Confined mesoporous silica membranes for albumin zero-order release
In this work, the transport capabilities of anodic alumina membranes confining SBA-15-like nanochannels in their pores... more In this work, the transport capabilities of anodic alumina membranes confining SBA-15-like nanochannels in their pores were investigated. The mean pore size of the confined mesophase was set around 7.0 nm, thus to achieve single passage of the selected Bovine Serum Albumin (BSA) protein, having comparable hydrodynamic diameter, through the nanochannels. Shape, size and orientation of the manufactured mesophase were characterized by means of small-angle X-ray scattering, transmission electron microscopy and N2 adsorption / desorption at 77 K. The usage of mesostructure-containing samples having pore tuned over the size of the released BSA allowed achieving a long-term zero-order release profile by single-file diffusion up to several weeks, which delivers a constant amount of drug by unit time independently from drug concentration and drug accessible area, while control anodic alumina membranes showed a classic Fickian diffusion release. The attained BSA constant release rate was about 2 μg/day. The possibility of rate tuning could be further exploited by varying the length of the siliceous nanochannels inside the alumina pores, i.e. through different amounts of mesostructure filling the host support.
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Download (.pdf) Estudio de la propagación no lineal de haces de ultrasonidos focalizados a través del cráneo para la apertura de la barrera hematoencefálica
by Noé Jiménez
Jiménez, N.; Marquet, F.; Camarena, F.; Konofagou, E.E.; Redondo, J.; Roig, B.; Picó, R.
Focused ultrasound techniques for Blood- Brain Barrier opening are emerging for localized and safe brain drug... more
Focused ultrasound techniques for Blood- Brain Barrier opening are emerging for localized and safe brain drug delivery. The aim of this work is to study how the nonlinear effects of the acoustic wave through the transcranial propagation affect to the focused beam properties. In order to do that, a nonlinear acoustics computational method based on FDTD (finite differences in time domain) has been developed in a cylindrical axisymmetric coordinate system. The boundary conditions are derived from a CT (X-ray computed tomography) mapping over a Rhesus monkey (Macaca mulatta). The results show that the nonlinear transcranial propagation induces amplitude dependent variations that can change the treatment area (focal position and beamwidth) and effective gain.
El empleo de haces de ultrasonidos focalizados para provocar la apertura de la barrera hematoencefálica es una técnica emergente y prometedora para la dosificación localizada y segura de fármacos en el sistema nervioso central. El objetivo de este trabajo es cuantificar como afectan los efectos no lineales a las propiedades del haz ultrasónico durante la propagación transcraneal. Para ello se emplea un método computacional basado en diferencias finitas en dominio temporal (FDTD) desarrollado bajo un sistema de coordenadas cilíndrico axisimétrico. Las condiciones de contorno han sido derivadas de un mapeado 3D adquirido mediante tomografía axial computarizada sobre un cráneo de mono Rhesus (Macaca mulatta). Los resultados muestran como la propagación no lineal a través del cráneo provoca variaciones en el área bajo tratamiento (posición de la focal y ancho de haz) así como en la ganancia efectiva en función de la presión de entrada.
SiO2 nanoparticles biocompatibility and their potential for gene delivery and silencing
M.A. Malvindi, V. Brunetti, G. Vecchio, A. Galeone, R. Cingolani, and P.P. Pompa
Nanoscale (2011), DOI: 10.1039/C1NR11269D
Despite the extensive use of silica nanoparticles (SiO2NPs) in many fields, the results about their potential toxicity... more Despite the extensive use of silica nanoparticles (SiO2NPs) in many fields, the results about their potential toxicity are still controversial. In this work, we have performed a systematic in vitro study to assess the biological impact of SiO2NPs, by investigating 3 different sizes (25, 60 and 115 nm) and 2 surface charges (positive and negative) of the nanoparticles in 5 cell lines (3 in adherence and 2 in suspension). We analyzed the cellular uptake and distribution of the NPs along with their possible effects on cell viability, membrane integrity and generation of reactive oxygen species (ROS). Experimental results show that all the investigated SiO2NPs do not induce detectable cytotoxic effects (up to 2.5 nM concentration) in all cell lines, and that cellular uptake is mediated by an endocytic process strongly dependent on the particle size and independent of its original surface charge, due to protein corona effects. Once having assessed the biocompatibility of SiO2NPs, we have evaluated their potential in gene delivery, showing their ability to silence specific protein expression. The results of this work indicate that monodisperse and stable SiO2NPs are not toxic, revealing their promising potential in various biomedical applications.
Biopharmaceutics of intrathecal baclofen-loaded microparticles in a goat model
International journal of Pharmaceutics 2005
The goal of this study was to develop a goat model allowing reliable pharmacokinetic (PK) studies of intrathecal... more The goal of this study was to develop a goat model allowing reliable pharmacokinetic (PK) studies of intrathecal baclofen (ITB) sustained release dosage forms using an implanted silicone catheter. ITB PK parameters (clearance, volume of distribution) following intrathecal bolus injection were determined for doses ranging from 100 to 560 microg and a comparison to human data was made. Baclofen-loaded microparticles were then implanted in the intrathecal space of goats and the resulting baclofen levels were determined during 28 days. Finally, PK parameters were used to predict cerebrospinal fluid (CSF) baclofen rates from in vitro release profiles of baclofen-loaded microspheres. The catheter was well tolerated and did not interfere with behavioral testings. Baclofen CSF clearance (mean = 8.59+/-2.43 ml/h) and volume of distribution (21.06+/-13.32 ml) were not significantly affected by the increase of the dose (p > 0.05). In vivo, the baclofen levels in CSF were stabilized at 200 microg/l after a period of 3 days. The predictive value of the in vitro release studies was good since the theoretical levels ranged between 128 and 257 microg/l. In conclusion, a large animal model was developed and allowed the biopharmaceutic evaluation of baclofen microparticles injected via intrathecal route.
Baclofen-loaded microspheres in gel suspensions for intrathecal drug delivery: In vitro and in vivo evaluation
Eur J Pharm Biopharm 2005
Severe spasticity is a very disabling disorder treated by continuous baclofen intrathecal infusion which unfortunately... more Severe spasticity is a very disabling disorder treated by continuous baclofen intrathecal infusion which unfortunately remains an expensive and uncomfortable treatment. In order to address these issues, new sustained release formulations designed for intrathecal baclofen delivery were sought with the aim of minimising the burst effect of baclofen which can lead to toxicity. Baclofen was encapsulated in poly(lactide-co-glycolide) (PLGA) microspheres which were then dispersed in chitosan thermosensitive gels, Pluronic PF-127 gels, carboxymethylcellulose solutions or Ringer lactate solution. The release rate was assessed in vitro using continuous flow cells and in vivo after intrathecal injection in goats: baclofen was quantified in cerebrospinal fluid (CSF) and plasma, and the associated pharmacological effect was evaluated. The results showed that the burst effect was reduced by at least a factor of 2 in vitro, after microsphere dispersion in viscous media. In vivo, PF-127 gel was found to be the best vehicle to reduce the burst effect by a factor of 10 in CSF, and by a factor of 2 in plasma. The toxic effect of baclofen due to the burst effect was reduced by the dispersion in PF127 gels. Therapeutic levels of baclofen in CSF were maintained during at least 1 month.
Lipid nanocarriers improve paclitaxel transport throughout human intestinal epithelial cells by using vesicle-mediated transcytosis
Journal of controlled release 2009
The use of lipid nanocapsules (LNCs) has enabled an improvement of the oral bioavailability of paclitaxel (Ptx).... more The use of lipid nanocapsules (LNCs) has enabled an improvement of the oral bioavailability of paclitaxel (Ptx). However, mechanisms that support this recent observation are not yet understood. By focusing on the well defined in vitro Caco-2 model, the purpose of this study was to evaluate the transport of LNCs across a model intestinal barrier. Firstly, four sizes of paclitaxel or dye (Nile Red)-loaded LNCs were formulated and LNCs with sizes between 26.3 ± 2.7 nm and 132.7 ± 5.5 nm were obtained. Different transport and uptake experiments were then performed across a Caco-2 cells culture model using these LNCs. Paclitaxel-loaded LNCs improved permeability of Ptx across intestinal epithelium compared with free Ptx or Taxol® by a factor of 3.5. At 37 °C particle size did not influence transport efficiency. However, at 4 °C a decrease in Ptx transport was observed with increasing size of LNCs. Thus, with LNCs of 25 nm size, the apparent permeability coefficient (Papp) was 5.3 ± 1.1 cm s− 1 at 37 °C and 2.2 ± 0.4 cm s− 1 at 4 °C. In comparison in LNCs of 130 nm size, the Papp decreased from 5.8 ± 0.8 cm s− 1 at 37 °C to 0.5 ± 0.1 cm s− 1 at 4 °C. The uptake of LNCs by Caco-2 cells and the incapacity of LNCs to open tight junctions were also demonstrated. Furthermore, experiment transports were performed in the presence of different inhibitors of endocytosis. Findings indicated a reduction of Ptx transport of 30 ± 6% when cell cholesterol was depleted, 65 ± 12% when caveolae-mediated endocytosis was inhibited and 20 ± 8% when clathrin-mediated endocytosis was inhibited. Finally, transmission electronic microscopy showed the presence of nano-objects on the basolateral side of the Caco-2 cell monolayers when LNCs were applied on the apical side.
Structure and Dynamics of a Thermoresponsive Microgel around Its Volume Phase Transition Temperature
by Mark Telling
Sustained drug delivery requires the use of multifunctional devices with enhanced properties. These properties include... more Sustained drug delivery requires the use of multifunctional devices with enhanced properties. These properties include responsiveness to external stimuli (such as temperature, pH, ionic strength), ability to deliver suitably designed ligands to specific receptors, enhanced bioadhesion to cells, and cytocompatibility. Microgels represent one of such multifunctional drug delivery devices. Recently, we described the fabrication of a stable colloidal aqueous suspension of cytocompatible microgel spheres based on a poly(vinyl alcohol)/poly(methacrylate-co-N-isopropylacrylamide) network (Ghugare, S.Mozetic, P.Paradossi, G. Biomacromolecules 2009, 10, 1589). These microgel spheres undergo an entropy-driven volume phase transition around the physiological temperature, this phase transition being driven by the incorporation of NiPAAm residues in the network. In that study, the microgel was loaded with the anticancer drug doxorubicin. As the microgel shrank, a marked increase in the amount of doxorubicin released was noted. Indeed, dynamic light scattering measurements showed the diameter reduction to be about 50%. In the present paper, we focus on some fundamental issues regarding modifications of the hydrogel architecture at a nanoscopic level as well as of the diffusive behavior of water associated with the polymer network around the volume phase transition temperature (VPTT). Sieving and size exclusion effects were studied by laser scanning confocal microscopy with the microgel exposed to fluorescent probes with different molecular weights. Confocal microscopy observations at room temperature and at 40 °C (i.e., below and above the VPTT) provided an evaluation of the variation of the average pore size (from 5 nm to less than 3 nm). Using quasielastic neutron scattering (QENS) with the IRIS spectrometer at ISIS, UK, the diffusive behavior of water molecules closely associated to the polymer network around the VPTT was investigated. A clear change in the values of diffusion coefficient of bound water was observed at the transition temperature. In addition, the local dynamics of the polymer itself was probed using the QENS spectrometer SPHERES at FRM II, Germany. For this study, the microgel was swollen in D2O. An average characteristic distance of about 5 Å for the localized chain motions was evaluated from the elastic incoherent structure factor (EISF) and from the Q-dependence of the Lorentzian width.
Baclofen-loaded microspheres: preparation and efficacy testing in a new rabbit model
Eur J Pharm Biopharm 2005
Intrathecal baclofen is the reference treatment for severe spasticity. This drug has to be injected chronically in the... more
Intrathecal baclofen is the reference treatment for severe spasticity. This drug has to be injected chronically in the intrathecal space by
implanted pumps which are very expensive, uncomfortable and sometimes lead to side effects. Previous work has been performed by our
group to assess the feasibility of encapsulating baclofen into poly(lactide-co-glycolide) (PLGA) microspheres and injecting these
preparations in the intrathecal space of rabbits. The aims of the present study were to improve the encapsulation process for industrial
application (scale-up), and to set up an animal model to assess the duration of effect of the new formulations. Modifications included the
replacement of methylene chloride by a less toxic solvent, ethyl acetate, and the use of high molecular weight polymers to extend the release
rate of the drug. The temperature and organic solvent extraction rate were fully controlled during the whole manufacturing process. All these
modifications resulted in high quality microsphere batches with a CV inferior to 5% for encapsulation efficiency and drug loading.
Encapsulation efficiency and release patterns were dependent on the drug payload and the polymer used. A formulation displaying a
sustained release of baclofen over 174 days and a moderate burst effect of 16% in the first day in vitro was evaluated in a new reliable model
of baclofen activity based on electrophysiological measurement of H-reflex in the rabbit. The activity of a very low dose of baclofen
microspheres in vivo was sustained over 35 days. Furthermore, the preparation was well tolerated. These newly developed preparations are a
very promising approach for enhancing the efficacy and comfort of patients undergoing spasticity treatment.
Sustained release formulations for spinal drug delivery
Review article published in J Drug Deliv Sci technol 2004
Spinal drug delivery is a field of growing interest since many active drugs are more potent and safer when injected... more
Spinal drug delivery is a field of growing interest since many active drugs are more potent and safer when injected directly in intrathecal or epidural spaces. Most of the drugs injected in the spinal structures are used for the treatment of chronic diseases (pain, spasticity, cancer, etc.). Thus, many formulation strategies have been used these last twenty years in order to enhance the residence time after spinal drug delivery. This review focuses on the formulations sequestering the active drug in a vehicle with the aim of modifying its distribution and elimination and finally its duration of action. After analyzing the specificities of formulations designed for spinal drug delivery, applications referring to diffusion modifiers
or depot dosage forms are then overviewed. The relation between performance and safety of these formulations and their interest in clinical practice is discussed.
Oxaliplatin loaded PLAGA microspheres: design of specific release profiles
Int J Pharmaceutics 2002
Oxaliplatin loaded PLAGA microspheres have been prepared by solvent extraction process. Parameters affecting the... more Oxaliplatin loaded PLAGA microspheres have been prepared by solvent extraction process. Parameters affecting the release kinetics in vitro have been studied in order to design specific release profiles suitable for direct intra-tumoral injection. By varying the nature and the relative proportions of different polymers we managed to prepare microspheres with good encapsulation efficiency (75-90%) and four different release profiles: zero order kinetics (type II) and the classical sigmoïd release profile with three different sizes of plateau and burst. These results, if correlated with in vivo activity, are promising to enhance effectiveness of local tumor treatment.
One-Pot Synthesis of Ethanolamine-Modified Mesoporous Silica
Pezhman Zarabadi-Poor, Alireza Badiei, Bradley D. Fahlman, Pezhman Arab, Ghodsi Mohammadi Ziarani
This work represents the first precedent for the one-pot synthesis of ethanolamine-modified mesoporous silica. The... more This work represents the first precedent for the one-pot synthesis of ethanolamine-modified mesoporous silica. The resultant material was characterized by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray diffraction, and BET/BJH surface area/porositymeasurements. The successful incorporation of ethanolaminemoieties in the structure of mesoporous silica was confirmed by its subsequent reaction with phenyl isocyanate. The observed morphology of this surfacefunctionalized mesoporous silica is significantly different from that of postmodified SBA-15 and also features a greater porosity.
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Functional hydrophobin-coating of thermally hydrocarbonized porous silicon microparticles.
by Luis Bimbo
Published in Biomaterials - Vol. 32, Issue 34 December 2011 Pages 9089-9099
Porous silicon (PSi) particles have been widely used in modulating the dissolution rate of various types of drugs... more Porous silicon (PSi) particles have been widely used in modulating the dissolution rate of various types of drugs loaded within its mesopores. This material can be surface treated in order to vary its hydrophobicity and several other properties, such as drug loading degree and release rate. Hydrophobins are a family of self-assembling proteins of fungal origin which have the ability to form layers on hydrophobic materials. This type of protein layer can modify the characteristics and control the binding properties of the surface on which it assembles. In this study, we have developed a procedure to coat thermally hydrocarbonized-PSi microparticles with hydrophobin II (HFBII) in order to modify the particles' hydrophobicity and to improve their biocompatibility, while maintaining intact the advantageous drug releasing properties of the PSi. The HFBII content adsorbed onto the particles was successfully quantified by a protein assay. Drug dissolution and permeation across Caco-2 cell monolayers were also conducted, together with viability studies in AGS, Caco-2 and HT-29 cells. The characterization and coating stability assessment showed that the HFBII-coating desorbs partially from the particles' surface as the pH increases. The HFBII coating also improved the biocompatibility of the particles without compromising the enhanced drug permeation or release.
Design and In-vitro Testing of Effective Poly(l-Lysine Iso-Phthalamide) Based Drug Targeting Systems for Solid Tumours
by Rongjun Chen
Published in Food and Bioproducts Processing 2005
The mode of cell uptake, relative cytotoxicity and efficacy of poly (l-lysine iso-phthalamide)-drug conjugates,... more The mode of cell uptake, relative cytotoxicity and efficacy of poly (l-lysine iso-phthalamide)-drug conjugates, PEG-graft poly (l-lysine iso-phthalamide)-drug containing micelles, poly (l-lysine iso-phthalamide) modified drug/protein nanospheres and unmodified protein nanospheres as potential delivery systems have been evaluated using doxorubicin and polymethine fluorophores as model drugs. pH dependent cell membrane lysis has been demonstrated using a haemolysis model and the cytotoxicity of the polymeric system evaluated using standard MTT and LDH activity assays. In-vitro toxicity and cellular targeting data are presented and the potential healthcare impact of such systems is discussed.
Aqueous Solution Behaviour and Membrane Disruptive Activity of PH-Responsive PEGylated Pseudo-Peptides and Their Intracellular Distribution
by Rongjun Chen
Published in Biomaterials 2008
The effect of PEGylation on the aqueous solution properties and cell membrane disruptive activity of a pH-responsive... more The effect of PEGylation on the aqueous solution properties and cell membrane disruptive activity of a pH-responsive pseudo-peptide, poly(l-lysine iso-phthalamide), has been investigated by dynamic light scattering, haemolysis and lactate dehydrogenase (LDH) assays. Intracellular trafficking of the polymers has been examined using confocal and fluorescence microscopy. With increasing degree of PEGylation, the modified polymers can form stabilised compact structures with reduced mean hydrodynamic diameters. Poly(l-lysine iso-phthalamide) with a low degree of PEGylation (17.4 wt%) retained pH-dependent solution behaviour and showed enhanced kinetic membrane disruptive activity compared to the parent polymer. It facilitated trafficking of endocytosed materials into the cytoplasm of HeLa cells. At levels of PEGylation in excess of 25.6 wt%, the modified polymers displayed a single particle size distribution unresponsive to pH, as well as a decrease in cell membrane lytic ability. The mechanism involved in membrane destabilisation was also investigated, and the potential applications of these modified polymers in drug delivery were discussed.
Synthesis and PH-Responsive Properties of Pseudo-Peptides Containing Hydrophobic Amino Acid Grafts
by Rongjun Chen
Published in Journal of Materials Chemistry 2009
Pseudo-peptidic polymers have been synthesised by grafting L-valine (PV), L-leucine (PL) and L-phenylalanine (PP) onto... more Pseudo-peptidic polymers have been synthesised by grafting L-valine (PV), L-leucine (PL) and L-phenylalanine (PP) onto the pendant carboxylic acid moieties of a pH-responsive polyamide, poly(L-lysine isophthalamide). The pH-responsive aqueous solution properties of PV-75, PL-75 and PP-75 with a stoichiometric degree of substitution of 75 mol% have been compared with those of the parent poly(L-lysine isophthalamide) using UV-visible and fluorescence spectroscopy. At low concentrations (≤0.1 mg mL−1), the grafted polymers displayed pH-dependent conformation. The pH at the onset of hydrophobic association (pHh) and the pH range over which association occurred varied significantly between the different amino acid grafts. The pHh values of PV-75, PL-75 and PP-75 at 0.025 mg mL−1 were 6.2, 7.0 and 7.2, respectively. Increasing concentration enhanced intermolecular aggregation. A bis-functional Cy5 derivative, incorporated within the backbones of poly(L-lysine isophthalamide) (polyCy5) and PP-75 (PDP-75), was demonstrated to act as a fluorescence reporter on the state of polymer conformation and aggregation. The intracellular trafficking of PDP-75, examined by confocal microscopy, indicates potential applications of the grafted polymers in drug delivery and medical imaging.
Effect of L-Leucine Graft Content on Aqueous Solution Behavior and Membrane-Lytic Activity of a PH-Responsive Pseudopeptide
by Rongjun Chen
Published in Biomacromolecules 2009
A series of pH-responsive polymers have been synthesized by grafting l-leucine onto the pendant carboxylic acid groups... more A series of pH-responsive polymers have been synthesized by grafting l-leucine onto the pendant carboxylic acid groups of the linear pseudopeptide, poly(l-lysine iso-phthalamide). The effect of the degree of grafting on aqueous solution properties, cell membrane-disruptive activity, and in vitro cytotoxicity was examined by UV−visible and fluorescence spectroscopy, hemolysis, alamar blue staining, and propidium iodide fluorescence assays. Modification of poly(l-lysine iso-phthalamide) with ≤23.6 mol % l-leucine caused a marginal effect on the pH-mediated hydrophobic association and hemolytic activity. Increasing the degree of grafting from 31.9 to 61.2 mol % resulted in polymers with progressively enhanced hydrophobic association and cell membrane disruption, thus confirming that the pH responsiveness and the extent of hydrophobic association and membrane disruption of the polymers can be modulated by varying the degree of grafting with hydrophobic amino acids. The pH responses were demonstrated to be concentration-dependent. At certain degrees of leucine grafting, the polymers were nonmembrane-lytic at physiological pH but mediated considerable membrane lysis at endosomal pH values (5.0−6.8), a feature critical for potential drug delivery applications.
The Role of Hydrophobic Amino Acid Grafts in the Enhancement of Membrane-Disruptive Activity of PH-Responsive Pseudo-Peptides
by Rongjun Chen
Published in Biomaterials 2009
pH-responsive polymers have been synthesised by grafting l-valine (PV-75), l-leucine (PL-75) and l-phenylalanine... more pH-responsive polymers have been synthesised by grafting l-valine (PV-75), l-leucine (PL-75) and l-phenylalanine (PP-75) onto the pendant carboxylic acid moieties of a pseudo-peptide, poly(l-lysine iso-phthalamide), at a stoichiometric degree of substitution of 75 mol%. The effect of such modification on the pH-, concentration- and time-dependent cell membrane-disruptive activity of the grafted polymers has been investigated using a haemolysis model. At 0.025 mg mL−1, the grafted polymers were almost non-haemolytic at pH 7.4, but mediated considerable membrane lysis after 60 min in the pH range characteristic of early endosomes, which ranked in the order: PP-75 > PL-75 > PV-75 > poly(l-lysine iso-phthalamide). PP-75 was 35-fold more lytic on a molar basis than the membrane-lytic peptide melittin. With increasing concentration, the grafted polymers showed an increased ability to lyse cell membranes and caused noticeable membrane disruption at physiological pH. The mechanism of the polymer-mediated membrane destabilisation has been investigated. The in-vitro cytotoxicity of the grafted polymers has been assessed using a propidium iodide fluorescence assay. It has been demonstrated by confocal microscopy that the grafted polymers can induce a significant release of endocytosed materials into the cytoplasm of HeLa cells, which is a feature critical for drug delivery applications.
The Influence of Aromatic Side-Chains on the Aqueous Properties of pH-Sensitive Poly (L-lysine iso-phthalamide) Derivatives
by Rongjun Chen
Published in Journal of Biomaterials Science, Polymer Edition 2010
The endosomal membrane has proven to be a challenging barrier for the delivery of therapeutic biomacromolecules,... more The endosomal membrane has proven to be a challenging barrier for the delivery of therapeutic biomacromolecules, including DNA, siRNA and proteins, which are taken up by endosomes but cannot freely diffuse across lipid bilayers. Anionic polymers that undergo conformational changes and become membrane disruptive in low-pH environments have the potential to assist in the delivery of these biomacromolecules across the endosomal membrane to the cytosol. Such endosomolytic polymers have been synthesized through the grafting of hydrophobic side-chains to a poly(L-lysine iso-phthalamide) backbone. The phenylalanine grafted form of poly(L-lysine iso-phthalamide) has a pH-sensitive membrane disruptive profile corresponding to the pH range of maturing endosomes and, thus, has a favourable endosomolytic profile. In order to understand the influence of hydrophobicity versus π-π interactions mediated by aromatic rings, a tyrosine grafted form of poly(L-lysine iso-phthalamide) was synthesized and its aqueous pH-sensitive properties, cytotoxicity and endosomal disruptive capacity were compared to phenylalanine-grafted poly(L-lysine iso-phthalamide). The similarity between these two polymers' properties, despite the large difference in hydrophobicity between their side-chains, supports the conclusion that the aromatic character of sidechains in poly(L-lysine iso-phthalamide) is an important property, as opposed to hydrophobicity alone, in determining the effectiveness of acidic pH triggered endosomolysis.
pH-responsive endosomolytic pseudo-peptides for drug delivery to multicellular spheroids tumour models
by Rongjun Chen
published in "Biomaterials" 2011
Endosomolytic polymers can aid in the endosomal release of therapeutics to improve intracellular drug delivery.... more Endosomolytic polymers can aid in the endosomal release of therapeutics to improve intracellular drug delivery. pH-responsive biomimetic pseudo-peptides were synthesised by grafting l-phenylalanine onto the pendant carboxylic acids of a polyamide, poly(l-lysine isophthalamide). PP-75 (stoichiometric l-phenylalanine grafting of 75 mol%) was determined to have the best endosomolytic property. The mean hydrodynamic size of PP-75 decreased with lower pH as the polymers adopted a more compact conformation due to protonation of acidic groups and increase in hydrophobicity. PP-75 was demonstrated to deliver model drugs effectively in three dimensional (3D) magnetic HeLa multicellular spheroids used as in vitro tumour models. These spheroids can be isolated easily and quickly by magnetic separation. Due to its relatively small size, PP-75 was able to penetrate from the exterior to the interior of these spheroids and was internalised by the cells in the spheroids. It could retain its pH-mediated membrane-lytic capability in 3D drug delivery by releasing internalised calcein from intracellular endosomes in the tumour models. Furthermore, cell viability results suggest that PP-75 showed no significant cytotoxicity towards cells in the spheroids. The pH-responsive PP-75 can potentially enhance the extracellular and intracellular delivery of therapeutics in tumours.
The Effects of Substituent Grafting on the Interaction of pH-Responsive Polymers with Phospholipid Monolayers
by Rongjun Chen
published in "Langmuir", 2011
pH-responsive amphiphilic polymers with suita- ble graftings have demonstrated highly efficient cell membrane activity... more pH-responsive amphiphilic polymers with suita- ble graftings have demonstrated highly efficient cell membrane activity and hence are promising applicants for drug-delivery. Grafting the hydrophobic amino acid L-phenylalanine and the hydrophilic methoxy poly(ethylene glycol) amine onto the pendant carboxylic acid moieties of a linear polyamide, poly- (L-lysine isophthalamide), can effectively modify the amphiphi- licity and conformation of the amphiphilic polymers. Here, the interactions of these polymers with phospholipid monolayers adsorbed on mercury (Hg) electrodes have been studied. AC voltammetry (ACV), rapid cyclic voltammetry (RCV), and electrochemical impedance spectroscopy (EIS) have been applied to monitor phospholipid monolayer associations with different polymer concentrations under different pH values. The polymers interact reversibly with the monolayer shown by altering the monolayer capacitance and inhibiting the phospholipid reorientation in electric field. Polymer grafting enhances the pH-mediated conformational change of the polymers which in turn increases their phospholipid monolayer activity. The most significant monolayer interactions have been observed with the polymer grafted with hydrophobic L-phenylalanine. A low level of PEGylation of the backbone also increases the monolayer activity. The polymer/DOPC interactions have been represented with an impedance model, which takes account of the interaction giving rise to an increase in monolayer capacitance and inhomogeneity and a Debye type dielectric relaxation. The extent of penetration of the polymers into the monolayer is inversely related to the electrical resistance they give rise to during the Debye relaxation. The cell membrane activities of these amphiphilic polymers have been successfully mirrored in this supported DOPC monolayer system, isolating the key parameters for biomembrane activities and giving insight into the mechanism of the interactions. The conclusions from this study provide strategic directions in material design catering to different requirements in biomedical applications.