Selective tuning of the self-assembly and gelation of a hydrophilic poloxamine by cyclodextrins

Nanocomposite gels of poloxamine and Laponite for β-Lapachone release in anticancer therapy

Nano-hybrid systems have been shown to be an attractive platform for drug delivery. Laponite® RD (LAP), a biocompatible synthetic clay, has been exploited for its ability to establish of strong secondary interactions with guest compounds and hybridization with polymers or small molecules that improves, for instance, cell adhesion, proliferation, and differentiation or facilitates drug attachment to their surfaces through charge interaction. In this work, LAP was combined with Tetronics, X-shaped amphiphilic PPO-PEO (poly (propylene oxide)-poly (ethylene oxide) block copolymers. β-Lapachone (BLPC) was selected for its anticancer activity and its limited bioavailability due to very low aqueous solubility, with the aim to improve this by using LAP/Tetronic nano-hybrid systems. The nanocarriers were prepared over a range of Tetronic 1304 concentrations (1 to 20% w/w) and LAP (0 to 3% w/w). A combination of physicochemical methods was employed to characterize the hybrid systems, including rheology, particle size and shape (DLS, TEM), thermal analysis (TG and DSC), FTIR, solubility studies and drug release experiments. In vitro cytotoxicity assays were performed with BALB/3T3 and MCF-7 cell lines. In hybrid systems, a sol-gel transition can occur below physiological temperature. BLPC exhibits the most significant increase in solubility in formulations with a high concentration of T1304 (over 10% w/w) and 1.5% w/w LAP, or systems with only LAP (1.5%), with a 50 and 100-fold increase in solubilisation, respectively. TEM images showed spherical micelles of T1304, which elongated into wormlike micelles with concentration (20%) and in the presence of LAP, a finding that has not been reported before. A sustained release of BLPC over 140 hours was achieved in one of the formulations (10% T1304 with 1.5% laponite), which also showed the best selectivity index towards cancer cells (MCF-7) over BALB/3T3 cell lines. In conclusion, BLPC-loaded T1304/LAP nano-hybrid systems proved safe and highly effective and are thus a promising formulation for anticancer therapy.

Correlation of the hierarchical structure with rheological behavior of polypseudorotaxane gel composed of pluronic and β-cyclodextrin

We have identified the hierarchical (primary, secondary, tertiary and quaternary) structures of a polypseudorotaxane (PPR) gel composed of the Pluronic F108 and β-cyclodextrin system to be β-cyclodextrin crystalline, lamellar sheets, lamellar stacks and "grains", respectively. The correlation between the rheological properties and the proposed structures under shear flows was rationalized. Alignment of lamellar stacks and reorganization of grain boundaries under shear flows were investigated by rheo-SANS, small angle X-ray scattering and small-angle light scattering. The relaxation of highly aligned lamellar stacks is slow (>2 h) after flow cessation compared to that of the regrouped grains (a few minutes). The main contribution to thixotropic behavior is likely from the faster relaxation of the reorganized grains containing highly oriented lamellar stacks. The comprehensive understanding of structure-function relationship of the PPR gel will facilitate the rational design for its applications.

Structural characterization by scattering and spectroscopic methods and biological evaluation of polymeric micelles of poloxamines and TPGS as nanocarriers for miltefosine delivery

Miltefosine (MF), an alkylphospholipid originally developed for breast cancer treatment, is a highly active drug for the treatment against leishmaniasis, a neglected tropical disease considered the world's second leading cause of death by a parasitic agent after malaria. MF exhibits dose-limiting gastrointestinal side effects in patients and its penetration through lipophilic barriers is reduced. In this work we propose a reformulation of MF by incorporating the drug to poly(ethylene)oxide (PEO)-based polymeric micelles, specifically, D-α-tocopheryl polyethylene glycol succinate (TPGS) and Tetronic block copolymers (T904 and T1107). A full structural characterization of the aggregates has been carried out by SANS (small-angle neutron scattering) and dynamic light scattering (DLS), in combination with proton 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, to determine the precise location of the drug. The structure of MF micelles has been characterized as a function of the temperature and concentration. In the presence of the block-copolymers, MF forms mixed micelles in a wide range of temperatures, TPGS being the co-surfactant that incorporates more MF unimers. The hydrophobic tail of MF and those of the block copolymers are in close contact within the micelles, which present a core-shell structure with a hydrophilic corona formed by the PEG blocks of the TPGS and the zwitterion head group of the MF. In order to identify the best carrier, the antileishmanicidal activity of MF in the different formulations has been tested on macrophages, promastigotes and intracellular amastigotes. The combination of the three vehicles with MF makes the formulated drug more active than MF alone against L. major promastigotes, however, only the combination with T904 increases the MF activity against intracellular amastigotes. With the aim of exploring gel-based formulations of the drug, the combination of MF and T1107 under gelation conditions has also been investigated.

Complex systems that incorporate cyclodextrins to get materials for some specific applications

Cyclodextrins (CDs) are a family of biodegradable cyclic hydrocarbons composed of α-(1,4) linked glucopyranose subunits, the more common containing 6, 7 or 8 glucose units are named α, β and γ-cyclodextrins respectively. Since the discovery of CDs, they have attracted interest among scientists and the first studies were about the properties of the native compounds and in particular their use as catalysts of organic reactions. Characteristics features of different types of cyclodextrins stimulated investigation in different areas of research, due to its non-toxic and non-inmunogenic properties and also to the development of an improved industrial production. In this way, many materials with important properties have been developed. This mini-review will focus on chemical systems that use cyclodextrins, whatever linked covalently or mediated by the non covalent interactions, to build complex systems developed mainly during the last five years.

Structural and Spectroscopic Characterization of TPGS Micelles: Disruptive Role of Cyclodextrins and Kinetic Pathways

The aggregation and structure of d-α-tocopheryl polyethylene glycol succinate micelles, TPGS-1000, an amphiphilic derivative of vitamin E, were characterized using scattering and spectroscopic methods, and the impact of different cyclodextrins (CDs) on the self-assembly was investigated, with the view of combining these two versatile pharmaceutical excipients in drug formulations. Combined small-angle neutron scattering (SANS), dynamic light scattering, and time-resolved and steady-state fluorescence emission experiments revealed a core-shell architecture with a high aggregation number (N_agg ≈ 100) and a highly hydrated poly(ethylene oxide) corona (∼11 molecules of solvent per ethylene oxide unit). Micelles form gradually, with no sharp onset. Structural parameters and hydration of the aggregates were surprisingly stable with both temperature and concentration, which is a critical advantage for their use in pharmaceutical formulations. CDs were shown to affect the self-assembly of TPGS in different ways. Whereas native CDs induced the precipitation of a solid complex (pseudopolyrotaxane), methylated β-CDs led to different outcomes: constructive (micellar expansion), destructive (micellar rupture), or no effect, depending on the number of substituents and whether the substitution pattern was regular or random on the rims of the macrocycle. Time-resolved SANS studies on mixtures of TPGS with regularly dimethylated β-CD (DIMEB), which ruptures the micelles, revealed an almost instantaneous demicellization (<100 ms) and showed that the process involved the formation of large aggregates whose size evolved over time. Micellar rupture is caused by the formation of a TPGS-DIMEB inclusion complex, involving the incorporation of up to three macrocycles on the tocopherol, as shown by proton nuclear magnetic resonance (NMR) and ROESY NMR. Analysis of NMR data using Hill's equation revealed that the binding is rather cooperative, with the threading of the CD favoring the subsequent inclusion of additional CDs on the aliphatic moiety.

Competitive and Synergistic Interactions between Polymer Micelles, Drugs, and Cyclodextrins: The Importance of Drug Solubilization Locus

Polymeric micelles, in particular PEO-PPO-based Pluronic, have emerged as promising drug carriers, while cyclodextrins (CD), cyclic oligosaccharides with an apolar cavity, have long been used for their capacity to form inclusion complexes with drugs. Dimethylated β-cyclodextrin (DIMEB) has the capacity to fully breakup F127 Pluronic micelles, while this effect is substantially hindered if drugs are loaded within the micellar aggregates. Four drugs were studied at physiological temperature: lidocaine (LD), pentobarbital sodium salt (PB), sodium naproxen (NP), and sodium salicylate (SAL); higher temperatures shift the equilibrium toward higher drug partitioning and lower drug/CD binding compared to 25 °C ( Valero, M.; Dreiss, C. A. Growth, Shrinking, and Breaking of Pluronic Micelles in the Presence of Drugs and/or β-Cyclodextrin, a Study by Small-Angle Neutron Scattering and Fluorescence Spectroscopy . Langmuir 2010 , 26 , 10561 - 10571 ). The impact of drugs on micellar structure was characterized by small-angle neutron scattering (SANS), while their solubilization locus was revealed by 2D NOESY NMR. UV and fluorescence spectroscopy, Dynamic and Static Light Scattering were employed to measure a range of micellar properties and drug:CD interactions: binding constant, drug partitioning within the micelles, critical micellar concentration of the loaded micelles, aggregation number (N_agg). Critically, time-resolved SANS (TR-SANS) reveal that micellar breakup in the presence of drugs is substantially slower (100s of seconds) than for the free micelles (<100 ms) ( Valero, M.; Grillo, I.; Dreiss, C. A. Rupture of Pluronic Micelles by Di-Methylated β-Cyclodextrin Is Not Due to Polypseudorotaxane Formation . J. Phys. Chem. B 2012 , 116 , 1273 - 1281 ). These results combined together give new insights into the mechanisms of protection of the drugs against CD-induced micellar breakup. The outcomes are practical guidelines to improve the design of drug delivery systems as well as a better understanding of competitive assembly mechanisms leading to shape and function modulation.

Structure and Rheology of Poloxamine T1107 and Its Nanocomposite Hydrogels with Cyclodextrin-Modified Barium Titanate Nanoparticles

We report the preparation of a nanocomposite hydrogel based on a poloxamine gel matrix (Tetronic T1107) and cyclodextrin (CD)-modified barium titanate (BT) nanoparticles. The micellization and sol-gel behavior of pH-responsive block copolymer T1107 were fully characterized by small-angle neutron scattering (SANS), dynamic light scattering (DLS), and Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy as a function of concentration, pH and temperature. SANS results reveal that spherical micelles in the low concentration regime present a dehydrated core and highly hydrated shell, with a small aggregation number and size, highly dependent on the degree of protonation of the central amine spacer. At high concentration, T1107 undergoes a sol-gel transition, which is inhibited at acidic pH. Nanocomposites were prepared by incorporating CD-modified BT of two different sizes (50 and 200 nm) in concentrated polymer solutions. Rheological measurements show a broadening of the gel region, as well as an improvement of the mechanical properties, as assessed by the shear elastic modulus, G' (up to 200% increase). Initial cytocompatibility studies of the nanocomposites show that the materials are nontoxic with viabilities over 70% for NIH3T3 fibroblast cell lines. Overall, the combination of Tetronics and modified BaTiO3 provides easily customizable systems with promising applications as soft piezoelectric materials.

Atomic elucidation of the cyclodextrin effects on DDT solubility and biodegradation

Different binding modes between DDT and CDs explain why only α-CD can promote the bioavailability and biodegradation of DDT by simultaneously increasing its aqueous solubility and membrane interaction.

NaCl-triggered self-assembly of hydrophilic poloxamine block copolymers

Tetronic 1307 (T1307) is a hydrophilic poloxamine (HLB>24) with a high molecular mass owing to its long PEO and PPO blocks. In spite of good biocompatibility, its use as a component of drug delivery systems is limited by its high critical micelle concentration (CMC) and temperature (CMT). The aim of this work was to elucidate whether the addition of NaCl or the combination of salts and temperature may bring T1307 micellization and gelling features into more practically useful values. Increasing NaCl concentration in the 0.154 M (isotonic) to 2M (hypertonic) range made the copolymer more hydrophobic and more prone to self-assemble into unimodal micelles, as observed by means of π-A isotherms, (1)H NMR, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and pyrene fluorescence. The decrease in CMC and CMT observed for T1307 in 0.5 M NaCl medium (tolerable hypertonic solution), compared to water, notably favored the solubility of hydrophobic drugs such as curcumin and quercetin. Moreover, phase diagram, intrinsic viscosity and sol-to-gel transition were markedly affected by NaCl concentration. Overall, the strong dependence of T1307 self-assembly features on NaCl opens interesting possibilities for tuning the performance of T1307 as a component of nanocarriers and in situ gelling systems.