Recent advances in zwitterionic nanoscale drug delivery systems to overcome biological barriers

Nanoscale drug delivery systems(nDDS)have been employed widely in enhancing the therapeutic efficacy of drugs against diseases with reduced side effects.Although several nDDS have been successfully approved for clinical use up to now,biological barriers between the administration site and the target site hinder the wider clinical adoption of nDDS in disease treatment.Polyethylene glycol(PEG)-modification(or PEGylation)has been regarded as the gold standard for stabilising nDDS in complex biological environment.However,the accelerated blood clearance(ABC)of PEGylated nDDS after repeated injections becomes great challenges for their clinical applications.Zwitterionic polymer,a novel family of antifouling materials,have evolved as an alternative to PEG due to their super-hydrophilicity and biocompatibility.Zwitterionic nDDS could avoid the generation of ABC phenomenon and exhibit longer blood circulation time than the PEGylated analogues.More impressively,zwitterionic nDDS have recently been shown to overcome multiple biological barriers such as nonspecific organ distribution,pressure gradients,impermeable cell membranes and lysosomal degradation without the need of any complex chemical modifications.The realization of overcoming multiple biological barriers by zwitterionic nDDS may simplify the current overly complex design of nDDS,which could facilitate their better clinical translation.Herein,we summarise the recent progress of zwitterionic nDDS at overcoming various biological barriers and analyse their underlyingmechanisms.Finally,prospects and challenges are introduced to guide the rational design of zwitterionic nDDS for disease treatment.

A Concise Review of Gold Nanoparticles-Based Photo-Responsive Liposomes for Controlled Drug Delivery

The focus of drug delivery is shifting toward smart drug carriers that release the cargo in response to a change in the microenvironment due to an internal or external trigger. As the most clinically successful nanosystem, liposomes naturally come under the spotlight of this trend. This review summarizes the latest development about the design and construction of photo-responsive liposomes with gold nanoparticles for the controlled drug release. Alongside, we overview the mechanism involved in this process and the representative applications.

Studies on thermoresponsive polymers:Phase behaviour,drug delivery and biomedical applications

The present review aims to highlight the applications of thermoresponsive polymers.Thermo-responsive polymers show a sharp change in properties upon a small or modest change in temperature.This behaviour can be utilized for the preparation of so-called‘smart’drug delivery systems,which mimic biological response behaviour to a certain extent.Such materials are used in the development of several applications,such as drug delivery systems,tissue engineering scaffolds and gene delivery.Advances in this field are particularly relevant to applications in the areas of regenerative medicine and drug delivery.This review addresses summary of the main applications of thermoresponsive polymers which are categorized based on their 3-dimensional structure;hydrogels,interpenetrating networks,micelles,films and particles.The physico-chemical behaviour underlying the phase transition is also discussed in brief.

BIODEGRADABLE POLYMERS WITH A PHOSPHORYL-CONTAINING BACKBONE:TISSUE ENGINEERING AND CONTROLLED DRUG DELIVERY APPLICATIONS

This review provides a glimpse of the potential of the biodegradable phos-phoryl-containing polymers in medical applications. Undoubtedly these polymerspossess unique properties that are yet to be fully understood. Many areas warrantfurther investigation and much optimization remains to be done. The fascinatingchemistry of phosphorus poses interesting hurdles but at the same time leavesample room for polymer scientists to exercise their creativity in designinginteresting biomaterials. As the mutual understanding between basic and clinicalscientists on the need of medical devices and the capabilities of these newbiomaterials expands, imaginative application of new biomaterials to other medi-cal applications can be expected.

Aqueous Self-Assembly of Block Copolymers to Form Manganese Oxide-Based Polymeric Vesicles for Tumor Microenvironment-Activated Drug Delivery

Molecular self-assembly is crucially fundamental to nature.However,the aqueous self-assembly of polymers is still a challenge.To achieve self-assembly of block copolymers [(polyacrylic acid-block-polyethylene glycol-block-polyacrylic acid(PAA68-b-PEG86-b-PAA68)] in an aqueous phase,manganese oxide(MnO2) is first generated to drive phase separation of the PAA block to form the PAA68-b-PEG68-b-PAA68/MnO2 polymeric assembly that exhibits a stable structure in a physiological medium.The polymeric assembly exhibits vesicular morphology with a diameter of approximately 30 nm and high doxorubicin(DOX) loading capacity of approximately 94%.The transformation from MnO2 to Mn2+caused by endogenous glutathione(GSH)facilitates the disassembly of PAA68-b-PEG68-b-PAA68/MnO2 to enable its drug delivery at the tumor sites.The toxicity of DOXloaded PAA68-b-PEG68-b-PAA69/MnO2 to tumor cells has been verified in vitro and in vivo.Notably,drug-loaded polymeric vesicles have been demonstrated,especially in in vivo studies,to overcome the cardiotoxicity of DOX.We expect this work to encourage the potential application of polymer self-assembly.

Surface-engineered liposomes for dual-drug delivery targeting strategy against methicillin-resistant Staphylococcus aureus(MRSA)

This study focused on the encapsulation of vancomycin(VAN) into liposomes coated with a red blood cell membrane with a targeting ligand, daptomycin–polyethylene glycol–1,2-distearoyl-sn-glycero-3-phosphoethanolamine, formed by conjugation of DAPT and Nhydroxysuccinimidyl-polyethylene glycol-1,2-distearoyl-sn-glycero-3-phosphoethanolamine.This formulation is capable of providing controlled and targeted drug delivery to the bacterial cytoplasm. We performed MALDI-TOF, NMR and FTIR analyses to confirm the conjugation of the targeting ligand via the formation of amide bonds. Approximately 45% of VAN could be loaded into the aqueous cores, whereas 90% DAPT was detected using UV–vis spectrophotometry. In comparison to free drugs, the formulations controlled the release of drugs for > 72 h. Additionally, as demonstrated using CLSM and flow cytometry, the resulting formulation was capable of evading detection by macrophage cells. In comparison to free drugs, red blood cell membrane–DAPT–VAN liposomes, DAPT liposomes, and VAN liposomes reduced the MIC and significantly increased bacterial permeability, resulting in > 80% bacterial death within 4 h. Cytotoxicity tests were performed in vitro and in vivo on mammalian cells,in addition to hemolytic activity tests in human erythrocytes, wherein drugs loaded into the liposomes and RBCDVL exhibited low toxicity. Thus, the findings of this study provide insight about a dual antibiotic targeting strategy that utilizes liposomes and red blood cell membranes to deliver targeted drugs against MRSA.

Multifunctional quantum dots and liposome complexes in drug delivery

Incorporating both diagnostic and therapeutic functions into a single nanoscale system is an effective modern drug delivery strategy. Combining liposomes with semiconductor quantum dots（QDs） has great potential to achieve such dual functions, referred to in this review as a liposomal QD hybrid system（L-QD）. Here we review the recent literature dealing with the design and application of L-QD for advances in bio-imaging and drug delivery. After a summary of L-QD synthesis processes and evaluation of their properties, we will focus on their multifunctional applications, ranging from in vitro cell imaging to theranostic drug delivery approaches.

Liposome based drug delivery as a potential treatment option for Alzheimer’s disease

Alzheimer’s disease is a neurodegenerative condition leading to atrophy of the brain and robbing nearly 5.8 million individuals in the United States age 65 and older of their cognitive functions.Alzheimer’s disease is associated with dementia and a progressive decline in memory,thinking,and social skills,eventually leading to a point that the individual can no longer perform daily activities independently.Currently available drugs on the market temporarily alleviate the symptoms,however,they are not successful in slowing down the progression of Alzheimer’s disease.Treatment and cures have been constricted due to the difficulty of drug delivery to the blood-brain barrier.Several studies have led to identification of vesicles to transport the necessary drugs through the blood-brain barrier that would typically not achieve the targeted area through systemic delivered medications.Recently,liposomes have emerged as a viable drug delivery agent to transport drugs that are not able to cross the blood-brain barrier.Liposomes are being used as a component of nanoparticle drug delivery;due to their biocompatible nature;and possessing the capability to carry both lipophilic and hydrophilic therapeutic agents across the blood brain barrier into the brain cells.Studies indicate the importance of liposomal based drug delivery in treatment of neurodegenerative disorders.The idea is to encapsulate the drugs inside the properly engineered liposome to generate a response of treatment.Liposomes are engineered to target specific diseased moieties and also several surface modifications of liposomes are under research to create a clinical path to the management of Alzheimer’s disease.This review deals with Alzheimer’s disease and emphasize on challenges associated with drug delivery to the brain,and how liposomal drug delivery can play an important role as a drug delivery method for the treatment of Alzheimer’s disease.This review also sheds some light on variation of liposomes.Additionally,it emphasizes on the liposomal formulations which are currently researched or used for treatment of Alzheimer’s disease and also discusses the future prospect of liposomal based drug delivery in Alzheimer’s disease.

Polymers in Drug Delivery

Polymers are being used extensively in drug delivery due to their surface and bulk properties. They are being used in drug formulations and in drug delivery devices. These drug delivery devices may be in the form of implants for controlled drug delivery. Polymers used in colloidal drug carrier systems, consisting of small particles, show great advantage in drug delivery systems because of optimized drug loading and releasing property. Polymeric nano particulate systems are available in wide variety and have established chemistry. Non toxic, biodegradable and biocompatible polymers are available. Some nano particulate polymeric systems possess ability to cross blood brain barrier. They offer protection against chemical degradation. Smart polymers are responsive to atmospheric stimulus like change in temperature;pressure, pH etc. thus are extremely beneficial for targeted drug delivery. Some polymeric systems conjugated with antibodies/specific biomarkers help in detecting molecular targets specifically in cancers. Surface coating with thiolated PEG, Silica-PEG improves water solubility and photo stability. Surface modification of drug carriers e.g. attachment with PEG or dextran to the lipid bilayer increases their blood circulation time. Polymer drug conjugates such as Zoladex, Lupron Depot, On Caspar PEG intron are used in treatment of prostate cancer and lymphoblastic leukemia. Polymeric Drug Delivery systems are being utilized for controlled drug delivery assuring patient compliance.

Current developments in drug delivery with thermosensitive liposomes

Thermosensitive liposomes(TSLs) have been an important research area in the field of tumor targeted chemotherapy. Since the first TSLs appeared that using 1,2-dipalmitoyl-snglyce-ro-3-phosphocholine(DPPC) as the primary liposomal lipid, many studies have been done using this type of liposome from basic and practical aspects. While TSLs composed of DPPC enhance the cargo release near the phase transition temperature, it has been shown that many factors affect their temperature sensitivity. Thus numerous attempts have been undertaken to develop new TSLs for improving their thermal response performance. The main objective of this review is to introduce the development and recent update of innovative TSLs formulations, including combination of radiofrequency ablation(RFA), highintensity focused ultrasound(HIFU), magnetic resonance imaging(MRI) and alternating magnetic field(AMF). In addition, various factors affecting the design of TSLs, such as lipid composition, surfactant, size and serum components are also discussed.

Functionalized liposomes for targeted breast cancer drug delivery

Despite the exceptional progress in breast cancer pathogenesis,prognosis,diagnosis,and treatment strategies,it remains a prominent cause of female mortality worldwide.Additionally,although chemotherapies are effective,they are associated with critical limitations,most notably their lack of specificity resulting in systemic toxicity and the eventual development of multi-drug resistance(MDR)cancer cells.Liposomes have proven to be an invaluable drug delivery system but of the multitudes of liposomal systems developed every year only a few have been approved for clinical use,none of which employ active targeting.In this review,we summarize the most recent strategies in development for actively targeted liposomal drug delivery systems for surface,transmembrane and internal cell receptors,enzymes,direct cell targeting and dual-targeting of breast cancer and breast cancer-associated cells,e.g.,cancer stem cells,cells associated with the tumor microenvironment,etc.

Polymer Nanoparticles Prepared by Supercritical Carbon Dioxide for in Vivo Anti-cancer Drug Delivery

A new approach for producing polymer nanoparticles made of bovine serum albumin-poly(methy methacrylate) conjugate by precipitating in supercritical CO2 is reported. The nanoparticles were loaded with the anti-tumor drug camptothecin. With albumin serving as a nutrient to cells, the drug-encapsulated nanoparticle shows an enhanced ability to kill cancer cells compared to that of the free drug in solution both in vitro and in vivo.

Zwitterionic polymers:Addressing the barriers for drug delivery

Nanocarriers play an important role in drug delivery for disease treatment.However,nanocarriers face a series of physiological barriers after administration such as blood clearance,nonspecific tissue/cell localization,poor cellular uptake,and endosome trapping.These physiological barriers seriously reduce the accumulation of drugs in target action site,which results in poor therapeutic efficiency.Although polyethylene glycol(PEG)can increase the blood circulation time of nanocarriers,its application is limited due to the“PEG dilemma”.Zwitterionic polymers have been emerging as an appealing alternative to PEG owing to their excellent performance in resisting nonspecific protein adsorption.Importantly,the diverse structures bring functional versatility to zwitterionic polymers beyond nonfouling.This review focuses on the structures and characters of zwitterionic polymers,and will discuss and summarize the application of zwitterionic polymers for drug delivery.We will highlight the strategies of zwitterionic polymers to address the physiological barriers during drug delivery.Finally,we will give some suggestions that can be utilized for the development of zwitterionic polymers for drug delivery.This review will also provide an outlook for this field.Our aim is to provide a comprehensive and systemic review on the application of zwitterionic polymers for drug delivery and promote the development of zwitterionic polymers.

Formation strategies,mechanism of intracellular delivery and potential clinical applications of pH-sensitive liposomes

pH-sensitive liposomes are designed to specifically triggered release the loaded drugs in response to the change of pH in the surrounding serum.So pH-sensitive liposomes can effectively deliver drug or gene fragments into the cytoplasm via the endocytotic pathway.Furthermore,pH-sensitive liposomes can be successfully used in clinical if they enable the encapsulated drugs to be targeted to pathological tissues(such as primary tumors,metastases,local ischemia,inflammation and infection)of the body in which pH is less than the normal physiological value.That’s the reason why a growing amount of literatures described the development and applications of pH-sensitive liposomes to improve the therapeutic index of the encapsulated active ingredients.In this review,the commonly used pH-sensitive molecules for pH-sensitive liposome and the mechanisms of intracellular delivery of pH-sensitive liposomes were addressed.Besides,the potential clinical applications were fully discussed in detail with an expectation to contribute to the clinical research of pH-sensitive liposomes.

Recent progresses of exosome-liposome fusions in drug delivery

Exosomes are membrane-bound nanoscale extracellular vesicles,which produced by almost all organisms.Due to the excellent biocompatibility,long circulation time as well as low immunogenicity,exosomes as naturally-derived drug delivery carriers have experienced explosive growth over the past decades.However,issues such as insufficient loading efficiency,heterogeneous delivery efficiency,uncontrollable targeting ability,and low production limit their wide application.Recently,the emerging exosome-liposome fusion strategy has become a potential approach to solve such issues.Thus,this review mainly focuses on the currently developed exosome-liposome fusion strategy and their application in drug delivery as well as disease treatment.This review aims to shed light on the advantages of fusion strategy in drug delivery and provides a better understanding for more rational design.The current challenge and future perspective regarding their clinical translation and application will also be discussed.

Recent advances in arsenic trioxide encapsulated nanoparticles as drug delivery agents to solid cancers

Since arsenic trioxide was first approved as the front line therapy for acute promyelocytic leukemia 25 years ago,its anti-cancer properties for various malignancies have been under intense investigation.However,the clinical successes of arsenic trioxide in treating hematological cancers have not been translated to solid cancers.This is due to arsenic＇s rapid clearance by the body＇s immune system before reaching the tumor site.Several attempts have henceforth been made to increase its bioavailability toward solid cancers without increasing its dosage albeit without much success.This review summarizes the past and current utilization of arsenic trioxide in the medical field with primary focus on the implementation of nanotechnology for arsenic trioxide delivery to solid cancer cells.Different approaches that have been employed to increase arsenic＇s efficacy,specificity and bioavailability to solid cancer cells were evaluated and compared.The potential of combining different approaches or tailoring delivery vehicles to target specific types of solid cancers according to individual cancer characteristics and arsenic chemistry is proposed and discussed.

Liposomal formulations for enhanced lymphatic drug delivery

The lymphatic system that extends throughout the whole body is one of useful targets for efficient drug delivery.The intestinal lymphatic drug delivery has been actively studied to date because administered drugs can avoid the first-pass metabolism in the liver,resulting in improvement of oral bioavailability.Drugs must be hydrophobic in order to be transported into the intestinal lymphatics because the lipid absorption mechanism in the intestine is involved in the lymphatic delivery.Therefore,various lipid-based drug carrier systems have been recently utilized to increase the transport of drug into the intestinal lymphatics.Lipidic molecules of the lipid-based drug delivery systems stimulate production of chylomicrons in the enterocytes,resulting in an increase in drug transport into lymphatic in the enterocytes.This review summarizes recently reported information on development of liposomal carriers for the intestinal lymphatic delivery and covers important determinants for successful lymphatic delivery.

Advances of cyclodextrin polymers for the delivery of biotech drugs

Currently,biological drugs such as gene,protein,and monoclonal antibody are widely applied in the clinic due to their excellent effectiveness.However,they still have some problems,including poor solubility,instability,toxicity,and weak capability to cross cell membranes.Owing to the specific structure of cyclodextrins(CDs)and the advantage of polymeric backbones,various cyclodextrin polymers(CDPs)have been designed as delivery systems for biotech drugs.In this review,after a brief introduction on CDPs and discussion of their physicochemical and biological properties,we will focus on recent advances in the use of CDPs for the delivery of biotech drugs.This review highlights the structure-function relationship of CDPs to their performance in biotech drug delivery.Finally,an outlook will be proposed on the developing trends and challenge in this field.

Research progress of in-situ gelling ophthalmic drug delivery system

Blindness and vision impairment are the most devastating global health problems resulting in a substantial economic and social burden.Delivery of drug to particular parts of the anterior or posterior segment has been a major challenge due to various protective barriers and elimination mechanisms associated with the unique anatomical and physiological nature of the ocular system.Drug administration to the eye by conventional delivery systems results in poor ocular bioavailability(<5%).The designing of a novel approach for a safe,simple,and effective ocular drug delivery is a major concern and requires innovative strategies to combat the problem.Over the past decades,several novel approaches involving different strategies have been developed to improve the ocular delivery system.Among these,the ophthalmic in-situ gel has attained a great attention over the past few years.This review discussed and summarized the recent and the promising research progress of in-situ gelling in ocular drug delivery system.

Film forming systems for topical and transdermal drug delivery

Skin is considered as an important route of administration of drugs for both local and systemic effects. The effectiveness of topical therapy depends on the physicochemical properties of the drug and adherence of the patient to the treatment regimen as well as the system’s ability to adhere to skin during the therapy so as to promote drug penetration through the skin barrier.Conventional formulations for topical and dermatological administration of drugs have certain limitations like poor adherence to skin, poor permeability and compromised patient compliance.For the treatment of diseases of body tissues and wounds, the drug has to be maintained at the site of treatment for an effective period of time. Topical film forming systems are such developing drug delivery systems meant for topical application to the skin, which adhere to the body, forming a thin transparent film and provide delivery of the active ingredients to the body tissue. These are intended for skin application as emollient or protective and for local action or transdermal penetration of medicament for systemic action. The transparency is an appreciable feature of this polymeric system which greatly influences the patient acceptance.In the current discussion, the film forming systems are described as a promising choice for topical and transdermal drug delivery. Further the various types of film forming systems (sprays/solutions, gels and emulsions) along with their evaluation parameters have also been reviewed.