Umesh Gupta

Dendrimer toxicity: Let's meet the challenge

Dendrimers are well-defined, versatile polymeric architecture with properties resembling biomolecules. Dendritic polymers emerged as outstanding carrier in modern medicine system because of its derivatisable branched architecture and flexibility in modifying it in numerous ways. Dendritic scaffold has been found to be suitable carrier for a variety of drugs including anticancer, anti-viral, anti-bacterial, antitubercular etc., with capacity to improve solubility and bioavailability of poorly soluble drugs. In spite of extensive applicability in pharmaceutical field, the use of dendrimers in biological system is constrained because of inherent toxicity associated with them. This toxicity is attributed to the interaction of surface cationic charge of dendrimers with negatively charged biological membranes in vivo. Interaction of dendrimers with biological membranes results in membrane disruption via nanohole formation, membrane thinning and erosion. Dendrimer toxicity in biological system is generally characterized by hemolytic toxicity, cytotoxicity and hematological toxicity. To minimize this toxicity two strategies have been utilized; first, designing and synthesis of biocompatible dendrimers; and second, masking of peripheral charge of dendrimers by surface engineering. Biocompatible dendrimers can be synthesized by employing biodegradable core and branching units or utilizing intermediates of various metabolic pathways. Dendrimer biocompatibility has been evaluated in vitro and in vivo for efficient presentation of biological performance. Surface engineering masks the cationic charge of dendrimer surface either by neutralization of charge, for example PEGylation, acetylation, carbohydrate and peptide conjugation; or by introducing negative charge such as half generation dendrimers. Neutral and negatively charged dendrimers do not interact with biological environment and hence are compatible for clinical applications as elucidated by various studies examined in this review. Chemical modification of the surface is an important strategy to overcome the toxicity problems associated with the dendrimers. The present review emphasizes on the approaches available to overcome the cationic toxicity inherently associated with the dendrimers.

Folate and folate-PEG-PAMAM dendrimers: synthesis, characterization, and targeted anticancer drug delivery potential in tumor bearing mice.

Ligand-mediated targeting of drugs especially in anticancer drug delivery is an effective approach. Dendrimers, due to unique surface topologies, can be a choice in this context. In the present study, PAMAM (polyamidoamine) dendrimers up to fourth generation were synthesized and characterized through infrared (IR), nuclear magnetic resonance (NMR), electrospray ionization (ESI) mass spectrometric, and transmission electron microscopic (TEM) techniques. Primary amines present on the dendritic surface were conjugated through folic acid and folic acid-PEG (poly(ethylene glycol))-NHS (N-hydroxysuccinimide) conjugates. Tumor in mice was induced through the use of KB cell culture. Prepared dendritic conjugates were evaluated for the anticancer drug delivery potential using 5-FU (5-fluorouracil) in tumor-bearing mice. Approximately 31% of 5-FU was loaded in folate-PEG-dendritic conjugates. Results indicated that folate-PEG-dendrimer conjugate was significantly safe and effective in tumor targeting compared to a non-PEGylated formulation. Tailoring of dendrimers via PEG-folic acid reduced hemolytic toxicity, which led to a sustained drug release pattern as well as highest accumulation in the tumor area.

A review of glycosylated carriers for drug delivery.

Carbohydrates not only represent a vast potential as structure building blocks of living cells but also have proved as a promising candidate for drug delivery. Glycosylation of nanocarriers instructs some gratifying characteristic, which leads to the evolution of promising delivery systems. Some path-breaking advantages of glycosylated carriers include the engineered release profile of bioactives when introduced into biological system. Being natural product of living system these carriers also upshots as a multifaceted drug delivery vehicle and reduces the toxicity associated with unmodified drug carrier and therapeutic agent. An additional attribute of these carriers is to alter the pharmacokinetic profile of drugs positively with stabilization of drug carrier. The presence of lectin receptors on different cell surfaces makes the glycosylated carrier appreciable for targeted delivery of drugs to improve their therapeutic index. Active participation of some lectin receptors in immune responses to antigen overlaid the application of glycosylated carriers in delivery of antigen and immunotherapy for treatment of ailments like cancer. These advantages revealed the promising potential of glycosylated carriers in each perspective of drug delivery. Collectively this review presents an overview of different applications of glycosylated carriers, with a focus on their applicability in development of a nanoconstruct with GRAS status.

Non-polymeric nano-carriers in HIV/AIDS drug delivery and targeting

Development of an effective drug delivery approach for the treatment of HIV/AIDS is a global challenge. The conventional drug delivery approaches including Highly Active Anti Retroviral Therapy (HAART) have increased the life span of the HIV/AIDS patient. However, the eradication of HIV is still not possible with these approaches due to some limitations. Emergence of polymeric and non-polymeric nanotechnological approaches can be opportunistic in this direction. Polymeric carriers like, dendrimers and nanoparticles have been reported for the targeting of anti HIV drugs. The synthetic pathways as well polymeric framework create some hurdles in their successful formulation development as well as in the possible drug delivery approaches. In the present article, we have discussed the general physiological aspects of the infection along with the relevance of non-polymeric nanocarriers like liposomes, solid lipid nanoparticles (SLN), ethosomes, etc. in the treatment of this disastrous disease.

Application of dendrimer–drug complexation in the enhancement of drug solubility and bioavailability

Dendrimers are 3D, hyperbranched, tree-like polymers having immense potential in drug delivery, targeting, diagnosis and as carriers for DNA/gene delivery. Dendrimers have hydrophilic exteriors and hydrophilic interiors, which are responsible for its unimolecular micellar nature. They form covalent as well as non-covalent complexes with drug molecules and hydrophobes, which are responsible for its solubilisation behaviour. Dendrimer mediated complexation is advantageous in terms of stability, controlled release, high drug payload and reduced toxicity of entrapped drug(s). Studies on non-covalent interaction of dendrimers with drugs are in abundance so far as solubilisation is concerned. However, the non-covalent complexation often leads to lower drug encapsulation and complex stability compared to covalent conjugation. High drug payload and stability leads to higher bioavailability of the drugs. In addition dendrimers can be surface engineered to release the drug at desired site, that is, as targeted drug delivery. This property along with the solubilisation behaviour could improve the bioavailability of drugs.

Dextran conjugated dendritic nanoconstructs as potential vectors for anti-cancer agent.

The purpose of the present investigation was to evaluate the potential of surface engineered polypropylene imine (PPI) dendrimers as nanoscale drug delivery units for site-specific delivery of a model anti-cancer agent, doxorubicin.hydrochloride (DOX). Dextran conjugated PPI dendrimers were synthesized, characterized and further loaded with DOX. The developed formulation was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and transmission electron microscopic (TEM) studies. Dendrimer formulation was evaluated for in vitro drug release and haemolytic studies under various pH conditions. Cell uptake and cytotoxicity studies were performed on A549 cell lines using MTT cell proliferation assay. In vivo studies were conducted for evaluation of various pharmacokinetic parameters and tissue distribution pattern. In vitro, formulation displayed initial rapid release of the drug followed by rather slow release. Further, the dextran conjugated dendrimer formulation was found to be least haemolytic but more cytotoxic as compared to free drug. Cell uptake studies depicted that the formulation was preferably taken up by the tumor cells when compared to free drug. The conjugation of oxidized polyaldehyde dextran imparts macromolecular nature to the dendritic carrier, consequently the formulation was found to selectively enter highly porous mass of tumor cells at the same time precluding normal tissues. Thus it was concluded that the drug loaded dendrimer formulation would selectively localize in the tumor mass, increasing the therapeutic margin of safety while reducing the side effects associated with anti-cancer agents.

Ligand anchored dendrimers based nanoconstructs for effective targeting to cancer cells

Dendrimers are considered versatile carriers especially for the treatment of diseases like cancer, AIDS, malaria etc. Cancer is a worldwide threat particularly in developing countries. A breakthrough research in this regard is a prime requirement. In the present study, folic acid was conjugated to fifth generation polypropylene imine (PPI) dendrimers and characterized through IR, NMR ((13)C and (1)H), ESI mass spectroscopy as well as electron microscopic studies. Doxorubicin (DOX), an effective anticancer drug, was used in the present study to develop and explore the anticancer potential of the dendrimer based formulations. DOX was loaded (approximately 26 and 65%) to the PPI dendrimers as well as folate conjugated PPI (PPI-FA) dendrimers, respectively. These ligand conjugated dendrimers displayed very less (approximately 3 and 4%, respectively, for PPI-FA and PPI-FA-DOX) hemolysis. The developed formulation PPI-FA-DOX was stable enough. In vitro drug release of the formulation was found to be faster in the acidic media than at the higher pH. The prepared formulation displayed a higher cell uptake in MCF-7 cancer cell lines as evidenced by fluorescence studies. The results suggested that, in future, folic acid conjugated PPI dendrimers may emerge as a better choice for anticancer drug targeting.

PEGylated PAMAM dendrimers: Enhancing efficacy and mitigating toxicity for effective anticancer drug and gene delivery

UNLABELLED Poly(amidoamine) dendrimers (PAMAM) are well-defined, highly branched, nanoscale macromolecules with numerous active amine groups on the surface. PAMAM dendrimer can enhance the solubility of hydrophobic drugs, and with numerous reactive groups on the surface PAMAM dendrimer can be engineered with various functional groups for specific targeting ability. However, in physiological conditions, these amine groups are toxic to cells and limit the application of PAMAM. In the recent years, polyethylene glycol (PEG) conjugation has been the most widely used approach to reduce the toxicity of the active group on dendrimer surface. PEG molecules are known to be inert, non-immunogenic, and non-antigenic with a significant water solubility. PEGylated PAMAM-mediated delivery could not only overcome the limitations of dendrimer such as drug leakage, immunogenicity, hemolytic toxicity, systemic cytotoxicity but they also have the ability to enhance the solubilization of hydrophobic drugs and facilitates the potential for DNA transfection, siRNA delivery and tumor targeting. This review focuses on the recent developments on the application and influence of PEGylation on various biopharmaceutical properties of PAMAM dendrimers. STATEMENT OF SIGNIFICANCE It is well established that dendrimers have demonstrated promising potentials for drug delivery. However, the inherent toxicity poses challenges for its clinical translation. In this regard, PEGylation has helped mitigate some of the toxicity concerns of dendrimers and have paved the way forward for testing its translational potentials. The review is a collection of articles demonstrating the utility of PEGylation of the most studied PAMAM dendrimers. To our knowledge, this is a first such attempt to draw readers attention, specifically, towards PEGylated PAMAM dendrimers.

Dendimer-Mediated Solubilization, Formulation Development and in Vitro−in Vivo Assessment of Piroxicam

The present investigation was aimed at exploring dendrimer-mediated solubilization and formulation development followed by in vitro, in vivo assessment of piroxicam (PXM) nanocomposite. For this, two dendrimer generations (3.0G and 4.0G) were synthesized and characterized by IR, (1)H NMR spectroscopic and electron microscopy techniques. The optimized formulations containing 0.2% w/v of PXM loaded PAMAM dendrimer at pH 7.4 referred to as 0.2-D(3)P(7.4) (3.0G) and 0.2-D(4)P(7.4) (4.0G) resulted in significant enhancements of PXM solubility approximately by 107- and 222-fold, respectively. The in vitro release behavior of PXM from the formulation in medium-I (PBS 7.4) and medium-II (PBS with 1% albumin) and stability studies were also favorable. Pharmacokinetic study showed higher area under curve (AUC(0-->t); microg/mL/h) of 293.78 +/- 2.04 and 321.54 +/- 2.37 with optimized 0.2-D(3)P(7.4) and 0.2-D(4)P(7.4) formulations, respectively, as opposed to 279.11 +/- 1.48 with plain PXM. The elimination half-life of the drug encapsulated in the formulation was significantly higher (0.2-D(3)P(7.4), 36.6 and 0.2-D(4)P(7.4), 41.1; h) than that of pure drug (33.7 h; p < 0.005), and the overall elimination rate constant of formulations was also less as compared to free drug (p < 0.005). Pharmacodynamic assessment by rat-paw model of 0.2-D(3)P(7.4) and 0.2-D(4)P(7.4) formulations displayed inhibition levels of 54.21 +/- 1.25% and 59.33 +/- 0.63%, respectively, which are higher than those of plain PXM (41.81 +/- 2.9) formulations, after the sixth hour of administration. The second, fourth and eighth hour organ distribution data showed significantly higher recovery of PXM in rat paw with dendrimer-based formulations in comparison to plain PXM. However, comparison of overall data suggested 4.0G-based formulations to be superior to 3.0G as well as pure PXM.

Polymeric Micelles: Recent Advancements in the Delivery of Anticancer Drugs

Nanotechnology, in health and medicine, extensively improves the safety and efficacy of different therapeutic agents, particularly the aspects related to drug delivery and targeting. Among various nano-carriers, polymer based macromolecular approaches have resulted in improved drug delivery for the diseases like cancers, diabetes, autoimmune disorders and many more. Polymeric micelles consisting of hydrophilic exterior and hydrophobic core have established a record of anticancer drug delivery from the laboratory to commercial reality. The nanometric size, tailor made functionality, multiple choices of polymeric micelle synthesis and stability are the unique properties, which have attracted scientists and researchers around the world to work upon in this opportunistic drug carrier. The capability of polymeric micelles as nano-carriers are nowhere less significant than nanoparticles, liposomes and other nanocarriers, as per as the commercial feasibility and presence is concerned. In fact polymeric micelles are among the most extensively studied delivery platforms for the effective treatment of different cancers as well as non-cancerous disorders. The present review highlights the sequential and recent developments in the design, synthesis, characterization and evaluation of polymeric micelles to achieve the effective anticancer drug delivery. The future possibilities and clinical outcome have also been discussed, briefly.