Dendrimer-Encapsulated Camptothecins: Increased Solubility, Cellular Uptake, and Cellular Retention Affords Enhanced Anticancer ActivityIn vitro

Dendrimers in combination with natural products and analogues as anti-cancer agents

Overview of the use of dendrimers in combination with encapsulated and conjugated natural products and analogues as anti-cancer agents.

A Novel Therapeutic Strategy for Cancer Using Phosphatidylserine Targeting Stearylamine-Bearing Cationic Liposomes

There is a pressing need for a ubiquitously expressed antigen or receptor on the tumor surface for successful mitigation of the deleterious side effects of chemotherapy. Phosphatidylserine (PS), normally constrained to the intracellular surface, is exposed on the external surface of tumors and most tumorigenic cell lines. Here we report that a novel PS-targeting liposome, phosphatidylcholine-stearylamine (PC-SA), induced apoptosis and showed potent anticancer effects as a single agent against a majority of cancer cell lines. We experimentally proved that this was due to a strong affinity for and direct interaction of these liposomes with PS. Complexation of the chemotherapeutic drugs doxorubicin and camptothecin in these vesicles demonstrated a manyfold enhancement in the efficacies of the drugs both in vitro and across three advanced tumor models without any signs of toxicity. Both free and drug-loaded liposomes were maximally confined to the tumor site with low tissue concentration. These data indicate that PC-SA is a unique and promising liposome that, alone and as a combination therapy, has anticancer potential across a wide range of cancer types.

Carrier-free, self-assembled pure drug nanorods composed of 10-hydroxycamptothecin and chlorin e6 for combinatorial chemo-photodynamic antitumor therapy in vivo

Carrier-free nanodrugs formulated from the supramolecular self-assembly of pure drug molecules have emerged as an innovative and promising strategy for tumor therapy. We report herein a new and simple method to directly assemble a small hydrophobic anticancer drug, 10-hydroxycamptothecin (HCPT), with a photosensitizer chlorin e6 (Ce6) to form stable, discrete nanorods (NRs), which not only circumvent the extreme hydrophobicity of HCPT but also incorporate two different modalities into one delivery system for combination therapy. Different ratios of HCPT to Ce6 were evaluated to afford the optimal nanoformulation. The as-prepared HCPT/Ce6 NRs were fully characterized, indicating a relatively uniform size of about 360 nm in length and 135 nm in width, and a surface charge of about -33 mV. Efficient internalization of the NRs by cancer cells was observed by using a confocal microscope and the generation of singlet oxygen species arising from the NRs under 655 nm laser irradiation was detected by DCFH-DA. As a result, very potent in vitro efficacy against several kinds of cancer cell lines was achieved through chemo-photodynamic dual therapy. The in vivo tumor suppression effect of HCPT/Ce6 NRs was verified on a subcutaneous xenograft mouse model, achieving almost complete inhibition of the tumor growth, which may benefit from the superiority of nanomedicine and combination therapy. The rationale of this facile and green strategy for carrier-free nanodrug formulation via the self-assembly approach might provide new opportunities for the development of combinatorial therapeutics for tumors.

Alpha-Tocopheryl Succinate-Conjugated G5 PAMAM Dendrimer Enables Effective Inhibition of Ulcerative Colitis

Ulcerative colitis (UC) is a severe inflammatory disease in colon, however, the therapeutic efficacy of the standard-of-care in clinic for UC patients is unsatisfactory. To explore new drugs for effective and safe treatment of UC, alpha-tocopheryl succinate (α-TOS) is conjugated to generation 5 (G5) poly(amidoamine) (PAMAM) dendrimer to construct a nanodevice of G5-NH-acetamide (Ac)-TOS. The inhibitory effects of the G5-NH-Ac-TOS on UC are evaluated in vivo in a dextran sulfate sodium induced UC mouse model, and its mechanisms are explored in vitro in lipopolysaccharide stimulated mouse peritoneal macrophages. The results indicate that the G5-NH-Ac-TOS exhibits greater inhibitive effects on UC than free α-TOS, through significant attenuation of the disease activity index and reduction of macrophage infiltration in the colon tissues. The protective mechanisms of the G5-NH-Ac-TOS are revealed to be related to inhibition of expression of nuclear translocation of NF-κB, phosphorylation of Akt, and reduction of reactive oxygen species production in the macrophages.

From Composition to Cure: A Systems Engineering Approach to Anticancer Drug Carriers

The molecular complexity and heterogeneity of cancer has led to a persistent, and as yet unsolved, challenge to develop cures for this disease. The pharmaceutical industry focuses the bulk of its efforts on the development of new drugs, but an alternative approach is to improve the delivery of existing drugs with drug carriers that can manipulate when, where, and how a drug exerts its therapeutic effect. For the treatment of solid tumors, systemically delivered drug carriers face significant challenges that are imposed by the pathophysiological barriers that lie between their site of administration and their site of therapeutic action in the tumor. Furthermore, drug carriers face additional challenges in their translation from preclinical validation to clinical approval and adoption. Addressing this diverse network of challenges requires a systems engineering approach for the rational design of optimized carriers that have a realistic prospect for translation from the laboratory to the patient.

Dendrimer pre-treatment enhances the skin permeation of chlorhexidine digluconate: Characterisation by in vitro percutaneous absorption studies and Time-of-Flight Secondary Ion Mass Spectrometry

Skin penetration and localisation of chlorhexidine digluconate (CHG) within the skin have been investigated in order to better understand and optimise the delivery using a nano polymeric delivery system of this topically-applied antimicrobial drug. Franz-type diffusion cell studies using in vitro porcine skin and tape stripping procedures were coupled with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) to visualise the skin during various treatments with CHG and polyamidoamine dendrimers (PAMAM). Pre-treatment of the skin with PAMAM dendrimers significantly increased the amount and depth of permeation of CHG into the skin in vitro. The effect observed was not concentration dependant in the range 0.5-10mM PAMAM. This could be important in terms of the efficiency of treatment of bacterial infection in the skin. It appears that the mechanism of enhancement is due to the PAMAM dendrimer disrupting skin barrier lipid conformation or by occluding the skin surface. Franz-type diffusion cell experiments are complimented by the detailed visualisation offered by the semi-quantitative ToF-SIMS method which provides excellent benefits in terms of sensitivity and fragment ion specificity. This allows a more accurate depth profile of chlorhexidine permeation within the skin to be obtained and potentially affords the opportunity to map the co-localisation of permeants with skin structures, thus providing a greater ability to characterise skin absorption and to understand the mechanism of permeation, providing opportunities for new and more effective therapies.

Drug delivery by supramolecular design

Principles rooted in supramolecular chemistry have empowered new and highly functional therapeutics and drug delivery devices. This general approach offers elegant tools rooted in molecular and materials engineered to address the many challenges faced in treating disease.

The Influence of Pluronic F68 and F127 Nanocarrier on Physicochemical Properties, In vitro Release, and Antiproliferative Activity of Thymoquinone Drug

BACKGROUND

This study reports on hydrophobic drug thymoquinone (TQ), an active compound found in the volatile oil of Nigella sativa that exhibits anticancer activities. Nanoformulation of this drug could potentially increase its bioavailability to specific target cells.

OBJECTIVE

The aim of this study was to formulate TQ into polymer micelle, Pluronic F127 (5.0 wt %) and Pluronic F68 (0.1 wt %), as a drug carrier to enhance its solubility and instability in aqueous media.

MATERIALS AND METHODS

Polymeric micelles encapsulated TQ were prepared by the microwave-assisted solvent evaporation technique. Fourier transform infrared spectroscopy and ultraviolet-visible spectrophotometer were utilized for qualitative confirmation of micelles encapsulation. The surface morphology and mean particle size of the prepared micelles were determined by using transmission electron microscopy (TEM). Cytotoxicity effect was studied using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay.

RESULTS

Dynamic laser light scattering (DLS) technique showed hydrodynamic size distribution of optimized micelles of 50 nm, which was in close agreement with the mean particle size obtained from TEM of about 51 nm. Drug release study showed the maximum percentage of TQ release at 61% after 72 h, while the entrapment efficiency of TQ obtained was 46% using PF127. The cytotoxic effect of PF127-encapsulated TQ was considerably higher compared to PF68-encapsulated TQ against MCF7 cells, as they exhibited IC₅₀value of 8 μM and 18 μM, respectively.

CONCLUSION

This study suggests higher molecular weight Pluronic polymer micelles (F127) with hydrophilic-hydrophobic segments which could be used as a suitable candidate for sustainable delivery of TQ. However, comprehensive studies should be carried out to establish the suitability of Pluronic F127 as a carrier for other drugs with similar challenges as TQ.

SUMMARY

There is a rising interest in integrating nanotechnology with medicine, creating a nanomedicine aiming for high efficiency and efficacy of disease diagnosis and treatment. In drug delivery, the term nanomedicine describes the nanometer-sized range (1-1000 nm) of a multi-component drug for disease treatments. As such, liposome-based nanoparticulate delivery vehicles have been approved by the Food and Drug Administration (FDA) for clinical applications. The main purpose of introducing nanoscale drug delivery is to improve the pharmacological and pharmacokinetic profiles of therapeutic molecules. Drug or therapeutic molecules can be either released through the cleavage of a covalent linkage between drug molecules and polymers (conjugation) or through the diffusion from a drug and polymer blended matrix (physical encapsulation). Polymers play an important role in the design of nanocarriers for therapeutic deliveries. In Asia, Nigella sativa seed oil has been used traditionally for its various medicinal benefits. One of its most potent compound which is thymoquinone has been intensively investigated for its anti-cancer effects in colorectal carcinoma, breast adenocarcinoma, osteosarcoma, ovarian carcinoma, myeloblastic leukemia, and pancreatic carcinoma. In addition, it is reported to show anti-inflammatory potential, antidiabetic, antihistaminic effects, as well as the ability to alleviate respiratory diseases, rheumatoid arthritis, multiple sclerosis, and Parkinson's disease. This study aims to formulate and characterize different pluronic-based thymoquinone nanocarrier and investigate its effect against breast cancer cells Abbreviations Used: ATR-IR: Attenuated Total Reflectance-Infrared Spectroscopy, CH₃CN: Acetonitrile, DLS: Dynamic Light Scattering, MTS: [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, NPs: Nanoparticles, PF127/TQ: Pluronic F127 encapsulated TQ, PF68/TQ: Pluronic F68 encapsulated TQ, PLGA: Poly-(D,L-lactide-co-glycolide), PVA: Poly-vinylalcohol, TQ: Thymoquinone, UV/VIS: Ultravioletvisible spectrophotometry.

Dendrimer nanoarchitectures for cancer diagnosis and anticancer drug delivery

Dendrimers are novel nanoarchitectures with unique properties including a globular 3D shape, a monodispersed unimicellar nature and a nanometric size range. The availability of multiple peripheral functional groups and tunable surface engineering enable the facile modification of the dendrimer surface with different therapeutic drugs, diagnostic agents and targeting ligands. Drug encapsulation, and solubilizing and passive targeting also equally contribute to the therapeutic use of dendrimers. In this review, we highlight recent advances in the delivery of anticancer drugs using dendrimers, as well as other biomedical and diagnostic applications. Taken together, the immense potential and utility of dendrimers are envisaged to have a significant positive impact on the growing arena of drug delivery and targeting.

Spatial Distributions of Guest Molecule and Hydration Level in Dendrimer-Based Guest-Host Complex

Using the electrostatic complex of G4 poly(amidoamine) (PAMAM) dendrimer with an amphiphilic surfactant as a model system, contrast variation small angle neutron scattering (SANS) is implemented to resolve the key structural characteristics of dendrimer-based guest-host system. Quantifications of the radial distributions of the scattering length density and the hydration level within the complex molecule reveal that the surfactant is embedded in the peripheral region of dendrimer and the steric crowding in this region increases the backfolding of the dendritic segments, thereby reducing the hydration level throughout the complex molecule. The insights into the spatial location of the guest molecules as well as the perturbations of dendrimer conformation and hydration level deduced here are crucial for the delicate design of dendrimer-based guest-host system for biomedical applications.

In vitro and in vivo uptake studies of PAMAM G4.5 dendrimers in breast cancer

Background

Breast cancer is the second leading cause of cancer death worldwide. Nanotechnology approaches can overcome the side effects of chemotherapy as well as improve the efficacy of drugs. Dendrimers are nanometric size polymers which are suitable as drug delivery systems. To the best of our knowledge, studies on the application of PAMAM G4.5 (polyamidoamine half generation 4) dendrimers as potential drug delivery systems in breast cancer have not been reported. In this work we developed a PAMAM G4.5 dendrimer containing FITC (fluorescein isothiocyanate) dye to study their uptake by murine breast cancer cells and BALB/c mice breast tumors.

Results

We performed a reaction between FITC and PAMAM G4.5 dendrimers which were previously derivatized with piperazine (linker molecule), characterized them by ¹H NMR (proton nuclear magnetic resonance) spectroscopy and MALDI-TOF (matrix-assisted laser desorption/ionization- time-of-flight) mass spectrometry. The experimental data indicated that 2 FITC molecules could be bound covalently at the PAMAM G4.5 dendrimer surface, with 17 FITC molecules probably occluded in PAMAM dendrimers cavity. PAMAM-FITC dendrimer (PAMAM G4.5-piperazinyl-FITC dendrimer) size distribution was evaluated by DLS (dynamic light scattering) and TEM (transmission electron microscopy). The nanoparticle hydrodynamic size was 96.3 ± 1.4 nm with a PdI (polydispersion index) of 0.0296 ± 0.0171, and the size distribution measured by TEM was 44.2 ± 9.2 nm. PAMAM-FITC dendrimers were neither cytotoxic in 4T1 cells nor hemolytic up to 24 h of incubation. In addition, they were uptaken in vitro by 4T1 cells and in vivo by BALB/c mice breast tumors. PAMAM G4.5-piperazinyl-FITC dendrimer intracellular distribution was observed through histologic analysis of the tumor by laser confocal microscopy.

Conclusion

These results indicate that PAMAM G4.5 dendrimers enter tumor tissue cells, being good candidates to be used as antitumor drug delivery systems for breast cancer treatment and diagnosis.

Synthetic Biomaterials from Metabolically Derived Synthons

The utility of metabolic synthons as the building blocks for new biomaterials is based on the early application and success of hydroxy acid based polyesters as degradable sutures and controlled drug delivery matrices. The sheer number of potential monomers derived from the metabolome (e.g., lactic acid, dihydroxyacetone, glycerol, fumarate) gives rise to almost limitless biomaterial structural possibilities, functionality, and performance characteristics, as well as opportunities for the synthesis of new polymers. This review describes recent advances in new chemistries, as well as the inventive use of traditional chemistries, toward the design and synthesis of new polymers. Specific polymeric biomaterials can be prepared for use in varied medical applications (e.g., drug delivery, tissue engineering, wound repair, etc.) through judicious selection of the monomer and backbone linkage.

Selenium-Platinum Coordination Dendrimers with Controlled Anti-Cancer Activity

Dendrimers are considered as good vectors for drug delivery in cancer treatment. However, most anticancer drugs are conjugated to the peripheral surface of dendrimers, sacrificing the advantages of monodispersity and stability belonging to dendrimers. Furthermore, dendrimers in current studies of cancer treatment are mostly used as vectors for drugs, whereas the anticancer activity of dendrimers on their own is less studied. Here we have prepared monodisperse selenium-platinum coordination dendrimers with a selenium-platinum core buried inside. Structures of the dendrimers were determined by various characterizations. The coordination dendrimers showed controlled anticancer activity by themselves, without loading additional drugs. The in vivo study further demonstrated their anticancer activity and low toxicity to normal tissues.

Cysteine and arginine-rich peptides as molecular carriers

A number of linear and cyclic peptides containing alternative arginine and cysteine residues, namely linear (CR)3, linear (CR)4, linear (CR)5, cyclic [CR]4, and cyclic [CR]5, were synthesized. The peptides were evaluated for their ability to deliver two molecular cargos, fluorescence-labeled cell-impermeable negatively charged phosphopeptide (F'-GpYEEI) and fluorescence-labeled lamivudine (F'-3TC), intracellularly in human leukemia cancer (CCRF-CEM) cells. We investigated the role of cyclization and the number of amino acids in improving the transporting ability of the peptides. The flow cytometry studies suggested that the synthesized peptides were able to work efficiently as transporters for both cargos. Among all compounds, cyclic [CR]4 was found to be the most efficient peptide in transporting the cargo into cells. For instance, the cellular uptake of F'-3TC (5μM) and F'-GpYEEI (5μM) was enhanced by 16- and 20-fold, respectively, in the presence of cyclic [CR]4 compared to that of the parent compound alone. The mechanism of F'-GpYEEI uptake by cells was found to be energy-independent. The results showed that the number of amino acids and their cyclic nature can impact the efficiency of the peptide in transporting the molecular cargos.

Branched polyethyleneimine modified with hyaluronic acid via a PEG spacer for targeted anticancer drug delivery

Branched polyethyleneimine can be modified with hyaluronic acid via a PEG spacer for targeted anticancer drug delivery to cancer cells.

Transepithelial Transport of PAMAM Dendrimers Across Isolated Human Intestinal Tissue

Poly(amido amine) (PAMAM) dendrimers have shown transepithelial transport across intestinal epithelial barrier in rats and across Caco-2 cell monolayers. Caco-2 models innately lack mucous barriers, and rat isolated intestinal tissue has been shown to overestimate human permeability. This study is the first report of transport of PAMAM dendrimers across isolated human intestinal epithelium. It was observed that FITC labeled G4-NH2 and G3.5-COOH PAMAM dendrimers at 1 mM concentration do not have a statistically higher permeability compared to free FITC controls in isolated human jejunum and colonic tissues. Mannitol permeability was increased at 10 mM concentrations of G3.5-COOH and G4-NH2 dendrimers. Significant histological changes in human colonic and jejunal tissues were observed at G3.5-COOH and G4-NH2 concentrations of 10 mM implying that dose limiting toxicity may occur at similar concentrations in vivo. The permeability through human isolated intestinal tissue in this study was compared to previous rat and Caco-2 permeability data. This study implicates that PAMAM dendrimer oral drug delivery may be feasible, but it may be limited to highly potent drugs.

Guest-Host Chemistry with Dendrimers—Binding of Carboxylates in Aqueous Solution

Recognition and binding of anions in water is difficult due to the ability of water molecules to form strong hydrogen bonds and to solvate the anions. The complexation of two different carboxylates with 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers was studied in aqueous solution using NMR and ITC binding models. Sodium 2-naphthoate and sodium 3-hydroxy-2-naphthoate were chosen as carboxylate model compounds, since they carry structural similarities to many non-steroidal anti-inflammatory drugs and they possess only a limited number of functional groups, making them ideal to study the carboxylate-dendrimer interaction selectively. The binding stoichiometry for 3-hydroxy-2-naphthoate was found to be two strongly bound guest molecules per dendrimer and an additional 40 molecules with weak binding affinity. The NOESY NMR showed a clear binding correlation of sodium 3-hydroxy-2-naphthoate with the lyophilic dendrimer core, possibly with the two high affinity guest molecules. In comparison, sodium 2-naphthoate showed a weaker binding strength and had a stoichiometry of two guests per dendrimer with no additional weakly bound guests. This stronger dendrimer interaction with sodium 3-hydroxy-2-naphthoate is possibly a result of the additional interactions of the dendrimer with the extra hydroxyl group and an internal stabilization of the negative charge due to the hydroxyl group. These findings illustrate the potential of the G4 1-(4-carbomethoxy) pyrrolidone dendrimer to complex carboxylate guests in water and act as a possible carrier of such molecules.

Nanodrug Formed by Coassembly of Dual Anticancer Drugs to Inhibit Cancer Cell Drug Resistance

Carrier-free pure nanodrugs (PNDs) that are composed entirely of pharmaceutically active molecules are regarded as promising candidates to be the next generation of drug formulations and are mainly formulated from supramolecular self-assembly of drug molecules. It benefits from the efficient use of drug compounds with poor aqueous solubility and takes advantage of nanoscale drug delivery systems. Here, a type of all-in-one nanoparticle consisting of multiple drugs with enhanced synergistic antiproliferation efficiency against drug-resistant cancer cells has been created. To nanoparticulate the anticancer drugs, 10-hydroxycamptothecin (HCPT) and doxorubicin (DOX) were chosen as a typical model. The resulting HD nanoparticles (HD NPs) were formulated by a "green" and convenient self-assembling method, and the water-solubility of 10-hydroxycamptothecin (HCPT) was improved 50-fold after nanosizing by coassembly with DOX. The formation process was studied by observing the morphological changes at various reaction times and molar ratios of DOX to HCPT. Molecular dynamics (MD) simulations showed that DOX molecules tend to assemble around HCPT molecules through intermolecular forces. With the advantage of nanosizing, HD NPs could improve the intracellular drug retention of DOX to as much as 2-fold in drug-resistant cancer cells (MCF-7R). As a dual-drug-loaded nanoformulation, HD NPs effectively enhanced drug cytotoxicity to drug-resistant cancer cells. The combination of HCPT and DOX exhibited a synergistic effect as the nanosized HD NPs improved drug retention in drug-resistant cancer cells against P-gp efflux in MCF-7R cells. Furthermore, colony forming assays were applied to evaluate long-term inhibition of cancer cell proliferation, and these assays confirmed the greatly improved cytotoxicity of HD NPs in drug-resistant cells compared to free drugs.

Applications of dendrimers for brain delivery and cancer therapy

Dendrimers are emerging as potential nonviral vectors for the efficient delivery of drugs and nucleic acids to the brain and cancer cells. These polymers are highly branched, 3D macromolecules with modifiable surface functionalities and available internal cavities that make them attractive as delivery systems for drug and gene delivery applications. This article highlights the recent therapeutic advances resulting from the use of dendrimers for brain targeting and cancer treatment.

The Present and the Future of Degradable Dendrimers and Derivatives in Theranostics

Interest in dendrimer-based nanomedicines has been growing recently, as it is possible to precisely manipulate the molecular weight, chemical composition, and surface functionality of dendrimers, tuning their properties according to the desired biomedical application. However, one important concern about dendrimer-based therapeutics remains-the nondegradability under physiological conditions of the most commonly used dendrimers. Therefore, biodegradable dendrimers represent an attractive class of nanomaterials, since they present advantages over conventional nondegradable dendrimers regarding the release of the loaded molecules and the prevention of bioaccumulation of synthetic materials and subsequent cytotoxicity. Here, we present an overview of the state-of-the-art of the design of biodegradable dendritic structures, with particular focus on the hurdles regarding the use of these as vectors of drugs and nucleic acids, as well as macromolecular contrast agents.

Advanced targeted therapies in cancer: Drug nanocarriers, the future of chemotherapy

Cancer is the second worldwide cause of death, exceeded only by cardiovascular diseases. It is characterized by uncontrolled cell proliferation and an absence of cell death that, except for hematological cancers, generates an abnormal cell mass or tumor. This primary tumor grows thanks to new vascularization and, in time, acquires metastatic potential and spreads to other body sites, which causes metastasis and finally death. Cancer is caused by damage or mutations in the genetic material of the cells due to environmental or inherited factors. While surgery and radiotherapy are the primary treatment used for local and non-metastatic cancers, anti-cancer drugs (chemotherapy, hormone and biological therapies) are the choice currently used in metastatic cancers. Chemotherapy is based on the inhibition of the division of rapidly growing cells, which is a characteristic of the cancerous cells, but unfortunately, it also affects normal cells with fast proliferation rates, such as the hair follicles, bone marrow and gastrointestinal tract cells, generating the characteristic side effects of chemotherapy. The indiscriminate destruction of normal cells, the toxicity of conventional chemotherapeutic drugs, as well as the development of multidrug resistance, support the need to find new effective targeted treatments based on the changes in the molecular biology of the tumor cells. These novel targeted therapies, of increasing interest as evidenced by FDA-approved targeted cancer drugs in recent years, block biologic transduction pathways and/or specific cancer proteins to induce the death of cancer cells by means of apoptosis and stimulation of the immune system, or specifically deliver chemotherapeutic agents to cancer cells, minimizing the undesirable side effects. Although targeted therapies can be achieved directly by altering specific cell signaling by means of monoclonal antibodies or small molecules inhibitors, this review focuses on indirect targeted approaches that mainly deliver chemotherapeutic agents to molecular targets overexpressed on the surface of tumor cells. In particular, we offer a detailed description of different cytotoxic drug carriers, such as liposomes, carbon nanotubes, dendrimers, polymeric micelles, polymeric conjugates and polymeric nanoparticles, in passive and active targeted cancer therapy, by enhancing the permeability and retention or by the functionalization of the surface of the carriers, respectively, emphasizing those that have received FDA approval or are part of the most important clinical studies up to date. These drug carriers not only transport the chemotherapeutic agents to tumors, avoiding normal tissues and reducing toxicity in the rest of the body, but also protect cytotoxic drugs from degradation, increase the half-life, payload and solubility of cytotoxic agents and reduce renal clearance. Despite the many advantages of all the anticancer drug carriers analyzed, only a few of them have reached the FDA approval, in particular, two polymer-protein conjugates, five liposomal formulations and one polymeric nanoparticle are available in the market, in contrast to the sixteen FDA approval of monoclonal antibodies. However, there are numerous clinical trials in progress of polymer-protein and polymer-drug conjugates, liposomal formulations, including immunoliposomes, polymeric micelles and polymeric nanoparticles. Regarding carbon nanotubes or dendrimers, there are no FDA approvals or clinical trials in process up to date due to their unresolved toxicity. Moreover, we analyze in detail the more promising and advanced preclinical studies of the particular case of polymeric nanoparticles as carriers of different cytotoxic agents to active and passive tumor targeting published in the last 5 years, since they have a huge potential in cancer therapy, being one of the most widely studied nano-platforms in this field in the last years. The interest that these formulations have recently achieved is stressed by the fact that 90% of the papers based on cancer therapeutics with polymeric nanoparticles have been published in the last 6 years (PubMed search).

Dendrimers in Medicine: Therapeutic Concepts and Pharmaceutical Challenges

Dendrimers are three-dimensional macromolecular structures originating from a central core molecule and surrounded by successive addition of branching layers (generation). These structures exhibit a high degree of molecular uniformity, narrow molecular weight distribution, tunable size and shape characteristics, as well as multivalency. Collectively, these physicochemical characteristics together with advancements in design of biodegradable backbones have conferred many applications to dendrimers in formulation science and nanopharmaceutical developments. These have included the use of dendrimers as pro-drugs and vehicles for solubilization, encapsulation, complexation, delivery, and site-specific targeting of small-molecule drugs, biopharmaceuticals, and contrast agents. We briefly review these advances, paying particular attention to attributes that make dendrimers versatile for drug formulation as well as challenging issues surrounding the future development of dendrimer-based medicines.

Polymeric nanoparticles for targeted treatment in oncology: current insights

Chemotherapy, a major strategy for cancer treatment, lacks the specificity to localize the cancer therapeutics in the tumor site, thereby affecting normal healthy tissues and advocating toxic adverse effects. Nanotechnological intervention has greatly revolutionized the therapy of cancer by surmounting the current limitations in conventional chemotherapy, which include undesirable biodistribution, cancer cell drug resistance, and severe systemic side effects. Nanoparticles (NPs) achieve preferential accumulation in the tumor site by virtue of their passive and ligand-based targeting mechanisms. Polymer-based nanomedicine, an arena that entails the use of polymeric NPs, polymer micelles, dendrimers, polymersomes, polyplexes, polymer–lipid hybrid systems, and polymer–drug/protein conjugates for improvement in efficacy of cancer therapeutics, has been widely explored. The broad scope for chemically modifying the polymer into desired construct makes it a versatile delivery system. Several polymer-based therapeutic NPs have been approved for clinical use. This review provides an insight into the advances in polymer-based targeted nanocarriers with focus on therapeutic aspects in the field of oncology.

Oral absorption enhancement of probucol by PEGylated G5 PAMAM dendrimer modified nanoliposomes

Probucol (PB), an antioxidant drug, is commonly used as a lipid concentration lowering drug to reduce blood plasma cholesterol levels in the clinic. However, the therapeutic effects of this drug are negatively impacted by its poor water solubility and low oral absorption efficiency. In this study, a PEGylated G5 PAMAM dendrimer (G5-PEG) modified nanoliposome was employed to increase water solubility, transepithelial transport, and oral absorption of PB. The uptake mechanism was explored in vitro in Caco-2 cells with the results suggesting that the absorption improvement of G5-PEG modified PB-liposome (PB-liposome/G5-PEG) was related to P-glycoprotein (P-gp) efflux pump but was independent of caveolae endocytosis pathways. Additionally, plasma lipid concentration lowering effects of PB-liposome/G5-PEG were evaluated in vivo in a LDLR-/- hyperlipidemia mouse model. Compared with saline treated group, treatment with PB-liposome/G5-PEG significantly inhibited the increase of plasma total cholesterol (TC) and triglyceride (TG) of mice induced by a high fat diet. Moreover, its lipid concentration lowering effects and plasma drug concentration were greater than PB alone or commercial PB tablets. Our results demonstrated that PB-liposome/G5-PEG significantly increased the oral absorption of PB and therefore significantly improved its pharmacodynamic effects.

Synthesis of novel types of polyester glycodendrimers as potential inhibitors of urinary tract infections

Syntheses of highly mannosylated polyester dendrimers with 2, 4, 8, and 16 α-d-mannopyranose residues on their peripheries connected by different linker arms are presented.

RGD peptide-modified multifunctional dendrimer platform for drug encapsulation and targeted inhibition of cancer cells

Development of multifunctional nanoscale drug-delivery systems for targeted cancer therapy still remains a great challenge. Here, we report the synthesis of cyclic arginine-glycine-aspartic acid (RGD) peptide-conjugated generation 5 (G5) poly(amidoamine) dendrimers for anticancer drug encapsulation and targeted therapy of cancer cells overexpressing αvβ3 integrins. In this study, amine-terminated G5 dendrimers were used as a platform to be sequentially modified with fluorescein isothiocyanate (FI) via a thiourea linkage and RGD peptide via a polyethylene glycol (PEG) spacer, followed by acetylation of the remaining dendrimer terminal amines. The developed multifunctional dendrimer platform (G5.NHAc-FI-PEG-RGD) was then used to encapsulate an anticancer drug doxorubicin (DOX). We show that approximately six DOX molecules are able to be encapsulated within each dendrimer platform. The formed complexes are water-soluble, stable, and able to release DOX in a sustained manner. One- and two-dimensional NMR techniques were applied to investigate the interaction between dendrimers and DOX, and the impact of the environmental pH on the release rate of DOX from the dendrimer/DOX complexes was also explored. Furthermore, cell biological studies demonstrate that the encapsulation of DOX within the G5.NHAc-FI-PEG-RGD dendrimers does not compromise the anticancer activity of DOX and that the therapeutic efficacy of the dendrimer/DOX complexes is solely related to the encapsulated DOX drug. Importantly, thanks to the role played by RGD-mediated targeting, the developed dendrimer/drug complexes are able to specifically target αvβ3 integrin-overexpressing cancer cells and display specific therapeutic efficacy to the target cells. The developed RGD peptide-targeted multifunctional dendrimers may thus be used as a versatile platform for targeted therapy of different types of αvβ3 integrin-overexpressing cancer cells.

Advances in combination therapies based on nanoparticles for efficacious cancer treatment: an analytical report

The main objective of nanomedicine research is the development of nanoparticles as drug delivery systems or drugs per se to tackle diseases as cancer, which are a leading cause of death with developed nations. Targeted treatments against solid tumors generally lead to dramatic regressions, but, unfortunately, the responses are often short-lived due to resistant cancer cells. In addition, one of the major challenges of combination drug therapy (called "cocktail") is the crucial optimization of different drug parameters. This issue can be solved using combination nanotherapy. Nanoparticles developed in oncology based on combination nanotherapy are either (a) those designed to combat multidrug resistance or (b) those used to circumvent resistance to clinical cancer drugs. This review provides an overview of the different nanoparticles currently used in clinical treatments in oncology. We analyze in detail the development of combinatorial nanoparticles including dendrimers for dual drug delivery via two strategic approaches: (a) use of chemotherapeutics and chemosensitizers to combat multidrug resistance and (b) use of multiple cytotoxic drugs. Finally, in this review, we discuss the challenges, clinical outlook, and perspectives of the nanoparticle-based combination therapy in cancer.

Advances in the application of nanotechnology in the diagnosis and treatment of gastrointestinal tumors

Nanotechnology has broad application prospects in the diagnosis and treatment of cancer. Integrating chemistry, engineering, biology and medicine, nanotechnology is a multidisciplinary research field. Nanoscale imaging technology significantly improves the precision and accuracy of tumor diagnosis. Nanocarriers are able to significantly improve the accuracy of dose and targeted drug delivery and reduce the toxic side effects. This review focuses on the emerging roles of these innovative technologies in gastrointestinal cancer diagnostics and therapeutics. Although several problems and barriers are hampering the development of nanodevices, the potential for nanotechnologies to function as multimodal nanotheranostic agents will likely pave the way for the fight against gastrointestinal cancer.

Recent advances in glycerol polymers: chemistry and biomedical applications

Glycerol polymers are attracting increased attention due to the diversity of polymer compositions and architectures available. This article provides a brief chronological review on the current status of these polymers along with representative examples of their use for biomedical applications. First, the underlying chemistry of glycerol that provides access to a range of monomers for subsequent polymerizations is described. Then, the various synthetic methodologies to prepare glycerol-based polymers including polyethers, polycarbonates, polyesters, and so forth are reviewed. Next, several biomedical applications where glycerol polymers are being investigated including carriers for drug delivery, sealants or coatings for tissue repair, and agents possessing antibacterial activity are described. Fourth, the growing market opportunity for the use of polymers in medicine is described. Finally, the findings are concluded and summarized, as well as the potential opportunities for continued research efforts are discussed.

Multifunctional lactobionic acid-modified dendrimers for targeted drug delivery to liver cancer cells: investigating the role played by PEG spacer

We report the development of a lactobionic acid (LA)-modified multifunctional dendrimer-based carrier system for targeted therapy of liver cancer cells overexpressing asialoglycoprotein receptors. In this study, generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers were sequentially modified with fluorescein isothiocyanate (FI) and LA (or polyethylene glycol (PEG)-linked LA, PEG-LA), followed by acetylation of the remaining dendrimer terminal amines. The synthesized G5.NHAc-FI-LA or G5.NHAc-FI-PEG-LA conjugates (NHAc denotes acetamide groups) were used to encapsulate a model anticancer drug doxorubicin (DOX). We show that both conjugates are able to encapsulate approximately 5.0 DOX molecules within each dendrimer and the formed dendrimer/DOX complexes are stable under different pH conditions and different aqueous media. The G5.NHAc-FI-PEG-LA conjugate appears to have a better cytocompatibility, enables a slightly faster DOX release rate, and displays better liver cancer cell targeting ability than the G5.NHAc-FI-LA conjugate without PEG under similar experimental conditions. Importantly, the developed G5.NHAc-FI-PEG-LA/DOX complexes are able to specifically inhibit the growth of the target cells with a better efficiency than the G5.NHAc-FI-LA/DOX complexes at a relatively high DOX concentration. Our results suggest a key role played by the PEG spacer that affords the dendrimer platform with enhanced targeting and therapeutic efficacy of cancer cells. The developed LA-modified multifunctional dendrimer conjugate with a PEG spacer may be used as a delivery system for targeted liver cancer therapy and offers new opportunities in the design of multifunctional drug carriers for targeted cancer therapy applications.

Cyclic peptide-capped gold nanoparticles for enhanced siRNA delivery

Previously, we have reported the synthesis of a homochiral l-cyclic peptide [WR]₅ and its use for delivery of anti-HIV drugs and biomolecules. A physical mixture of HAuCl₄ and the peptide generated peptide-capped gold nanoparticles. Here, [WR]₅ and [WR]₅-AuNPs were tested for their efficiency to deliver a small interfering RNA molecule (siRNA) in human cervix adenocarcinoma (HeLa) cells. Flow cytometry investigation revealed that the intracellular uptake of a fluorescence-labeled non-targeting siRNA (200 nM) was enhanced in the presence of [WR]₅ and [WR]₅-AuNPs by 2- and 3.8-fold when compared with that of siRNA alone after 24 h incubation. Comparative toxicity results showed that [WR]₅ and [WR]₅-AuNPs were less toxic in cells compared to other available carrier systems, such as Lipofectamine.

Nanocarrier for poorly water-soluble anticancer drugs--barriers of translation and solutions

Many existing chemotherapeutic drugs, repurposed drugs and newly developed small-molecule anticancer compounds have high lipophilicity and low water-solubility. Currently, these poorly water-soluble anticancer drugs (PWSAD) are generally solubilized using high concentrations of surfactants and co-solvents, which frequently lead to adverse side effects. In recent years, researchers have been actively exploring the use of nanotechnology as an alternative to the solvent-based drug solubilization approach. Several classes of nanocarrier systems (lipid-based, polymer-based and albumin-based) are widely studied for encapsulation and delivery of the existing and new PWSAD. These nanocarriers were also shown to offer several additional advantages such as enhanced tumour accumulation, reduced systemic toxicity and improved therapeutic effectiveness. In this article, the recent nanotechnological advances in PWSAD delivery will be reviewed. The barriers commonly encountered in the development of PWSAD nanoformulations (e.g. formulation issues and nanotoxicity issues) and the strategies to overcome these barriers will also be discussed. It is our goal to provide the pharmaceutical scientists and clinicians with more in-depth information about the nanodelivery approach, thus, more efficacious and safe PWSAD nanoformulations can be developed with improved translational success.