Design of stimuli-responsive dendrimers

Research progress related to thermosensitive hydrogel dressings in wound healing: a review

Wound healing is a dynamic and complex process in which the microenvironment at the wound site plays an important role. As a common material for wound healing, dressings accelerate wound healing and prevent external wound infections. Hydrogels have become a hot topic in wound-dressing research because of their high water content, good biocompatibility, and adjustable physical and chemical properties. Intelligent hydrogel dressings have attracted considerable attention because of their excellent environmental responsiveness. As smart polymer hydrogels, thermosensitive hydrogels can respond to small temperature changes in the environment, and their special properties make them superior to other hydrogels. This review mainly focuses on the research progress in thermosensitive intelligent hydrogel dressings for wound healing. Polymers suitable for hydrogel formation and the appropriate molecular design of the hydrogel network to achieve thermosensitive hydrogel properties are discussed, followed by the application of thermosensitive hydrogels as wound dressings. We also discuss the future perspectives of thermosensitive hydrogels as wound dressings and provide systematic theoretical support for wound healing.

Control of Stimuli Sensitivity in pH-Switchable LCST/UCST-Type Thermosensitive Dendrimers by Changing the Dendrimer Structure

Stimuli-sensitive materials, such as pH- and temperature-responsive polymers, are useful as smart materials. Phenylalanine (Phe)-modified polyamidoamine (PAMAM) dendrimers with succinic acid termini, PAMAM-Phe-Suc, have been reported as unique pH-switchable lower critical solution temperature (LCST)-/upper critical solution temperature (UCST)-type thermosensitive polymers. Regulating the phase transition behavior of dendrimers is important for their applications. This study investigated the relationship between the dendrimer structure and stimuli sensitivity. Phe-modified PAMAM dendrimers with cyclohexanedicarboxylate termini (PAMAM-Phe-CHex) and sulfonate termini (PAMAM-Phe-SO₃Na) were synthesized. The temperature-dependent transmittance of these aqueous dendrimer solutions was examined at various pH values. PAMAM-Phe-CHex with Phe at all termini (PAMAM-Phe64-CHex) demonstrated a broad UCST-like phase transition at pH 7.0 but lacked an LCST-type phase transition. PAMAM-Phe-CHex with ≤ 27 Phe residues showed both LCST- and UCST-like phase transitions at different pH values, but the phase transition was broad. PAMAM-Phe-SO₃Na showed both LCST- and UCST-type phase transitions at different pH values, and the transition temperature increased as the bound Phe number decreased. Thus, the phase transition behavior of PAMAM-Phe-SO₃Na dendrimers can be regulated by varying the Phe/PAMAM ratios.

Thermosensitive Hydrogels and Advances in Their Application in Disease Therapy

Thermosensitive hydrogels, having unique sol–gel transition properties, have recently received special research attention. These hydrogels exhibit a phase transition near body temperature. This feature is the key to their applications in human medicine. In addition, hydrogels can quickly gel at the application site with simple temperature stimulation and without additional organic solvents, cross-linking agents, or external equipment, and the loaded drugs can be retained locally to improve the local drug concentration and avoid unexpected toxicity or side effects caused by systemic administration. All of these features have led to thermosensitive hydrogels being some of the most promising and practical drug delivery systems. In this paper, we review thermosensitive hydrogel materials with biomedical application potential, including natural and synthetic materials. We describe their structural characteristics and gelation mechanism and briefly summarize the mechanism of drug release from thermosensitive hydrogels. Our focus in this review was to summarize the application of thermosensitive hydrogels in disease treatment, including the postoperative recurrence of tumors, the delivery of vaccines, the prevention of postoperative adhesions, the treatment of nervous system diseases via nasal brain targeting, wound healing, and osteoarthritis treatment.

Functionalization of Nanoparticulate Drug Delivery Systems and Its Influence in Cancer Therapy

Research into the application of nanocarriers in the delivery of cancer-fighting drugs has been a promising research area for decades. On the other hand, their cytotoxic effects on cells, low uptake efficiency, and therapeutic resistance have limited their therapeutic use. However, the urgency of pressing healthcare needs has resulted in the functionalization of nanoparticles' (NPs) physicochemical properties to improve clinical outcomes of new, old, and repurposed drugs. This article reviews recent research on methods for targeting functionalized nanoparticles to the tumor microenvironment (TME). Additionally, the use of relevant engineering techniques for surface functionalization of nanocarriers (liposomes, dendrimers, and mesoporous silica) and their critical roles in overcoming the current limitations in cancer therapy-targeting ligands used for targeted delivery, stimuli strategies, and multifunctional nanoparticles-were all reviewed. The limitations and future perspectives of functionalized nanoparticles were also finally discussed. Using relevant keywords, published scientific literature from all credible sources was retrieved. A quick search of the literature yielded almost 400 publications. The subject matter of this review was addressed adequately using an inclusion/exclusion criterion. The content of this review provides a reasonable basis for further studies to fully exploit the potential of these nanoparticles in cancer therapy.

Carboxy-terminal dendrimers with phenylalanine for a pH-sensitive delivery system into immune cells including T cells

Although T cells play important roles in various immune reactions, there are only a few reports on delivery systems into T cells. Our previous study showed that carboxy-terminal phenylalanine (Phe)-modified polyamidoamine (PAMAM) dendrimers have both temperature- and pH-sensitive properties, which are affected by the chemical structure. The self-assembled structures of Phe, observed in phenylketonuria, enhance the protein aggregation, the association with the cell membrane and the membrane permeability. In this study, we applied the Phe-modified dendrimers to a pH-sensitive drug delivery system into T cells. Dendrimers with different amino acids and acid anhydrides were synthesized, and their pH-responsive association with T cells and their subsets was investigated. The dendrimers modified with Phe and cyclohexanedicarboxylic acid (CHex) showed higher uptake into various cells, including Jurkat cells, CD3+ T cells, CD3 + CD4+ helper T cells and CD3 + CD8+ killer T cells. These dendrimers were internalized into T cells via endocytosis, and their cellular uptake was enhanced under weak acidic conditions (pH 6.5). Our results showed that Phe- and CHex-modified dendrimers have a delivery potential to T cells and their subsets, which may be useful for cancer immunotherapy.

Recent Advancements in Stimuli Responsive Drug Delivery Platforms for Active and Passive Cancer Targeting

The tumor-specific targeting of chemotherapeutic agents for specific necrosis of cancer cells without affecting the normal cells poses a great challenge for researchers and scientists. Though extensive research has been carried out to investigate chemotherapy-based targeted drug delivery, the identification of the most promising strategy capable of bypassing non-specific cytotoxicity is still a major concern. Recent advancements in the arena of onco-targeted therapies have enabled safe and effective tumor-specific localization through stimuli-responsive drug delivery systems. Owing to their promising characteristic features, stimuli-responsive drug delivery platforms have revolutionized the chemotherapy-based treatments with added benefits of enhanced bioavailability and selective cytotoxicity of cancer cells compared to the conventional modalities. The insensitivity of stimuli-responsive drug delivery platforms when exposed to normal cells prevents the release of cytotoxic drugs into the normal cells and therefore alleviates the off-target events associated with chemotherapy. Contrastingly, they showed amplified sensitivity and triggered release of chemotherapeutic payload when internalized into the tumor microenvironment causing maximum cytotoxic responses and the induction of cancer cell necrosis. This review focuses on the physical stimuli-responsive drug delivery systems and chemical stimuli-responsive drug delivery systems for triggered cancer chemotherapy through active and/or passive targeting. Moreover, the review also provided a brief insight into the molecular dynamic simulations associated with stimuli-based tumor targeting.

pH-Switchable LCST/UCST-type thermosensitive behaviors of phenylalanine-modified zwitterionic dendrimers

Thermosensitive polymers are useful as intelligent materials. Dendrimers have well-defined structures, which can work as multifunctional polymers. In this study, we designed and synthesized various phenylalanine (Phe)-modified zwitterionic dendrimers as pH- and thermo-sensitive polymers. First, polyamidoamine (PAMAM) dendrimers were modified with Phe and succinic anhydride (Suc) to prepare carboxy-terminal Phe-modified dendrimers (PAMAM-Suc-Phe and PAMAM-Phe-Suc). Both these dendrimers showed upper critical solution temperature (UCST)-type thermosensitivity. Interestingly, PAMAM-Phe-Suc demonstrated lower critical solution temperature (LCST)-type thermosensitivity at lower pH, but PAMAM-Suc-Phe did not. This indicates that PAMAM-Phe-Suc can switch LCST/UCST-type thermosensitivity according to the solution's pH. PAMAM-Phe-SO₃Na with sulfonic acid termini also demonstrated LCST/UCST-type thermosensitivity switched by pH, with a higher sensitivity than PAMAM-Phe-Suc. Coacervation occurred during the phase separation. The quaternized dendrimers (QPAMAM-Phe-Suc and QPAMAM-Phe-SO₃Na) and dendrimers conjugating isoleucine or 4-(amino methyl)benzoic acid did not show the unique thermosensitive properties, indicating that the tertiary amines in the dendrimer core and the Phe residues at the termini are indispensable. PAMAM-Phe-SO₃Na could separate a model compound (rose bengal) from an aqueous solution because of its encapsulation ability. This is the first report of pH-switchable LCST/UCST-type thermosensitive dendrimers.

We synthesized phenylalanine-modified zwitterionic dendrimers as pH- and thermo-responsive polymers. This is the first report of pH-switchable LCST/UCST-type thermosensitive dendrimers.

A combination drug delivery system employing thermosensitive liposomes for enhanced cell penetration and improved in vitro efficacy

Drug-loaded thermosensitive liposomes are investigated as drug delivery systems in combination with local mild hyperthermia therapy due to their capacity to release their cargo at a specific temperature range (40-42 °C). Additional benefit can be achieved by the development of such systems that combine two different anticancer drugs, have cell penetration properties and, when heated, release their drug payload in a controlled fashion. To this end, liposomes were developed incorporating at low concentration (5 mol%) a number of monoalkylether phosphatidylcholine lipids, encompassing the platelet activating factor, PAF, and its analogues that induce thermoresponsiveness and have anticancer biological activity. These thermoresponsive liposomes were efficiently (>90%) loaded with doxorubicin (DOX), and their thermal properties, stability and drug release were investigated both at 37 ^◦C and at elevated temperatures. In vitro studies of the most advantageous liposomal formulation containing the methylated PAF derivative (methyl-PAF, edelfosine), an established antitumor agent, were performed on human prostate cancer cell lines. This system exhibits controlled release of DOX at 40-42 °C, enhanced cell uptake due to the presence of methyl-PAF, and improved cell viability inhibition due to the combined action of both medications.

Recent Progress and Advances of Multi-Stimuli-Responsive Dendrimers in Drug Delivery for Cancer Treatment

Despite the fact that nanocarriers as drug delivery systems overcome the limitation of chemotherapy, the leakage of encapsulated drugs during the delivery process to the target site can still cause toxic effects to healthy cells in other tissues and organs in the body. Controlling drug release at the target site, responding to stimuli that originated from internal changes within the body, as well as stimuli manipulated by external sources has recently received significant attention. Owning to the spherical shape and porous structure, dendrimer is utilized as a material for drug delivery. Moreover, the surface region of dendrimer has various moieties facilitating the surface functionalization to develop the desired material. Therefore, multi-stimuli-responsive dendrimers or 'smart' dendrimers that respond to more than two stimuli will be an inspired attempt to achieve the site-specific release and reduce as much as possible the side effects of the drug. The aim of this review was to delve much deeper into the recent progress of multi-stimuli-responsive dendrimers in the delivery of anticancer drugs in addition to the major potential challenges.

Surface functionalized dendrimers as controlled-release delivery nanosystems for tumor targeting

Dendrimers are nano-sized and three-dimensional macromolecules with well-defined globular architecture and are widely used in various aspects such as drug and gene delivery owing to multivalent and host-guest entrapment properties. However, dendrimers like other nanomaterials have some disadvantages for example rapid clearance by reticuloendothelial system, toxicity due to interaction of amine terminated group with cell membrane, low transfection efficiency and lack of controlled release behavior, which reduce their therapeutic efficiency. To solve these problems, surface functionalization of dendrimers can be carried out. Surface functionalization not only mitigates this obstacle but also renders excessive specificity to dendrimer to improve efficiency of cancer therapy. Specific properties in cancer cell compared to normal cells such as overexpression of various receptors and difference in biological condition like pH, temperature and redox of tumor environment can be an appropriate strategy to increase site-specific targeting efficiency. Therefore, in this article we focus on numerous functionalization strategies, which are used in the modification of dendrimers through attachment of lipid, amino acid, protein/peptide, aptamer, vitamin, antibody. Moreover, increased biocompatibility, site-specific delivery based on various ligands, enhanced transfection efficiency, sustained and controlled release behavior based on stimuli responsiveness are benefits of functionalized dendrimer which we discuss in this review. Overall, these functionalized dendrimers can open a new horizon in the field of targeted drug and gene delivery.

Functionalized Hyperbranched Polyethylenimines as Thermosensitive Drug Delivery Nanocarriers with Controlled Transition Temperatures

The low critical solution temperature phase transition (T_c) that is exhibited by thermosensitive polymers is strongly dependent on polymer concentration, pH, ionic strength, as well as the presence of specific molecules or ions in solution. Therefore, polymers with T_c values above 37 °C that are useful for hyperthermia therapy are not readily available. In the present study, temperature-sensitive hyperbranched polyethylenimine derivatives were developed through stepwise functionalization with isobutylamide groups. Although factors such as the concentration of polymer, sodium chloride, phosphate ions, and pH considerably affect the transition temperature, it was possible to obtain a hyperbranched derivative having the required T_c (38-39 °C) for the given aqueous medium required in cell experiments through careful selection of the degree of substitution. This thermosensitive derivative can encapsulate doxorubicin (DOX), a well-known anticancer agent, and was further studied as a temperature-triggered drug delivery system. Although the polymeric carrier showed no notable toxicity at temperatures either below or above the transition temperature, the thermoresponsive drug-loaded formulation exhibited increased DOX cellular uptake and improved in vitro cytotoxicity at 40 °C.

Dual pH-sensitive and UCST-type thermosensitive dendrimers: phenylalanine-modified polyamidoamine dendrimers with carboxyl termini

We designed carboxyl-terminal Phe-modified PAMAM dendrimers by using various acid anhydrides. These dendrimers exhibited UCST-type thermosensitivity, which was dependent on both pH and the anhydride modifier.

Synthesis of enzyme-responsive phosphoramidate dendrimers for cancer drug delivery

Enzyme-responsive phosphoramidate dendrimers were successfully synthesized and their surfaces were modified with zwitterionic groups for cancer drug delivery.

Nanoparticles for bone tissue engineering

Tissue engineering (TE) envisions the creation of functional substitutes for damaged tissues through integrated solutions, where medical, biological, and engineering principles are combined. Bone regeneration is one of the areas in which designing a model that mimics all tissue properties is still a challenge. The hierarchical structure and high vascularization of bone hampers a TE approach, especially in large bone defects. Nanotechnology can open up a new era for TE, allowing the creation of nanostructures that are comparable in size to those appearing in natural bone. Therefore, nanoengineered systems are now able to more closely mimic the structures observed in naturally occurring systems, and it is also possible to combine several approaches - such as drug delivery and cell labeling - within a single system. This review aims to cover the most recent developments on the use of different nanoparticles for bone TE, with emphasis on their application for scaffolds improvement; drug and gene delivery carriers, and labeling techniques. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:590-611, 2017.

Stimuli-responsive dendrimers in drug delivery

Dendrimers have shown great promise as carriers in drug delivery due to their unique structures and superior properties. However, the precise control of payload release from a dendrimer matrix still presents a great challenge. Stimuli-responsive dendrimers that release payloads in response to a specific trigger could offer distinct clinical advantages over those dendrimers that release payloads passively. These smart polymers are designed to specifically release their payloads at targeted regions or at constant release profiles for specific therapies. They represent an attractive alternative to targeted dendrimers and enable dendrimer-based therapeutics to be more effective, more convenient, and much safer. The wide range of stimuli, either endogenous (acid, enzyme, and redox potentials) or exogenous (light, ultrasound, and temperature change), allows great flexibility in the design of stimuli-responsive dendrimers. In this review article, we will highlight recent advances and opportunities in the development of stimuli-responsive dendrimers for the treatment of various diseases, with emphasis on cancer. Specifically, the applications of stimuli-responsive dendrimers in drug delivery as well as their mechanisms are intensively reviewed.

Glycoproteins functionalized natural and synthetic polymers for prospective biomedical applications: A review

Glycoproteins have multidimensional properties such as biodegradability, biocompatibility, non-toxicity, antimicrobial and adsorption properties; therefore, they have wide range of applications. They are blended with different polymers such as chitosan, carboxymethyl cellulose (CMC), polyvinyl pyrrolidone (PVP), polycaprolactone (PCL), heparin, polystyrene fluorescent nanoparticles (PS-NPs) and carboxyl pullulan (PC) to improve their properties like thermal stability, mechanical properties, resistance to pH, chemical stability and toughness. Considering the versatile charateristics of glycoprotein based polymers, this review sheds light on synthesis and characterization of blends and composites of glycoproteins, with natural and synthetic polymers and their potential applications in biomedical field such as drug delivery system, insulin delivery, antimicrobial wound dressing uses, targeting of cancer cells, development of anticancer vaccines, development of new biopolymers, glycoproteome research, food product and detection of dengue glycoproteins. All the technical scientific issues have been addressed; highlighting the recent advancement.

Dendritic Polymers for Theranostics

Dendritic polymers are highly branched polymers with controllable structures, which possess a large population of terminal functional groups, low solution or melt viscosity, and good solubility. Their size, degree of branching and functionality can be adjusted and controlled through the synthetic procedures. These tunable structures correspond to application-related properties, such as biodegradability, biocompatibility, stimuli-responsiveness and self-assembly ability, which are the key points for theranostic applications, including chemotherapeutic theranostics, biotherapeutic theranostics, phototherapeutic theranostics, radiotherapeutic theranostics and combined therapeutic theranostics. Up to now, significant progress has been made for the dendritic polymers in solving some of the fundamental and technical questions toward their theranostic applications. In this review, we briefly summarize how to control the structures of dendritic polymers, the theranostics-related properties derived from their structures and their theranostics-related applications.

Fabrication of dual responsive co-delivery system based on three-armed peptides for tumor therapy

Introducing drugs into gene delivery systems to fabricate co-delivery systems for synergy therapy has become a promising strategy for tumor therapy. In this study, a dual responsive co-delivery system RHD/p53 was fabricated to enhance the antitumor efficacy with a low dose of doxorubicin (DOX). The reducible branched cationic polypeptide (RBCP), which was cross-linked via the thiol groups of two three-armed cationic peptides (CRR)2KRRC and (CHH)2KHHC, was designated as RH. Then, DOX was immobilized on RH via pH-sensitive hydrazone bonds to obtain RHD. The positively charged RHD could compress p53 plasmid to form RHD/p53 complexes. After RHD/p53 complexes accumulated in tumor sites, the ability of cell penetrating by cationic peptide (CRR)2KRRC would facilitate the cellular internalization of complexes. Then, the complexes would be trapped in endosome, and the cleavage of hydrazone bonds in the intracellular acidic endosome could lead to pH-induced release of DOX. Additionally, the ability of protonation by (CHH)2KHHC could promote the escape of complexes from endosome to cytoplasm. Due to the cleavage of disulfide bonds triggered by the high-content GSH in cytoplasm, the complexes would be degraded and released p53 for co-therapy to improve antitumor efficacy. Both in vitro and in vivo studies indicated that dual responsive co-delivery system RHD/p53 could enhance antitumor efficacy, which provides a useful strategy for co-delivery of different therapeutic agents in tumor treatment.

Dual stimuli-sensitive dendrimers: Photothermogenic gold nanoparticle-loaded thermo-responsive elastin-mimetic dendrimers

Dendrimers are synthetic macromolecules with unique structures that can work as nanoplatforms for both photothermogenic gold nanoparticles (AuNPs) and thermosensitive elastin-like peptides (ELPs) with valine-proline-glycine-valine-glycine (VPGVG) repeats. In this study, photothermogenic AuNPs were loaded into thermo-responsive elastin-mimetic dendrimers (dendrimers conjugating ELPs at their periphery) to produce dual stimuli-sensitive nanoparticles. Polyamidoamine G4 dendrimers were modified with acetylated VPGVG and (VPGVG)2, and the resulting materials were named ELP1-den and ELP2-den, respectively. The AuNPs were prepared by the reduction of Au ions using a dendrimer-nanotemplated method. The AuNP-loaded elastin-mimetic dendrimers exhibited photothermal properties. ELP1-den and ELP2-den showed similar temperature-dependent changes in their conformations. Phase transitions were observed at around 55°C and 35°C for the AuNP-loaded ELP1-den and AuNP-loaded ELP2-den, respectively, but not for the corresponding PEGylated dendrimer. In contrast to the AuNP-loaded PEGylated dendrimer, AuNP-loaded ELP2-den readily associated with cells and induced efficient photocytotoxicity at 37°C. The cell association and the photocytotoxicity properties of AuNP-loaded ELP2-den could be controlled by temperature. These results therefore suggest that dual stimuli-sensitive dendrimer nanoparticles of this type could be used for photothermal therapy.

Effect of main chain conformation on thermosensitivity in elastin-like peptide-grafted polylysine

Conformation change of the main chain promoted the phase transition of elastin-like peptide-grafted polymer.

Recent advances in liposomal nanohybrid cerasomes as promising drug nanocarriers

Liposomes have been extensively investigated as possible carriers for diagnostic or therapeutic agents due to their unique properties. However, liposomes still have not attained their full potential as drug and gene delivery vehicles because of their insufficient morphological stability. Recently, a super-stable and freestanding hybrid liposomal cerasome (partially ceramic- or silica-coated liposome) has drawn much attention as a novel drug delivery system because its atomic layer of polyorganosiloxane surface imparts higher morphological stability than conventional liposomes and its liposomal bilayer structure reduces the overall rigidity and density greatly compared to silica nanoparticles. Cerasomes are more biocompatible than silica nanoparticles due to the incorporation of the liposomal architecture into cerasomes. Cerasomes combine the advantages of both liposomes and silica nanoparticles but overcome their disadvantages so cerasomes are ideal drug delivery systems. The present review will first highlights some of the key advances of the past decade in the technology of cerasome production and then review current biomedical applications of cerasomes, with a view to stimulating further research in this area of study.

Protein-triggered supramolecular disassembly: insights based on variations in ligand location in amphiphilic dendrons

We use monodisperse dendrons that allow control over functional group presentation to investigate the influence of the location of a ligand on protein-induced disassembly and release of encapsulated small molecules. Based on both experiments and molecular dynamics simulations, we demonstrate that ligand location greatly influences release of guest molecules from the dendron-based supramolecular assembly. We show that a ligand moiety grafted to the dendron periphery is more accessible for the target protein in aqueous solution. On the other hand, the ligand moiety placed at the focal point or at the intermediate layer within the dendritic scaffold is less accessible, since it is surrounded by an environment rich in PEG chains, which hinders binding and even influences nonspecific interactions. We also demonstrate that the specific binding between one ligand and the target protein can destabilize the dendritic assembly. Furthermore, if more ligands are available, multivalent interactions are also possible with extravidin, which speed up disassembly and trigger the release of hydrophobic guests.

pH-responsive mesoporous silica nanoparticles employed in controlled drug delivery systems for cancer treatment

In the fight against cancer, controlled drug delivery systems have emerged to enhance the therapeutic efficacy and safety of anti-cancer drugs. Among these systems, mesoporous silica nanoparticles (MSNs) with a functional surface possess obvious advantages and were thus rapidly developed for cancer treatment. Many stimuli-responsive materials, such as nanoparticles, polymers, and inorganic materials, have been applied as caps and gatekeepers to control drug release from MSNs. This review presents an overview of the recent progress in the production of pH-responsive MSNs based on the pH gradient between normal tissues and the tumor microenvironment. Four main categories of gatekeepers can respond to acidic conditions. These categories will be described in detail.

Carbon nanotubes as vaccine scaffolds

Carbon nanotubes display characteristics that are potentially useful in their development as scaffolds for vaccine compositions. These features include stability in vivo, lack of intrinsic immunogenicity, low toxicity, and the ability to be appended with multiple copies of antigens. In addition, the particulate nature of carbon nanotubes and their unusual properties of rapid entry into antigen-presenting cells, such as dendritic cells, make them especially useful as carriers of antigens. Early attempts demonstrating carbon nanotube-based vaccines can be used in both infectious disease settings and cancer are promising.

Design and synthesis of lipidic organoalkoxysilanes for the self-assembly of liposomal nanohybrid cerasomes with controlled drug release properties

This paper reports the facile design and synthesis of a series of lipidic organoalkoxysilanes with different numbers of triethoxysilane headgroups and hydrophobic alkyl chains linked by glycerol and pentaerythritol for the construction of cerasomes with regulated surface siloxane density and controlled release behavior. It was found that the number of triethoxysilane headgroups affected the properties of the cerasomes for encapsulation efficiency, drug loading capacity, and release behavior. For both water-soluble doxorubicin (DOX) and water-insoluble paclitaxel (PTX), the release rate from the cerasomes decreased as the number of triethoxysilane headgroups increased. The slower release rate from the cerasomes was attributed to the higher density of the siloxane network on the surface of the cerasomes, which blocks the drug release channels. In contrast to the release results with DOX, the introduction of one more hydrophobic alkyl chain into the cerasome-forming lipid resulted in a slower release rate of PTX from the cerasomes due to the formation of a more compact cerasome bilayer. An MTT viability assay showed that all of these drug-loaded cerasomes inhibited proliferation of the HepG2 cancer cell line. The fine tuning of the chemical structure of the cerasome-forming lipids would foster a new strategy to precisely regulate the release rate of drugs from cerasomes.

Expand classical drug administration ways by emerging routes using dendrimer drug delivery systems: a concise overview

Drugs are introduced into the body by numerous routes such as enteral (oral, sublingual and rectum administration), parenteral (intravascular, intramuscular, subcutaneous and inhalation administration), or topical (skin and mucosal membranes). Each route has specific purposes, advantages and disadvantages. Today, the oral route remains the preferred one for different reasons such as ease and compliance by patients. Several nanoformulated drugs have been already approved by the FDA, such as Abelcet®, Doxil®, Abraxane® or Vivagel®(Starpharma) which is an anionic G4-poly(L-lysine)-type dendrimer showing potent topical vaginal microbicide activity. Numerous biochemical studies, as well as biological and pharmacological applications of both dendrimer based products (dendrimers as therapeutic compounds per se, like Vivagel®) and dendrimers as drug carriers (covalent conjugation or noncovalent encapsulation of drugs) were described. It is widely known that due to their outstanding physical and chemical properties, dendrimers afforded improvement of corresponding carried-drugs as dendrimer-drug complexes or conjugates (versus plain drug) such as biodistribution and pharmacokinetic behaviors. The purpose of this manuscript is to review the recent progresses of dendrimers as nanoscale drug delivery systems for the delivery of drugs using enteral, parenteral and topical routes. In particular, we focus our attention on the emerging and promising routes such as oral, transdermal, ocular and transmucosal routes using dendrimers as delivery systems.

Multimodal delivery of irinotecan from microparticles with two distinct compartments

In the last several decades, research in the field of drug delivery has been challenged with the fabrication of carrier systems engineered to deliver therapeutics to the target site with sustained and controlled release kinetics. Herein, we report the fabrication of microparticles composed of two distinct compartments: i) one compartment containing a pH responsive polymer, acetal-modified dextran, and PLGA (polylactide-co-glycolide), and ii) one compartment composed entirely of PLGA. We demonstrate the complete release of dextran from the microparticles during a 10-hour period in an acidic pH environment and the complete degradation of one compartment in less than 24h. This is in congruence with the stability of the same microparticles in neutral pH over the 24-hour period. Such microparticles can be used as pH responsive carrier systems for drug delivery applications where their cargo will only be released when the optimum pH window is reached. The feasibility of the microparticle system for such an application was confirmed by encapsulating a cancer therapeutic, irinotecan, in the compartment containing the acetal-modified dextran polymer and the pH dependent release over a 5-day period was studied. It was found that upon pH change to an acidic environment, over 50% of the drug was first released at a rapid rate for 10h, similar to that observed for the dextran release, before continuing at a more controlled rate for 4 days. As such, these microparticles can play an important role in the fabrication of novel drug delivery systems due to the selective, controlled, and pH responsive release of their encapsulated therapeutics.

Doxorubicin-conjugated dendrimer/collagen hybrid gels for metastasis-associated drug delivery systems

Metastasis is a characteristic property of cancer cells, which degrade extracellular matrix containing collagen. We prepared a polymer prodrug-embedded collagen gel for metastasis-associated drug delivery. A collagen peptide-modified dendrimer that attached doxorubicin (Dox) via a pH-degradable linkage was synthesized as a polymer prodrug. Compared with free Dox, the diffusion of the dendrimer prodrug from the collagen gel was suppressed. Highly invasive MDA-MB-231 cells were more sensitive to the prodrug-hybrid collagen gel than poorly invasive MCF-7 cells, even though the cytotoxicity of the dendrimer prodrug by itself against these cells was almost identical. The cytotoxicity against MDA-MB-231 cells decreased in the presence of a matrix metalloproteinase (MMP) inhibitor, suggesting that the dendrimer prodrug/collagen hybrid gel was affected by MMP activity. The dendrimer prodrug/collagen hybrid gel not only suppressed tumor growth but also attenuated metastatic activity in vivo. Therefore, the dendrimer prodrug-embedded collagen gel is useful for cancer chemotherapy.

The anti-tumor efficiency of poly(L-glutamic acid) dendrimers with polyhedral oligomeric silsesquioxane cores

Peptide dendrimers represent superior drug carriers for their unique nanoarchitectures, excellent degradability and biocompatibility. In this research, poly(L-glutamic acid) dendrimers with polyhedral oligomeric silsesquioxane (POSS) as cores were synthesized. Tumor targeting moiety (biotin) and therapeutic drug doxorubicin (DOX) were immobilized on the dendrimers via pH-sensitive hydrazone bonds. The size distribution and morphology of the drug-dendrimer conjugates were characterized by DLS, AFM, and TEM. The drug release profiles, cellular uptake, in vitro and in vivo anti-tumor activities of the conjugates were investigated. The results revealed that the conjugates aggregated nanoparticles with the size around 100 nm. The drug-dendrimer conjugates could be internalized in mice breast cancer 4T1 cells efficiently. The IC50 of the conjugates was comparable to that of DOX·HCl. The in vivo experiments were carried out in mice xerograft breast cancer models, the results indicated that the inhibition efficiency of the DOX-dendrimer conjugates was much better than that of free DOX·HCl.

The synthesis and evaluation of polymer prodrug/collagen hybrid gels for delivery into metastatic cancer cells

Metastatic cancer cells degrade extracellular matrix containing collagen. In this study, a variety of different polymer prodrugs have been synthesized and embedded in collagen gels for application in a metastasis-associated drug delivery system (DDS). Dendrimer-doxorubicin (Dox) prodrugs were prepared with different surfaces, including collagen peptides and polyethylene glycol. Furthermore, Dox was conjugated to linear poly(glutamic acid) (poly-Glu) instead of the dendrimer. The cytotoxicities of each of these polymer prodrug systems against the poorly invasive MCF-7 and highly invasive MDA-MB-231 cells were similar. The highly invasive MDA-MB-231 cells, however, were more sensitive than the MCF-7 cells to the polymer prodrugs-embedded collagen gels, suggesting that these polymer prodrugs/collagen hybrid gels would be useful for the development of metastasis-associated DDSs. The cytotoxicities of the polymer prodrugs were dependent on their chemical compositions. The collagen peptide-conjugated dendrimer prodrug/collagen hybrid gel demonstrated in vivo anticancer effects in an orthotopic metastatic mouse model.

FROM THE CLINICAL EDITOR

In this study, a variety of polymer prodrugs have been synthesized and embedded in collagen gels to be used in a metastasis-associated drug delivery system, demonstrating in vivo anticancer effects in an orthotopic metastatic mouse model.