death occurred when both DOX and CodA were simultaneously entrapped and delivered to cells in the presence of 5-FC.

Targeting therapeutics to endothelium: are we there yet?

Vascular endothelial cells represent an important therapeutic target in many pathologies, including inflammation, oxidative stress, and thrombosis; however, delivery of drugs to this site is often limited by the lack of specific affinity of therapeutics for these cells. Selective delivery of both small molecule drugs and therapeutic proteins to the endothelium has been achieved through the use of targeting ligands, such as monoclonal antibodies, directed against endothelial cell surface markers, particularly cell adhesion molecules (CAMs). Careful selection of target molecules and targeting agents allows for precise delivery to sites of inflammation, thereby maximizing therapeutic drug concentrations at the site of injury. A good understanding of the physiological and pathological determinants of drug and drug carrier pharmacokinetics and biodistribution may allow for a priori identification of optimal properties of drug carrier and targeting agent. Targeted delivery of therapeutics such as antioxidants and antithrombotic agents to the injured endothelium has shown efficacy in preclinical models, suggesting the potential for translation into clinical practice. As with all therapeutics, demonstration of both efficacy and safety are required for successful clinical implementation, which must be considered not only for the individual components (drug, targeting agent, etc.) but also for the sum of the parts (e.g., the drug delivery system), as unexpected toxicities may arise with complex delivery systems. While the use of endothelial targeting has not been translated into the clinic to date, the preclinical results summarized here suggest that there is hope for successful implementation of these agents in the years to come.

The environmental pollutant, polychlorinated biphenyls, and cardiovascular disease: a potential target for antioxidant nanotherapeutics

Despite production having stopped in the 1970s, polychlorinated biphenyls (PCBs) represent persistent organic pollutants that continue to pose a serious human health risk. Exposure to PCBs has been linked to chronic inflammatory diseases, such as cardiovascular disease, type 2 diabetes, obesity, as well as hepatic disorders, endocrine dysfunction, neurological deficits, and many others. This is further complicated by the PCB's strong hydrophobicity, resulting in their ability to accumulate up the food chain and to be stored in fat deposits. This means that completely avoiding exposure is not possible, thus requiring the need to develop intervention strategies that can mitigate disease risks associated with exposure to PCBs. Currently, there is excitement in the use of nutritional compounds as a way of inhibiting the inflammation associated with PCBs, yet the suboptimal delivery and pharmacology of these compounds may not be sufficient in more acute exposures. In this review, we discuss the current state of knowledge of PCB toxicity and some of the antioxidant and anti-inflammatory nanocarrier systems that may be useful as an enhanced treatment modality for reducing PCB toxicity.

Cerium Oxide Nanoparticles: A Brief Review of Their Synthesis Methods and Biomedical Applications

Cerium oxide nanoparticles (CeNPs) exhibit antioxidant properties both in vitro and in vivo. This is due to the self-regeneration of their surface, which is based on redox-cycling between 3+ and 4+ states for cerium, in response to their immediate environment. Additionally, oxygen vacancies in the lattice structure allow for alternating between CeO₂ and CeO2-x during redox reactions. Research to identify and characterize the biomedical applications of CeNPs has been heavily focused on investigating their use in treating diseases that are characterized by higher levels of reactive oxygen species (ROS). Although the bio-mimetic activities of CeNPs have been extensively studied in vitro, in vivo interactions and associated protein corona formation are not well understood. This review describes: (1) the methods of synthesis for CeNPs, including the recent green synthesis methods that offer enhanced biocompatibility and a need for establishing a reference CeNP material for consistency across studies; (2) their enzyme-mimetic activities, with a focus on their antioxidant activities; and, (3) recent experimental evidence that demonstrates their ROS scavenging abilities and their potential use in personalized medicine.

The new frontiers of the targeted interventions in the pulmonary vasculature: precision and safety (2017 Grover Conference Series)

The pulmonary vasculature plays an important role in many lung pathologies, such as pulmonary arterial hypertension, primary graft dysfunction of lung transplant, and acute respiratory distress syndrome. Therapy for these diseases is quite limited, largely due to dose-limiting side effects of numerous drugs that have been trialed or approved. High doses of drugs targeting the pulmonary vasculature are needed due to the lack of specific affinity of therapeutic compounds to the vasculature. To overcome this problem, the field of targeted drug delivery aims to target drugs to the pulmonary endothelial cells, especially those in pathological regions. The field uses a variety of drug delivery systems (DDSs), ranging from nano-scale drug carriers, such as liposomes, to methods of conjugating drugs to affinity moieites, such as antibodies. These DDSs can deliver small molecule drugs, protein therapeutics, and imaging agents. Here we review targeted drug delivery to the pulmonary endothelium for the treatment of pulmonary diseases. Cautionary notes are made of the risk–benefit ratio and safety—parameters one should keep in mind when developing a translational therapeutic.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Targeting vascular (endothelial) dysfunction

Cardiovascular diseases are major contributors to global deaths and disability-adjusted life years, with hypertension a significant risk factor for all causes of death. The endothelium that lines the inner wall of the vasculature regulates essential haemostatic functions, such as vascular tone, circulation of blood cells, inflammation and platelet activity. Endothelial dysfunction is an early predictor of atherosclerosis and future cardiovascular events. We review the prognostic value of obtaining measurements of endothelial function, the clinical techniques for its determination, the mechanisms leading to endothelial dysfunction and the therapeutic treatment of endothelial dysfunction. Since vascular oxidative stress and inflammation are major determinants of endothelial function, we have also addressed current antioxidant and anti-inflammatory therapies. In the light of recent data that dispute the prognostic value of endothelial function in healthy human cohorts, we also discuss alternative diagnostic parameters such as vascular stiffness index and intima/media thickness ratio. We also suggest that assessing vascular function, including that of smooth muscle and even perivascular adipose tissue, may be an appropriate parameter for clinical investigations.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Functionalized Polymers for Enhance Oral Bioavailability of Sensitive Molecules

Currently, many sensitive molecules have been studied for effective oral administration. These substances are biologically active compounds that mainly suffer early degradation in the gastrointestinal tract (GIT) and physicochemical instability, inactivation and poor solubility and permeability. The sensibility of the biomolecules has limited their oral administration in the body and today is an important research topic to achieve desired effects in medicine field. Under this perspective, various enhancement approaches have been studied as alternatives to increase their oral bioavailability. Some of these strategies include functionalized polymers to provide specific useful benefits as protection to the intestinal tract by preventing its degradation by stomach enzymes, to increase their absorption, permeability, stability, and to make a proper release in the GIT. Due to specific chemical groups, shapes and sizes, morphologies, mechanical properties, and degradation, recent advances in functionalized polymers have opened the door to great possibilities to improve the physicochemical characteristics of these biopharmaceuticals. Today, many biomolecules are found in basic studies, preclinical steps, and others are late stage clinical development. This review summarizes the contribution of functionalized polymers to enhance oral bioavailability of sensitive molecules and their application status in medicine for different diseases. Future trends of these polymers and their possible uses to achieve different formulation goals for oral delivery are also covered in this manuscript.

Targeted endothelial nanomedicine for common acute pathological conditions

Endothelium, a thin monolayer of specialized cells lining the lumen of blood vessels is the key regulatory interface between blood and tissues. Endothelial abnormalities are implicated in many diseases, including common acute conditions with high morbidity and mortality lacking therapy, in part because drugs and drug carriers have no natural endothelial affinity. Precise endothelial drug delivery may improve management of these conditions. Using ligands of molecules exposed to the bloodstream on the endothelial surface enables design of diverse targeted endothelial nanomedicine agents. Target molecules and binding epitopes must be accessible to drug carriers, carriers must be free of harmful effects, and targeting should provide desirable sub-cellular addressing of the drug cargo. The roster of current candidate target molecules for endothelial nanomedicine includes peptidases and other enzymes, cell adhesion molecules and integrins, localized in different domains of the endothelial plasmalemma and differentially distributed throughout the vasculature. Endowing carriers with an affinity to specific endothelial epitopes enables an unprecedented level of precision of control of drug delivery: binding to selected endothelial cell phenotypes, cellular addressing and duration of therapeutic effects. Features of nanocarrier design such as choice of epitope and ligand control delivery and effect of targeted endothelial nanomedicine agents. Pathological factors modulate endothelial targeting and uptake of nanocarriers. Selection of optimal binding sites and design features of nanocarriers are key controllable factors that can be iteratively engineered based on their performance from in vitro to pre-clinical in vivo experimental models. Targeted endothelial nanomedicine agents provide antioxidant, anti-inflammatory and other therapeutic effects unattainable by non-targeted counterparts in animal models of common acute severe human disease conditions. The results of animal studies provide the basis for the challenging translation endothelial nanomedicine into the clinical domain.

Strategies for delivery of therapeutics into the central nervous system for treatment of lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a group of about fifty life-threatening conditions caused by genetic defects affecting lysosomal components. The underscoring molecular deficiency leads to widespread cellular dysfunction through most tissues in the body, including peripheral organs and the central nervous system (CNS). Efforts during the last few decades have rendered a remarkable advance regarding our knowledge, medical awareness, and early detection of these genetic defects, as well as development of several treatment modalities. Clinical and experimental strategies encompassing enzyme replacement, gene and cell therapies, substrate reduction, and chemical chaperones are showing considerable potential in attenuating the peripheral pathology. However, a major drawback has been encountered regarding the suboptimal impact of these approaches on the CNS pathology. Particular anatomical and biochemical constraints of this tissue pose a major obstacle to the delivery of therapeutics into the CNS. Approaches to overcome these obstacles include modalities of local administration, strategies to enhance the blood-CNS permeability, intranasal delivery, use of exosomes, and those exploiting targeting of transporters and transcytosis pathways in the endothelial lining. The later two approaches are being pursued at the time by coupling therapeutic agents to affinity moieties and drug delivery systems capable of targeting these natural transport routes. This approach is particularly promising, as using paths naturally active at this interface may render safe and effective delivery of LSD therapies into the CNS.

Delivery aspects of antioxidants in diabetes management

INTRODUCTION

Ample research has been done to study the role of oxidative stress due to the generation of excess reactive species in initiation and progression of diabetic complications. A positive result has been indicated hypothesizing that abating this oxidative stress can prove to be an alternate strategy in therapy apart from oral antidiabetic drugs. But these dietary antioxidants are less efficient because of poor solubility, permeability, instability on storage, gastrointestinal degradation and first-pass metabolism.

AREAS COVERED

This review gives a brief insight into the molecular mechanism of oxidative stress in development of diabetic complications. Major hurdles limiting the translation of antioxidants to clinical area are also discussed. Various delivery approaches including both conventional and novel drug delivery systems explored so far for combating these challenges in antioxidant delivery are also explored. Mitochondrial targeting of such molecules is also briefly discussed.

EXPERT OPINION

A thorough study of clinical efficacy and safety of antioxidants on long-term use judging its clinical applicability is required. The clinical success of antioxidants as a therapeutic strategy involves a combination of effective design of drug delivery carrier that are in turn related to their degradation profile, possibility of cellular uptake at defined site of action and so on and clinical and preclinical trials that will provide a base for the design of dose and administration regimen.

Endothelial nanomedicine for the treatment of pulmonary disease

INTRODUCTION

Even though pulmonary diseases are among the leading causes of morbidity and mortality in the world, exceedingly few life-prolonging therapies have been developed for these maladies. Relief may finally come from nanomedicine and targeted drug delivery.

AREAS COVERED

Here, we focus on four conditions for which the pulmonary endothelium plays a pivotal role: acute respiratory distress syndrome, primary graft dysfunction occurring immediately after lung transplantation, pulmonary arterial hypertension and pulmonary embolism. For each of these diseases, we first evaluate the targeted drug delivery approaches that have been tested in animals. Then we suggest a 'need specification' for each disease: a list of criteria (e.g., macroscale delivery method, stability, etc.) that nanomedicine agents must meet in order to warrant human clinical trials and investment from industry.

EXPERT OPINION

For the diseases profiled here, numerous nanomedicine agents have shown promise in animal models. However, to maximize the chances of creating products that reach patients, nanomedicine engineers and clinicians must work together and use each disease's need specification to guide the design of practical and effective nanomedicine agents.

Nanocarriers for vascular delivery of anti-inflammatory agents

There is a need for improved treatment of acute vascular inflammation in conditions such as ischemia-reperfusion injury, acute lung injury, sepsis, and stroke. The vascular endothelium represents an important therapeutic target in these conditions. Furthermore, some anti-inflammatory agents (AIAs) (e.g., biotherapeutics) require precise delivery into subcellular compartments. In theory, optimized delivery to the desired site of action may improve the effects and enable new mechanisms of action of these AIAs. Diverse nanocarriers (NCs) and strategies for targeting them to endothelial cells have been designed and explored for this purpose. Studies in animal models suggest that delivery of AIAs using NCs may provide potent and specific molecular interventions in inflammatory pathways. However, the industrial development and clinical translation of complex NC-AIA formulations are challenging. Rigorous analysis of therapeutic/side effect and benefit/cost ratios is necessary to identify and optimize the approaches that may find clinical utility in the management of acute inflammation.

Dual-porosity hollow nanoparticles for the immunoprotection and delivery of nonhuman enzymes

Although enzymes of nonhuman origin have been studied for a variety of therapeutic and diagnostic applications, their use has been limited by the immune responses generated against them. The described dual-porosity hollow nanoparticle platform obviates immune attack on nonhuman enzymes paving the way to in vivo applications including enzyme-prodrug therapies and enzymatic depletion of tumor nutrients. This platform is manufactured with a versatile, scalable, and robust fabrication method. It efficiently encapsulates macromolecular cargos filled through mesopores into a hollow interior, shielding them from antibodies and proteases once the mesopores are sealed with nanoporous material. The nanoporous shell allows small molecule diffusion allowing interaction with the large macromolecular payload in the hollow center. The approach has been validated in vivo using l-asparaginase to achieve l-asparagine depletion in the presence of neutralizing antibodies.

Endothelial targeting of nanocarriers loaded with antioxidant enzymes for protection against vascular oxidative stress and inflammation

Endothelial-targeted delivery of antioxidant enzymes, catalase and superoxide dismutase (SOD), is a promising strategy for protecting organs and tissues from inflammation and oxidative stress. Here we describe Protective Antioxidant Carriers for Endothelial Targeting (PACkET), the first carriers capable of targeted endothelial delivery of both catalase and SOD. PACkET formed through controlled precipitation loaded ~30% enzyme and protected it from proteolytic degradation, whereas attachment of PECAM monoclonal antibodies to surface of the enzyme-loaded carriers, achieved without adversely affecting their stability and functionality, provided targeting. Isotope tracing and microscopy showed that PACkET exhibited specific endothelial binding and internalization in vitro. Endothelial targeting of PACkET was validated in vivo by specific (vs IgG-control) accumulation in the pulmonary vasculature after intravenous injection achieving 33% of injected dose at 30 min. Catalase loaded PACkET protects endothelial cells from killing by H2O2 and alleviated the pulmonary edema and leukocyte infiltration in mouse model of endotoxin-induced lung injury, whereas SOD-loaded PACkET mitigated cytokine-induced endothelial pro-inflammatory activation and endotoxin-induced lung inflammation. These studies indicate that PACkET offers a modular approach for vascular targeting of therapeutic enzymes.

Synthesis and Characterization of a Poly(ethylene glycol)-Poly(simvastatin) Diblock Copolymer

Biodegradable polyesters are commonly used as drug delivery vehicles, but their role is typically passive, and encapsulation approaches have limited drug payload. An alternative drug delivery method is to polymerize the active agent or its precursor into a degradable polymer. The prodrug simvastatin contains a lactone ring that lends itself to ring-opening polymerization (ROP). Consequently, simvastatin polymerization was initiated with 5 kDa monomethyl ether poly(ethylene glycol) (mPEG) and catalyzed via stannous octoate. Melt condensation reactions produced a 9.5 kDa copolymer with a polydispersity index of 1.1 at 150 °C up to a 75 kDa copolymer with an index of 6.9 at 250 °C. Kinetic analysis revealed first-order propagation rates. Infrared spectroscopy of the copolymer showed carboxylic and methyl ether stretches unique to simvastatin and mPEG, respectively. Slow degradation was demonstrated in neutral and alkaline conditions. Lastly, simvastatin, simvastatin-incorporated molecules, and mPEG were identified as the degradation products released. The present results show the potential of using ROP to polymerize lactone-containing drugs such as simvastatin.

Biosynthetic alginate–polyester hydrogels with inherent free radical scavenging activity promote cellular response

The prevention of deleterious effects of reactive oxygen species on the cell growth by biosynthetic hydrogels based on alginate–polyester copolymer was studied using H2O2 as the model ROS molecule. Chemically cross-linked biosynthetic hydrogels of alginate- co-poly(propylene fumarate)–n-butyl methacrylate, alginate- co-poly(propylene fumarate)–methyl methacrylate, alginate- co-poly(propylene fumarate)–2-hydroxyethyl methacrylate, and alginate- co-poly(propylene fumarate)– N,N′-methylene bisacrylamide with different biostabilities were prepared. We found that they were able to resist reactive oxygen species penetration into the cell to a greater extent which was evident from the live/dead assay, and increased intracellular glutathione levels compared to the H2O2-treated control. The hydrogels maintained the genomic integrity which was confirmed by comet assay. The inherent protective effects of these hydrogels without any antioxidant moiety may be mediated by dual mechanism: (a) prevention of migration of H2O2 into the cells by calcium-induced conformational changes and rigidity in phospholipids present in the surface membrane of cells by the calcium generated from degradation of hydrogel and (b) by the dilution of H2O2 by the free water in the hydrogel. These hydrogels have potential as injectable hydrogels to manage myocardial infarction and ischemia.

Targeted Drug Delivery to Endothelial Adhesion Molecules

Endothelial cells represent important targets for therapeutic and diagnostic interventions in many cardiovascular, pulmonary, neurological, inflammatory, and metabolic diseases. Targeted delivery of drugs (especially potent and labile biotherapeutics that require specific subcellular addressing) and imaging probes to endothelium holds promise to improve management of these maladies. In order to achieve this goal, drug cargoes or their carriers including liposomes and polymeric nanoparticles are chemically conjugated or fused using recombinant techniques with affinity ligands of endothelial surface molecules. Cell adhesion molecules, constitutively expressed on the endothelial surface and exposed on the surface of pathologically altered endothelium—selectins, VCAM-1, PECAM-1, and ICAM-1—represent good determinants for such a delivery. In particular, PECAM-1 and ICAM-1 meet criteria of accessibility, safety, and relevance to the (patho)physiological context of treatment of inflammation, ischemia, and thrombosis and offer a unique combination of targeting options including surface anchoring as well as intra- and transcellular targeting, modulated by parameters of the design of drug delivery system and local biological factors including flow and endothelial phenotype. This review includes analysis of these factors and examples of targeting selected classes of therapeutics showing promising results in animal studies, supporting translational potential of these interventions.

Suppressing iron oxide nanoparticle toxicity by vascular targeted antioxidant polymer nanoparticles

The biomedical use of superparamagnetic iron oxide nanoparticles has been of continued interest in the literature and clinic. Their ability to be used as contrast agents for imaging and/or responsive agents for remote actuation makes them exciting materials for a wide range of clinical applications. Recently, however, concern has arisen regarding the potential health effects of these particles. Iron oxide toxicity has been demonstrated in in vivo and in vitro models, with oxidative stress being implicated as playing a key role in this pathology. One of the key cell types implicated in this injury is the vascular endothelial cells. Here, we report on the development of a targeted polymeric antioxidant, poly(trolox ester), nanoparticle that can suppress oxidative damage. As the polymer undergoes enzymatic hydrolysis, active trolox is locally released, providing a long term protection against pro-oxidant agents. In this work, poly(trolox) nanoparticles are targeted to platelet endothelial cell adhesion molecules (PECAM-1), which are able to bind to and internalize in endothelial cells and provide localized protection against the cytotoxicity caused by iron oxide nanoparticles. These results indicate the potential of using poly(trolox ester) as a means of mitigating iron oxide toxicity, potentially expanding the clinical use and relevance of these exciting systems.

An integrated experimental and modeling approach to propose biotinylated PLGA microparticles as versatile targeting vehicles for drug delivery

Polymeric microparticles with covalently attached biotin are proposed as versatile targeting vehicles for drug delivery. The proposed microparticles made of 85/15 poly (lactic-co-glycolic acid) (PLGA) will have biotin available on the outside of the particle for the further attachment with an avidin group. Taking advantage of biotin's high affinity for avidin, and avidin's well-known chemistry, the particle has the potential to be easily coated with a variety of targeting moieties. This paper focuses on the design and resulting effect of adding biotin to PLGA microparticles using an integrated experimental and modeling approach. A fluorescent-tagged avidin (488-streptavidin) was used to confirm the presence and bioavailability of biotin on the outside of the particles. For the purpose of this study, bovine serum albumin (BSA) was used as a model therapeutic drug. Microparticles were created using two different types of polyvinyl alcohol 88 and 98 mol% hydrolyzed, which were then analyzed for their size, morphology, and encapsulation capacity of BSA. Release studies performed in vitro confirmed the slow release of the BSA over a 28-day period. Based on these release profiles, a release kinetics model was used to further quantify the effect of biotinylation of PLGA microparticles on their release characteristics by quantitatively extracting the effective drug diffusivity and drug desorption rate from the release profiles. It was found that the biotinylation of the PLGA microparticles slowed down both the drug desorption and drug diffusion process, which confirmed that biotinylated PLGA microparticles can be used for controlled drug release. The presented technology, as well as the proposed integrated experimental and modeling approach, forms a solid foundation for future studies using a cell-specific ligand that can be attached to avidin and incorporated onto the microparticles for targeted delivery.

Engineered silica nanocarriers as a high-payload delivery vehicle for antioxidant enzymes

Antioxidant enzymes for the treatment of oxidative stress-related diseases remain a highly promising therapeutic approach. As poor localization and stability have been the greatest challenges to their clinical translation, a variety of nanocarrier systems have been developed to directly address these limitations. In most cases, there has been a trade-off between the delivered mass of enzyme loaded and the carrier's ability to protect the enzyme from proteolytic degradation. One potential method of overcoming this limitation is the use of ordered mesoporous silica materials as potential antioxidant enzyme nanocarriers. The present study compared the loading, activity and retention activity of an anti-oxidant enzyme, catalase, on four engineered mesoporous silica types: non-porous silica particles, spherical silica particles with radially oriented pores and hollow spherical silica particles with pores oriented either parallel to the hollow core or expanded, interconnected bimodal pores. All these silica types, except non-porous silica, displayed potential for effective catalase loading and protection against the proteolytic enzyme, pronase. Hollow particles with interconnected pores exhibit protein loading of up to 50 wt.% carrier mass, while still maintaining significant protection against proteolysis.

Targeted interception of signaling reactive oxygen species in the vascular endothelium

Reactive oxygen species (ROS) are implicated as injurious and as signaling agents in human maladies including inflammation, hyperoxia, ischemia-reperfusion and acute lung injury. ROS produced by the endothelium play an important role in vascular pathology. They quench, for example, nitric oxide, and mediate pro-inflammatory signaling. Antioxidant interventions targeted for the vascular endothelium may help to control these mechanisms. Animal studies have demonstrated superiority of targeting ROS-quenching enzymes catalase and superoxide dismutase to endothelial cells over nontargeted formulations. A diverse arsenal of targeted antioxidant formulations devised in the last decade shows promising results for specific quenching of endothelial ROS. In addition to alleviation of toxic effects of excessive ROS, these targeted interventions suppress pro-inflammatory mechanisms, including endothelial cytokine activation and barrier disruption. These interventions may prove useful in experimental biomedicine and, perhaps, in translational medicine.

Nanocarriers for vascular delivery of antioxidants

Antioxidant enzymes (AOEs) catalase and superoxide dismutase (SOD) detoxify harmful reactive oxygen species, but the therapeutic utility of AOEs is hindered by inadequate delivery. AOE modification by poly-ethylene glycol (PEG) and encapsulation in PEG-coated liposomes increases the AOE bioavailability and enhances protective effects in animal models. Pluronic-based micelles formed with AOEs show even more potent protective effects. Furthermore, polymeric nanocarriers (PNCs) based on PEG-copolymers protect encapsulated AOEs from proteolysis and improve delivery to the target cells, such as the endothelium lining the vascular lumen. Antibodies to endothelial determinants conjugated to AOEs or AOE carriers provide targeting and intracellular delivery. Targeted liposomes, protein conjugates and magnetic nanoparticles deliver AOEs to sites of vascular oxidative stress in the cardiovascular, pulmonary and nervous systems. Further advances in nanodevices for AOE delivery will provide a basis for the translation of this approach in the clinical domain.

Cross-linked antioxidant nanozymes for improved delivery to CNS

Formulations of antioxidant enzymes, superoxide dismutase 1 (SOD1, also known as Cu/Zn SOD) and catalase were prepared by electrostatic coupling of enzymes with cationic block copolymers, polyethyleneimine-poly(ethylene glycol) or poly(L-lysine)-poly(ethylene glycol), followed by covalent cross-linking to stabilize nanoparticles (NPs). Different cross-linking strategies (using glutaraldehyde, bis-(sulfosuccinimidyl)suberate sodium salt or 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride with N-hydroxysulfosuccinimide) and reaction conditions (pH and polycation/protein charge ratio) were investigated that allowed immobilizing active enzymes in cross-linked NPs, termed "nanozymes." Bienzyme NPs, containing both SOD1 and catalase were also formulated. Formation of complexes was confirmed using denaturing gel electrophoresis and western blotting; physicochemical characterization was conducted using dynamic light scattering and atomic force microscopy. In vivo studies of (125)I-labeled SOD1-containing nanozymes in mice demonstrated their increased stability in both blood and brain and increased accumulation in brain tissues, in comparison with non-cross-linked complexes and native SOD1. Future studies will evaluate the potential of these formulations for delivery of antioxidant enzymes to the central nervous system to attenuate oxidative stress associated with neurological diseases.

FROM THE CLINICAL EDITOR

Formulations of antioxidant enzyme complexes were demonstrated along with their increased stability in both blood and brain and increased accumulation in CNS tissue. Future studies will evaluate the potential of these formulations for antioxidant enzyme deliver to the CNS to attenuate oxidative stress in neurodegenerative diseases.