Fabrication of 3-Dimensional Polymeric Drug Delivery Systems

Development of new polymer structures for local drug delivery to the brain is an exciting research area. The main aim of this study is to develop biocompatible controlled drug delivery systems, using biodegradable or conducting polymers, for the treatment of central nervous system disorders such as epilepsy

Development of polymeric drug delivery systems for biotech products

Since the early 80’s the forward steps in genetics and proteomics, have led a particular interest to biotech products, such as DNA and proteins. Although difficult, their large-scale production enabled the therapeutic use of this compounds. Proteins and DNA sequences can be very interesting therapeutic molecules owing to their high selectivity/affinity for the receptor or the specific site of action. Unfortunately, some issues still limit their pharmaceutical use, such as the susceptibility to enzymatic degradation, rapid renal clearance and immunogenicity. To overcome these limitations, many researchers are seeking solutions in the field of drug delivery systems (DDSs). In this respect, many systems have been developed and conjugation with PEG (polyethylene glycol) can be considered one of the leading approaches. PEGylation brings to the conjugated molecule great solubility and stability to proteolytic digestion, furthermore it reduces the tendency to aggregate and reduces the immunogenicity. Thanks to these advantages and the particular characteristics of PEG, to date, there are on the market 12 pegylated compounds: 9 are proteins, one peptide, one aptamer and a liposomal formulation, containing doxorubicin. The improvements in the pharmacokinetic profile of these drugs, thanks to the use of drug delivery systems, can be also applied in the field of tissue engineering, where the same issues are of fundamental importance for the development of scaffolds for cells capable of releasing growth factors. In the last years various polymers have been studied by many research groups to find an alternative to PEG, but its excellent biocompatibility and the know-how in its use has not brought any polymer to be truly competitive against PEG. Nevertheless, PEG presents some limits such as its non-biodegradability and in some case there are reports of antibodies against PEG. Therefore, there is an increased need for a PEG substitute. In the first section of this work hyaluronic acid (HA) has been studied as a candidate polymer for bioconjugation of proteins (HAylation). HA, being biodegradable can compensate this limit of PEG. HA, is also present in humans and is metabolized by hyaluronidase. Moreover, HA has the advantage of a high loading compared to PEG, thanks to the presence of repetitive functional groups in each monomer. This part of the work was focused on the study of HA conjugation (HAylation) to two model enzymes, trypsin and Ribonuclease A, and then to an interesting protein in pharmaceutical field, insulin. In order to avoid cross-linking phenomena, only a fraction of all carboxyl groups of the polymer has been modified to aldehyde allowing the conjugation with the amino groups of the protein models. Furthermore, by modulating the pH of reaction two protein-HA conjugates were obtained, selective N-terminal (pH 6) or random (pH 8), this taking advantage of the different pKa values of the amino groups in the proteins. The first products obtained with the enzymes Ribonuclease A and trypsin were tested verifying the residual activity compared to the native proteins. All conjugates, in particular those obtained by N-terminal selective conjugation, maintain a good activity on small substrates (30% decrease); only the HA-derived trypsin retains about 60% of residual activity against the substrate with a high weight molecular. Furthermore, enhanced stability over time was found for HA-trypsin respect to the free enzyme (45% on average) and also susceptibility to hyaluronidase was confirmed for both conjugates. Polymer validation as potential protein carrier was then evaluated by preparing conjugates with bovine insulin, as an example of pharmacologically active protein. Two conjugates were synthesized by N-terminal selective conjugation starting from polymers with different degree of aldehyde derivatization, 4% and 21%, yielding products with a protein loading of 17% and 32% (w/w), respectively. The therapeutic efficacy of the conjugates in comparison with insulin was tested in Sprague Dawley rats with induced diabetes. The conjugate with a lower protein loading was more effective and with a longer pharmacodynamic effect on the reduction on blood glucose level. The second section of the work was focused on an innovative strategy of enzymatic PEGylation of oligonucleotides. Briefly, the method investigated on model oligonucleotides is composed of two steps: the first consists in the chemical conjugation of a short oligonucleotide to a PEG chain, the second step is the enzymatic-mediated conjuagation of the PEGylated oligonucleotide with a DNA sequence by the DNA T4 ligase. To study the enzymatic PEGylation, 4 oligo sequences have been prepared as ligation model: two complementary pairs ending with sticky-ends in turn complementary (18-mer + 21-mer and 16-mer + 19-mer). The 18-mer has a thiol group in 5’-ending, in order to perform the coupling with PEG. Applying some modifications to ligation classical protocols, excellent results were obtained: PEGylated portion completely ligate the other ds-DNA and no undesired products were found. To further confirm the effective ligation, the ligated and PEGylated sequence was restricted with EcoRI. Indeed, the EcoRI recognized a sequence that is present only the ligated DNA. Complete restriction was found in absence and even in the presence of the polymer, further confirming the successes of ligation. Furthermore it was investigated if a reduced number of bases coupled to PEG can still preserve the requirements for the ligase enzyme activity. Thus, the pair of the complementary sequences then coupled to PEG has been reduced to half (9-mer + 12-mer). Even with a shorter PEGylated sequence a complete ligation was obtained. In conclusion in this thesis it has been demonstrated that HA can be a valid alternative to PEG for protein conjugation. In the field of oligonucleotide delivery an enzymatic approach of oligonucleotide conjugation can open new horizons that so far have not been completely explored

Biopharmaceutical studies of slow release, subcutaneous polymeric drug delivery systems

Subcutaneously injected polymeric dosage forms have been used successfully to achieve sustained release of various drugs and peptides. A complex interplay of factors affect drug release rates from such dosage forms, such as nature of dosage form, drug and polymer properties, formulation variables etc. making the prediction of release characteristics challenging. In this thesis, the effect of drug lipophilicity on absorption rates from PLGA microspheres and in situ-forming depots was investigated. The beta-blockers were chosen as model drug compounds, being a homologous group of drugs having similar molecular weights and pKa values, yet widely differing lipophilicities. Alprenolol, metoprolol and atenolol were selected to represent the series based on their experimentally determined octanol-buffer partition coefficients. The first part of the study focused on formulation and characterisation of beta-blocker loaded microspheres with suitable in vitro release profiles. Microspheres were prepared by spray drying, and characterised in terms of particle size, surface morphology, drug loading and release. The beta-blockers represented a considerable challenge owing to their surface-active nature and tendency to suffer a large burst release from microspheres. Efforts were therefore directed towards modifying the formulation to improve the drug release profiles, including emulsion spray drying, addition of competing surfactants and hydrophobic ion pairing. The latter was successful in reducing burst and prolonging release, and microspheres were deemed suitable for in vivo investigation. In situ-forming depot preparations were also formulated with the aim of comparing release profiles and tissue compatibility with the preformed microspheres. Following initial experiments to ascertain intravenous clearance kinetics, the polymeric dosage forms were injected subcutaneously in rats. Drug plasma concentrations were analysed and absorption profiles were determined by deconvolution. It was found that the nature of the dosage form had a significantly greater impact on the rate and extent of absorption than the lipophilicity of the encapsulated drugs

Polymers Enhancing Bioavailability in Drug Delivery

This Special Issue provides an update on the state of the art and current trends in polymeric drug-delivery systems specifically designed for improving drug bioavailability. The multiple contributions received further strengthen the role of polymers in modern drug delivery and targeting, illustrating the different approaches possible and unveiling what the future may bring

Properties of polymeric drug delivery systems prepared by hot-melt extrusion

textThe purpose of this research project was to investigate the physicochemical and drug release properties of polymeric drug delivery systems prepared by hot-melt extrusion containing either highly water-soluble drugs or a poorly water-soluble drug. The properties of processed materials were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), stability indicating RP- HPLC assay, dissolution studies, scanning electron microscopy (SEM), X-ray diffractometry, electronic torque rheometry, Zeta potential particle size analysis, and helium pycnometry. Chlorpheniramine maleate (CPM), diltiazem hydrochloride (DTZ), indomethacin (IDM), and the excipients were thermally and chemically stable following hot-melt extrusion. CPM decreased the glass transition temperature (Tg) of Eudragit RS PO and exhibited a solid-state plasticization effect. CPM and IDM were in the amorphous state and DTZ was in the crystalline state following hot-melt extrusion processing. Triethyl citrate (TEC) facilitated the hot-melt extrusion process by decreasing the Tg and the melt viscosity of Eudragit RS PO. However, the thermal lubricant, glyceryl monostearate (GMS), only decreased the melt viscosity of the Eudragit RS PO. The CPM release rate constant decreased in the order from tablets prepared by direct compression, hot-melt granulation, and hot-melt extrusion. This was due to an increase in the intermolecular binding and entanglement between drug molecules and polymer molecules that occurred during thermal processing. Post- processing thermal treatment of the hot-melt extrudates had a minimal effect on decreasing the drug release rate since the hot-melt extrusion process enhanced the entanglement of the drug and polymer to a greater extent. Drug release rates from both DTZ and CPM hot-melt extrudates increased with an increase in the TEC level in the formulations, while DTZ release from the Eudragit RS 30D coated pellets decreased with an increase of TEC in the coating layer. This could be attributed to the fact that a continuous polymeric structure was formed following hot-melt extrusion regardless of the TEC level. However, for the film coated pellets, coalescence of the polymer particles was enhanced with higher levels of TEC. Due to the lower solubility of IDM, no significant difference in drug release was observed in the IDM hot-melt extrudated granules containing 0%, 4%, and 8% TEC.Pharmac

Polymeric drug delivery systems for biological antimicrobial agents

The objective of this work was to develop suitable delivery systems for biological agents that have antimicrobial activities using biocompatible polymers, aiming to reduce their toxicity when administered. Two biological agents, colistin as an antibacterial agent and nystatin (Nys) as an antifungal agent, are the focus of this thesis as they are potent treatments for current pathogen infections, especially to the multidrug-resistant (MDR) bacteria/fungi, but have potential toxicity to human. Polymeric drug delivery systems, including prodrug, hydrogel and micelle formulations, have been developed and discussed for their potential as topical and systemic regimes. The majority of the work was focused on the effect of the covalently attachment of synthetic polymers onto the biological agents upon their antimicrobial activities and the toxicity. The conjugation between colistin and polymers was achieved successfully through either irreversible or releasable linkages. Although irreversible polymer modifications on colistin showed no antimicrobial activity (chapter 2), an acceptable antibacterial activity was observed from the polymer-colistin conjugates with a releasable linkage through either ‘grafting-to’ (chapter 3) or ‘grafting-from’ (chapter 4) approaches. On the other hand, even though the pure polymer-Nys conjugate with a releasable imine linkage cannot be obtained due to the nature of the labile imine bond, the crude conjugate showed an excellent antifungal activity and a reduced toxicity compared to the native Nys (chapter 6). Other polymeric delivery systems were also discussed in this thesis. The incorporation of colistin within a developed hydrogel delivery system as an antibacterial patch for burn infections was investigated through in vitro and in vivo studies, showing a similar antibacterial activity as the native colistin solution against MDR Gram-negative bacteria with no systemic toxicity (chapter 5). Finally, an amphiphilic polymer containing boronic acid groups on the side chains was synthesised and used to target the hydroxyl groups on Nys, expecting to build up an environmental responsive micelle through dynamic boronate ester bond (chapter 7). Although more work is still needed, this system showed a potential to improve Nys solubility

Synthesis and Evaluation of Some Polymeric Drug Delivery Systems

This thesis deals with the investigations carried out by the writer on the synthesis, characterization and evaluation of some polymeric pro-drugs. The First chapter of the thesis deals with a brief introduction to controlled drug delivery systems, passive drug targeting and specific tissue targeting , cellular uptake of polymers, site specific drug release, polymer conjugates, incorporation of spacers in pro-drug conjugates, PEG chemistry and use of Dextran in drug delivery. The use of antiviral drug namely, zidivudine, problems associated with its use and a literature survey on the investigations that have been carried out on polymeric drug conjugates of zidovudine are briefly given. The Second chapter of the thesis deals with the scope and objective of the present investigations in detail. It explains, in particular, how when zidovudine is linked covalently to biocompatible polymers through succnic spacer should lead to a better drug delivery system capable of releasing of the drug in a sustained manner. The Third chapter of the thesis deals with the experimental procedures that are adopted in the preparation of the polymeric pro-drugs, estimation of the drug content, in vitro drug release studies, enzymatic hydrolysis, stability studies and bioavailability studies. The Fourth chapter of the thesis deals with the results obtained in the present study along with a detailed discussion of the results supported by chemical equations, tables, figures, etc. The following are some of the important findings in the present study: • Two macromolecular pro-drugs of the known antiviral drug zidovudine were synthesized by conjugating it with poly (ethylene glycol)1500, and detrain through succinic spacer. The pro-drugs were thoroughly characterized in terms of IR, and H1NMR. • In order to obtain some preliminary information about the potential use of the PEG-O-succinylzidovudine and DEX-O-succinylzidovudine as drug delivery systems for both oral and systemic administration, in vitro hydrolysis studies were performed by subjecting the conjugates to hydrolysis in buffer solutions at pH 1.1 (simulated gastric juice), at pH 5.5 (endosomal compartments) and at pH 7.4 (extracellular fluids) and at pH 8 in the presence and in the absence of α-chymotrypsin. It was found that, at all pH values considered, free zidovudine was always released from 5’-O-succinylzidovudine derivative. Even if 5’-O-succinylzidovudine was released from the macromolecular pro-drugs, it was in turn be hydrolysed to give free and active zidivudine. The amount of zidovudine released from PEG-O-succinylzidovudine was more than that from DEX-O-succinylzidovudine. It was also found that the release rate of zidovudine from 5’-O-succinylzidovudine derivative decreased as the pH value increased. A different trend was noticed in the case of release of zidovudine from the polymer drug conjugates. The release of drug was minimum at pH 5.5 buffer solution. This drug release can be attributed to influence of pH value on the hydrolysis rate of low molecular weight ester compounds. • It was found that nearly 45% and 28% and 16% of zidovudine was released from PEG-O-succinylzidovudine and DEX-O-succinylzidovudine and 5’-O-succinylzidovudine respectively. These results confirm the capacity of macromolecular conjugates to release free drug by hydrolytic activity of α-chymotrypsin. The ester bond between zidovudine and the succinic spacer would seem more susceptible to this enzymatic hydrolysis than the ester bond between 5’-O-succinylzidovudine and the polymeric carrier. • Stability studies carried out for the pro-drugs for a period of three months as per ICH guidelines indicate that no major physical and chemical changes occur in the polymeric pro-drugs during storage period indicating the stability of the pro-drugs. • The ability of the synthesized macromolecular pro-drugs to release free drug was also evaluated in human plasma. It was found that nearly 60% of linked zidovidine was released from PEG-O-succinylzidovudine within 12h, were as nearly 25 of zidovidine was released from DEX-O-succinylzidovudine. The plasmatic hydrolysis of 5’-O-succinylzidovudine showed that about 30% of the drug derivative was hydrolysed to give free zidovudine within 12h indicating that the amount of 5’-O-succinylzidovudine released from the polymeric pro-drug can in turn be hydrolysed to give free zidovudine. • The release of Zidovudine and 5’-O-succinylzidovudine from the macromolecular pro-drugs was found to be pH dependent. It was found that the release of Zidovudine and 5’-O-succinylzidovudine from PEG-O-succinylzidovudine follows first order kinetics at different pH. However, the release of zidovudine and 5’- -succinylzidovudine from DEX-O-succinylzidovudine follows zero order kinatics. • An analysis of pharmacokinetic data shows that there is a distinct difference in plasma concentration response between the free drug and the pro-drugs. There is a slower rate of drug absorption for the polymeric pro-drugs when compared to the free drug as evident from the delayed tmax values for the pro-drugs. Further, the extent of absorption of the pro-drugs is complete and is comparable with the free drug. This reveals the potential of the polymeric pro-drugs in the present study in sustaining the drug release in In-vivo conditions also. However it was found that the absorption of the drug was comparatively more in the case of DEX-O-succinylzidovudine than that from PEG-O-succinylzidovudine. This may be due to the biodegradation of dextran itself in the system by the enzyme dextranase. This reveals the potential of these pro-drugs in sustaining the drug release in In-vivo conditions thus leading to drug release systems capable of avoiding or minimizing the side effects. The macromolecular pro-drugs are thus capable of reducing the frequency of drug administration and improve patient compliance

Insilico modeling of chitosan as a drug delivery system

Computational modeling of polymeric nanoparticles as drug carriers have been extensively studied due to their varied functionalities, tunable structures and the capability of controlled drug release. Nano particulate polymeric drug delivery systems enable a cell specific targeting with negligible side effects and drug release based on change in physiological conditions. Eight common polymers are modeled and the various properties have been predicted. ADMET, QSAR, thermodynamic and electronic properties have been predicted and compared using SAR as well as quantum mechanical density functional methods. Comparison of the predicted properties suggests that chitosan, which is a natural polymer and has some advantages over others is a promising drug carrier candidate for tumor

Modelling drug coatings: A parallel cellular automata model of ethylcellulose-coated microspheres

Pharmaceutical companies today face a growing demand for more complex drug designs. In the past few decades, a number of probabilistic models have been developed, with the aim of improving insight on microscopic features of these complex designs. Of particular interest are models of controlled release systems, which can provide tools to study targeted dose delivery. Controlled release is achieved by using polymers with different dissolution characteristics. We present here an approach for parallelising a large-scale model of a drug delivery system based on Monte Carlo methods, as a framework for Cellular Automata mobility. The model simulates drug release in the gastro-intestinal tract, from coated ethylcellulose microspheres. The objective is high performance simulation of coated drugs for targeted delivery. The overall aim is to understand the importance of various molecular effects with respect to system evolution over time. Important underlying mechanisms of the process, such as erosion and diffusion, are described

Smart Polymers in Drug Delivery Applications

Acknowledgements: The authors sincerely acknowledge the financial supports of the UGC, New Delhi under UPE-FARI Program [F.No. 14-3/2012 (NS/PE)] and the DST, New Delhi under DST-PURSE-Phase-II Program [F.No. SR/PURSE Phase 2/13(G)]. Furthermore, this research was supported by the European Regional Development Fund (FEDER), through COMPETE2020 under the PT2020 program (POCI-01-0145-FEDER-023423), and by the Portuguese Foundation for Science and Technology (UID/Multi/04044/2013) and PAMI (ROTEIRO/0328/2013; Nº 022158).The most important components of living cells such as carbohydrates, proteins and nucleic acids are the polymeric molecules. Nature utilizes polymers both as constructive elements and as a part of the complicated cell machinery of living things. The rapid advancement in biomedical research has led to many creative applications for biocompatible polymers. With the development of newer and more potent drugs, a parallel expansion in more sophisticated drug delivery systems becomes mandatory. Smart polymeric drug delivery systems can respond to environmental changes and consequently, alter their properties reversibly enabling an efficient and safe drug delivery. This review comprehensively discusses various aspects of these polymers classified in different categories as per the type of stimulus.info:eu-repo/semantics/publishedVersio