Elastin-like polypeptides and their applications in anticancer drug delivery systems: a review

Abstract

Elastin-like polypeptides (ELPs) are large molecular weight biopolymers. They have been widely studied as macromolecular carriers for targeted delivery of drugs. The aim of the present article is to review the available information on ELPs (including our recent investigations), their properties, drug delivery applications to tumor sites and future perspectives. This review also provides information on the use of short synthetic ELPs for making ELP-drug conjugates, for targeted delivery of anticancer drugs. In the present review we also focus on the point that short ELPs can also be used for targeting anticancer drugs to tumor sites as they behave similar to long ELPs regarding their capacity to undergo inverse temperature transition (ITT) behavior.     

A polypeptide drug carrier for maternal delivery and prevention of fetal exposure

Abstract

Background: Pregnant females are largely overlooked in drug development due to concerns for fetal health. Additionally, pregnancy is often an exclusion criterion in clinical trials, so the safety of many drugs during pregnancy is unknown.

Purpose: The goal of this study was to evaluate Elastin-like Polypeptide (ELP), a synthetic protein derived from human elastin, for maternally sequestered drug delivery. ELP is a versatile drug carrier with a long plasma half-life, low immunogenicity, and the ability to be fused to nearly any small molecule or protein-based therapeutic.

Methods: We determined the pharmacokinetics, biodistribution, and fetal exposure to the ELP drug carrier using quantitative fluorescence techniques in a rat pregnancy model.

Results: After either bolus IV administration or continuous infusion over five days, ELPs accumulated strongly in the kidneys, liver, and placenta, but importantly, little to no ELPs were detectable in the fetus. Within the placenta, ELPs were localized to the chorionic plate and broadly distributed within the labyrinth, but were excluded from the fetal portion of the chorionic villi.

Conclusion: These data indicate that ELP does not cross the placenta, and they suggest that this adaptable drug delivery system is a promising platform for prevention of fetal drug exposure.     

类弹性蛋白聚合物(ELPs)水凝胶的药物控释研究进展

综合国内外文献报道,简要介绍新型刺激响应性水凝胶类弹性蛋白聚合物(ELPs)的性质,并重点阐述其在药物控制释放方面的应用研究。ELPs是一种通过基因工程方法合成的多肽聚合物,其结构由类弹性蛋白的肽段单元重复串连组成。在一定浓度下具有特殊的反向热胶凝性质,即低温时为液体,升温至一定温度时形成凝胶。因其良好的生物相容性、生物可降解性和低免疫原性,ELPs在药物控制释放方面展示了广泛的应用前景。     

Vaxfectin: a versatile adjuvant for plasmid DNA- and protein-based vaccines

Importance of the field: Many vaccines require the use of an adjuvant to achieve immunity. So far, few adjuvants have advanced successfully through clinical trials to become part of licensed vaccines. Vaxfectin (Vical, CA, USA) represents a next-generation adjuvant with promise as a platform technology, showing utility with both plasmid DNA (pDNA) and protein-based vaccines.

Areas covered in this review: This review describes the chemical, physical, preclinical and clinical development of Vaxfectin for pDNA-based vaccines. Also included is the preclinical development of Vaxfectin-adjuvanted protein- and peptide-based vaccines.

What the reader will gain: The reader will gain knowledge of vaccine adjuvant development from bench to bedside.

Take home message: Vaxfectin has effectively boosted the immune response against a range of pDNA-expressed pathogenic antigens in preclinical models extending from rodents to non-human primates. In the clinic, Vaxfectin-adjuvanted pDNA-based H5N1 influenza vaccines have been shown to be well tolerated and to result in durable immune responses within the predicted protective range reported for protein-based vaccines.     

Delivery of a peptide via poly(d,l-lactic-co-glycolic) acid nanoparticles enhances its dendritic cell–stimulatory capacity

Nanoparticles (NPs) are attractive carriers for vaccines. We have previously shown that a short peptide (Hp91) activates dendritic cells (DCs), which are critical for initiation of immune responses. In an effort to develop Hp91 as a vaccine adjuvant with NP carriers, we evaluated its activity when encapsulated in or conjugated to the surface of poly(d,l-lactic-co-glycolic) acid (PLGA) NPs. We found that Hp91, when encapsulated in or conjugated to the surface of PLGA-NPs, not only activates both human and mouse DCs, but is in fact more potent than free Hp91. Hp91 packaged within NPs was about fivefold more potent than the free peptide, and Hp91 conjugated to the surface of NPs was ～20-fold more potent than free Hp91. Because of their capacity to activate DCs, such NP-Hp91 systems are promising as delivery vehicles for subunit vaccines against infectious disease or cancer.From the Clinical EditorIn this paper, nanoparticle-based dendritic cell activating vaccines are described and discussed. The authors report that the presented PLGA NP based vaccine constructs increase the potency of the studied vaccine by up to 20-fold, making them promising as delivery vehicles for subunit vaccines against infectious diseases or cancer.     

A nano-liposome vaccine carrying E75, a HER-2/neu-derived peptide,exhibits significant antitumour activity in mice

E75 (HER-2/neu-369–377), is an immunogenic peptide which is highly expressed in breast cancer patients. The purpose of this study was to develop an effective vaccine delivery/adjuvant system by attachment of this peptide to the surface of liposomes consisting of phospholipids including distearoylphosphocholine (DSPC) and distearoyl phosphoglycerol (DSPG) with high transition temperature (Tm) and dioleoylphosphatidylethanolamine (DOPE) (a pH-sensitive lipid for cytosolic antigen delivery) to improve antitumour immune activity against the E75 peptide. For this purpose, the E75 peptide was incorporated into liposomes consisting of DSPC/DSPG/cholesterol (Chol)/DOPE (15/2/3/5 molar ratio) through conjugation with distearoylphosphoethanolamine-N-[maleimide(polyethylene glycol)-2000] (maleimide-PEG₂₀₀₀-DSPE). Immunization of BALB/c mice was performed three times with different forms of liposomal formulations at 2-week intervals and antitumour immunity responses were evaluated. Results of ELISpot and flow cytometry analysis showed that mice vaccinated with DSPC/DSPG/Chol/DOPE/E75 have significantly enhanced the antigen-specific IFN-γ response of CD8⁺ T cells and generated cytotoxic T lymphocytes (CTL) antitumour responses. CTL responses induced by this formulation resulted in inhibition of tumour progression and longer survival time in the mice TUBO tumour model. The results revealed that the liposomes consist of DSPC/DSPG/Chol/DOPE could be suitable candidates for vaccine delivery of E75 peptide for the prevention and therapy of HER2-positive breast cancer and merit further investigation.     

Cell penetrating elastin-like polypeptides for therapeutic peptide delivery

Current treatment of solid tumors is limited by side effects that result from the non-specific delivery of drugs to the tumor site. Alternative targeted therapeutic approaches for localized tumors would significantly reduce systemic toxicity. Peptide therapeutics are a promising new strategy for targeted cancer therapy because of the ease of peptide design and the specificity of peptides for their intracellular molecular targets. However, the utility of peptides is limited by their poor pharmacokinetic parameters and poor tissue and cellular membrane permeability in vivo. This review article summarizes the development of elastin-like polypeptide (ELP) as a potential carrier for thermally targeted delivery of therapeutic peptides (TP), and the use of cell penetrating peptides (CPP) to enhance the intracellular delivery of the ELP-fused TPs. CPP-fused ELPs have been used to deliver a peptide inhibitor of c-Myc function and a peptide mimetic of p21 in several cancer models in vitro, and both polypeptides are currently yielding promising results in in vivo models of breast and brain cancer.     

Targeting the TLR9–MyD88 pathway in the regulation of adaptive immune responses

Importance of the field: Toll-like receptors (TLRs) are innate immune receptors critical in the innate immune defense against invading pathogens. Recent advances also reveal a crucial role for TLRs in shaping adaptive immune responses, conferring a potential therapeutic value to their modulation in the treatment of diseases.

Areas covered in this review: The aim of this review is to discuss TLR9, the TLR9–MyD88 signaling pathway and its role in regulation of adaptive immune responses, as well as potential therapeutic implications by targeting this pathway.

What the reader will gain: This review shows that the TLR9–MyD88 signaling pathway plays a critical role in promoting adaptive immune responses and that modulation of this pathway may have enormous therapeutic potential in enhancing vaccine potency, controlling autoimmunity, as well as improving the outcome of viral-vector-mediated gene therapy.

Take home message: Although TLR9 agonists have been used as adjuvants for enhancing vaccine potency, further exploitation of the TLR9–MyD88 pathway and its dynamic interaction with the immune system in vivo is needed to provide more effective therapeutic inventions in the design of vaccines for infectious diseases, allergies and cancer, in the control of autoimmunity, as well as in the improvement of viral-vector-mediated gene therapy.     

早产儿疫苗免疫接种研究进展

目的：疫苗的免疫程序和疫苗使用指导原则是保证疫苗免疫效果的重要环节,也是《疫苗管理法》的重要内容之一。早产儿免疫系统发育不成熟,对于各种疫苗免疫反应低于足月儿。本综述为制定早产儿免疫程序提供参考。方法：本文对在早产儿中使用灭活脊髓灰质炎疫苗、百日咳-白喉-破伤风疫苗、乙型肝炎疫苗、肺炎链球菌疫苗、脑膜炎球菌结合疫苗和流感嗜血杆菌疫苗、轮状病毒疫苗、麻疹、腮腺炎、风疹和水痘疫苗等疫苗的免疫效果、安全性及耐受性研究进展进行了归纳整理。结果：本文对早产儿在接种不同疫苗、采取不同免疫策略时体液免疫和细胞免疫效果的研究进行了归纳总结,结果表明虽然早产儿的免疫功能相对较弱,但参照足月新生儿免疫方案接种疫苗后,大部分早产儿可以具有足够的免疫保护力。结论：本文为疫苗免疫程序的制定提供更全面的理解,为制定疫苗使用指导原则提供参考。     

Recent advances in mucosal delivery of vaccines: role of mucoadhesive/biodegradable polymeric carriers

Importance of the field: The mucosal delivery of vaccines provides the basis for induction of humoral, cellular and mucosal immune responses against infectious diseases. The delivery of antigens to and through mucosal barriers always remains challenging due to adverse physiological conditions (pH and enzymes) and biological barriers created by tight epithelial junctions restricting transportation of macromolecules. Mucoadhesive and biodegradable polymers offer numerous advantages in therapeutic delivery of proteins/antigens particularly through the mucosal route by protecting antigens from degradation, increasing concentration of antigen in the vicinity of mucosal tissue for better absorption, extending their residence time in the body and/or targeting them to sites of antigen uptake. Furthermore, antigen can be delivered more effectively to the antigen presenting cells by anchoring the ligand having affinity on the surface of carrier for the receptors present on the mucosal epithelial cells.

Areas covered in this review: The present review covers various polymeric carriers, which allow the possibility of modification and manipulation of their properties, thereby, enhancing the effectiveness of mucosal vaccines. This article reviews the recent literature and patents in the field of vaccine delivery using mucoadhesive polymeric carriers.

What the reader will gain: The reader will gain insights into various natural polymers, synthetic polymers and ligand derived polymeric carrier systems studied to enhance mucosal immunization.

Take home message: Biodegradable polymeric carriers represent a promising approach for mucosal delivery of vaccine.     

Clinical studies assessing immunogenicity and safety of intradermally administered influenza vaccines

Importance of the field: Human influenza A and B are major respiratory pathogens and cause high mortality and severe morbidity, especially in at-risk populations. Most of the vaccines are administered intramusculary or subcutaneously. Owing to vaccine shortage and low vaccine coverage, intradermal administration of vaccines has gained renewed interest. In addition, higher immune responses with the same quantity of antigen have been elicited with intradermal vaccine administration, offering dose-sparing capacity.

Areas covered in this review: This review summarizes the immunogenicity and safety data accumulated from influenza vaccine trials where vaccines were administered intradermally. Clinical trials performed using reduced vaccine antigen doses in healthy volunteers or in at-risk populations and target groups are discussed as well as new devices for intradermal delivery of influenza vaccines. The studies addressed in this review were identified through a MEDLINE search.

What the reader will gain: The review provides insights into the potential of intradermal vaccines to overcome hurdles such as vaccine shortage in view of mass vaccination campaigns. Moreover, evidence is provided of improved immunological responses after intradermal vaccination when new intradermal devices are being used.

Take home message: In the authors' opinion, intradermal vaccination can be considered an equally immunogenic, safe and feasible alternative to intramuscular and subcutaneous vaccination. The future looks promising because of the recent development of new intradermal vaccine delivery devices.     

Advances in hepatitis C virus vaccines,part two: advances in hepatitis C virus vaccine formulations and modalities

Introduction: Developing a vaccine against HCV is an important medical and global priority. Unavailability and potential dangers associated with using attenuated HCV viral particles for vaccine preparation have resulted in the use of HCV genes and proteins formulated in novel vaccine modalities.

Areas covered: In part one of this review, advances in basic knowledge for HCV vaccine design were provided. Herein, a detailed and correlated patents (searched by Espacenet) and literatures (searched by Pubmed) review on HCV vaccine formulations and modalities is provided, including: subunit, DNA, epitopic-peptide/polytopic, live vector- and whole yeast-based vaccines. Less-touched areas in vaccine studies such as mucosal, plant-based, and chimeric HBV/HCV vaccines are also discussed. Furthermore, results of preclinical/clinical studies on selected HCV vaccines as well as pros and cons of different strategies are reviewed. Finally, potential strategies for creation and/or improvement of HCV vaccine formulations are discussed.

Expert opinion: Promising outcomes of a few HCV vaccine modalities in phase I/II clinical trials predict the accessibility of at least partially effective vaccines to inhibit or treat the chronic state of HCV infection (specially in combination with standard antiviral therapy). ChronVac-C (plasmid DNA), TG4040 (MVA-based), and GI-5005 (whole yeast-based) might be the most obvious HCV vaccine candidates to be approved in the near future.     

基于脂质载体的mRNA疫苗递送系统研究进展

转录信使RNA（mRNA）具有安全有效的蛋白质表达谱,在遗传病新疗法、表达功能性蛋白和抗体、疫苗或基因编辑的开发上具有良好的应用前景。随着病原生物学与免疫学的发展,mRNA疫苗凭借其高效性与稳定性而愈发被重视。目前,有效的体内递送手段是mRNA疫苗所面临的较大挑战,脂质载体的mRNA疫苗递送系统具有靶向性强、包封率高、细胞亲和性好的特点,部分脂质载体能够使mRNA疫苗在体内以非侵入性的方式进行靶向递送。从mRNA疫苗递送的主要难点、脂质载体在mRNA疫苗递送中的研究现状以及针对新型冠状病毒（SARS-CoV-2）的mRNA脂质载体疫苗开发进展,共3个方面总结了目前基于脂质载体的mRNA疫苗递送系统研究进展,并对未来的基因疫苗递送系统研究方向进行展望。     

Surveillance systems and methods for monitoring the post-marketing safety of influenza vaccines at the Centers for Disease Control and Prevention

ABSTRACT

Introduction: Annual influenza vaccine safety monitoring is an important component of the influenza vaccination program in the United States to ensure that vaccines are safe, which is important for maintaining public trust in the national vaccination program. This is specially the case for influenza vaccines since the antigen composition of the viruses of which the vaccine is made often changes from one season to the next, based on the circulating strain of influenza virus.

Areas covered: This review describes the two surveillance systems used by the Centers for Disease Control and Prevention (CDC) to monitor the safety of influenza vaccines: 1) the Vaccine Adverse Event Reporting System (VAERS); and 2) the Vaccine Safety datalink (VSD).

Expert opinion: VAERS and VSD are used routinely to monitor the safety of influenza vaccines in the United States, and over the years they have demonstrated their value in monitoring vaccine safety since their implementation in 1990. Both systems, although different, complemented each other well to study febrile seizures in young children following influenza vaccination during the 2010–2011 influenza season. Other examples of potential safety concerns after influenza vaccines are also presented and discussed.     

Liposomal adjuvants for human vaccines

ABSTRACT

Introduction: Liposomes are well-known as drug carriers, and are now critical components of two of six types of adjuvants present in licensed vaccines. The liposomal vaccine adjuvant field has long been dynamic and innovative, and research in this area is further examined as new commercial products appear in parallel with new vaccines. In an arena where successful products exist the potential for new types of vaccines with liposomal adjuvants, and alternative liposomal adjuvants that could emerge for new types of vaccines, are discussed.

Areas covered: Major areas include: virosomes, constructed from phospholipids and proteins from influenza virus particles; liposomes containing natural and synthetic neutral or anionic phospholipids, cholesterol, natural or synthetic monophosphoryl lipid A, and QS21 saponin; non-phospholipid cationic liposomes; and combinations and mixtures of liposomes and immunostimulating ingredients as adjuvants for experimental vaccines.

Expert opinion: Liposomes containing monophosphoryl lipid A and QS21 have considerable momentum that will result soon in emergence of prophylactic vaccines to malaria and shingles, and possible novel cancer vaccines. The licensed virosome vaccines to influenza and hepatitis A will be replaced with virosome vaccines to other infectious diseases. Alternative liposomal formulations are likely to emerge for difficult diseases such as tuberculosis or HIV-1 infection.     

Microneedle arrays for vaccine delivery: the possibilities,challenges and use of nanoparticles as a combinatorial approach for enhanced vaccine immunogenicity

Introduction: Vaccination is one of the greatest breakthroughs of modern preventative medicine. Despite this, there remain problems surrounding delivery, efficacy and compliance. Thus, there is a pressing need to develop cost-effective vaccine delivery systems that could expand the use of vaccines, particularly within developing countries. Microneedle (MN) arrays, given their ease of use, painlessness and ability to target skin antigen presenting cells, provide an attractive platform for improved vaccine delivery and efficacy. Studies have demonstrated enhanced immunogenicity with the use of MN in comparison to conventional needle. More recently, dissolving MN have been used for efficient delivery of nanoparticles (NP), as a means to enhance antigen immunogenicity.

Areas covered: This review introduces the fields of MN technology and nanotechnology, highlighting the recent advances which have been made with these two technologies combined for enhanced vaccine delivery and efficacy. Some key questions that remain to be addressed for adoption of MN in a clinical setting are also evaluated.

Expert opinion: MN-mediated vaccine delivery holds potential for expanding access to vaccines, with individuals in developing countries likely to be the principal beneficiaries. The combinatorial approach of utilizing MN coupled with NP, provides opportunities to enhance the immunogenicity of vaccine antigens.     

Nucleic acid vaccines: prospects for non-viral delivery of mRNA vaccines

Introduction: Nucleic acid-based vaccines are being developed as a means to combine the positive attributes of both live-attenuated and subunit vaccines. Viral vectors and plasmid DNA vaccines have been extensively evaluated in human clinical trials and have been shown to be safe and immunogenic, although none have been licensed for human use. More recently, mRNA-based vaccine alternatives have emerged and might offer certain advantages over their DNA-based counterparts.

Areas covered: This review describes the two main categories of mRNA vaccines: conventional non-amplifying and self-amplifying mRNA. It summarizes the initial clinical proof-of-concept studies and outlines the preclinical testing of the next wave of innovations for the technology. Finally, this review highlights the versatile functionality of the mRNA molecule and introduces opportunities for future improvements in vaccine design.

Expert opinion: The prospects for mRNA vaccines are very promising. Like other types of nucleic acid vaccines, mRNA vaccines have the potential to combine the positive attributes of live attenuated vaccines while obviating many potential safety limitations. Although data from initial clinical trials appear encouraging, mRNA vaccines are far from a commercial product. These initial approaches have spurred innovations in vector design, non-viral delivery, large-scale production and purification of mRNA to quickly move the technology forward. Some improvements have already been tested in preclinical models for both prophylactic and therapeutic vaccine targets and have demonstrated their ability to elicit potent and broad immune responses, including functional antibodies, type 1 T helper cells-type T cell responses and cytotoxic T cells. Though the initial barriers for this nucleic acid vaccine approach seem to be overcome, in our opinion, the future and continued success of this approach lies in a more extensive evaluation of the many non-viral delivery systems described in the literature and gaining a better understanding of the mechanism of action to allow rational design of next generation technologies.     

Microneedle-mediated vaccine delivery: Harnessing cutaneous immunobiology to improve efficacy

Introduction: Breaching the skin's stratum corneum barrier raises the possibility of the administration of vaccines, gene vectors, antibodies and even nanoparticles, all of which have at least their initial effect on populations of skin cells.

Areas covered: Intradermal vaccine delivery holds enormous potential for improved therapeutic outcomes for patients, particularly those in the developing world. Various vaccine-delivery strategies have been employed, which are discussed in this review. The importance of cutaneous immunobiology on the effect produced by microneedle-mediated intradermal vaccination is also discussed.

Expert opinion: Microneedle-mediated vaccines hold enormous potential for patient benefit. However, in order for microneedle vaccine strategies to fulfill their potential, the proportion of an immune response that is due to the local action of delivered vaccines on skin antigen-presenting cells, and what is due to a systemic effect from vaccines reaching the systemic circulation, must be determined. Moreover, industry will need to invest significantly in new equipment and instrumentation in order to mass-produce microneedle vaccines consistently. Finally, microneedles will need to demonstrate consistent dose delivery across patient groups and match this to reliable immune responses before they will replace tried-and-tested needle-and-syringe-based approaches.     

Safety of human papillomavirus vaccines: a review

Introduction: Between 2006 and 2009, two different human papillomavirus virus (HPV) vaccines were licensed for use: a quadrivalent (qHPVv) and a bivalent (bHPVv) vaccine. Since 2008, HPV vaccination programmes have been implemented in the majority of the industrialized countries. Since 2013, HPV vaccination has been part of the national programs of 66 countries including almost all countries in North America and Western Europe. Despite all the efforts made by individual countries, coverage rates are lower than expected. Vaccine safety represents one of the main concerns associated with the lack of acceptance of HPV vaccination both in the European Union/European Economic Area and elsewhere.

Areas covered: Safety data published on bivalent and quadrivalent HPV vaccines, both in pre-licensure and post-licensure phase, are reviewed.

Expert opinion: Based on the latest scientific evidence, both HPV vaccines seem to be safe. Nevertheless, public concern and rumors about adverse events (AE) represent an important barrier to overcome in order to increase vaccine coverage. Passive surveillance of AEs is an important tool for detecting safety signals, but it should be complemented by activities aimed at assessing the real cause of all suspect AEs. Improved vaccine safety surveillance is the first step for effective communication based on scientific evidence.