Transepithelial transport of poly(amidoamine) dendrimers across Caco-2 cell monolayers

Polyamidoamine Dendrimers: Brain-Targeted Drug Delivery Systems in Glioma Therapy

Glioma is the most common primary intracranial tumor, which is formed by the malignant transformation of glial cells in the brain and spinal cord. It has the characteristics of high incidence, high recurrence rate, high mortality and low cure rate. The treatments for glioma include surgical removal, chemotherapy and radiotherapy. Due to the obstruction of the biological barrier of brain tissue, it is difficult to achieve the desired therapeutic effects. To address the limitations imposed by the brain's natural barriers and enhance the treatment efficacy, researchers have effectively used brain-targeted drug delivery systems (DDSs) in glioma therapy. Polyamidoamine (PAMAM) dendrimers, as branched macromolecular architectures, represent promising candidates for studies in glioma therapy. This review focuses on PAMAM-based DDSs in the treatment of glioma, highlighting their physicochemical characteristics, structural properties as well as an overview of the toxicity and safety profiles.

Nanostructure-Mediated Transport of Therapeutics through Epithelial Barriers

The ability to precisely treat human disease is facilitated by the sophisticated design of pharmacologic agents. Nanotechnology has emerged as a valuable approach to creating vehicles that can specifically target organ systems, effectively traverse epithelial barriers, and protect agents from premature degradation. In this review, we discuss the molecular basis for epithelial barrier function, focusing on tight junctions, and describe different pathways that drugs can use to cross barrier-forming tissue, including the paracellular route and transcytosis. Unique features of drug delivery applied to different organ systems are addressed: transdermal, ocular, pulmonary, and oral delivery. We also discuss how design elements of different nanoscale systems, such as composition and nanostructured architecture, can be used to specifically enhance transepithelial delivery. The ability to tailor nanoscale drug delivery vehicles to leverage epithelial barrier biology is an emerging theme in the pursuit of facilitating the efficacious delivery of pharmacologic agents.

Functionalized PAMAM constructed nanosystems for biomacromolecule delivery

Polyamidoamines (PAMAMs) are a class of dendrimer with monodispersity and controlled topology, which can deliver biologically active macromolecules (e.g., genes and proteins) to specific regions with high efficiency and minimum side effects. In detail, PAMAMs can be functionalized easily by core modification or surface amendment to encapsulate a wide range of biomacromolecules. Besides, self-assembled, cross-linked and hybrid PAMAMs with customized therapeutic purposes are developed as delivery vehicles, which makes PAMAMs promising for biomacromolecule therapy. In this review, we comprehensively summarize the application of PAMAMs in biomacromolecule delivery from the synthesis of functionalized PAMAM carriers to the development of PAMAM-based drug delivery systems. The underlying strategies for PAMAM functionalization and assembly are first systematically discussed, and then the current applications of PAMAMs for biomacromolecule delivery are reviewed. Finally, a brief perspective on the further applications of PAMAMs concludes, aiming to provide insights into developing PAMAM-based biomacromolecule delivery systems.

Clinical translational barriers against nanoparticle-based imaging agents

Nanoparticle based imaging agents (NIAs) have been intensively explored in bench studies. Unfortunately, only a few cases have made their ways to clinical translation. In this review, clinical trials of NIAs were investigated for understanding possible barriers behind that. First, the complexity of multifunctional NIAs is considered a main barrier because it brings uncertainty to batch-to-batch fabrication, and results in sophisticated in vivo behaviors. Second, inadequate biosafety studies slow down the translational work. Third, NIA uptake at disease sites is highly heterogeneous, and often exhibits poor targeting efficiency. Focusing on the aforementioned problems, key design parameters were analyzed including NIAs' size, composition, surface characteristics, dosage, administration route, toxicity, whole-body distribution and clearance in clinical trials. Possible strategies were suggested to overcome these barriers. Besides, regulatory guidelines as well as scale-up and reproducibility during manufacturing process were covered as they are also key factors to consider during clinical translation of NIAs.

Surface Engineered Dendrimers: A Potential Nanocarrier for the Effective Management of Glioblastoma Multiforme

Gliomas are the most prevailing intracranial tumors, which account for approximately 36% of the primary brain tumors of glial cells. Glioblastoma multiforme (GBM) possesses a higher degree of malignancy among different gliomas. The blood-brain barrier (BBB) protects the brain against infections and toxic substances by preventing foreign molecules or unwanted cells from entering the brain parenchyma. Nano-carriers such as liposomes, nanoparticles, dendrimers, etc. boost the brain permeability of various anticancer drugs or other drugs. The favorable properties like small size, better solubility, and the modifiable surface of dendrimers have proven their broad applicability in the better management of GBM. However, in vitro and in vivo toxicities caused by dendrimers have been a significant concern. The presence of multiple functionalities on the surface of dendrimers enables the grafting of target ligand and/or therapeutic moieties. Surface engineering improves certain properties like targeting efficiency, pharmacokinetic profile, therapeutic effect, and toxicity reduction. This review will be focused on the role of different surface-modified dendrimers in the effective management of GBM.

Safety Challenges and Application Strategies for the Use of Dendrimers in Medicine

Dendrimers are used for a variety of applications in medicine but, due to their host–guest and entrapment characteristics, are particularly used for the delivery of genes and drugs. However, dendrimers are intrinsically toxic, thus creating a major limitation for their use in biological systems. To reduce such toxicity, biocompatible dendrimers have been designed and synthesized, and surface engineering has been used to create advantageous changes at the periphery of dendrimers. Although dendrimers have been reviewed previously in the literature, there has yet to be a systematic and comprehensive review of the harmful effects of dendrimers. In this review, we describe the routes of dendrimer exposure and their distribution in vivo. Then, we discuss the toxicity of dendrimers at the organ, cellular, and sub-cellular levels. In this review, we also describe how technology can be used to reduce dendrimer toxicity, by changing their size and surface functionalization, how dendrimers can be combined with other materials to generate a composite formulation, and how dendrimers can be used for the diagnosis of disease. Finally, we discuss future challenges, developments, and research directions in developing biocompatible and safe dendrimers for medical purposes.

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.

Dendrimers as Antiamyloid Agents

Dendrimer-protein conjugates have significant prospects for biological applications. The complexation changes the biophysical behavior of both proteins and dendrimers. The dendrimers could influence the secondary structure of proteins, zeta-potential, distribution of charged regions on the surface, the protein-protein interactions, etc. These changes offer significant possibilities for the application of these features in nanotheranostics and biomedicine. Based on the dendrimer-protein interactions, several therapeutic applications of dendrimers have emerged. Thus, the formation of stable complexes retains the disordered proteins on the aggregation, which is especially important in neurodegenerative diseases. To clarify the origin of these properties and assess the efficiency of action, the mechanism of protein-dendrimer interaction and the nature and driving force of binding are considered in this review. The review outlines the antiamyloid activity of dendrimers and discusses the effect of dendrimer structures and external factors on their antiamyloid properties.

Reversing Aβ Fibrillation and Inhibiting Aβ Primary Neuronal Cell Toxicity Using Amphiphilic Polyphenylene Dendrons

Uncontrolled amyloid-beta (Aβ) fibrillation leads to the deposition of neurotoxic amyloid plaques and is associated with Alzheimer's disease. Inhibiting Aβ monomer fibrillation and dissociation of the formed fibers is regarded as a promising therapeutic strategy. Here, amphiphilic polyphenylene dendrons (APDs) are demonstrated to interrupt Aβ assembly and reduce Aβ-cell interactions. Containing alternating negatively charged sulfonic acid and hydrophobic n-propyl peripheral groups, APDs bind to the secondary structure of the Aβ aggregates, inhibiting fibrillation and disassemble the already formed Aβ fibrils. APDs reveal vesicular cellular uptake in endosomes as well as cell compatibility for endothelial and neuronal cells, and significantly reduce Aβ-induced neuron cytotoxicity in vitro. Moreover, they are transported into the brain and successfully cross the blood-brain barrier after systemic application in mice, indicating their high potential to inhibit Aβ fibrillation in vivo, which can be beneficial for developing therapeutic strategy for Alzheimer's disease.

Emerging innate biological properties of nano-drug delivery systems: A focus on PAMAM dendrimers and their clinical potential

Drug delivery systems or vectors are usually needed to improve the bioavailability and effectiveness of a drug through improving its pharmacokinetics/pharmacodynamics at an organ, tissue or cellular level. However, emerging technologies with sensitive readouts as well as a greater understanding of physiological/biological systems have revealed that polymeric drug delivery systems are not biologically inert but can have innate or intrinsic biological actions. In this article, we review the emerging multiple innate biological/toxicological properties of naked polyamidoamine (PAMAM) dendrimer delivery systems in the absence of any drug cargo and discuss their correlation with the defined physicochemical properties of PAMAMs in terms of molecular size (generation), architecture, surface charge and chemistry. Further, we assess whether any of the reported intrinsic biological actions of PAMAMs such as their antimicrobial activity or their ability to sequester glucose and modulate key protein interactions or cell signaling pathways, can be exploited clinically such as in the treatment of diabetes and its complications.

There and back again: a dendrimer's tale

The development of molecular nanostructures with well-defined particle size and shape is of eminent interest in biomedicine. Among many studied nanostructures, dendrimers represent the group of those most thoroughly characterized ones. Due to their unique structure and properties, dendrimers are very attractive for medical and pharmaceutical applications. Owing to the controllable cavities inside the dendrimer, guest molecules may be encapsulated, and highly reactive terminal groups are susceptible to further modifications, e.g., to facilitate target delivery. To understand the potential of these nanoparticles and to predict and avoid any adverse cellular reactions, it is necessary to know the mechanisms responsible for an efficient dendrimer uptake and the destination of their intracellular journey. In this article, we summarize the results of studies describing the dendrimer uptake, traffic, and efflux mechanisms depending on features of specific nanoparticles and cell types. We also present mechanisms of dendrimers responsible for toxicity and alteration in signal transduction pathways at the cellular level.

Remineralization of dentin induced by a compound of polyamide-amine and chlorhexidine in a resin dentin bonding microenvironment

Background

The purpose of this study was to investigate the effect of a complex of polyamide-amine dendrimer (PAMAM) and chlorhexidine gluconate (CG) on remineralization of dentin in an artificial simulated resin dentin bonding microenvironment.

Methods

The structure of this complex was characterized by FT-IR. Twelve standard dentin samples were randomly divided into four treatment fluid groups namely a PAMAM group, CG group, PAMAM + CG group, and deionized water group. A microenvironmental mineralization model was established in vitro with 50 µm gap width between resin and dentin. The dentin surface was observed by a scanning electron microscope (SEM), and the chemical structure of the surface was analyzed by X-ray energy spectrum (EDS), X-ray diffraction (XRD), and laser Raman spectroscopy.

Results

SEM showed the density of dentinal tubules exposed in the PAMAM group decreased after a 14-day immersion, with corn rod-shaped crystal structures gathered around the tubules. In addition, visible mineralization occurred in partial areas of the CG group, rod-shaped crystals and in comparison, dentinal tubules in the PAMAM + CG group were almost completely covered by flaky crystal structures. Raman spectrum analysis showed that crystals formed by PAMAM, CG, and PAMAM + CG solution all had strong phosphate characteristic peaks, indicating the presence of hydroxyapatite (HA), that of the PAMAM + CG group was the strongest. The EDS results showed that the Ca and P levels of the PAMAM group and the CG group were slightly higher than those of the deionized water group, while PAMAM + CG group significantly higher than the others, Ca/P value approaching 1.67. The results of XRD showed the characteristic peaks of hydroxyapatite detected by the PAMAM + CG group at 2θ=26.0 (002), 2θ=32.0 (211), and 2θ=33.0 (112) were high and sharp, with a few diffraction line burrs indicating it had high crystallinity and purity. The Scherrer equation results showed that the appearance and size of the grains formed by the PAMAM + CG group were basically consistent with those of healthy dentin.

Conclusions

Altogether, the compound of polyamide-amine dendrimer and chlorhexidine could induce the remineralization of human dentin in a resin dentin bonding microenvironment with a gap of 50 µm to form a crystal structure similar to dentin hydroxyapatite.

Evaluation of Cytotoxicity of Self-Emulsifying Formulations Containing Long-Chain Lipids Using Caco-2 Cell Model: Superior Safety Profile Compared to Medium-Chain Lipids

Medium-chain (MC) and long-chain (LC) lipids are used for development of self-emulsifying drug delivery systems (SEDDS). MC lipids are often preferred because of their ability to form stable microemulsions with relatively high drug solubilization capacity. On the other hand, LC lipids could be more biocompatible as most endogenous and dietary lipids are LC glycerides. They also maintain high drug solubilization capacity after digestion. The present study was undertaken to determine the cytotoxicity of LC lipids and their formulations on Caco-2 cells of 1-day, 5-day, and 21-day maturity. The results were compared with the cytotoxicity profiles of MC lipids reported previously from our laboratory. The cell viability and cell membrane integrity were, respectively, determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and the lactate dehydrogenase assay. The cytotoxicity was partially due to lipid surfactant-induced membrane rupture, and it was influenced by cell maturity and formulation composition. The lipid-surfactant combinations showed greater tolerance than surfactants alone, and LC-SEDDS were well-tolerated at almost 10-fold higher concentration than corresponding MC-SEDDS. Furthermore, the cytotoxicity of digestion end products of both LC and MC triglycerides in the presence of 3 mM sodium taurocholate was compared on 21-day Caco-2 cultures by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The LC lipid formulations showed better tolerance than MC lipid formulations after digestion. Thus, although MC and LC lipids are well-tolerated at doses normally administered to humans, LC lipids show much better safety than MC lipids in a cell-culture model.

pH-Sensitive Magnetite Nanoparticles Modified with Hyperbranched Polymers and Folic Acid for Targeted Imaging and Therapy

Objective:

A novel pH-sensitive superparamagnetic drug delivery system was developed based on quercetin loaded hyperbranched polyamidoamine-b-polyethylene glycol-folic acid-modified Fe3O4 nanoparticles (Fe3O4@PAMAM-b-PEG-FA).

Methods:

The nanoparticles exhibit excellent water dispersity with well-defined size distribution (around 51.8 nm) and strong magnetisability. In vitro release studies demonstrated that the quercetinloaded Fe3O4@PAMAM-b-PEG-FA nanoparticles are stable at normal physiologic conditions (pH 7.4 and 37°C) but sensitive to acidic conditions (pH 5.6 and 37°C), which led to the rapid release of the loaded drug.

Results:

Fluorescent microscopy results indicated that the Fe3O4@PAMAM-b-PEG-FA nanoparticles could be efficiently accumulated in tumor tissue compared with non-folate conjugated nanoparticles. Also, in comparison with free quercetin, the quercetin loaded Fe3O4@PAMAM-b-PEG-FA exerts higher cytotoxicity. Furthermore, this magnetic nanocarrier showed high MRI sensitivity, even in its lower iron content.

Conclusion:

The results indicated that the prepared nanoparticles are an effective chemotherapy and diagnosis system to inhibit proliferation and monitor the progression of tumor cells, respectively.

Advances in drug delivery, gene delivery and therapeutic agents based on dendritic materials

Dendrimers are synthetic polymers that grow in three dimensions into well-defined structures. Their morphological appearance resembles a number of trees connected by a common point. Dendritic nanoparticles have been studied for a large number of pharmaceutical and biomedical applications including gene and drug delivery, clinical diagnosis and MRI. Despite the application of dendrimers, research is still in its childhood in comparison with liposomes and other nanomaterials. They are now playing a key role in several therapeutic strategies, with dendrimer-based products in clinical trials. The aim of this review is to describe the state-of-the-art of biomedical applications of dendrimers – and dendrimer conjugates – such as drug and gene delivery and antiviral activity.

Exploration of biomedical dendrimer space based on in-vitro physicochemical parameters: key factor analysis (Part 1)

Dendrimers are highly branched, star-shaped macromolecules with nanometer-scale dimensions that can be readily modified with a range of functional groups, thus modifying their physicochemical and biological properties. In nanomedicine, dendrimers can be used as vectors for the targeted delivery strategy of a variety of biologically active agents or can be used as drug per se. In the future, it will be necessary to designate and develop 'safe' dendrimers, which is currently a crucial concern. Here, we analyze the key in vitro physicochemical parameters to be considered for preclinical evaluation of biomedical dendrimers.

Polymeric Nanoparticles in Gene Therapy: New Avenues of Design and Optimization for Delivery Applications

The field of polymeric nanoparticles is quickly expanding and playing a pivotal role in a wide spectrum of areas ranging from electronics, photonics, conducting materials, and sensors to medicine, pollution control, and environmental technology. Among the applications of polymers in medicine, gene therapy has emerged as one of the most advanced, with the capability to tackle disorders from the modern era. However, there are several barriers associated with the delivery of genes in the living system that need to be mitigated by polymer engineering. One of the most crucial challenges is the effectiveness of the delivery vehicle or vector. In last few decades, non-viral delivery systems have gained attention because of their low toxicity, potential for targeted delivery, long-term stability, lack of immunogenicity, and relatively low production cost. In 1987, Felgner et al. used the cationic lipid based non-viral gene delivery system for the very first time. This breakthrough opened the opportunity for other non-viral vectors, such as polymers. Cationic polymers have emerged as promising candidates for non-viral gene delivery systems because of their facile synthesis and flexible properties. These polymers can be conjugated with genetic material via electrostatic attraction at physiological pH, thereby facilitating gene delivery. Many factors influence the gene transfection efficiency of cationic polymers, including their structure, molecular weight, and surface charge. Outstanding representatives of polymers that have emerged over the last decade to be used in gene therapy are synthetic polymers such as poly(l-lysine), poly(l-ornithine), linear and branched polyethyleneimine, diethylaminoethyl-dextran, poly(amidoamine) dendrimers, and poly(dimethylaminoethyl methacrylate). Natural polymers, such as chitosan, dextran, gelatin, pullulan, and synthetic analogs, with sophisticated features like guanidinylated bio-reducible polymers were also explored. This review outlines the introduction of polymers in medicine, discusses the methods of polymer synthesis, addressing top down and bottom up techniques. Evaluation of functionalization strategies for therapeutic and formulation stability are also highlighted. The overview of the properties, challenges, and functionalization approaches and, finally, the applications of the polymeric delivery systems in gene therapy marks this review as a unique one-stop summary of developments in this field.

Chlorambucil Conjugated Ugi Dendrimers with PAMAM-NH₂ Core and Evaluation of Their Anticancer Activity

Herein, a new Ugi multicomponent reaction strategy is described to enhance activity and solubility of the chemotherapeutic drug chlorambucil through its conjugation to poly(amidoamine) (PAMAM-NH₂) dendrimers with the simultaneous introduction of lipidic (i-Pr) and cationic (⁻NH₂) or anionic (⁻COOH) groups. Standard viability assays were used to evaluate the anticancer potential of the water-soluble dendrimers against PC-3 prostate and HT-29 colon cancer cell lines, as well as non-cancerous mouse NIH3T3 fibroblasts. It could be demonstrated that the anticancer activity against PC-3 cells was considerably improved when both chlorambucil and ⁻NH₂ (cationic) groups were present on the dendrimer surface (1b). Additionally, this dendrimer showed activity only against the prostate cancer cells (PC-3), while it did not affect colon cancer cells and fibroblasts significantly. The cationic chlorambucil-dendrimer 1b blocks PC-3 cells in the G2/M phase and induces caspase independent apoptosis.

New Advances in General Biomedical Applications of PAMAM Dendrimers

Dendrimers are nanoscopic compounds, which are monodispersed, and they are generally considered as homogeneous. PAMAM (polyamidoamine) was introduced in 1985, by Donald A. Tomalia, as a new class of polymers, named 'starburst polymers'. This important contribution of Professor Tomalia opened a new research field involving nanotechnological approaches. From then on, many groups have been using PAMAM for diverse applications in many areas, including biomedical applications. The possibility of either linking drugs and bioactive compounds, or entrapping them into the dendrimer frame can improve many relevant biological properties, such as bioavailability, solubility, and selectivity. Directing groups to reach selective delivery in a specific organ is one of the advanced applications of PAMAM. In this review, structural and safety aspects of PAMAM and its derivatives are discussed, and some relevant applications are briefly presented. Emphasis has been given to gene delivery and targeting drugs, as advanced delivery systems using PAMAM and an incentive for its use on neglected diseases are briefly mentioned.

Perspectives of Dendrimer-based Nanoparticles in Cancer Therapy

Currently, cancer is the second most common cause of death in the United States, exceeded only by heart disease. Chemotherapy traditionally suffers from a non-specific distribution, with only a small fraction of the drug reaching the tumor, in this sense, the use of dendrimers incorporating drugs non-covalently encapsulated inside the dendrimer or covalently conjugated have proven to be effectives against different cancer cell lines. However, at present the dendrimers used as drug-carriers still do not meet the necessary characteristic to be considered as an ideal dendrimer for drug delivery; high toxicity, bio-degradability, low toxicity, biodistribution characteristics, and favorable retention with appropriate specificity and bioavailability have not been fully covered by the current available dendrimers. However, the development and study of new dendrimers drug-carriers continues to be an important tool in the cancer therapy as they can be functionalized with varied ligands to reach the tumor tissue through the different body barriers in the body with minimal loss of activity in the bloodstream, have the ability to selectively kill tumor cells without affecting the normal cells and most important with a release mechanism controlling actively. Given the continuous efforts and research in this area of interest, we presented in this review the work done with a special emphasis on the development of dendrimers as a major tool in the combination with drugs, as a potential adjunctive agent in anticancer therapy.

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.

PAMAM dendrimer - cell membrane interactions

PAMAM dendrimers have been conjectured for a wide range of biomedical applications due to their tuneable physicochemical properties. However, their application has been hindered by uncertainties in their cytotoxicity, which is influenced by dendrimer generation (i.e. size and surface group density), surface chemistry, and dosage, as well as cell specificity. In this review, biomedical applications of polyamidoamine (PAMAM) dendrimers and some related cytotoxicity studies are first outlined. Alongside these in vitro experiments, lipid membranes such as supported lipid bilayers (SLBs), liposomes, and Langmuir monolayers have been used as cell membrane models to study PAMAM dendrimer-membrane interactions. Related experimental and theoretical studies are summarized, and the physical insights from these studies are discussed to shed light on the fundamental understanding of PAMAM dendrimer-cell membrane interactions. We conclude with a summary of some questions that call for further investigations.

Drug Delivery Systems from Self-Assembly of Dendron-Polymer Conjugates †

This review highlights the utilization of dendron-polymer conjugates as building blocks for the fabrication of nanosized drug delivery vehicles. The examples given provide an overview of the evolution of these delivery platforms, from simple micellar containers to smart stimuli- responsive drug delivery systems through their design at the macromolecular level. Variations in chemical composition and connectivity of the dendritic and polymeric segments provide a variety of self-assembled micellar nanostructures that embody desirable attributes of viable drug delivery systems.

Bendamustine-PAMAM Conjugates for Improved Apoptosis, Efficacy, and in Vivo Pharmacokinetics: A Sustainable Delivery Tactic

Successful delivery of a chemotherapeutic agent like bendamustine still remains a challenge in clinical conditions like chronic lymphatic leukemia (CLL), non-Hodgkin lymphoma (NHL), and multiple myeloma. We have conjugated bendamustine to polyamidoamine (PAMAM) dendrimers after conjugating with N-(hydroxyethyl)maleimide (spacer) via an ester bond. The particle size of PAMAM-bendamustine conjugate was 49.8 ± 2.5 nm. In vitro drug release resulted in sustained release with improved solution stability of drug up to 72 h. In a 24 h cytotoxicity study by MTT assay against human monoblastic leukemia cells (THP-1), the IC50 value for PAMAM-bendamustine was 32.1 ± 4.8 μM compared to 50.42 ± 3.4 μM and 2303 ± 106.5 μM for bendamustine and PAMAM dendrimer, respectively. Significantly higher cell uptake and apoptosis were observed in THP-1 cells by PAMAM-bendamustine conjugate which was confirmed by flow cytometry and confocal laser scanning microscopy. Preliminary in vivo studies undertaken included pharmacokinetics studies, organ distribution studies, and tumor inhibition studies. In healthy Wistar rat model (1CBM IV push model), the pharmacokinetic studies revealed that bioavailability and t_1/2 increased significantly, i.e., almost 8.5-fold (193.8 ± 1.116 vs 22.8 ± 0.158 μg mL^-1/h) and 5.1-fold (0.75 ± 0.005 vs 3.85 ± 0.015 h), respectively, for PAMAM-bendamustine conjugate compared to pure bendamustine ( p < 0.05), however, clearance and volume of distribution were found to be decreased compared to those of free drug. The study suggests that PAMAM-bendamustine conjugate was not only stable for the longer period but also least toxic and highly taken up by THP-1 cells to exert an anticancer effect at the reduced dose. Tumor inhibition and biodistribution studies in tumor-bearing BALB/c mice revealed that PAMAM-bendamustine conjugate was more effective than the pure drug and showed higher accumulation in the tumor.

Pediatric oral formulation of dendrimer-N-acetyl-l-cysteine conjugates for the treatment of neuroinflammation

N-Acetyl-l-cysteine (NAC) commonly used as an antidote in acetaminophen poisoning has shown promise in the treatment of neurological disorders such as cerebral palsy (CP). However, NAC suffers from drawbacks such as poor oral bioavailability and suboptimal blood-brain-barrier (BBB) permeability limiting its clinical success. It was previously demonstrated that intravenous administration of dendrimer-NAC (D-NAC) conjugates have shown significant promise in the targeted treatment of neuroinflammation, in multiple preclinical models. Development of an oral formulation of D-NAC may open new administrative routes for this compound. Here, we report the gastrointestinal stability, in vitro transepithelial permeability, and in vivo oral absorption and pharmacokinetics in rats of a pediatric formulation of D-NAC containing Capmul MCM (glycerol monocaprylate) as a penetration enhancer. D-NAC was stable for 6 h in all five simulated gastrointestinal fluids with no signs of chemical degradation. The apparent permeability (P_app) of D-NAC increased 9-fold in the formulation containing Capmul. The area under the curve [AUC]_0-∞ of D-NAC with Capmul increased by 47% when compared to D-NAC alone. These results indicate that an oral pediatric formulation containing D-NAC and Capmul can be an effective option for the treatment of neuroinflammation.

Dendritic polymers for dermal drug delivery

Skin-mediated therapeutic delivery is a potential alternative to traditional drug delivery approaches. However, dermal drug delivery is limited to the molecules with optimal physico-chemical properties. To overcome this barrier for delivering ‘nonideal’ drug molecules across the skin, different drug carriers and penetration enhancement methods have been investigated. Conventional chemical and physical approaches for dermal drug delivery are limited by their skin irritation potential, complexity of application and poor patient compliance. In recent years, dendritic polymers have shown potential in improving the dermal delivery of various molecules. With minimal skin irritation potential and high drug loading capacity, dendrimers offer multiple advantages for improving delivery of drugs across the skin. The current review aims to provide an overview of dendritic polymers for dermal (topical and transdermal) drug delivery.

[Formula: see text]

In Vitro Evaluation of Third Generation PAMAM Dendrimer Conjugates

The present study compares the use of high generation G3 and low generation G0 Polyamidoamine (PAMAM) dendrimers as drug carriers of naproxen (NAP), a poorly water soluble drug. Naproxen was conjugated to G3 in different ratios and to G0 in a 1:1 ratio via a diethylene glycol linker. A lauroyl chain (L), a lipophilic permeability enhancer, was attached to G3 and G0 prodrugs. The G3 and G0 conjugates were more hydrophilic than naproxen as evaluated by the measurement of partitioning between 1-octanol and a phosphate buffer at pH 7.4 and pH 1.2. The unmodified surface PAMAM-NAP conjugates showed significant solubility enhancements of NAP at pH 1.2; however, with the number of NAP conjugated to G3, this was limited to 10 molecules. The lactate dehydrogenase (LDH) assay indicated that the G3 dendrimer conjugates had a concentration dependent toxicity towards Caco-2 cells. Attaching naproxen to the surface of the dendrimer increased the IC₅₀ of the resulting prodrugs towards Caco-2 cells. The lauroyl G3 conjugates showed the highest toxicity amongst the PAMAM dendrimer conjugates investigated and were significantly more toxic than the lauroyl-G0-naproxen conjugates. The permeability of naproxen across monolayers of Caco-2 cells was significantly increased by its conjugation to either G3 or G0 PAMAM dendrimers. Lauroyl-G0 conjugates displayed considerably lower cytotoxicity than G3 conjugates and may be preferable for use as a drug carrier for low soluble drugs such as naproxen.

Dendrimers for Ocular Drug Delivery

Existing methods of administering ocular drugs are limited in either their safety or efficiency. Nanomedicine therapies have the potential to address this deficiency by creating vehicles that can control drug biodistribution. Dendrimers are synthetic polymeric nanoparticles with a unique highly organized branching structure. In recent years, promising results using dendrimer vehicles to deliver ocular drugs through different routes of administration have been reported. In this review, we briefly summarize these results with emphasis on the dendrimer modifications used to target different ocular structures.

Skin Delivery of EGCG and Silibinin: Potential of Peptide Dendrimers for Enhanced Skin Permeation and Deposition

The aim of the present study was to evaluate the ability of the peptide dendrimers to facilitate transdermal delivery of antioxidants, silibinin, and epigallocatechin-3-gallate (EGCG). Drug-peptide dendrimer complexes were prepared and evaluated for their ability to permeate across the skin. The data revealed the ready formation of complexes between drug and peptide dendrimer in a molar ratio of 1:1. In vitro permeation studies using excised rat skin and drug-peptide dendrimer complexes showed highest values for cumulative drug permeation at the end of 12 h (Q₁₂), with corresponding permeability coefficient (Kp) and enhancement ratio values also determined at this time point. With silibinin, 3.96-, 1.81-, and 1.06-fold increase in skin permeation was observed from silibinin-peptide dendrimer complex, simultaneous application of silibinin + peptide dendrimer, and pretreatment of skin with peptide dendrimer, respectively, in comparison with passive diffusion. With EGCG, 9.82-, 2.04-, and 1.72-fold increase in skin permeation was observed from EGCG-peptide dendrimer complex, simultaneous application of EGCG + peptide dendrimer, and pretreatment of skin with peptide dendrimer, respectively, in comparison with passive diffusion. The present study demonstrates the application of peptide dendrimers in effectively delivering antioxidants such as EGCG and silibinin into the skin, thus offering the potential to provide antioxidant effects when delivered via appropriately formulated topical preparations.

Perspectives on dendritic architectures and their biological applications: From core to cell

The challenges of medicine today include the increasing stipulation for sensitive and effective systems that can improve the pathological responses with a simultaneous reduction in accumulation and drug side effects. The demand can be fulfilled through the advancements in nanomedicine that includes nanostructures and nanodevices for diagnosing, treating, and prevention of various diseases. In this respect, the nanoscience provides various novel techniques with carriers such as micelles, dendrimers, particles and vesicles for the transportation of active moieties. Further, an efficient way to improve these systems is through stimuli a responsive system that utilizes supramolecular hyperbranched structures to meet the above criteria. The stimuli-responsive dendritic architectures exhibit spatial, temporal, convenient, effective, safety and controlled drug release in response to specific trigger through electrostatic interactions plus π stacking. The stimuli-responsive systems are capable of sequestering the drug molecules underneath a predefined set of conditions and discharge them in a different environment through either exogenous or endogenous stimulus. The incorporation of photoresponsive moieties at various components of dendrimer such as core, branches or at the peripheral end exaggerates its significance in various allied fields of nanotechnology which includes sensors, photoswitch, electronic widgets and in drug delivery systems. This is due to the light instigated geometrical modifications at the core or at the surface molecules which generates huge conformational changes throughout the hyperbranched structure. Further, numerous synthetic methodologies have been investigated for utilization of dendrimers in therapeutic drug delivery and its applicability towards stimuli responsive systems such as photo-instigated, thermal-instigated, and pH-instigated hyperbranched structures and their advancement in the field of nanomedicine. This paper highlights the fascinating theoretical advances and principal mechanisms of dendrimer synthesis and their ability to capture light that strengthens its applicability from radiant energy to medical photonics.

Polyvalent Folate-Dendrimer-Coated Iron Oxide Theranostic Nanoparticles for Simultaneous Magnetic Resonance Imaging and Precise Cancer Cell Targeting

The low therapeutic index of conventional chemotherapy and poor prognosis of patients diagnosed with metastatic cancers are prompting clinicians to adopt newer strategies to simultaneously detect cancer lesions at an early stage and to precisely deliver anticancer drugs to tumor sites. In this study, we employed a novel strategy to engineer a polyvalent theranostic nanocarrier consisting of superparamagnetic iron oxide nanoparticle core (SPIONs) decorated with folic acid-polyamidoamine dendrimers surface (FA-PAMAM). In addition, a highly potent hydrophobic anticancer agent 3,4-difluorobenzylidene-curcumin (CDF) was coloaded in the FA-PAMAM dendrimer to increase its solubility and assess its therapeutic potentials. The resulting targeted nanoparticles (SPIONs@FA-PAMAM-CDF) exhibited high MR contrast. When tested on folate receptor overexpressing ovarian (SKOV3) and cervical (HeLa) cancer cells, the CDF loaded targeted nanoformulations showed higher accumulation with a better anticancer activity as compared to the nontargeted counterparts, possibly due to multivalent folate receptor binding interaction with cells overexpressing the target. The results were corroborated by observation of a larger population of cells undergoing apoptosis due to upregulation of tumor suppressor phosphatase and tensis homologue (PTEN), caspase 3, and inhibition of NF-κB in groups treated with the targeted formulations, which further confirmed the ability of the multivalent theranostic nanoparticles for simultaneous imaging and therapy of cancers.

The effect of G3 PAMAM dendrimer conjugated with B-group vitamins on cell morphology, motility and ATP level in normal and cancer cells

In a search for the safe vitamin carrier the PAMAM G3 dendrimer covalently substituted with 9 and 10 molecules of vitamin B7 (biotin) and B6 (pyridoxal), respectively (BC-PAMAM) was investigated. Dendrimer substitution with B-group vitamins significantly alters its biological properties as compared to native form. Observed effects on investigated cell parameters including morphology, adhesion, migration and ATP level were different for normal human fibroblasts (BJ) and squamous cell carcinoma (SCC-15) cell lines. BC-PAMAM revealed significantly less pronounced effects on investigated parameters, particularly at higher concentrations (5-50μM), which is relevant with its lower positive surface charge, as compared with native form. The bioconjugate, up to 50μM concentration, appeared to be a safe vitamin carrier to normal fibroblasts, without significant effect on their adhesion, shape and migration as well as on intracellular ATP level. In SCC-15 cells BC-PAMAM, at low concentrations (0.1-0.5μM), altered the cell shape and increase adhesion, whereas at higher concentrations opposite effects were seen. Measurements of cellular level of ATP showed that higher resistance of cancer cells to toxic effects of native PAMAM dendrimers may be due to higher energy supply of cancer cells.

Mechanisms of transport of polymeric and lipidic nanoparticles across the intestinal barrier

Unraveling the mechanisms of nanoparticle transport across the intestinal barrier is essential for designing more efficient nanoparticles for oral administration. The physicochemical parameters of the nanoparticles (e.g., size, surface charge, chemical composition) dictate nanoparticle fate across the intestinal barrier. This review aims to address the most important findings regarding polymeric and lipidic nanoparticle transport across the intestinal barrier, including the evaluation of critical physicochemical parameters of nanoparticles that affect nanocarrier interactions with the intestinal barrier.

In vitro toxicity assessment of oral nanocarriers

The fascinating properties of nanomaterials opened new frontiers in medicine. Nanocarriers are useful systems in transporting drugs to site-specific targets. The unique physico-chemical characteristics making nanocarriers promising devices to treat diseases may also be responsible for potential adverse effects. In order to develop functional nano-based drug delivery systems, efficacy and safety should be carefully evaluated. To date, no common testing strategy to address nanomaterial toxicological challenges has been generated. Different cell culture models are currently used to evaluate nanocarrier safety using conventional in vitro assays, but overall they have generated a huge amount of conflicting data. In this review we describe state-of-the-art approaches for in vitro testing of orally administered nanocarriers, highlighting the importance of developing harmonized and validated standard operating procedures. These procedures should be applied in a safe-by-design context with the aim to reduce and/or eliminate the uncertainties and risks associated with nanomedicine development.