PEGylated nanomedicines: recent progress and remaining concerns

Introduction: Recent biopharma deals related to nanocarrier drug delivery technologies highlight the emergence of nanomedicine. This is perhaps an expected culmination of many years of research demonstrating the potential of nanomedicine as the next generation of therapeutics with improved performance. PEGylated nanocarriers play a key role within this field.

Areas covered: The drug delivery advantages of nanomedicines in general are discussed, focusing on nanocarriers and PEGylated nanomedicines, including products under current development/clinical evaluation. Well-established drug delivery benefits of PEGylation (e.g., prolonged circulation) are only briefly covered. Instead, attention is deliberately made to less commonly reported advantages of PEGylation, including mucosal delivery of nanomedicines. Finally, some of the issues related to the safety of PEGylated nanomedicines in clinical application are discussed.

Expert opinion: The advent of nanomedicine providing therapeutic options of refined performance continues. Although PEGylation as a tool to improve the pharmacokinetics of nanomedicines is well established and is used clinically, other benefits of ‘PEGnology', including enhancement of physicochemical properties and/or biocompatibility of actives and/or drug carriers, as well as mucosal delivery, have attracted less attention. While concerns regarding the clinical use of PEGylated nanomedicines remain, evidence suggests that at least some safety issues may be controlled by adequate designs of nanosystems.     

Structure and biological activity of pathogen-like synthetic nanomedicines

Here we characterize the structure, stability and intracellular mode of action of DermaVir nanomedicine that is under clinical development for the treatment of HIV/AIDS. This nanomedicine comprises pathogen-like pDNA/PEIm nanoparticles (NPs) having the structure and function resembling spherical viruses that naturally evolved to deliver nucleic acids to the cells. Atomic force microscopy demonstrated spherical 100 - 200 nm NPs with a smooth polymer surface protecting the pDNA in the core. Optical absorption determined both the NP structural stability and biological activity relevant to their ability to escape from the endosome and release the pDNA at the nucleus. Salt, pH and temperature influence nanomedicine shelf-life and intracellular stability. This approach facilitates the development of diverse polyplex nanomedicines where the delivered pDNA-expressed antigens induce immune responses to kill infected cells. FROM THE CLINICAL EDITOR: The authors investigated DermaVir nanomedicine comprised of pathogen-like pDNA/PEIm nanoparticles with structure and function resembling spherical viruses. DermaVir delivery of pDNA expresses antigens that induce immune responses to kill HIV infected cells.     

The Growing Field of Nanomedicine and Its Relevance to Pharmacy Curricula

The field of nanomedicine is a rapidly growing scientific domain. Nanomedicine encompasses a diverse number of active pharmaceutical ingredients. Submissions of Investigational New Drugs and New Drug Applications have risen dramatically over the last decade. There are over 50 nanomedicines approved for use by the US Food and Drug Administration (FDA). Because of the fundamental role pharmacists will play in therapeutic and administrative decisions regarding nanomedicines, it is imperative for future pharmacists to gain exposure early in their training to this rapidly evolving class of drugs. This commentary describes nanomedicines, discusses current regulatory challenges, and provides recommendations for judicious incorporation of nanomedicine topics into the Doctor of Pharmacy curriculum based on emerging pharmaceutical and clinical science applications.     

“Alternative” endocytic mechanisms exploited by pathogens: New avenues for therapeutic delivery?

Some pathogens utilize unique routes to enter cells that may evade the intracellular barriers encountered by the typical clathrin-mediated endocytic pathway. Retrograde transport and caveolar uptake are among the better characterized pathways, as alternatives to clathrin-mediated endocytosis, that are known to facilitate entry of pathogens and potential delivery agents. Recent characterization of the trafficking mechanisms of prion proteins and certain bacteria may present new paradigms for strategizing improvements in therapeutic spread and retention of therapy. This review will provide an overview of such endocytic pathways, and discuss current and future possibilities in using these routes as a means to improve therapeutic delivery.     

Polyplexes traffic through caveolae to the Golgi and endoplasmic reticulum en route to the nucleus

The cellular machinery involved in the internalization of nonviral gene carriers and their subsequent trafficking to the nucleus directly impacts their therapeutic efficiency. Hence, identifying key endocytic pathways and organelles that contribute to the successful transfer of polyplexes to the nucleus generates new opportunities for improving carrier design. Previously, we showed that histone H3 tail peptides encoding a sequence known to participate in chromatin activation exhibit synergistic gene delivery activity with poly(ethylenimine) (PEI). Polyplexes containing H3 and PEI exhibited a reduced dependence on endocytic pathways that trafficked to lysosomes, and had enhanced sensitivity to an inhibitor associated with retrograde trafficking through the Golgi apparatus. Thus, we sought to determine whether caveolar uptake and transport through the Golgi and/or endoplasmic reticulum (ER) preceded nuclear delivery. By the use of a panel of chemical endocytic inhibitors, we determined that H3 polyplexes utilized caveolar pathways to a greater degree than PEI polyplexes. Caveolae-mediated endocytosis was found to be a productive route for gene expression by the H3/PEI-pDNA polyplexes, consistent with previous studies of polymer-mediated gene delivery. Additionally, the polyplexes substantially colocalized within the ER after only 5 min of incubation, and utilized retrograde Golgi-to-ER pathways at levels similar to pathogens known to traffic by these routes during infection. The results of this study have expanded our understanding of how caveolar polyplexes are trafficked to cell nuclei, and provide new evidence for the role of Golgi-ER pathways in transfection. These findings suggest new design criteria and opportunities to stragetically target nonviral gene delivery vehicles.     

Intracellular trafficking pathways and drug delivery: fluorescence imaging of living and fixed cells

Cellular processes depend on the fidelity of intracellular membrane traffic. Lipids, proteins, receptor ligands and solute molecules are trafficked to distinct compartments within the cell through both the biosynthetic and endocytic pathways. An appreciation of these pathways is vital for a complete understanding of intracellular drug delivery. Recent advances in fluorescence imaging have facilitated the analysis of these pathways in great detail. It is now possible to gain insight into the real-time dynamics of cellular components and macromolecular pharmacological agents as they are delivered into and traffic within single cells. Here, we discuss the analysis of intracellular drug delivery from the perspective of fluorescence imaging of both living and fixed cells. This review aims to cover trafficking pathways, markers for subcellular compartments, fluorescent labels for intracellular structures and pharmacological agents and relevant recent developments in imaging technology. In particular, we shall focus on the application of live cell imaging to the study of endocytic drug delivery.     

Delivery of biologics to select organelles--the role of biologically active polymers

Biologics (i.e., nucleic acid and protein-based drugs) suffer from poor bioavailability, as membrane partitioning and intracellular targeting are a significant problem. Various strategies have been developed in an attempt to modulate biologics bioavailability by means of manipulating whole body pharmacokinetics and subcellular trafficking. Limited direct success has been observed. This review focuses on the components of nanomedicine systems rather than the whole, facilitating an overview of materials that may be of clinical relevance in the future. Some of the advantages and disadvantages associated with the use of soluble drug delivery systems are considered. Although the focus is on linear poly(amidoamine) polymers, emerging technologies capable of the delivery of large molecules to other specific intracellular compartments are also examined. The focus is maintained on cytosolic access for two reasons, initially because this intracellular compartment may be viewed as a 'gateway' to other intracellular organelles and also because this is where the greatest therapeutic benefit is likely to be found. It is likely that in the coming years and in combination with other existing, well-characterized drug delivery platform technologies, such as liposomal formulation or polymer conjugation, that the targeting of specific organelles will become more accessible.     

Rab GTPases, membrane trafficking and diseases

The Rab family of GTPases contains over 60 genes in the human genome and contributes to regulation of intracellular membrane trafficking along endocytic and exocytic pathways as well as specialized pathways in specific cell types. It has become increasingly clear that disruption of the intracellular membrane trafficking system at different stages can cause various diseases. In the past decade, altered expression levels and mutations of Rab GTPases have been associated with such diseases as cancer, Alzheimer's disease, and various genetic disorders. This review discusses the specific Rab GTPases and their involvement in the diseases.     

Nanomedicine Drug Development: A Scientific Symposium Entitled “Charting a Roadmap to Commercialization”

The use of nanotechnology in medicine holds great promise for revolutionizing a variety of therapies. The past decade witnessed dramatic advancements in scientific research in nanomedicines, although significant challenges still exist in nanomedicine design, characterization, development, and manufacturing. In March 2013, a two-day symposium “Nanomedicines: Charting a Roadmap to Commercialization,” sponsored and organized by the Nanomedicines Alliance, was held to facilitate better understanding of the current science and investigative approaches and to identify and discuss challenges and knowledge gaps in nanomedicine development programs. The symposium provided a forum for constructive dialogue among key stakeholders in five distinct areas: nanomedicine design, preclinical pharmacology, toxicology, CMC (chemistry, manufacturing, and control), and clinical development. In this meeting synopsis, we highlight key points from plenary presentations and focus on discussions and recommendations from breakout sessions of the symposium.     

Can nanomedicines kill cancer stem cells?

Most tumors are heterogeneous and many cancers contain small population of highly tumorigenic and intrinsically drug resistant cancer stem cells (CSCs). Like normal stem cell, CSCs have the ability to self-renew and differentiate to other tumor cell types. They are believed to be a source for drug resistance, tumor recurrence and metastasis. CSCs often overexpress drug efflux transporters, spend most of their time in non-dividing G₀ cell cycle state, and therefore, can escape the conventional chemotherapies. Thus, targeting CSCs is essential for developing novel therapies to prevent cancer relapse and emerging of drug resistance. Nanocarrier-based therapeutic agents (nanomedicines) have been used to achieve longer circulation times, better stability and bioavailability over current therapeutics. Recently, some groups have successfully applied nanomedicines to target CSCs to eliminate the tumor and prevent its recurrence. These approaches include 1) delivery of therapeutic agents (small molecules, siRNA, antibodies) that affect embryonic signaling pathways implicated in self-renewal and differentiation in CSCs, 2) inhibiting drug efflux transporters in an attempt to sensitize CSCs to therapy, 3) targeting metabolism in CSCs through nanoformulated chemicals and field-responsive magnetic nanoparticles and carbon nanotubes, and 4) disruption of multiple pathways in drug resistant cells using combination of chemotherapeutic drugs with amphiphilic Pluronic block copolymers. Despite clear progress of these studies the challenges of targeting CSCs by nanomedicines still exist and leave plenty of room for improvement and development. This review summarizes biological processes that are related to CSCs, overviews the current state of anti-CSCs therapies, and discusses state-of-the-art nanomedicine approaches developed to kill CSCs.     

Synthetic cell surface receptors for delivery of therapeutics and probes

Receptor-mediated endocytosis is a highly efficient mechanism for cellular uptake of membrane-impermeant ligands. Cells use this process to acquire nutrients, initiate signal transduction, promote development, regulate neurotransmission, and maintain homeostasis. Natural receptors that participate in receptor-mediated endocytosis are structurally diverse, ranging from large transmembrane proteins to small glycolipids embedded in the outer leaflet of cellular plasma membranes. Despite their vast structural differences, these receptors share common features of binding to extracellular ligands, clustering in dynamic membrane regions that pinch off to yield intracellular vesicles, and accumulation of receptor-ligand complexes in membrane-sealed endosomes. Receptors typically dissociate from ligands in endosomes and cycle back to the cell surface, whereas internalized ligands are usually delivered into lysosomes, where they are degraded, but some can escape and penetrate into the cytosol. Here, we review efforts to develop synthetic cell surface receptors, defined as nonnatural compounds, exemplified by mimics of cholesterol, that insert into plasma membranes, bind extracellular ligands including therapeutics, probes, and endogenous proteins, and engage endocytic membrane trafficking pathways. By mimicking natural mechanisms of receptor-mediated endocytosis, synthetic cell surface receptors have the potential to function as prosthetic molecules capable of seamlessly augmenting the endocytic uptake machinery of living mammalian cells.     

Role of nanotechnology in targeted drug delivery and imaging: a concise review

The use of nanotechnology in drug delivery and imaging in vivo is a rapidly expanding field. The emphases of this review are on biophysical attributes of the drug delivery and imaging platforms as well as the biological aspects that enable targeting of these platforms to injured and diseased tissues and cells. The principles of passive and active targeting of nanosized carriers to inflamed and cancerous tissues with increased vascular leakiness, overexpression of specific epitopes, and cellular uptake of these nanoscale systems are discussed. Preparation methods-properties of nanoscale systems including liposomes, micelles, emulsions, nanoparticulates, and dendrimer nanocomposites, and clinical indications are outlined separately for drug delivery and imaging in vivo. Taken together, these relatively new and exciting data indicate that the future of nanomedicine is very promising, and that additional preclinical and clinical studies in relevant animal models and disease states, as well as long-term toxicity studies, should be conducted beyond the "proof-of-concept" stage. Large-scale manufacturing and costs of nanomedicines are also important issues to be addressed during development for clinical indications.     

The nanomedicines alliance: an industry perspective on nanomedicines

The field of nanomedicines has expanded significantly in recent years in the breadth of compounds under development as well as in the types of technology that are being applied to generate nanomedicines. The pathway to licensure of new nanomedicines is sufficiently well defined by existing regulations and guidance. The future of nanomedicines requires collaboration between industry and regulatory agencies to ensure that safe and effective nanomedicines emerge from this field.From the Clinical EditorWith the expansion of translational nanomedicine research, the “last steps” of translation, such as making sure all regulatory approvals are met, the availability of appropriate larger-scale production technologies, are becoming critically important. This review provides a perspective from the biomedical and pharmaceutical industry on the above issues.     

Challenges in Development of Nanoparticle-Based Therapeutics

In recent years, nanotechnology has been increasingly applied to the area of drug development. Nanoparticle-based therapeutics can confer the ability to overcome biological barriers, effectively deliver hydrophobic drugs and biologics, and preferentially target sites of disease. However, despite these potential advantages, only a relatively small number of nanoparticle-based medicines have been approved for clinical use, with numerous challenges and hurdles at different stages of development. The complexity of nanoparticles as multi-component three dimensional constructs requires careful design and engineering, detailed orthogonal analysis methods, and reproducible scale-up and manufacturing process to achieve a consistent product with the intended physicochemical characteristics, biological behaviors, and pharmacological profiles. The safety and efficacy of nanomedicines can be influenced by minor variations in multiple parameters and need to be carefully examined in preclinical and clinical studies, particularly in context of the biodistribution, targeting to intended sites, and potential immune toxicities. Overall, nanomedicines may present additional development and regulatory considerations compared with conventional medicines, and while there is generally a lack of regulatory standards in the examination of nanoparticle-based medicines as a unique category of therapeutic agents, efforts are being made in this direction. This review summarizes challenges likely to be encountered during the development and approval of nanoparticle-based therapeutics, and discusses potential strategies for drug developers and regulatory agencies to accelerate the growth of this important field.     

用于肿瘤免疫治疗的细胞膜包裹纳米药物研究进展

免疫治疗是肿瘤治疗领域的革命性进展。然而,现有疗法临床响应率低,其主要原因包括患者的抗肿瘤免疫细胞激活不足、瘤内浸润受限和活性抑制等。纳米药物因其与肿瘤细胞和免疫细胞独特的相互作用,在肿瘤免疫治疗中极具潜力。近年来,为调控纳米药物与肿瘤免疫相关细胞的作用,研究者们用天然或工程化细胞膜对纳米粒进行表面改性,获得的细胞膜包裹纳米药物具有广阔的设计空间和良好的生物相容性,在肿瘤免疫治疗中展现出明显优势。近期研究发现,细胞膜包裹纳米药物能通过一系列免疫应答过程提高抗肿瘤免疫治疗效果,包括促进肿瘤细胞免疫原性死亡、增加抗原递呈、增强T细胞活化、加强T细胞对肿瘤细胞识别以及杀伤能力等。通过对上述研究进行综述为用于肿瘤免疫治疗的细胞膜包裹纳米药物的优化和临床转化提供参考。     

Endocytosis and cationic cell-penetrating peptides--a merger of concepts and methods

With the identification of fixation as a major source of artefacts in the cell biological research on cell-penetrating peptides (CPPs), the past two years have witnessed a dramatic development in the CPP field. At least for some of these molecules, endocytosis is now considered to be the major if not the exclusive route of cellular import. However, endocytosis comprises a variety of different pathways with very different implications for the delivery of bioactive molecules to the cytoplasm and nucleus. The endocytosis of CPPs is governed by complex mechanisms similar to those responsible for the internalization of other molecules. Therefore the investigation of uptake and intracellular trafficking of CPPs can benefit enormously from the understanding of the endocytic machinery as well as from the tools that have already been developed for the analysis of endocytosis. This review will introduce aspects of endocytosis relevant to the analysis of CPPs. In addition to the methods, that have already been used for the analysis of CPP trafficking, we will also present other tools and approaches which can be helpful for the research of CPP uptake. Furthermore this review will analyze and summarize recent data providing new insights in endocytosis and intracellular trafficking of CPPs.     

Exploration and insights into the cellular internalization and intracellular fate of amphiphilic polymeric nanocarriers

The beneficial or deleterious effects of nanomedicines emerge from their complex interactions with intracellular pathways and their subcellular fate. Moreover, the dynamic nature of plasma membrane accounts for the movement of these nanocarriers within the cell towards different organelles thereby not only influencing their pharmacokinetic and pharmacodynamic properties but also bioavailability, therapeutic efficacy and toxicity. Therefore, an in-depth understanding of underlying parameters controlling nanocarrier endocytosis and intracellular fate is essential. In order to direct nanoparticles towards specific sub-cellular organelles the physicochemical attributes of nanocarriers can be manipulated. These include particle size, shape and surface charge/chemistry. Restricting the particle size of nanocarriers below 200 nm contributes to internalization via clathrin and caveolae mediated pathways. Similarly, a moderate negative surface potential confers endolysosomal escape and targeting towards mitochondria, endoplasmic reticulum (ER) and Golgi. This review aims to provide an insight into these physicochemical attributes of nanocarriers fabricated using amphiphilic graft copolymers affecting cellular internalization. Fundamental principles understood from experimental studies have been extrapolated to draw a general conclusion for the designing of optimized nanoparticulate drug delivery systems and enhanced intracellular uptake via specific endocytic pathway.KEY WORDS: Amphiphilic, Copolymer, Nanoparticles, Internalization, Intracellular fate     

纳米药物粒度分析方法

纳米药物在研究和应用领域都在快速发展,根据具体纳米药物的特性,运用合理的分析方法来建立质量标准是一项需要深入研究的重要课题。本文综述了可用于纳米药物质量控制的粒度分析方法,考察了几种重要技术的原理、适用范围、优点和不足。结合不同剂型纳米药物的特性,讨论了各方法在纳米药物分析中的应用,为纳米药物的检测和监管提供借鉴。     

Nanomedicines: From Bench to Bedside and Beyond

Advancing nanomedicines from concept to clinic requires integration of new science with traditional pharmaceutical development. The medical and commercial success of nanomedicines is greatly facilitated when those charged with developing nanomedicines are cognizant of the unique opportunities and technical challenges that these products present. These individuals must also be knowledgeable about the processes of clinical and product development, including regulatory considerations, to maximize the odds for successful product registration. This article outlines these topics with a goal to accelerate the combination of academic innovation with collaborative industrial scientists who understand pharmaceutical development and regulatory approval requirements—only together can they realize the full potential of nanomedicines for patients.     

Cellular delivery of siRNA and antisense oligonucleotides via receptor-mediated endocytosis

INTRODUCTION: There is great potential for antisense and siRNA oligonucleotides to become mainstream therapeutic entities thanks to their high specificity and wide therapeutic target space compared with small molecules. Despite this potential, the pharmacological targets within the cells are less accessible to oligonucleotides that are hydrophilic and often charged. Oligonucleotides access their intracellular targets mainly by means of endocytosis, but only a fraction of them reach their targets, as delivery requires functional synergy of cellular uptake and intracellular trafficking. AREAS COVERED: This review provides an update on the progress of receptor-targeted delivery of oligonucleotides over the last 15 years and summarizes various targeting moieties for oligonucleotide delivery and coupling strategies. To inspire new strategies that can lead to oligonucleotides in the clinic, this review highlights how oligonucleotides successfully reach their intracellular targets by means of receptor-mediated endocytosis. EXPERT OPINION: Understanding the mechanisms of oligonucleotide internalization has led to greater cellular uptake and superior endosomal release through the rational design of receptor-targeted delivery systems. Further improvements will again depend on a better understanding of the intracellular trafficking of oligonucleotides.