Structural and Property Characterizations of Dual-Responsive Core-Shell Tecto Dendrimers for Tumor Penetration and Gene Delivery Applications.

Core-shell tecto dendrimers (CSTDs) with excellent physicochemical properties and good tumor penetration and gene transfection efficiency have been demonstrated to have the potential to replace high-generation dendrimers in biomedical applications. However, their characterization and related biological properties of CSTDs for enhanced tumor penetration and gene delivery still lack in-depth investigation. Herein, three types of dual-responsive CSTDs are designed for thorough physicochemical characterization and investigation of their tumor penetration and gene delivery efficiency. Three types of CSTDs are prepared through phenylborate ester bonds of phenylboronic acid (PBA)-decorated generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers as cores and monose (galactose, glucose, or mannose)-conjugated G3 PAMAM dendrimers as shells and thoroughly characterized via NMR and other techniques. It is shown that the produced CSTDs display strong correlation signals between the PBA and monose protons, similar hydrodynamic diameters, and dual reactive oxygen species- and pH-responsivenesses. The dual-responsive CSTDs are proven to have structure-dependent tumor penetration property and gene delivery efficiency in terms of small interference RNA for gene silencing and plasmid DNA for gene editing, thus revealing a great potential for different biomedical applications.

A Simple Elimination of the Thermal Convection Effect in NMR Diffusiometry Experiments.

Thermal convection is always present when the temperature of an NMR experiment is different from the ambient one. Most often, it falsifies the value of the diffusion coefficient determined by NMR diffusiometry using a PGSE NMR experiment. In spite of common belief, it acts not only at higher temperatures but also at temperatures lower than in the laboratory. Sodium alkyl-sulfate monomers and micelles in D2O solvent were used as model molecules measured at T = 319 K in order to show that thermal convection sometimes remains hidden in experiments. In this paper, we demonstrate that the increase in apparent diffusion coefficient with increasing diffusion time is a definite indicator of thermal convection. Extrapolation to zero diffusion time can also be used to obtain the real diffusion coefficient, likewise applying the less sensitive pulse sequences designed for flow compensation or the expensive hardware, e.g., sapphire or Shigemi NMR tubes, to decrease the temperature gradient. Further, we show experiments illustrating the effect of a long diffusion time in which the periodic changes of the echo intensity with gradient strength appear as predicted by theories.

Exploring Cyclic Aminopolycarboxylate Ligands for Sb(III) Complexation: PCTA and Its Derivatives as a Promising Solution.

In recent years Auger electron emitters have been suggested as promising candidates for radiotherapy with no side effects in cancer treatment. In this work we report a detailed coordination chemistry study of [Sb(PCTA)] (PCTA: 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid), a macrocyclic aminopolycarboxylate-type complex of antimony(III), whose 119Sb isotope could be a suitable low-energy electron emitter for radiotherapy. The thermodynamic stability of the chelate obtained by pH-potentiometry and UV-vis spectrophotometry is high enough (log K[Sb(PCTA)] = 23.2(1)) to prevent the hydrolysis of the metal ion near physiological pH. The formation of [Sb(PCTA)] is confirmed by NMR and electrospray ionization mass spectrometry measurements in solution; furthermore, the structure of [Sb(PCTA)]·NaCl·3H2O and [Sb(PCTA)]·HCl·3H2O is described by X-ray and density functional theory calculations. Consequently, the [Sb(PCTA)] is the first thermodynamically stable antimony(III) complex bearing polyamino-polycarboxylate macrocyclic platform. Our results demonstrate the potential of rigid (pyclen derivative) ligands as chelators for future applications of Sb(III) in a targeted radiotherapy based on the 119Sb isotope.

Complexes of Bifunctional DO3A-N-(α-amino)propinate Ligands with Mg(II), Ca(II), Cu(II), Zn(II), and Lanthanide(III) Ions: Thermodynamic Stability, Formation and Dissociation Kinetics, and Solution Dynamic NMR Studies.

The thermodynamic, kinetic, and structural properties of Ln3+ complexes with the bifunctional DO3A-ACE4- ligand and its amide derivative DO3A-BACE4- (modelling the case where DO3A-ACE4- ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd3+ complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg2+ and Ca2+ complexes of DO3A-ACE4- and DO3A-BACE4- complexes are lower than for DOTA4- and DO3A3-, while the Zn2+ and Cu2+ complexes have similar and higher stability than for DOTA4- and DO3A3- complexes. The stability constants of the Ln(DO3A-BACE)- complexes increase from Ce3+ to Gd3+ but remain practically constant for the late Ln3+ ions (represented by Yb3+). The stability constants of the Ln(DO3A-ACE)4- and Ln(DO3A-BACE)4- complexes are several orders of magnitude lower than those of the corresponding DOTA4- and DO3A3- complexes. The formation rate of Eu(DO3A-ACE)- is one order of magnitude slower than for Eu(DOTA)-, due to the presence of the protonated amine group, which destabilizes the protonated intermediate complex. This protonated group causes the Ln(DO3A-ACE)- complexes to dissociate several orders of magnitude faster than Ln(DOTA)- and its absence in the Ln(DO3A-BACE)- complexes results in inertness similar to Ln(DOTA)- (as judged by the rate constants of acid assisted dissociation). The 1H NMR spectra of the diamagnetic Y(DO3A-ACE)- and Y(DO3A-BACE)- reflect the slow dynamics at low temperatures of the intramolecular isomerization process between the SA pair of enantiomers, R-Λ(λλλλ) and S-Δ(δδδδ). The conformation of the Cα-substituted pendant arm is different in the two complexes, where the bulky substituent is further away from the macrocyclic ring in Y(DO3A-BACE)- than the amino group in Y(DO3A-ACE)- to minimize steric hindrance. The temperature dependence of the spectra reflects slower ring motions than pendant arms rearrangements in both complexes. Although losing some thermodynamic stability relative to Gd(DOTA)-, Gd(DO3A-BACE)- is still quite inert, indicating the usefulness of the bifunctional DO3A-ACE4- in the design of GBCAs and Ln3+-based tags for protein structural NMR analysis.

Characterization of zwitterion-modified poly(amidoamine) dendrimers in aqueous solution via a thorough NMR investigation.

Zwitterions are a class of unique molecules that can be modified onto nanomaterials to render them with antifouling properties. Here we report a thorough NMR investigation of dendrimers modified with zwitterions in terms of their structure, hydrodynamic size, and diffusion time in aqueous solution. In this present work, poly(amidoamine) (PAMAM) dendrimers of generation 5 (G5) were partially decorated with carboxybetaine acrylamide (CBAA), 2-methacryloyloxyethyl phosphorylcholine (MPC), and 1,3-propane sultone (1,3-PS), respectively with different modification degrees. The formed zwitterion-modified G5 dendrimers were characterized using NMR techniques. We show that the zwitterion modification leads to increased G5 dendrimer size in aqueous solution, suggesting that the modified zwitterions can form a hydration layer on the surface of G5 dendrimers. In addition, the hydrodynamic sizes of G5 dendrimers modified with different zwitterions but with the same degree of surface modification are discrepant depending on the type of zwitterions. The present study provides a new physical insight into the structure of zwitterion-modified G5 dendrimers by NMR techniques, which is beneficial for further design of different biomedical applications.

Indium in Polyoxopalladate(II) Chemistry: Synthesis of All-Acetate-Capped [InPd12O8(OAc)16]5- and Controlled Transformation to Phosphate-Capped Double-Cube and Monocube.

We have prepared the indium(III)-centered, all-acetate-capped polyoxopalladate(II) nanocube [InPd12O8(OAc)16]5- (InPd12Ac16), which can be further used as precursor to form the phosphate-capped (i) double-cube [In2Pd23O17(OH)(PO4)12(PO3OH)]21- (In2Pd23P13) and (ii) monocube [InPd12O8(PO4)8]13- (InPd12P8). All three novel polyoxopalladates (POPs) were synthesized using conventional one-pot techniques in aqueous solution and characterized in the solid state (single-crystal XRD, IR, elemental analysis), in solution (115In, 31P, and 13C NMR), and in the gas phase (ESI-MS).

Dithallium(III)-Containing 30-Tungsto-4-phosphate, [Tl2Na2(H2O)2(P2W15O56)2]16-: Synthesis, Structural Characterization, and Biological Studies.

Here we report on the synthesis and structural characterization of the dithallium(III)-containing 30-tungsto -4-phosphate [Tl2Na2(H2O)2{P2W15O56}2]16- (1) by a multitude of solid-state and solution techniques. Polyanion 1 comprises two octahedrally coordinated Tl3+ ions sandwiched between two trilacunary {P2W15} Wells-Dawson fragments and represents only the second structurally characterized, discrete thallium-containing polyoxometalate to date. The two outer positions of the central rhombus are occupied by sodium ions. The title polyanion is solution-stable as shown by 31P and 203/205Tl NMR. This was also supported by Tl NMR spectra simulations including several spin systems of isotopologues with half-spin nuclei (203Tl, 205Tl, 31P, 183W). 23Na NMR showed a time-averaged signal of the Na+ counter cations and the structurally bonded Na+ ions. 203/205Tl NMR spectra also showed a minor signal tentatively attributed to the trithallium-containing derivative [Tl3Na(H2O)2(P2W15O56)2]14-, which could also be identified in the solid state by single-crystal X-ray diffraction. The bioactivity of polyanion 1 was also tested against bacteria and Leishmania.

Beware of phosphate: evidence of specific dendrimer-phosphate interactions.

Dendrimers are extensively studied for drug delivery and catalysis, most of which are pH dependent. Phosphate buffer solutions (PBSs) are often used to adjust the pH. We have found that phosphate ions become incorporated into poly(amidoamine) (PAMAM) dendrimer molecules by forming H-bonds with tertiary nitrogens. We show that this specific interaction between H2PO4- and HPO42- ions and generation five PAMAM dendrimers causes a decrease in hydrodynamic size, disturbing the outcome of the size exclusion chromatography analysis. We monitored this interaction by 1H and 31P high resolution NMR, NMR-diffusiometry, pH-potentiometry and infrared spectroscopy. Failing to take into account this effect may lead to incorrect conclusions and misinterpreting interactions of PAMAM dendrimers with drug molecules and subsequently incorrect dosing. The phosphate salts of amino terminated generation five PAMAM dendrimers are stable for years when stored in the dark, even in dilute aqueous solutions, which has important implications for the shelf-life of dendrimer-based drug delivery systems.

Structural characterization of PEGylated polyethylenimine-entrapped gold nanoparticles: an NMR study.

NMR spectroscopy has been proven to be a useful method to characterize the spatial structure of polymer-protected nanoparticles (NPs). In the present study, polyethylenimine (PEI) partially modified with polyethylene glycol (PEG) was used as a template to form gold NPs (Au NPs) via either sodium borohydride reduction or PEI amine-mediated self-reduction of Au salt. The formed two types of PEGylated PEI-entrapped Au NPs (PEI-mPEG-Au NPs) were characterized by UV-vis spectroscopy and transmission electron microscopy, and their internal structures were characterized using NMR techniques. We show that the formed PEI-mPEG-Au NPs display a significant downfield shift in the proton signals of the innermost PEI methylene rather than the outer PEG methylene when compared to that of PEI-mPEG without Au NP entrapment. This result indicates that a strong interaction exists between the Au NPs and the innermost PEI, suggesting that the Au NPs are entrapped within individual PEI-mPEG instead of being stabilized by the surface PEG chains. In addition, the NMR diffusion coefficients of PEI (or PEG) in the PEI-mPEG-Au NPs are much higher than that of PEI-mPEG (without Au NPs), further demonstrating the effective Au NP entrapment. The present study provides a new physical insight into the internal spatial structure of polymer-protected Au NPs disclosed by NMR techniques, which may be used for structural characterization of other NP/polymer nanocomposites.

Simple (17) O NMR method for studying electron self-exchange reaction between UO2 (2+) and U(4+) aqua ions in acidic solution.

(17) O NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of (17) O-enrichment in U(17) OO(2+) ion in the presence of U(4+) ion in aqueous solution. The reactions have been performed at room temperature using I = 5 M ClO4 (-) ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U(4+) and UO2 (2+) aqua ions. The rate equation is given as R = a[H(+) ](-2) + R', where R' is an acid independent parallel path. R' depends on the concentration of the uranium species according to the following empirical rate equation: R' = k1 [UO(2 +) ](1/2) [U(4 +) ](1/2) + k2 [UO(2 +) ](3/2) [U(4 +) ](1/2) . The mechanism of the inverse H(+) concentration-dependent path is interpreted as equilibrium formation of reactive UO2 (+) species from UO2 (2+) and U(4+) aqua ions and its electron exchange with UO2 (2+) . The determined rate constant of this reaction path is in agreement with the rate constant of UO2 (2+) -UO2 (+) , one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO(3+) , which loses enrichment mainly by electron exchange with UO2 (2+) ions. One can also conclude that (17) O NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes. Copyright © 2015 John Wiley & Sons, Ltd.

[Tl(III)(dota)](-): An Extraordinarily Robust Macrocyclic Complex.

The X-ray structure of {C(NH2)3}[Tl(dota)]·H2O shows that the Tl(3+) ion is deeply buried in the macrocyclic cavity of the dota(4-) ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) with average Tl-N and Tl-O distances of 2.464 and 2.365 Å, respectively. The metal ion is directly coordinated to the eight donor atoms of the ligand, which results in a twisted square antiprismatic (TSAP') coordination around Tl(3+). A multinuclear (1)H, (13)C, and (205)Tl NMR study combined with DFT calculations confirmed the TSAP' structure of the complex in aqueous solution, which exists as the Λ(λλλλ)/Δ(δδδδ) enantiomeric pair. (205)Tl NMR spectroscopy allowed the protonation constant associated with the protonation of the complex according to [Tl(dota)](-) + H(+) ⇆ [Tl(Hdota)] to be determined, which turned out to be pK(H)Tl(dota) = 1.4 ± 0.1. [Tl(dota)](-) does not react with Br(-), even when using an excess of the anion, but it forms a weak mixed complex with cyanide, [Tl(dota)](-) + CN(-) ⇆ [Tl(dota)(CN)](2-), with an equilibrium constant of Kmix = 6.0 ± 0.8. The dissociation of the [Tl(dota)](-) complex was determined by UV-vis spectrophotometry under acidic conditions using a large excess of Br(-), and it was found to follow proton-assisted kinetics and to take place very slowly (∼10 days), even in 1 M HClO4, with the estimated half-life of the process being in the 10(9) h range at neutral pH. The solution dynamics of [Tl(dota)](-) were investigated using (13)C NMR spectroscopy and DFT calculations. The (13)C NMR spectra recorded at low temperature (272 K) point to C4 symmetry of the complex in solution, which averages to C4v as the temperature increases. This dynamic behavior was attributed to the Λ(λλλλ) ↔ Δ(δδδδ) enantiomerization process, which involves both the inversion of the macrocyclic unit and the rotation of the pendant arms. According to our calculations, the arm-rotation process limits the Λ(λλλλ) ↔ Δ(δδδδ) interconversion.

Intelligent design of iron-doped LDH nanosheets for cooperative chemo-chemodynamic therapy of tumors.

Chemodynamic therapy (CDT) has received increasing attention due to its unique tumor microenvironment (TME) responsiveness and minimal adverse side effects, but the therapeutic effect of CDT alone is always limited due to the low Fenton or Fenton-like reaction efficiency at tumor sites. Herein, Fe-doped layered double hydroxide (LDH) nanosheets were synthesized to load the anticancer drug epigallocatechin-3-O-gallate (EGCG) and then conjugated with boronic acid-modified hyaluronic acid for targeted and cooperative chemo-chemodynamic therapy of tumors. The formed LDH-EGCG-HA nanoplatforms could specifically target tumor cells overexpressing CD44 receptors, quickly release iron ions and EGCG in the TME, and efficiently generate toxic hydroxyl radicals with the acceleration of Fe3+/Fe2+ cycling in the Fenton reaction by EGCG. The cooperative cancer cell inhibition effect through chemotherapy and chemodynamic therapy was achieved by the significant upregulation of caspase-3 and p53 expression to induce cell apoptosis, and the deactivation of xCT and GPX-4 to inhibit GSH synthesis and reduce lipid peroxides for reinforced ferroptosis. In vivo experiments further verified that the intelligently designed LDH-EGCG-HA nanoplatforms had a superior biocompatibility with normal organs with an excellent inhibition efficacy towards tumors overexpressing CD44 receptors by targeted chemo-chemodynamic therapy.

An NMR and DFT investigation on the conformational properties of lanthanide(III) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate analogues containing methylenephosphonate pendant arms.

The conformational properties of lanthanide(III) complexes with the mono- and biphosphonate analogues of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) are investigated by means of density functional theory (DFT) calculations and NMR spectroscopy. Geometry optimizations performed at the B3LYP/6-31G(d) level and using a 46 + 4f(n) effective core potential for lanthanides provide two energy minima corresponding to the square-antiprismatic (SAP) and twisted square-antiprismatic (TSAP) geometries. Our calculations give relative free energies between the SAP and TSAP isomers in fairly good agreement with the experimental values. The SAP isomer presents the highest binding energy of the ligand to the metal ion, which further increases with respect to that of the TSAP isomer across the lanthanide series as the charge density of the metal ion increases. The stabilization of the TSAP isomer upon substitution of the acetate arms of DOTA by methylenephosphonate ones is attributed to the higher steric demand of the phosphonate groups and the higher strain of the ligand in the SAP isomer. A (1)H NMR band-shape analysis performed on the [Ln(DO2A2P)](3-) (Ln = La and Lu) complexes provided the activation parameters for enantiomerization of the TSAP form of the complexes. The TSAP isomerization process was also investigated by using DFT calculations on the [Lu(DOTA)](-) and [Ln(DO2A2P)](3-) (Ln = La and Lu) systems. Our results confirm that enantiomerization requires both rotation of the pendant arms and inversion of the four five-membered chelate rings formed upon coordination of the macrocyclic unit. According to our calculations, the arm rotation pathway in [Lu(DOTA)](-) is a one-step process involving the simultaneous rotation of the four acetate arms, while in the DO2A2P analogue, the arm-rotation process is a multistep path involving the stepwise rotation of each of the four pendant arms. The calculated activation free energies are in reasonably good agreement with the experimental data. A comparison of the experimental (13)C NMR shifts of [Ln(DO2A2P)](3-) (Ln = La and Lu) complexes and those calculated by using the GIAO method confirms that the major isomer observed in solution for these complexes corresponds to the TSAP isomer.

Gelatin content governs hydration induced structural changes in silica-gelatin hybrid aerogels - Implications in drug delivery.

Silica-gelatin hybrid aerogels of varying gelatin content (from 4 wt.% to 24 wt.%) can be conveniently impregnated with hydrophobic active agents (e.g. ibuprofen, ketoprofen) in supercritical CO2 and used as drug delivery systems. Contrast variation neutron scattering (SANS) experiments show the molecular level hybridization of the silica and the gelatin components of the aerogel carriers. The active agents are amorphous, and homogeneously dispersed in these porous, hybrid matrices. Importantly, both fast and retarded drug release can be achieved with silica-gelatin hybrid aerogels, and the kinetics of drug release is governed by the gelatin content of the carrier. In this paper, for the first time, a molecular level explanation is given for the strong correlation between the composition and the functionality of a family of aerogel based drug delivery systems. Characterization of the wet aerogels by SANS and by NMR diffusiometry, cryoporometry and relaxometry revealed that the different hydration mechanisms of the aerogels are responsible for the broad spectrum of release kinetics. Low-gelatin (4-11 wt.%) aerogels retain their open-porous structure in water, thus rapid matrix erosion dictates fast drug release from these carriers. In contrast to this, wet aerogels of high gelatin content (18-24 wt.%) show well pronounced hydrogel-like characteristics, and a wide gradual transition zone forms in the solid-liquid interface. The extensive swelling of the high-gelatin hybrid backbone results in the collapse of the open porous structure, that limits mass transport towards the release medium, resulting in slower, diffusion controlled drug release. STATEMENT OF SIGNIFICANCE: Developing new drug delivery systems is a key aspect of pharmaceutical research. Supercritically dried mesoporous aerogels are ideal carriers for small molecular weight drugs due to their open porous structures and large specific surface areas. Hybrid silica-gelatin aerogels can display both fast and retarded drug release properties based on the gelatin contents of their backbones. The structural characterization of the aerogels by SANS and by NMR diffusiometry, cryoporometry and relaxometry revealed that the different hydration mechanisms of the hybrid backbones are responsible for the broad spectrum of release kinetics. The molecular level understanding of the functionality of these hybrid inorganic-biopolymer drug delivery systems facilitates the realization of quality-by-design in this research field.

Design of dual drug-loaded dendrimer/carbon dot nanohybrids for fluorescence imaging and enhanced chemotherapy of cancer cells.

Design of powerful nanosystems to overcome multidrug resistance (MDR) for effective chemotherapy of cancer currently remains a great challenge. Herein, we report the development of a poly(amidoamine) (PAMAM) dendrimer/carbon dot nanohybrid for dual drug loading to overcome MDR and simultaneously monitor cancer cells via fluorescence imaging. First, blue-emitting carbon dots (CDs) were synthesized using sodium citrate as a carbon source via the hydrothermal method and used as a carrier to load the anticancer drug doxorubicin (DOX) through non-covalent interactions, thus forming CDs/DOX complexes. In parallel, PAMAM dendrimers of generation 5 (G5) were covalently modified by the targeting ligand cyclic arginine-glycine-aspartic (RGD) peptide and the drug efflux inhibitor d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS). Then, through electrostatic interaction, functional dendrimers (G5-RGD-TPGS) were complexed with CDs/DOX complexes to form a dual drug-loaded nanohybrid system. The dual drug-loaded dendrimer/CD nanohybrids were well characterized. We showed that the nanohybrids possessed good colloidal stability and enabled significant inhibition of cancer cells due to the presence of TPGS, which can inhibit P-glycoprotein (P-gp) by decreasing ATP levels and increasing ROS levels; simultaneously, fluorescence imaging of cancer cells could be achieved in vitro due to the luminescence of CDs. In addition, the attached RGD ligands rendered the nanohybrid with targeting specificity to cancer cells expressing αvß3 integrin receptors. The developed dual drug-loaded dendrimer/CD nanohybrid may be used as a promising theranostic platform to overcome MDR for enhanced chemotherapy as well as for fluorescence imaging of cancer cells.

99mTc-Labeled RGD-Polyethylenimine Conjugates with Entrapped Gold Nanoparticles in the Cavities for Dual-Mode SPECT/CT Imaging of Hepatic Carcinoma.

We report the construction and characterization of 99mTc-labeled arginine-glycine-aspartic acid (RGD)-polyethylenimine (PEI) conjugates with entrapped gold nanoparticles in the cavities (RGD-99mTc-Au PENPs) for dual-mode single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging of an orthotopic hepatic carcinoma model. In this study, PEI was successively decorated with diethylenetriaminepentaacetic acid, poly(ethylene glycol) (PEG), and PEGylated RGD segments, and was utilized as an effective nanoplatform to entrap Au NPs and to be labeled with 99mTc. We showed that the designed RGD-99mTc-Au PENPs displayed desirable colloidal stability and radiostability, and cytocompatibility in the investigated concentration range, and could be specifically uptaken by αvß3 integrin-overexpressing liver cancer cells in vitro. In vivo CT and SPECT imaging results indicated that the particles were able to be accumulated within an orthotopic hepatic carcinoma and displayed both CT and SPECT contrast enhancement in the tumor tissue. With the proven biocompatibility in vivo via histological examinations, the designed RGD-99mTc-Au PENPs may be potentially employed as an effective nanoprobe for a highly efficient dual-mode SPECT/CT imaging of various αvß3 integrin-overexpressing tumors.

Mechanism of drug release from silica-gelatin aerogel-Relationship between matrix structure and release kinetics.

Specific features of a silica-gelatin aerogel (3 wt.% gelatin content) in relation to drug delivery has been studied. It was confirmed that the release of both ibuprofen (IBU) and ketoprofen (KET) is about tenfold faster from loaded silica-gelatin aerogel than from pure silica aerogel, although the two matrices are structurally very similar. The main goal of the study was to understand the mechanistic background of the striking difference between the delivery properties of these closely related porous materials. Hydrated and dispersed silica-gelatin aerogel has been characterized by NMR cryoporometry, diffusiometry and relaxometry. The pore structure of the silica aerogel remains intact when it disintegrates in water. In contrast, dispersed silica-gelatin aerogel develops a strong hydration sphere, which reshapes the pore walls and deforms the pore structure. The drug release kinetics was studied on a few minutes time scale with 1s time resolution. Simultaneous evaluation of all relevant kinetic and structural information confirmed that strong hydration of the silica-gelatin skeleton facilitates the rapid desorption and dissolution of the drugs from the loaded aerogel. Such a driving force is not operative in pure silica aerogels.

Slow water diffusion in micellar solutions.

Slowly diffusing water molecules were found by quasi-elastic neutron scattering (QENS) in a sodium dodecyl sulfate (SDS) micellar solution, and both their diffusion coefficient (4.33 x 10(-6) cm2 x s(-1)) and mole fraction (0.057) were determined. After successfully checking the mean slowing down of solvent molecules by the gradient compensated stimulated spin-echo (GCSTE) pulse sequence NMR method, a similar effect was observed with this technique in the solvent phase of dodecyl trimethylammonium bromide (DTAB) and differing chain length (X = 12, 20, 30, and 40) ethoxylated nonyl phenol (9NX) micellar systems. Following the literature, the experimental results are qualitatively explained by assuming that, apart from ionic hydration, H-bonds may form between the solvent molecules and the O or N atoms present in the hydrophilic (head)groups of the micelle-forming monomers.

NMR characterization of PAMAM_G5.NH2 entrapped atomic and molecular assemblies.

High resolution NMR spectroscopy, NMR diffusiometry, and NMR cryoporometry have been used to investigate aqueous solution (D2O) of PAMAM_G5.NH2-(Au)(25-100) and PAMAM_G5.NH2-(H2O)1000-(H2O)4000 systems. In the case of dendrimer entrapped gold nanoparticles, the detailed analysis of high resolution NMR spectra has shown that no precursor complex formation happens under the circumstances applied for reduction. Further PGSE results verify that gold nanoparticles of 1.9-2.6 nm size are entrapped in the outermost part of the dendrimers and probably more than one dendrimer molecule takes part in the stabilization process. This system looks like a transition state between dendrimer encapsulated nanoparticles (DENs) and dendrimer stabilized nanoparticles (DSNs), and we deal with it in details for what this means. NMR cryoporometry experiments were performed to detect the encapsulation of water molecules. The results show that, in the swelling PAMAM_G5.NH2 dendrimers, by adding water step by step, there are specific cavities for water with diameters of 3.6 and 5.2 nm. These cavities have a penetrable wall for water molecules and probably exist very close to the terminal groups. The permeability of the cavities is increasing with the increase of the water content. In dilute solution, the formation of nanoparticles is determined by the ratio of the rate of nucleation and aggregation and the latter is affected by the PAMAM_G5.NH2.

RGD peptide-modified multifunctional dendrimer platform for drug encapsulation and targeted inhibition of cancer cells.

Development of multifunctional nanoscale drug-delivery systems for targeted cancer therapy still remains a great challenge. Here, we report the synthesis of cyclic arginine-glycine-aspartic acid (RGD) peptide-conjugated generation 5 (G5) poly(amidoamine) dendrimers for anticancer drug encapsulation and targeted therapy of cancer cells overexpressing αvß3 integrins. In this study, amine-terminated G5 dendrimers were used as a platform to be sequentially modified with fluorescein isothiocyanate (FI) via a thiourea linkage and RGD peptide via a polyethylene glycol (PEG) spacer, followed by acetylation of the remaining dendrimer terminal amines. The developed multifunctional dendrimer platform (G5.NHAc-FI-PEG-RGD) was then used to encapsulate an anticancer drug doxorubicin (DOX). We show that approximately six DOX molecules are able to be encapsulated within each dendrimer platform. The formed complexes are water-soluble, stable, and able to release DOX in a sustained manner. One- and two-dimensional NMR techniques were applied to investigate the interaction between dendrimers and DOX, and the impact of the environmental pH on the release rate of DOX from the dendrimer/DOX complexes was also explored. Furthermore, cell biological studies demonstrate that the encapsulation of DOX within the G5.NHAc-FI-PEG-RGD dendrimers does not compromise the anticancer activity of DOX and that the therapeutic efficacy of the dendrimer/DOX complexes is solely related to the encapsulated DOX drug. Importantly, thanks to the role played by RGD-mediated targeting, the developed dendrimer/drug complexes are able to specifically target αvß3 integrin-overexpressing cancer cells and display specific therapeutic efficacy to the target cells. The developed RGD peptide-targeted multifunctional dendrimers may thus be used as a versatile platform for targeted therapy of different types of αvß3 integrin-overexpressing cancer cells.