Kathryn E. Uhrich

Drug release characteristics of unimolecular polymeric micelles

Biodegradable, unimolecular polymeric micelles possess several features that are attractive for drug delivery applications: Thermodynamic stability, ability to encapsulate and solubilize a hydrophobic guest molecule, biodegradability, as well as size and surface characteristics that prevent rapid clearance by the RES. Here we investigate the potential of these unimolecular polymeric micelles to release a drug for an extended time. Lidocaine was used as a model drug for in vitro studies using a horizontal diffusion cell and cellulose membrane that prevented polymer transport from the source to the receiver compartment. The transport of free lidocaine from source to receiver under sink conditions was zero-order and complete within 8 h. The transport of lidocaine initially encapsulated in polymer was zero-order for the first 14 h, and 96% of the lidocaine was detected within 24 h.

Synthesis and degradation characteristics of salicylic acid-derived poly(anhydride-esters)

A biodegradable poly(anhydride-ester) was synthesized by melt condensation polymerization of the acetylated monomer to yield a novel polymeric prodrug. The polymer we have synthesized is composed of alkyl chains linked by ester bonds to aromatic moieties, specifically salicylic acid--the active component of aspirin. With the medicinal properties attributed to salicylic acid and the ease of metabolism, the incorporation of this compound into a polymer backbone yields a polymeric prodrug that may have potential in a variety of applications (i.e., inflammatory bowel disease). For these reasons, we have designed a synthetic scheme that yields the desired poly(anhydride-ester). The in vitro hydrolytic degradation of these polymers has been performed and results indicate that the polymer degradation rate is pH-dependent.

Acetylation of PAMAM dendrimers for cellular delivery of siRNA

BackgroundThe advancement of gene silencing via RNA interference is limited by the lack of effective short interfering RNA (siRNA) delivery vectors. Rational design of polymeric carriers has been complicated by the fact that most chemical modifications affect multiple aspects of the delivery process. In this work, the extent of primary amine acetylation of generation 5 poly(amidoamine) (PAMAM) dendrimers was studied as a modification for the delivery of siRNA to U87 malignant glioma cells.ResultsPAMAM dendrimers were reacted with acetic anhydride to obtain controlled extents of primary amine acetylation. Acetylated dendrimers were complexed with siRNA, and physical properties of the complexes were studied. Dendrimers with up to 60% of primary amines acetylated formed ~200 nm complexes with siRNA. Increasing amine acetylation resulted in reduced polymer cytotoxicity to U87 cells, as well as enhanced dissociation of dendrimer/siRNA complexes. Acetylation of dendrimers reduced the cellular delivery of siRNA which correlated with a reduction in the buffering capacity of dendrimers upon amine acetylation. Confocal microscopy confirmed that escape from endosomes is a major barrier to siRNA delivery in this system.ConclusionPrimary amine acetylation of PAMAM dendrimers reduced their cytotoxicity to U87 cells, and promoted the release of siRNA from dendrimer/siRNA complexes. A modest fraction (approximately 20%) of primary amines of PAMAM can be modified while maintaining the siRNA delivery efficiency of unmodified PAMAM, but higher degrees of amine neutralization reduced the gene silencing efficiency of PAMAM/siRNA delivery vectors.

Unimolecular micelles: Synthesis and characterization of amphiphilic polymer systems

Unimolecular micelles were successfully synthesized from mucic acid, fatty acids, and poly(ethylene glycols) to create biocompatible polymers. These polymers consist of a core-shell structure that resembles conventional micellar structures but with significant thermodynamic stability in aqueous media. The core of the polymers provide a hydrophobic environment for drug encapsulation via hydrophobic interactions, whereas the shell provides excellent water solubility. The polymers were characterized by nuclear magnetic resonance, infrared and mass spectroscopies, as well as gel permeation chromatography, differential scanning calorimetry, and thermogravimetric and elemental analyses. Encapsulation ability was measured using high-pressure liquid chromatography to monitor lidocaine, a hydrophobic molecule. Encapsulation capabilities increased as lipophilicity of the core increased. To verify that encapsulation was caused by individual unimolecular micelles, surface tension and dynamic light scattering measurements were performed. The results indicated that these unimolecular micelles have great potential as drug carriers.

Poly(anhydride-co-imides): in vivo biocompatibility in a rat model.

The degradation and tissue compatibility characteristics of a novel class of biodegradable poly(anhydride-co-imide) polymers: poly[trimellitylimidoglycine-co-1,6-bis(carboxyphenoxy)hexan e] (TMA-gly: CPH) (in 10:90; 30:70 and 50: 50 molar ratios) and poly[pyromellitylimidoalanine-co-1,6-bis(carboxyphenoxy)hexa ne] (PMA-ala:CPH) (in 10:90 and 30:70 molar ratios) were investigated and compared with control poly(lactic acid/glycolic acid) (PLAGA in 50:50 molar ratio) matrices, a well-characterized biocompatible polymer, in rat subcutaneous tissues for 60 days. Polymers were compression-molded into circular discs of 14 mm x 1 mm in diameter. On post-operative days 7, 14, 28 and 60, histological tissue samples were removed, prepared by fixation and staining, and analyzed by light microscopy. PLAGA matrices produced mild inflammatory reactions and were completely degraded at the end of 60 days, leaving implant tissues that were similar to surgical wounds without implants. TMA-gly:CPH (10:90 and 30:70) matrices produced mild inflammatory reactions by the end of 60 days, similar to those seen with PLAGA. TMA-gly: CPH (50: 50) produced moderate inflammatory reactions characterized by macrophages and edema. PMA-ala:CPH matrices elicited minimal inflammatory reactions that were characterized by fibrous encapsulation by the end of 60 days. In vivo degradation rates of poly(anhydride-co-imides) were similar to PLAGA. Both PMA-ala:CPH and TMA-gly: CPH matrices maintained their shapes and degraded at a constant rate over the period of two months. These polymers, possessing good mechanical properties and tissue compatibility, may be useful in weight-bearing applications in bone.

Preliminary in vivo report on the osteocompatibility of poly(anhydride-co-imides) evaluated in a tibial model

A novel class of polymers with mechanical properties similar to cancellous bone are being investigated for their ability to be used in weight-bearing areas for orthopedic applications. The poly(anhydride-co-imide) polymers based on poly[trimellitylimidoglycine-co-1,6-bis(carboxyphenoxy)hexan e] (TMA-Gly:CPH) and poly[pyromellitylimidoalanine-co-1,6-bis(carboxyphenoxy)hexa ne] (PMA-Ala:CPH) in molar ratios of 30:70 were investigated for osteocompatibility, with effects on the healing of unicortical 3-mm defects in rat tibias examined over a 30-day period. Defects were made with surgical drill bits (3-mm diameter) and sites were filled with poly(anhydride-co-imide) matrices and compared to the control poly(lactic acid-glycolic acid) (PLAGA) (50:50), a well-characterized matrix frequently used in bone regeneration studies, and defects without polymeric implants. At predetermined time intervals (3, 6, 9, 12, 20, and 30 days), animals were sacrificed and tissue histology was examined for bone formation, polymer-tissue interaction, and local tissue response by light microscopy. The studies revealed that matrices of TMA-Gly:CPH and PMA-Ala:CPH produced responses similar to the control PLAGA with tissue compatibility characterized by a mild response involving neutrophils, macrophages, and giant cells throughout the experiment for all matrices studied. Matrices of PLAGA were nearly completely degraded by 21 days in contrast to matrices of TMA-Gly:CPH and PMA-Ala:CPH that displayed slow erosion characteristics and maintenance of shape. Defects in control rats without polymer healed by day 12, defects containing PLAGA healed after 20 days, and defects containing poly(anhydride-co-imide) matrices produced endosteal bone growth as early as day 3 and formed bridges of cortical bone around matrices by 30 days. In addition, there was marrow reconstitution at the defect site for all matrices studied along with matured bone-forming cells. This study suggests that novel poly(anhydride-co-imides) are promising polymers that may be suitable for use as implants in bone surgery, especially in weight-bearing areas.

Polymeric Micelles Based on Amphiphilic Scorpion-like Macromolecules: Novel Carriers for Water-Insoluble Drugs

No HeadingPurpose.The objective was to evaluate amphiphilic scorpion-like macromolecules (AScMs) as drug carriers for hydrophobic drugs.Methods.Indomethacin (IMC) was incorporated into two AScM micelles (M12P5 and M12P2) by the O/W emulsion technique. The influences of IMC:polymer feed ratio and molecular weight of the hydrophilic block of AScMs on the micelle size, IMC entrapment efficiency and release behavior were investigated. Furthermore, cytotoxicity of the AScMs was evaluated with human umbilical vein endothelial cells (HUVEC).Results.The maximal IMC entrapment efficiency in M12P5 and M12P2 micelles (72.3 and 20.2%, respectively) was obtained at ratios of 0.1 to 1 for indomethacin:polymer. The sizes of IMC-loaded M12P5 and M12P2 polymeric micelles were <20 nm with a narrow size distribution. In vitro release studies revealed that IMC released from M12P5 and M12P2 polymeric micelles showed sustained release behavior during the 24 h of experiment. Additionally, M12P5 and M12P2 polymeric micelles did not induce remarkable cytotoxicity against HUVEC cells at concentrations up to 1 and 0.5 mM, respectively.Conclusions.The amphiphilic scorpion-like macromolecules may be useful as novel drug carriers because of their small size, ability to encapsulate hydrophobic drugs and release them in a sustained manner as well as low cytotoxicity.

Biodegradable Ferulic Acid-Containing Poly(anhydride-ester): Degradation Products with Controlled Release and Sustained Antioxidant Activity

Ferulic acid (FA) is an antioxidant and photoprotective agent used in biomedical and cosmetic formulations to prevent skin cancer and senescence. Although FA exhibits numerous health benefits, physicochemical instability leading to decomposition hinders its efficacy. To minimize inherent decomposition, a FA-containing biodegradable polymer was prepared via solution polymerization to chemically incorporate FA into a poly(anhydride-ester). The polymer was characterized using nuclear magnetic resonance and infrared spectroscopies. The molecular weight and thermal properties were also determined. In vitro studies demonstrated that the polymer was hydrolytically degradable, thus providing controlled release of the chemically incorporated bioactive with no detectable decomposition. The polymer degradation products were found to exhibit antioxidant and antibacterial activity comparable to that of free FA, and in vitro cell viability studies demonstrated that the polymer is noncytotoxic toward fibroblasts. This renders the polymer a potential candidate for use as a controlled release system for skin care formulations.

Salicylic acid‐based poly(anhydride esters) for control of biofilm formation in Salmonella enterica serovar Typhimurium

Aims:  Bacterial biofilms generally are more resistant to stresses as compared with free planktonic cells. Therefore, the discovery of antimicrobial stress factors that have strong inhibitory effects on bacterial biofilm formation would have great impact on the food, personal care, and medical industries.

Proliferation, morphology, and protein expression by osteoblasts cultured on poly(anhydride-co-imides)

In vitro cell biocompatibility models are crucial in the study of any newly synthesized material. Our focus has been on the development of a new class of biocompatible, degradable, high-strength polymeric materials, the poly(anhydride-co-imides), for use in bone regeneration. This study examined osteoblast cell adherence, proliferation, viability, and phenotypic preservation on the surface of the poly(anhydride-co-imide) poly[pyromellitylimidoalanine (PMA-ala):1,6-bis(carboxyphenoxy) hexane (CPH)] over a period of time. Cell proliferation on PMA-ala:CPH degradable matrices over 21 days was examined. Throughout the 21-day period of study, osteoblast proliferation was similar on PMA-ala:CPH and on tissue culture polystyrene controls. Osteoblasts maintained their characteristic morphology as demonstrated by both scanning electron microscopy and immunofluorescence studies. Alkaline phosphatase activity for cells grown on PMA-ala:CPH was confirmed. Retention of the osteoblastic phenotype was demonstrated using immunofluorescence techniques and staining with antibodies against osteocalcin (an extracellular matrix protein of bone) and osteopontin (a marker of cell adhesion). Radioimmunoassay results provided evidence that levels of osteocalcin production by osteoblasts were similar when cells were cultured on PMA-ala:CPH and on tissue culture polystyrene controls. The present study provided evidence of normal osteoblast function on PMA-ala:CPH surfaces. PMA-ala:CPH may therefore be useful as a synthetic material for orthopedic applications.