PEGylated Biodegradable Polyesters for PGSS Microparticles Formulation: Processability, Physical and Release Properties.

BACKGROUND: Particles from Gas Saturated Solution (PGSS) is an emergent method that employs supercritical carbon dioxide (scCO2) to produce microparticles. It is suitable for encapsulating biologically active compounds including therapeutic peptides and proteins. Poly(lactide acid) (PLA) and/or poly(lactic-coglycolic acid) (PLGA) are the most commonly used materials in PGSS, due to their good processability in scCO2. Previous studies demonstrated that the properties of the microparticles can be modulated by adding polyethylene glycol (PEG) or tri-block PEGylated copolymers. OBJECTIVE: In the present work, the effect of the addition of biodegradable PEGylated di-block copolymers on the physical properties and drug release performance of microparticles prepared by PGSS technique was evaluated. METHOD: mPEG5kDa-P(L)LA and mPEG5kDa-P(L)LGA with similar molecular weights were synthesized and their behaviour, when exposed to supercritical CO2, was investigated. Different microparticle formulations, composed of a high (81%) or low (9%) percentage of the synthesized copolymers were prepared and compared in terms of particle size distribution, morphology, yield and protein release. Drug release studies were performed using bovine serum albumin (BSA) as a model protein. RESULTS: PEGylated copolymers showed good processability in PGSS without significant changes to the physical properties of the microparticles. However, the addition of PEG exerted a modulating effect on the microparticle drug dissolution behaviour, increasing the rate of BSA release as a function of its content in the formulation. CONCLUSION: This study demonstrated the feasibility of producing microparticles by using PEGylated di-block copolymers through a PGSS technique at mild operating conditions (low operating pressure and temperature).

Optimization of Melatonin Dissolution from Extended Release Matrices Using Artificial Neural Networking.

BACKGROUND: Efficacy of melatonin in treating sleep disorders has been demonstrated in numerous studies. Being with short half-life, melatonin needs to be formulated in extended-release tablets to prevent the fast drop of its plasma concentration. However, an attempt to mimic melatonin natural plasma levels during night time is challenging. METHODS: In this work, Artificial Neural Networks (ANNs) were used to optimize melatonin release from hydrophilic polymer matrices. Twenty-seven different tablet formulations with different amounts of hydroxypropyl methylcellulose, xanthan gum and Carbopol®974P NF were prepared and subjected to drug release studies. Using dissolution test data as inputs for ANN designed by Visual Basic programming language, the ideal number of neurons in the hidden layer was determined trial and error methodology to guarantee the best performance of constructed ANN. RESULTS: Results showed that the ANN with nine neurons in the hidden layer had the best results. ANN was examined to check its predictability and then used to determine the best formula that can mimic the release of melatonin from a marketed brand using similarity fit factor. CONCLUSION: This work shows the possibility of using ANN to optimize the composition of prolonged-release melatonin tablets having dissolution profile desired.

Folate conjugated phosphorylcholine-based polycations for specific targeting in nucleic acids delivery.

Folic acid has been investigated as a targeting ligand for imaging and therapeutic agent for over a decade; however, studies on its use in targeting of nonviral gene or nucleic acids delivery systems are sparse. This study assesses potential application of a new folic acid conjugate with aminomethacrylate-phosphoryl-choline based copolymer (DMAEMA-MPC-FA) as a targeting gene delivery vector. The folate-conjugated polymers produce colloidally stable polyplexes with a particle size <200 nm and demonstrate the ability to protect DNA from enzymatic degradation to a certain extent. In cells that overexpress folate receptors (MCF-7 and KB cultures), the conjugated systems show a folate-specific association and achieved significantly enhanced transfection efficiency, compared to the nonconjugated control, with a dramatically reduced nonspecific cellular association. The transfection enhancement is achieved without a corresponding increase in cellular association, suggesting that an internal cellular trafficking of folate-conjugated system may be altered, resulting in an increased transfection efficacy. In summary, a new folate-conjugated aminomethacrylate-phosphorylcholine copolymer is capable of forming colloidal complexes with DNA, modulating their specific cell uptake and improving the level of cell transfection in folate expressing cells.

Structural study of DNA condensation induced by novel phosphorylcholine-based copolymers for gene delivery and relevance to DNA protection.

Poly[2-(dimethylamino)ethyl methacrylate-b-2-methacryloyloxyethyl phosphorylcholine] (DMA-MPC) is currently under investigation as a new vector candidate for gene therapy. The DMA block has been previously demonstrated to condense DNA effectively. The MPC block contains a phosphorylcholine (PC) headgroup, which can be found naturally in the outside of the cell membrane. This PC-based polymer is extremely hydrophilic and acts as a biocompatible steric stabilizer. In this study, we assess in detail the morphologies of DNA complexes obtained using the diblock copolymer series DMA(x)MPC30 (where the mean degree of polymerization of the MPC block was fixed at 30 and the DMA block length was systematically varied) using transmission electron microscopy (TEM) and liquid atomic force microscopy (AFM). Both techniques indicate more compact complex morphologies (more efficient condensation) as the length of the cationic DMA block increases. However, the detailed morphologies of the DMA(x)MPC30-DNA complexes observed by TEM in vacuo and by AFM in aqueous medium are different. This phenomena is believed to be related to the highly hydrophilic nature of the MPC block. TEM studies revealed that the morphology of the complexes changes from loosely condensed structures to highly condensed rods, toroids, and oval-shaped particles as the DMA moiety increases. In contrast, morphological changes from plectonemic loops to flower-like and rectangular block-like structures, with an increase in highly condensed central regions, are observed by in situ AFM studies. The relative population of each structure is clearly dependent on the polymer molecular composition. Enzymatic degradation assays revealed that only the DMA homopolymer provided effective DNA protection against DNase I degradation, while other highly condensed copolymer complexes, as judged from TEM and gel electrophoresis, only partially protected the DNA. However, AFM images indicated that the same highly condensed complexes have less condensed regions, which we believe to be the initiation sites for enzymatic attack. This indicates that the open structures observed by AFM of the DNA complexation by the DMA(x)MPC30 copolymer series are closer to in vivo morphology when compared to TEM.

Phosphorylcholine-polycation diblock copolymers as synthetic vectors for gene delivery.

A novel 2-(dimethylamino)ethyl methacrylate-block-2-(methacryloyloxyethyl phosphorylcholine) (DMAEMA-MPC) diblock copolymer was synthesized and investigated as a new non-viral vector for gene delivery. The attractive perspective of this phosphorylcholine (PC)-based material is its propensity to condense DNA efficiently via the cationic DMAEMA block, as previously demonstrated for the respective homopolymer, with the MPC block acting as a biocompatible steric stabilizer. Two series of DMAEMA-MPC diblock copolymers were synthesized for evaluation, varying independently and systematically either MPC or DMAEMA block length. Markedly different DNA-copolymer complexes were observed depending on the copolymer molecular composition. Certain polymeric structures led to formation of highly condensed, sterically stabilized DNA complexes of 120-140 nm diameter, while some resulted in partly condensed DNA-polymer complexes with 'spaghetti' structures, indicating the importance of a copolymer composition to balance condensing and steric stabilization effect. A low level of non-specific cellular association of the complexes with optimized physicochemical properties was seen, indicating the role of MPC surface layer in the interactions with biological membranes and important property in preventing promiscuous interactions with tissues in the body and potentially allowing for cellular specific delivery of the condensates following the attachment of a targeting ligand.