Vascular Drug Delivery Using Carrier Red Blood Cells: Focus on RBC Surface Loading and Pharmacokinetics

Dextran-Mimetic Quantum Dots for Multimodal Macrophage Imaging In Vivo, Ex Vivo, and In Situ

Macrophages are white blood cells with diverse functions contributing to a healthy immune response as well as the pathogenesis of cancer, osteoarthritis, atherosclerosis, and obesity. Due to their pleiotropic and dynamic nature, tools for imaging and tracking these cells at scales spanning the whole body down to microns could help to understand their role in disease states. Here we report fluorescent and radioisotopic quantum dots (QDs) for multimodal imaging of macrophage cells in vivo, ex vivo, and in situ. Macrophage specificity is imparted by click-conjugation to dextran, a biocompatible polysaccharide that natively targets these cell types. The emission spectral band of the crystalline semiconductor core was tuned to the near-infrared for optical imaging deep in tissue, and probes were covalently conjugated to radioactive iodine for nuclear imaging. The performance of these probes was compared with all-organic dextran probe analogues in terms of their capacity to target macrophages in visceral adipose tissue using in vivo positron emission tomography/computed tomography (PET/CT) imaging, in vivo fluorescence imaging, ex vivo fluorescence, post-mortem isotopic analyses, and optical microscopy. All probe classes exhibited equivalent physicochemical characteristics in aqueous solution and similar in vivo targeting specificity. However, dextran-mimetic QDs provided enhanced signal-to-noise ratio for improved optical quantification, long-term photostability, and resistance to chemical fixation. In addition, the vascular circulation time for the QD-based probes was extended 9-fold compared with dextran, likely due to differences in conformational flexibility. The enhanced photophysical and photochemical properties of dextran-mimetic QDs may accelerate applications in macrophage targeting, tracking, and imaging across broad resolution scales, particularly advancing capabilities in single-cell and single-molecule imaging and quantification.

Biophysical targeting of high-risk cerebral aneurysms

Localized delivery of diagnostic/therapeutic agents to cerebral aneurysms, lesions in brain arteries, may offer a new treatment paradigm. Since aneurysm rupture leading to subarachnoid hemorrhage is a devastating medical emergency with high mortality, the ability to noninvasively diagnose high-risk aneurysms is of paramount importance. Moreover, treatment of unruptured aneurysms with invasive surgery or minimally invasive neurointerventional surgery poses relatively high risk and there is presently no medical treatment of aneurysms. Here, leveraging the endogenous biophysical properties of brain aneurysms, we develop particulate carriers designed to localize in aneurysm low-shear flows as well as to adhere to a diseased vessel wall, a known characteristic of high-risk aneurysms. We first show, in an in vitro model, flow guided targeting to aneurysms using micron-sized (2 μm) particles, that exhibited enhanced targeting (>7 folds) to the aneurysm cavity while smaller nanoparticles (200 nm) showed no preferable accumulation. We then functionalize the microparticles with glycoprotein VI (GPVI), the main platelet receptor for collagen under low-medium shear, and study their targeting in an in vitro reconstructed patient-specific aneurysm that contained a disrupted endothelium at the cavity. Results in this model showed that GPVI microparticles localize at the injured aneurysm an order of magnitude (>9 folds) more than control particles. Finally, effective targeting to aneurysm sites was also demonstrated in an in vivo rabbit aneurysm model with a disrupted endothelium. Altogether, the presented biophysical strategy for targeted delivery may offer new treatment opportunities for cerebral aneurysms.

Inspiring biomimetic system based on red blood cell membrane vesicles for effective curcumin loading and release

The aim of this study is to introduce an inspiring biomimetic system based on the red blood cell membrane (RBCM) vesicles for improved encapsulation efficiency and release of curcumin (Cur). Here, the role of the sonication time (0.5, 1.5, 3 and 5 min) on the properties of RBCM-CUR vesicles is investigated. It is determined that the hydrodynamic vesicle size, zeta potential, and release behavior are tunable by changing the sonication time. Noticeably, the average size of vesicles decreased from 163.0 ± 21 nm to 116.3 ± 16 nm by increasing the sonication time from 0.5 to 5 min. Moreover, the drug release value, after 24 h incubation, enhances from 57 to 99% with the expansion of sonication from 0.5 to 5 min. Additionally, the entrapment efficiency of Cur as a model drug is high in whole sonication time, owing to the amphiphilic nature of RBCM. Finally, the RBCM-CUR vesicles are not only cytocompatible, but also could support the attachment and proliferation of fibroblast cells in vitro. The RBCM based system for delivery of Cur could be a promising system for the wound healing applications.

RBC-hitchhiking chitosan nanoparticles loading methylprednisolone for lung-targeting delivery

Hyper-inflammation associated with cytokine storm syndrome causes high mortality in patients with COVID-19. Glucocorticoids, such as methylprednisolone sodium succinate (MPSS), effectively inhibit this inflammatory response. However, frequent and chronic administration of glucocorticoids at high doses leads to hormone dependence and serious side effects. The aim of the present study was to combine nanoparticles with erythrocytes for the targeted delivery of MPSS to the lungs. Chitosan nanoparticles loading MPSS (MPSS-CSNPs) were prepared and adsorbed on the surface of red blood cells (RBC-MPSS-CSNPs) by non-covalent interaction. In vivo pharmacokinetic study indicated that RBC-hitchhiking could significantly reduce the plasma concentration of the drug and prolong the circulation time. The mean residence time (MRT) and area under the curve (AUC) of the RBC-MPSS-CSNPs group were significantly higher than those of the MPSS-CSNPs group and the MPSS injection group. Moreover, in vivo imaging and tissue distribution indicated that RBC-hitchhiking facilitated the accumulation of nanoparticles loading fluorescein in the lung, preventing uptake of these nanoparticles by the liver. Furthermore, compared with the MPSS-CSNPs and MPSS treatment groups, treatment with RBC-MPSS-CSNPs considerably inhibited the production of inflammatory cytokines such as TNF-α and IL-6, and consequently attenuated lung injury induced by lipopolysaccharide in rats. Therefore, RBC-hitchhiking is a potentially effective strategy for the delivery of nanoparticles to the lungs for the treatment of acute lung injury and acute respiratory distress syndrome.

Uptake of oxidative stress-mediated extracellular vesicles by vascular endothelial cells under low magnitude shear stress

Extracellular vesicles (EVs) are increasingly used as delivery vehicles for drugs and bioactive molecules, which usually require intravascular administration. The endothelial cells covering the inner surface of blood vessels are susceptible to the shear stress of blood flow. Few studies demonstrate the interplay of red blood cell-derived EVs (RBCEVs) and endothelial cells. Thus, the phagocytosis of EVs by vascular endothelial cells during blood flow needs to be elucidated. In this study, red blood cell-derived extracellular vesicles (RBCEVs) were constructed to investigate endothelial cell phagocytosis in vitro and animal models. Results showed that low magnitude shear stress including low shear stress (LSS) and oscillatory shear stress (OSS) could promote the uptake of RBCEVs by endothelial cells in vitro. In addition, in zebrafish and mouse models, RBCEVs tend to be internalized by endothelial cells under LSS or OSS. Moreover, RBCEVs are easily engulfed by endothelial cells in atherosclerotic plaques exposed to LSS or OSS. In terms of mechanism, oxidative stress induced by LSS is part of the reason for the increased uptake of endothelial cells. Overall, this study shows that vascular endothelial cells can easily engulf EVs in areas of low magnitude shear stress, which will provide a theoretical basis for the development and utilization of EVs-based nano-drug delivery systems in vivo.

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We recently reported that endothelial cells were amateur phagocytic cells for RBCEVs engulfment.

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Low magnitude shear stress (LSS and OSS) can increase the uptake of RBCEVs by endothelial cells in vitro and in vivo.

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ROS induced by low magnitude shear stress acts as an accelerator to enhance endothelial cells uptake of RBCEVs.

Red blood cells: The metamorphosis of a neglected carrier into the natural mothership for artificial nanocarriers

Drug delivery research pursues many types of carriers including proteins and other macromolecules, natural and synthetic polymeric structures, nanocarriers of diverse compositions and cells. In particular, liposomes and lipid nanoparticles represent arguably the most advanced and popular human-made nanocarriers, already in multiple clinical applications. On the other hand, red blood cells (RBCs) represent attractive natural carriers for the vascular route, featuring at least two distinct compartments for loading pharmacological cargoes, namely inner space enclosed by the plasma membrane and the outer surface of this membrane. Historically, studies of liposomal drug delivery systems (DDS) astronomically outnumbered and surpassed the RBC-based DDS. Nevertheless, these two types of carriers have different profile of advantages and disadvantages. Recent studies showed that RBC-based drug carriers indeed may feature unique pharmacokinetic and biodistribution characteristics favorably changing benefit/risk ratio of some cargo agents. Furthermore, RBC carriage cardinally alters behavior and effect of nanocarriers in the bloodstream, so called RBC hitchhiking (RBC-HH). This article represents an attempt for the comparative analysis of liposomal vs RBC drug delivery, culminating with design of hybrid DDSs enabling mutual collaborative advantages such as RBC-HH and camouflaging nanoparticles by RBC membrane. Finally, we discuss the key current challenges faced by these and other RBC-based DDSs including the issue of potential unintended and adverse effect and contingency measures to ameliorate this and other concerns.

Clinical progress and advanced research of red blood cells based drug delivery system

Red blood cells (RBCs) are biocompatible carriers that can be employed to deliver different bioactive substances. In the past few decades, many strategies have been developed to encapsulate or attach drugs to RBCs. Osmotic-based encapsulation methods have been industrialized recently, and some encapsulated RBC formulations have reached the clinical stage for treating tumors and neurological diseases. Inspired by the intrinsic properties of intact RBCs, some advanced delivery strategies have also been proposed. These delivery systems combine RBCs with other novel systems to further exploit and expand the application of RBCs. This review summarizes the clinical progress of drugs encapsulated into intact RBCs, focusing on the loading and clinical trials. It also introduces the latest advanced research based on developing prospects and limitations of intact RBCs drug delivery system (DDS), hoping to provide a reference for related research fields and further application potential of intact RBCs based drug delivery system.

Asparaginyl Ligase-Catalyzed One-Step Cell Surface Modification of Red Blood Cells

Red blood cells (RBCs) can serve as vascular carriers for drugs, proteins, peptides, and nanoparticles. Human RBCs remain in the circulation for ∼120 days, are biocompatible, and are immunologically largely inert. RBCs are cleared by the reticuloendothelial system and can induce immune tolerance to foreign components attached to the RBC surface. RBC conjugates have been pursued in clinical trials to treat cancers and autoimmune diseases and to correct genetic disorders. Still, most methods used to modify RBCs require multiple steps, are resource-intensive and time-consuming, and increase the risk of inflicting damage to the RBCs. Here, we describe direct conjugation of peptides and proteins onto the surface of RBCs in a single step, catalyzed by a highly efficient, recombinant asparaginyl ligase under mild, physiological conditions. In mice, the modified RBCs remain intact in the circulation, display a normal circulatory half-life, and retain their immune tolerance-inducing properties, as shown for protection against an accelerated model for type 1 diabetes. We conjugated different nanobodies to RBCs with retention of their binding properties, and these modified RBCs can target cancer cells in vitro. This approach provides an appealing alternative to current methods of RBC engineering. It provides ready access to more complex RBC constructs and highlights the general utility of asparaginyl ligases for the modification of native cell surfaces.

Hemocompatibility and Hemolytic Effects of Functionalized Nanoparticles on Red Blood Cells: A Recent Review Study

In this paper (from 2010 to 2020), the effects of polymeric, metallic and nonmetallic nanoparticles on red blood cells’ hemocompatibility were investigated for the first time. Here, we have considered the latest findings which can help to improve the hemocompatibility of RBCs. It is important to maintain the quality of red blood cells for improving the hemocompatibility because blood products directly affect the health of patients after blood transfusion. Although RBCs can be stored for up to 42 days at 2–6∘C, hypothermic storage lesions (HSLs) are very common in these products. This problem affects the quality of RBC products. Thus, it is necessary to modify the surface molecules of RBCs during storage time to reduce HSLs and alloimmunization complications. Therefore, we reviewed the reported effects of polymeric, metallic and carbon-based nanoparticles on RBCs between 2010 and 2020. The results of our study have shown that the use of negatively charged dendrimers, unsaturated/uncharged liposomes, and PEGylated forms of NPs and RBCs are the best approaches to improve the hemocompatibility conditions of red blood cells. However, large cationic dendrimers, liposomes composed of saturated lipid with long acyl chain, and cationic chitosan nanoparticles have less RBC compatibility. In addition, polymeric nanoparticles have more capacity for surface modification, which makes it possible to make more hemocompatible derivatives. Among metallic nanoparticles, gold and iron nanoparticles were more RBC compatible. However, the smaller size, higher concentration and longer exposure time of these nanoparticles can induce hemolysis and morphological changes in RBCs. On the other side, nonmetallic nanoparticles mostly had poor RBC compatibility, but their effects on RBCs strongly depended on their concentration and physicochemical properties and could be controllable. As a result, the use of polyethylene glycol (PEG), gold, polymeric, and iron nanoparticles in the design of protocols to maintain the survival, structure and activity of red blood cells for improving hemocompatibility can be more effective.

Surface loading of nanoparticles on engineered or natural erythrocytes for prolonged circulation time: strategies and applications

Nano drug-delivery systems (DDS) may significantly improve efficiency and reduce toxicity of loaded drugs, but a few nano-DDS are highly successful in clinical use. Unprotected nanoparticles in blood flow are often quickly cleared, which could limit their circulation time and drug delivery efficiency. Elongating their blood circulation time may improve their delivery efficiency or grant them new therapeutic possibilities. Erythrocytes are abundant endogenous cells in blood and are continuously renewed, with a long life span of 100-120 days. Hence, loading nanoparticles on the surface of erythrocytes to protect the nanoparticles could be highly effective for enhancing their in vivo circulation time. One of the key questions here is how to properly attach nanoparticles on erythrocytes for different purposes and different types of nanoparticles to achieve ideal results. In this review, we describe various methods to attach nanoparticles and drugs to the erythrocyte surface, and discuss the key factors that influence the stability and circulation properties of the erythrocytes-based delivery system in vivo. These data show that using erythrocytes as a host for nanoparticles possesses great potential for further development.

In vitro characterization of engineered red blood cells as viral traps against HIV-1 and SARS-CoV-2

Engineered red blood cells (RBCs) expressing viral receptors could be used therapeutically as viral traps, as RBCs lack nuclei and other organelles required for viral replication. However, expression of viral receptors on RBCs is difficult to achieve since mature erythrocytes lack the cellular machinery to synthesize proteins. Herein, we show that the combination of a powerful erythroid-specific expression system and transgene codon optimization yields high expression levels of the HIV-1 receptors CD4 and CCR5, as well as a CD4-glycophorin A (CD4-GpA) fusion protein in erythroid progenitor cells, which efficiently differentiated into enucleated RBCs. HIV-1 efficiently entered RBCs that co-expressed CD4 and CCR5, but viral entry was not required for neutralization, as CD4 or CD4-GpA expression in the absence of CCR5 was sufficient to potently neutralize HIV-1 and prevent infection of CD4+ T cells in vitro due to the formation of high-avidity interactions with trimeric HIV-1 Env spikes on virions. To facilitate continuous large-scale production of RBC viral traps, we generated erythroblast cell lines stably expressing CD4-GpA or ACE2-GpA fusion proteins, which produced potent RBC viral traps against HIV-1 and SARS-CoV-2. Our in vitro results suggest that this approach warrants further investigation as a potential treatment against acute and chronic viral infections.

Nucleic Acid Delivery with Red-Blood-Cell-Based Carriers

Gene therapy has the potential to become a staple of 21st-century medicine. However, to overcome the limitations of existing gene-delivery therapies, that is, poor stability and inefficient and delivery and accumulation of nucleic acids (NAs), safe drug-delivery systems (DDSs) allowing the prolonged circulation and expression of the administered genes in vivo are needed. In this review article, the development of DDSs over the past 70 years is briefly described. Since synthetic DDSs can be recognized and eliminated as foreign substances by the immune system, new approaches must be found. Using the body's own cells as DDSs is a unique and exciting strategy and can be used in a completely new way to overcome the critical limitations of existing drug-delivery approaches. Among the different circulatory cells, red blood cells (RBCs) are the most abundant and thus can be isolated in sufficiently large quantities to decrease the complexity and cost of the treatment compared to other cell-based carriers. Therefore, in the second part, this article describes 70 years of research on the development of RBCs as DDSs, covering the most important RBC properties and loading methods. In the third part, it focuses on RBCs as the NA delivery system with advantages and drawbacks discussed to decide whether they are suitable for NA delivery in vivo.

Mechanisms of thrombosis and research progress on targeted antithrombotic drugs

Globally, the incidence of thromboembolic diseases has increased in recent years, accompanied by an increase in patient mortality. Currently, several targeting delivery strategies have been developed to treat thromboembolic diseases. In this review, we discuss the mechanisms of thrombolysis and current anticoagulant drugs, particularly those with targeting capability, highlighting advances in the accurate treatment of thrombolysis with fewer adverse effects. Such approaches include magnetic drug-loading systems combined with molecular imaging to recanalize blood vessels and systems based on chimeric Arg-Gly-Asp (RGD) sequences that can target platelet glycoprotein receptor. With such progress in targeted antithrombotic drugs, targeted thrombolysis treatment shows significant potential benefit for patients.

In vivo nano-biosensing element of red blood cell-mediated delivery

Biosensors based on nanotechnology are developing rapidly and are widely applied in many fields including biomedicine, environmental monitoring, national defense and analytical chemistry, and have achieved vital positions in these fields. Novel nano-materials are intensively developed and manufactured for potential biosensing and theranostic applications while lacking comprehensive assessment of their potential health risks. The integration of diagnostic in vivo biosensors and the DDSs for delivery of therapeutic drugs holds an enormous potential in next-generation theranostic platforms. Controllable, precise, and safe delivery of diagnostic biosensing devices and therapeutic agents to the target tissues, organs, or cells is an important determinant in developing advanced nanobiosensor-based theranostic platforms. Particularly, inspired by the comprehensive biological investigations on the red blood cells (RBCs), advanced strategies of RBC-mediated in vivo delivery have been developed rapidly and are currently in different stages of transforming from research and design to pre-clinical and clinical investigations. In this review, the RBC-mediated delivery of in vivo nanobiosensors for applications of bio-imaging at the single-cell level, advanced medical diagnostics, and analytical detection of biomolecules and cellular activities are presented. A comprehensive perspective of the technical framework of the state-of-the-art RBC-mediated delivery systems is explained in detail to inspire the design and implementation of advanced nanobiosensor-based theranostic platforms taking advantage of RBC-delivery modalities.

Red blood cell hitchhiking enhances the accumulation of nano- and micro-particles in the constriction of a stenosed microvessel

We investigate the circulation of nano- and micro-particles, including spherical particles and filamentous nanoworms, with red blood cells (RBCs) suspension in a constricted channel that mimics a stenosed microvessel. Through three-dimensional simulations using the immersed boundary-based Lattice Boltzmann method, the influence of channel geometries, such as the length and ratio of the constriction, on the accumulation of particles is systematically studied. Firstly, we find that the accumulation of spherical particles with 1 μm diameter in the constriction increases with the increases of both the length and ratio of the constriction. This is attributed to the interaction between spheres and RBCs. The RBCs "carry" the spheres and they accumulate inside the constriction together, due to the altered local hydrodynamics induced by the existence of the constriction. Secondly, nanoworms demonstrate higher accumulation than that of spheres inside the constriction, which is associated with the escape of nanoworms from RBC clusters and their accumulation near the wall of main channel. The accumulated near-wall nanoworms will eventually enter the constriction, thus enhancing their concentration inside the constriction. However, an exceptional case occurs in the case of constrictions with large ratio and long length. In such circumstances, the RBCs aggregate together tightly and concentrate at the center of the channel, which makes the nanoworms hardly able to escape from RBC clusters, leading to a similar accumulation of nanoworms and spheres inside the constriction. This study may provide theoretical guidance for the design of nano- and micro-particles for biomedical engineering applications, such as drug delivery systems for patients with stenosed microvessels.

Immunocyte Membrane-Coated Nanoparticles for Cancer Immunotherapy

Despite the advances in surface bioconjugation of synthetic nanoparticles for targeted drug delivery, simple biological functionalization is still insufficient to replicate complex intercellular interactions naturally. Therefore, these foreign nanoparticles are inevitably exposed to the immune system, which results in phagocytosis by the reticuloendothelial system and thus, loss of their biological significance. Immunocyte membranes play a key role in intercellular interactions, and can protect foreign nanomaterials as a natural barrier. Therefore, biomimetic nanotechnology based on cell membranes has developed rapidly in recent years. This paper summarizes the development of immunocyte membrane-coated nanoparticles in the immunotherapy of tumors. We will introduce several immunocyte membrane-coated nanocarriers and review the challenges to their large-scale preparation and application.

Preclinical developments of enzyme-loaded red blood cells

INTRODUCTION

Therapeutic enzymes are currently used in the treatment of several diseases. In most cases, the benefits are limited due to poor in vivo stability, immunogenicity, and drug-induced inactivating antibodies. A partial solution to the problem is obtained by masking the therapeutic protein by chemical modifications. Unfortunately, this is not a satisfactory solution because frequent adverse events, including anaphylaxis, can arise.

AREA COVERED

Among the delivery systems, we focused on red blood cells for the delivery of therapeutic enzymes. Erythrocytes possess a long circulation time, a reduced immunogenicity, there is no need of chemical modifications and the encapsulated enzyme remains active because it is protected by the cell membrane. Here we discuss some representative applications of the preclinical developments of the field. Some of these are currently in clinic, others are approaching the clinic and others are illustrative of the development process. The selected examples are not always the most recent, but they are the most useful for a comparative approach.

EXPERT OPINION

The results discussed confirm the central role that red blood cells can play in the treatment of several conditions and suggest the benefit in using a natural cellular carrier in terms of pharmacokinetic, biodistribution, safety, and efficacy.

A potential hypothesis for 2019-nCoV infection therapy through delivery of recombinant ACE2 by red blood cell-hitchhiking

A novel infectious disease, caused by 2019 Novel Coronavirus (2019-nCoV) is responsible for the recent outbreak of severe respiratory disease. The 2019-nCoV spread rapidly and reaching epidemic proportions in many countries of the world. ACE2 was identified as a key receptor for 2019-nCoV infections. Excessive form of soluble ACE2 rescues cellular ACE2 activity which has a protective role in acute lung failure and neutralizes the virus. The short half-life of ACE2 is a major limitation to its practical application. Nanoparticle-based drug delivery systems are one of the most widely investigated approaches for developing novel therapies for a variety of diseases. Nevertheless, nanoparticles suffer from the rapid removal from the bloodstream by the reticuloendothelial system (RES). A noncovalent attachment of nanoparticles to RBCs increases their half-life in blood and allows transient accumulation in the lungs, while decreases their uptake by the liver and spleen. Connecting the recombinant ACE2 into the surface of nanoparticles that were attached to RBCs can be a potential therapeutic approach for 2019-nCoV infection through increasing their lung targeting to naturalize the virus and also acting as a bioreactor in the blood circulation to decrease serum level of Angiotensin II and protects lungs from injury/ARDS.

Red blood cell-hitchhiking chitosan nanoparticles for prolonged blood circulation time of vitamin K1

Nanocarriers have been extensively applied for intravascular drug delivery. However, rapid clearance from circulation by mononuclear phagocyte system has limited their applications. Erythrocytes carriers are potential solutions to overcome the limitations of nanocarriers and considered to be ideal natural carriers for drug delivery because of their unique properties. The purpose of this work is to combine nanocarriers with erythrocytes carriers for sustained release and prolonged circulation time of vitamin K₁. Chitosan nanoparticles loading VK₁ (VK-CSNPs) were prepared using ionotropic gelation method, which was optimized using box-behnken design and response surface methodology. VK-CSNPs adsorbed onto red blood cells (RBC-VK-CSNPs) rapidly via electrostatic interactions. The exposure of phosphatidylserine, osmotic fragility and turbulence fragility of RBC loading nanoparticles were investigated to study the toxicity of nanoparticles to erythrocytes. In vivo pharmacokinetic study indicated that C_max, AUC and MRT of RBC-VK-CSNPs group were remarkably higher than that of VK-CSNPs group. Flow cytometry showed VK-CSNPs steadily retained on the surface of RBC for a long time without affecting the circulation profiles of RBC themselves. The nanoparticles carried on RBC released drug, desorbed and were eliminated in vivo. Therefore, the circulation time of RBC-hitchhiking chitosan nanoparticles was greatly prolonged compared with nanoparticles alone. RBC-hitchhiking could be a valuable hybrid strategy for prolonging the in vivo life of nanocarriers.

Williams G, Brocchini S, Awwad S. Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.