Hydrophobically derivatized hyperbranched polyglycerol as a human serum albumin substitute

Hyperbranched polyglycerol is an efficacious and biocompatible novel osmotic agent in a rodent model of peritoneal dialysis

OBJECTIVES

To enhance the effectiveness of peritoneal dialysis (PD), new biocompatible PD solutions may be needed. The present study was designed to test the efficacy and biocompatibility of hyperbranched polyglycerol (HPG)-a nontoxic, nonimmunogenic water-soluble polyether polymer-in PD.

METHODS

Adult Sprague-Dawley rats were instilled with 30 mL HPG solution (molecular weight 3 kDa; 2.5% - 15%) or control glucose PD solution (2.5% Dianeal: Baxter Healthcare Corporation, Deerfield, IL, USA), and intraperitoneal fluid was recovered after 4 hours. Peritoneal injury and cellular infiltration were determined by histologic and flow cytometric analysis. Human peritoneal mesothelial cells were assessed for viability in vitro after 3 hours of PD fluid exposure.

RESULTS

The 15% HPG solution achieved a 4-hour dose-related ultrafiltration up to 43.33 ± 5.24 mL and a dose-related urea clearance up to 39.17 ± 5.21 mL, results that were superior to those with control PD solution (p < 0.05). The dialysate-to-plasma (D/P) ratios of urea with 7.5% and 15% HPG solution were not statistically different from those with control PD solution. Compared with fluid recovered from the control group, fluid recovered from the HPG group contained proportionally fewer neutrophils (3.63% ± 0.87% vs 9.31% ± 2.89%, p < 0.0001). Detachment of mesothelial cells positive for human bone marrow endothelial protein 1 did not increase in the HPG group compared with the stain control (p = 0.1832), but it was elevated in the control PD solution group (1.62% ± 0.68% vs 0.41% ± 0.31%, p = 0.0031). Peritoneal biopsies from animals in the HPG PD group, compared with those from control PD animals, demonstrated less neutrophilic infiltration and reduced thickness. Human peritoneal mesothelial cell survival after HPG exposure was superior in vitro (p < 0.0001, 7.5% HPG vs control; p < 0.01, 15% HPG vs control). Exposure to glucose PD solution induced cytoplasmic vacuolation and caspase 3-independent necrotic cell death that was not seen with HPG solution.

CONCLUSIONS

Our novel HPG PD solution demonstrated effective ultrafiltration and waste removal with reduced peritoneal injury in a rodent model of PD.

Polyvalent choline phosphate as a universal biomembrane adhesive

Phospholipids in the cell membranes of all eukaryotic cells contain phosphatidyl choline (PC) as the headgroup. Here we show that hyperbranched polyglycerols (HPGs) decorated with the 'PC-inverse' choline phosphate (CP) in a polyvalent fashion can electrostatically bind to a variety of cell membranes and to PC-containing liposomes, the binding strength depending on the number density of CP groups per macromolecule. We also show that HPG-CPs can cause cells to adhere with varying affinity to other cells, and that binding can be reversed by subsequent exposure to low molecular weight HPGs carrying small numbers of PCs. Moreover, PC-rich membranes adsorb and rapidly internalize fluorescent HPG-CP but not HPG-PC molecules, which suggests that HPG-CPs could be used as drug-delivery agents. CP-decorated polymers should find broad use, for instance as tissue sealants and in the self-assembly of lipid nanostructures.

Synthesis of biodegradable amphiphilic nanocarriers by chemo-enzymatic transformations for the solubilization of hydrophobic compounds

Polymeric nanocarriers possess advanced physicochemical properties that improve bioavailability, enhance cellular dynamics, and control target ability in drug delivery. In particular, dendritic polyglycerol is a promising new biocompatible scaffold for drug delivery. The present study explores the chemo-enzymatic modifications on dendritic hyperbranched polyglycerol (dPG) leading to amphiphilic polymeric architectures with easily hydrolysable ester linkages. Furthermore, these architectures were studied for nile red solubilization with capacity up to 5.6 mg/L at 0.1 wt % polymer conc. This corresponds to an ~10 fold increase in solubility of nile red. The release of nile red from these polymers was observed with a half life of 8 hours at pH 5.0, while no release was found at pH 7.4. The cell viability studies of our polymeric architectures showed them to be relatively nontoxic and to have the potential for future drug delivery applications.

Synthesis and characterization of carboxylic acid conjugated, hydrophobically derivatized, hyperbranched polyglycerols as nanoparticulate drug carriers for cisplatin

Hyperbranched polyglycerols (HPGs) with hydrophobic cores and derivatized with methoxy poly(ethylene glycol) were synthesized and further functionalized with carboxylate groups to bind and deliver cisplatin. Low and high levels of carboxylate were conjugated to HPGs (HPG-C(8/10)-MePEG(6.5)-COOH(113) and HPG-C(8/10)-MePEG(6.5)-COOH(348)) and their structures were confirmed through NMR and FTIR spectroscopy and potentiometric titration. The hydrodynamic diameter of the HPGs ranged from 5-10 nm and the addition of COOH groups decreased the zeta potential of the polymers. HPG-C(8/10)-MePEG(6.5)-COOH(113) bound up to 10% w/w cisplatin, whereas HPG-C(8/10)-MePEG(6.5)-COOH(348) bound up to 20% w/w drug with 100% efficiency. Drug was released from HPG-C(8/10)-MePEG(6.5)-COOH(113) over 7 days at the same rate, regardless of the pH. Cisplatin release from HPG-C(8/10)-MePEG(6.5)-COOH(348) was significantly slower than HPG-C(8/10)-MePEG(6.5)-COOH(113) at pH 6 and 7.4, but similar at pH 4.5. Release of cisplatin into artificial urine was considerably faster than into buffer. Carboxylated HPGs demonstrated good biocompatibility, and drug-loaded HPGs effectively inhibited proliferation of KU-7-luc bladder cancer cells.

Development and in vitro characterization of paclitaxel and docetaxel loaded into hydrophobically derivatized hyperbranched polyglycerols

In this study we report the development and in vitro characterization of paclitaxel (PTX) and docetaxel (DTX) loaded into hydrophobically derivatized hyperbranched polyglycerols (HPGs). Several HPGs derivatized with hydrophobic groups (C(8/10) alkyl chains) (HPG-C(8/10)-OH) and/or methoxy polyethylene glycol (MePEG) chains (HPG-C(8/10)-MePEG) were synthesized. PTX or DTX were loaded into these polymers by a solvent evaporation method and the resulting nanoparticle formulations were characterized in terms of size, drug loading, stability, release profiles, cytotoxicity, and cellular uptake. PTX and DTX were found to be chemically unstable in unpurified HPGs and large fractions (∼80%) of the drugs were degraded during the preparation of the formulations. However, both PTX and DTX were found to be chemically stable in purified HPGs. HPGs possessed hydrodynamic radii of less than 10nm and incorporation of PTX or DTX did not affect their size. The release profiles for both PTX and DTX from HPG-C(8/10)-MePEG nanoparticles were characterized by a continuous controlled release with little or no burst phase of release. In vitro cytotoxicity evaluations of PTX and DTX formulations demonstrated a concentration-dependent inhibition of proliferation in KU7 cell line. Cellular uptake studies of rhodamine-labeled HPG (HPG-C(8/10)-MePEG(13)-TMRCA) showed that these nanoparticles were rapidly taken up into cells, and reside in the cytoplasm without entering the nuclear compartment and were highly biocompatible with the KU7 cells.

Adsorption of amphiphilic hyperbranched polyglycerol derivatives onto human red blood cells

Hydrophobically derivatized hyperbranched polyglycerol (HPG)-polyethylene glycol (PEG) polymers bearing stearoyl chains (HPG-C18-PEG) were originally developed as human serum albumin substitutes and further as a unimolecular drug delivery system. In view of these in vivo applications and the potential for membrane interaction by these materials due to their amphiphilic structure, determining the adsorption of the polymers to human red blood cells (RBCs) is an important issue. This paper reports on the in vitro adsorption to RBCs of tritium-radiolabeled HPG-C18-PEG polymers. The morphological changes of RBCs associated with the adsorption were also examined by light and scanning electron microscopy (SEM). Laser scanning confocal microscopy (LSCM) suggests that the binding site of the polymers on RBCs is the cell membrane. Adsorption experiments show that, in the medium of either saline or plasma, the binding amount of the polymers to RBCs increases with increased polymer concentration in a manner which implies simple Langmurian behavior. The binding amount in saline is of the order of 10(5) molecules/cell at an equilibrium concentration of 1 mg/mL of HPG-C18-PEG polymer. The RBC morphology depends on the adsorbed amount; the cells become crenated in high concentrations (5 and 10 mg/mL) of the polymer solutions in the absence of plasma proteins. Interestingly, a large amount of polymers remain bound to RBCs even after washes with plasma (of the order of 10(4) molecules/cell). Thus, the bound polymers might have an extended circulating time by "hitchhiking" on RBCs in the bloodstream. These results provide significant information and insight for related studies of the interaction of amphiphilic molecules with cell membranes and for in vivo applications of biopolymers as drug delivery systems.

Hyperbranched polyglycerols: from the controlled synthesis of biocompatible polyether polyols to multipurpose applications

Dendritic macromolecules with random branch-on-branch topology, termed hyperbranched polymers in the late 1980s, have a decided advantage over symmetrical dendrimers by virtue of typically being accessible in a one-step synthesis. Saving this synthetic effort once had an unfortunate consequence, though: hyperbranching polymerization used to result in a broad distribution of molecular weights (that is, very high polydispersities, often M(w)/M(n) > 5). By contrast, a typical dendrimer synthesis yields a single molecule (in other words, M(w)/M(n) = 1.0), albeit by a labor-intensive, multistep process. But 10 years ago, Sunder and colleagues reported the controlled synthesis of well-defined hyperbranched polyglycerol (PG) via ring-opening multibranching polymerization (ROMBP) of glycidol. Since then, hyperbranched and polyfunctional polyethers with controlled molar mass and low polydispersities (M(w)/M(n) = 1.2-1.9) have been prepared, through various monomer addition protocols, by ROMBP. In this Account, we review the progress in the preparation and application of these uniquely versatile polyether polyols over the past decade. Hyperbranched PGs combine several remarkable features, including a highly flexible aliphatic polyether backbone, multiple hydrophilic groups, and excellent biocompatibility. Within the past decade, intense efforts have been directed at the optimization of synthetic procedures affording PG homo- and copolymers with different molecular weight characteristics and topology. Fundamental parameters of hyperbranched polymers include molar mass, polydispersity, degree of branching, and end-group functionality. Selected approaches for optimizing and tailoring these characteristics are presented and classified with respect to their application potential. Specific functionalization in the core and at the periphery of hyperbranched PG has been pursued to meet the growing demand for novel specialty materials in academia and industry. A variety of fascinating synthetic approaches now provide access to well-defined, complex macromolecular architectures based on polyether polyols with low polydispersity. For instance, a variety of linear-hyperbranched block copolymers has been reported. The inherent attributes of PG-based materials are useful for a number of individual implementation concepts, such as drug encapsulation or surface modification. The excellent biocompatibility of PG has also led to rapidly growing significance in biomedical applications, for example, bioconjugation with peptides, as well as surface attachment for the creation of protein-resistant surfaces.

Dendritic polyglycerols for biomedical applications

The application of nanotechnology in medicine and pharmaceuticals is a rapidly advancing field that is quickly gaining acceptance and recognition as an independent area of research called "nanomedicine". Urgent needs in this field, however, are biocompatible and bioactive materials for antifouling surfaces and nanoparticles for drug delivery. Therefore, extensive attention has been given to the design and development of new macromolecular structures. Among the various polymeric architectures, dendritic ("treelike") polymers have experienced an exponential development due to their highly branched, multifunctional, and well-defined structures. This Review describes the diverse syntheses and biomedical applications of dendritic polyglycerols (PGs). These polymers exhibit good chemical stability and inertness under biological conditions and are highly biocompatible. Oligoglycerols and their fatty acid esters are FDA-approved and are already being used in a variety of consumer applications, e.g., cosmetics and toiletries, food industries, cleaning and softening agents, pharmaceuticals, polymers and polymer additives, printing photographing materials, and electronics. Herein, we present the current status of dendritic PGs as functional dendritic architectures with particular focus on their application in nanomedicine, in drug, dye, and gene delivery, as well as in regenerative medicine in the form of non-fouling surfaces and matrix materials.

Supramolecular approaches to biological therapy

Supramolecular chemistry is a useful methodology for construction of nano- or micro-sized objects and can significantly contribute to nanotechnology through so-called bottom-up processing. In addition, supramolecular self-assembled structures can mimic some aspects of biological systems. Bio-related functions such as molecular sensing, controlled release, signaling and materials separations have been realized. Supramolecular chemistry is a multidisciplinary field that includes subjects such as molecular design and nanosized materials. In this article recent examples of supramolecular chemistry in the context of biological therapy are introduced and classified into five categories: small supramolecular systems; designer polymers; self-assembled structures; predesigned assemblies; and nanomaterials. Finally, hierarchic organization of supramolecular structures for advanced functions is introduced to illustrate future directions of investigation. We hope that scientists studying therapeutic applications receive inspiration from this review to exploit the opportunities offered by supramolecular chemistry in their respective research areas.

Unimolecular micelles based on hydrophobically derivatized hyperbranched polyglycerols: biodistribution studies

We recently reported the synthesis and testing of a new class of unimolecular micelles based on hyperbranched polyglycerols as second generation synthetic plasma expanders and as general drug delivery vehicles. A detailed biodistribution study of two derivatized hyperbranched polyglycerols of different molecular weights derivatized with hydrophobic groups and short poly(ethylene glycol) chains is reported in this article. In mice, these materials are nontoxic with circulation half-lives as high as 31 h, controllable by manipulating the molecular weight and the degree of PEG derivatization. Organ accumulation is low, presumably due to the "pegylation" effect. Thermal degradation and hydrolysis data suggest that these polymers are highly stable with a long shelf life, a major advantage for a pharmaceutical product. Degradation under acidic conditions has been observed for these polymers.