Alessandro Jäger

pH-triggered block copolymer micelles based on a pH-responsive PDPA (poly[2-(diisopropylamino)ethyl methacrylate]) inner core and a PEO (poly(ethylene oxide)) outer shell as a potential tool for the cancer therapy

The potential of a novel pH-triggered block copolymer as a promising drug delivery platform for the cancer therapy has been explored. The block copolymer poly(ethylene oxide)-b-poly(glycerol monomethacrylate)-b-poly[2-(diisopropylamino)ethyl methacrylate] herein referred to as PEO113-b-PG2MA30-b-PDPA50 upon dissolution in ethanol followed by single-step nanoprecipitation in phosphate buffered saline (PBS) self-assembled into highly regular spherical micelles whose structure was characterized in detail by static (SLS), dynamic (DLS) and electrophoretic (ELS) light scattering, small angle X-ray scattering (SAXS), fluorescence spectroscopy and transmission electron microscopy (TEM). The micellar size (2RH = 42 nm) and micellar molecular weight (Mw(micelles) > 106 kDa) were found to be in the range to avoid renal clearance providing a long blood circulation time. Their size is below the cut-off size of the leaky pathological vasculature (DH < 200 nm), making them candidates for the use in cancer therapy based on the EPR effect. The pH-responsive PDPA core could be loaded with the poorly water-soluble anti-cancer drug paclitaxel (PTX) with encapsulation efficiency ∼70% and drug loading content ∼7% wdrug/wpolymer. The pKa of the diisopropylamino group of the PDPA block was determined as pKa = 6.8 in the simulated physiological condition, which is remarkably close to the pH microenvironment of tumoral cells. The release experiments evidenced that approximately 90% of the encapsulated PTX was sustained at the PDPA micellar core within the first 9 h at pH 7.4 whilst only 18 h were required for complete drug release at pH 5.0. These results suggest that the micellar dissociation might be triggered at the slightly acid tumoral extracellular environments (pH < pKa(PDPA)). The nanostructures were further placed in contact with human plasma or human serum albumin (HSA) diluted in PBS. The DLS experiments revealed that the micelles are especially stable for up to at least 48 h in such conditions, attesting the possibly long blood circulation time of the nanoparticles at serum environments which is a pre-requisite for the drug delivery applications. The cell viability experiments demonstrated that the drug-free block copolymer micelles are non-toxic and the number of viable cells is always greater than 85% compared to the survival number of a control group.

Lipid-core nanocapsules restrained the indomethacin ethyl ester hydrolysis in the gastrointestinal lumen and wall acting as mucoadhesive reservoirs.

The aim of this work was to investigate if the indomethacin ethyl ester (IndOEt) released from lipid-core nanocapsules (NC) is converted into indomethacin (IndOH) in the intestine lumen, intestine wall or after the particles reach the blood stream. NC-IndOEt had monomodal size distribution (242 nm; PDI 0.2) and zeta potential of -11 mV. The everted rat gut sac model showed IndOEt passage of 0.16 micromol m(-2) through the serosal fluid (30 min). From 15 to 120 min, the IndOEt concentrations in the tissue increased from 6.13 to 27.47 micromol m(-2). No IndOH was formed ex vivo. A fluorescent-NC formulation was used to determine the copolymer bioadhesion (0.012 micromol m(-2)). After NC-IndOEt oral administration to rats, IndOEt and IndOH were detected in the gastrointestinal tract (contents and tissues). In the tissues, the IndOEt concentrations decreased from 459 to 5 microg g(-1) after scrapping, demonstrating the NC mucoadhesion. In plasma (peripheric and portal vein), in spleen and liver, exclusively IndOH was detected. In conclusion, after oral dosing of NC-IndOEt, IndOEt is converted into IndOH in the intestinal lumen and wall before reaching the blood stream. The complexity of a living system was not predicted by the ex vivo gut sac model.

Light scattering evidence of selective protein fouling on biocompatible block copolymer micelles

Selective protein fouling on block copolymer micelles with well-known potential for tumour-targeting drug delivery was evidenced by using dynamic light scattering measurements. The stability and interaction of block copolymer micelles with model proteins (BSA, IgG, lysozyme and CytC) is reported for systems featuring a hydrophobic (poly[2-(diisopropylamino)-ethyl methacrylate]) (PDPA) core and hydrophilic coronas comprising poly(ethylene oxide)/poly(glycerol monomethacrylate) (PEO-b-PG2MA) or poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC). The results revealed that protein size and hydrophilic chain density play important roles in the observed interactions. The PEO(113)-b-PG2MA(30)-b-PDPA(50) nanoparticles are stable and protein adsorption is prevented at all investigated protein environments. The successful protein-repellent characteristic of these nanoparticles is attributed to a high hydrophilic surface chain density (>0.1 chains per nm(2)) and to the length of the hydrophilic chains. On the other hand, although PMPC also has protein-repellent characteristics, the low surface chain density of the hydrophilic shell is supposed to enable interactions with small proteins. The PMPC(40)-b-PDPA(70) micelles are stable in BSA and IgG environments due to weak repulsion forces between PMPC and the proteins, to the hydration layer, and particularly to a size-effect where the large BSA (R(H) = 4.2 nm) and IgG (R(H) = 7.0 nm) do not easily diffuse within the PMPC shell. Conversely, a clear interaction was observed with the 2.1 nm radius lysozyme. The lysozyme protein can diffuse within the PMPC micellar shell towards the PDPA hydrophobic core in a process favored by its smaller size and the low hydrophilic PMPC surface chain density (∼0.049 chains per nm(2)) as compared to PEO-b-PG2MA (∼0.110 chains per nm(2)). The same behavior was not evidenced with the 2.3 nm radius positively charged CytC, probably due to its higher surface hydrophilicity and the consequent chemical incompatibility with PDPA.

Understanding the Structural Parameters of Biocompatible Nanoparticles Dictating Protein Fouling

The development of nanocarriers for biomedical applications requires that these nanocarriers have special properties, including resistance to nonspecific protein adsorption. In this study, the fouling properties of PLA- and PCL-based block copolymer nanoparticles (NPs) have been evaluated by placing them in contact with model proteins. Block copolymer NPs were produced through the self-assembly of PEOm-b-PLAn and PEOm-b-PCLn. This procedure yielded nanosized objects with distinct structural features dependent on the length of the hydrophobic and hydrophilic blocks and the volume ratio. The protein adsorption events were examined in relation to size, chain length, surface curvature, and hydrophilic chain density. Fouling by BSA and lysozyme was considerably reduced as the length of the hydrophilic PEO-stabilizing shell increases. In contrast to the case of hydrophilic polymer-grafted planar surfaces, the current investigations suggest that the hydrophilic chain density did not markedly influence protein fouling. The protein adsorption took place at the outer surface of the NPs since neither BSA nor lysozyme was able to diffuse within the hydrophilic layer due to geometric restrictions. Protein binding is an exothermic process, and it is modulated mainly by polymer features. The secondary structures of BSA and lysozyme were not affected by the adhesion phenomena.

Morphology and Kinetics of Aggregation of Silver Nanoparticles Induced with Regioregular Cationic Polythiophene

The aggregation kinetics of negatively charged borate-stabilized silver nanoparticles (NPs) induced by the cationic regioregular polythiophene polyelectrolyte poly{3-[6-(1-methylimidazolium-3-yl)hexyl]thiophene-2,5-diyl bromide} (PMHT-Br) and the morphology of formed aggregates have been investigated via ultraviolet-visible light (UV-vis) spectroscopy, transmission electron microscopy (TEM), zeta (ζ) potential measurements, dynamic light scattering (DLS), and time-resolved small-angle X-ray scattering (SAXS). Two or three populations of NPs are formed within milliseconds upon mixing the components, which differ in the mean size, extent of polymer coating, and time stability. These characteristics are primarily controlled by the PMHT-Br to Ag-NPs ratio. Population of single NPs of a mean size of ∼5 nm is present in every system and is mostly stable for a long time. At low ratios, the single NPs are most probably almost free of polymer chains and the second population includes slow, but in a limited extent, growing NPs in which single NPs might be interconnected by polymer chains. At the ratios corresponding to the charge balance in the system (ca. zero ζ-potential of NPs), the NPs aggregate, forming a second population that continuously grows in size, and finally undergo sedimentation. At the high ratios, three long-time stable populations of NPs are observed, having mean sizes of ca. 5, 13, and 35 nm; all NPs should be fully coated with PMHT-Br, giving them a positively charged stabilizing shell.

Poly(ethylene oxide monomethyl ether)-block-poly(propylene succinate) Nanoparticles: Synthesis and Characterization, Enzymatic and Cellular Degradation, Micellar Solubilization of Paclitaxel, and in Vitro and in Vivo Evaluation

Polyester-based nanostructures are widely studied as drug-delivery systems due to their biocompatibility and biodegradability. They are already used in the clinic. In this work, we describe a new and simple biodegradable and biocompatible system as the Food and Drug Administration approved polyesters (poly-ε-caprolactone, polylactic acid, and poly(lactic- co-glycolic acid)) for the delivery of the anticancer drug paclitaxel (PTX) as a model drug. A hydrophobic polyester, poly(propylene succinate) (PPS), was prepared from a nontoxic alcohol (propylene glycol) and monomer from the Krebss cycle (succinic acid) in two steps via esterification and melt polycondensation. Furthermore, their amphiphilic block copolyester, poly(ethylene oxide monomethyl ether)- block-poly(propylene succinate) (mPEO- b-PPS), was prepared by three steps via esterification followed by melt polycondensation and the addition of mPEO to the PPS macromolecules. Analysis of the in vitro cellular behavior of the prepared nanoparticle carriers (NPs) (enzymatic degradation, uptake, localization, and fluorescence resonance energy-transfer pair degradation studies) was performed by fluorescence studies. PTX was loaded to the NPs of variable sizes (30, 70, and 150 nm), and their in vitro release was evaluated in different cell models and compared with commercial PTX formulations. The mPEO- b-PPS copolymer analysis displays glass transition temperature < body temperature < melting temperature, lower toxicity (including the toxicity of their degradation products), drug solubilization efficacy, stability against spontaneous hydrolysis during transport in bloodstream, and simultaneous enzymatic degradability after uptake into the cells. The detailed cytotoxicity in vitro and in vivo tumor efficacy studies have shown the superior efficacy of the NPs compared with PTX and PTX commercial formulations.