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We have synthesized a new macromolecular architecture, (PAMAM)-CD8, which consists of eight β-cyclodextrin units (β-CD) attached to a generation 1 poly(amidoamine) (PAMAM) dendrimer through a disulfide bond, which can be cleaved under reducing conditions. This system shows a pronounced hosting capability towards GdIII chelates functionalized with hydrophobic groups, thus leading to well-defined supramolecular adducts. 1H NMR relaxometric investigations were carried out to follow the formation of adducts with three GdIII chelates based on the ligand architectures of 6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid (AAZTA) or 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) suitably functionalized with benzyl or adamantyl (Ad) pendant groups. In particular, the ditopic complex composed of two AAZTA chelating units connected to a central aromatic ring that bears an adamantyl group showed a strong affinity (ca. 106 M−1) for the CD units of the dendrimer, which is two orders of magnitude higher than toward human serum albumin (HSA). Remarkable relaxivity enhancements (i.e., up to 71 % at 1 T and 25 °C) were observed upon the formation of the macromolecular host-guest adducts due to a decrease in the molecular tumbling rate and fast water-exchange. Reduction experiments and competition studies between the paramagnetic dendrimer and HSA were carried out by relaxometric techniques. The results show that the metal complexes are not displaced by the protein, thus suggesting that this novel macromolecular probe is potentially suitable for applications in vivo. [ABSTRACT FROM AUTHOR]

N-Substituted aminoethyl groups were attached to 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) with the aim to design pH-responsive LnIII complexes based on the pH-dependent on/off ligation of the amine nitrogen to the metal ion. The following ligands were synthesized: AE- DO3A (aminoethyl-DO3A), MAE- DO3A ( N-methylaminoethyl-DO3A), DMAE- DO3A ( N, N-dimethylaminoethyl-DO3A) and MEM- AE- DO3A ( N-methoxyethyl- N-methylaminoethyl-DO3A). The physicochemical properties of the LnIII complexes were investigated for the evaluation of their potential applicability as magnetic resonance imaging (MRI) contrast agents. In particular, a 1H and 17O NMR relaxometric study was carried out for these GdIII complexes at two different pH values: at basic pH (pendant amino group coordinated to the metal centre) and at acidic pH (protonated amine, not interacting with the metal ion). EuIII complexes allow one to estimate the number of inner-sphere water molecules through luminescence lifetime measurements and obtain some structural information through variable-temperature (VT) high-resolution 1H NMR studies. Equilibria between differently hydrated species were found for most of the complexes at both acidic and basic pH. The thermodynamic stability of CaII, ZnII, CuII and LnIII complexes and kinetics of formation and dissociation reactions of LnIII complexes of AE- DO3A and DMAE- DO3A were investigated showing stabilities comparable to currently approved GdIII-based CAs. In detail, higher total basicity (Σlog KiH) and higher stability constants of LnIII complexes were found for AE- DO3A with respect to DMAE- DO3A (i.e., log KGd- AE-DO3A=22.40 and log KGd- DMAE-DO3A=20.56). The transmetallation reactions of GdIII complexes are very slow (Gd- AE- DO3A: t1/2=2.7×104 h; Gd- DMAE- DO3A: 1.1×105 h at pH 7.4 and 298 K) and occur through proton-assisted dissociation. [ABSTRACT FROM AUTHOR]

The optimization of the physico-chemical properties of both GdIII chelates and nanocarriers is of great importance for the development of effective nanosystems for magnetic resonance imaging (MRI) applications. With this aim, macrocyclic GdIII chelates were selectively attached to the pendant amino groups exposed to the external surface of spheroidal mesoporous silica nanoparticles (MSNs). This was achieved by treating the metal complexes with MSNs that contained the templating surfactant molecules confined within the silica channels (hexadecyltrimethylammonium (CTA)/MSN), followed by extraction of the surfactant. The nanoparticles showed greatly improved 1H relaxometric efficiency relative to corresponding systems that also feature GdIII chelates conjugated inside the pores. A further significant relaxivity enhancement was observed after chemical transformation of the free amino groups into amides. The ionic relaxivity of the final nanoparticles ( r1p=79.1 m M−1 s−1; 0.5 T, 310 K) is one of the highest reported so far. [ABSTRACT FROM AUTHOR]

A complete potentiometric and NMR relaxometric solution study on the heptadentate 2,2',2?,2'?-[(6-piperidinyl-1,3,5-triazine-2,4-diyl)dihydrazin-2-yl-1-ylidene]tetraacetic acid (PTDITA) ligand has been carried out. This ligand is based on the 1,3,5-triazine ring with two hydrazine-N,N-diacetate groups in positions 2 and 4 and a piperidine moiety in position 6. The introduction of the triazine ring into the ligand backbone is expected to modify its flexibility and then to affect the stability of the corresponding complexes with transition-metal and lanthanide ions. Thermodynamic stabilities have been determined by pH potentiometry, UV spectrophotometry, and 1H NMR spectroscopy for formation of the complexes with Mg2+, Ca2+, Cu2+, Zn2+, La3+, Gd3+, and Lu3+ ions. PTDITA shows a good binding affinity for Gd3+ (logK = 18.49, pGd = 18.6) and an optimal selectivity for Gd3+ over the endogenous Ca2+, Zn2+, and Cu2+ (Ksel = 6.78 × 107), which is 3 orders of magnitude higher that that reported for Gd(DTPA) (Ksel = 2.85 × 104). This is mainly due to the lower stability of the CuII- and ZnII(PTDITA) complexes compared to the corresponding DTPA complexes, which suggests an important role of the triazine ring on the selectivity for the Gd3+ ion. The relaxometric properties of Gd(PTDITA) have been investigated in aqueous solution by measuring the 1H relaxivity as a function of the pH, temperature, and magnetic field strength (nuclear magnetic relaxation dispersion profile). Variable-temperature 17O NMR data have provided direct information on the kinetic parameters for exchange of the coordinated water molecules. A simultaneous fit of the data suggests that the high relaxivity value (r1 = 10.2 mM-1 s-1) is a result of the presence of two inner-sphere water molecules along with the occurrence of relatively slow rotation and electronic relaxation. The water residence lifetime, 298τM = 299 ns, is quite comparable to that of clinically approved magnetic resonance imaging contrast agents. The displacement of the inner-sphere water molecules by bidentate endogeneous anions (citrate, phosphate, and carbonate) has also been evaluated by 1H relaxometry. In general, the binding interaction is markedly weak, and only in the case of citrate, a ca. 35% decrease in relaxivity was observed in the presence of 60 equiv of the anion. Phosphate and carbonate also interact with the paramagnetic ion, likely as monodentate ligands, but formation of the ternary complex is accompanied by a modest increase of r1 due to the contribution of second-sphere water molecules. [ABSTRACT FROM AUTHOR]

In this work, we designed, developed, characterized, and investigated a new chelator and its bifunctional derivative for 89Zr labeling and PET-imaging. In a preliminary study, we synthesized two hexadentate chelators named AAZTHAS and AAZTHAG, based on the seven-membered heterocycle AMPED (6-amino-6-methylperhydro-1,4-diazepine) with the aim to increase the rigidity of the 89Zr complex by using N-methyl-N-(hydroxy)succinamide or N-methyl-N-(hydroxy)glutaramide pendant arms attached to the cyclic structure. N-methylhydroxamate groups are the donor groups chosen to efficiently coordinate 89Zr. After in vitro stability tests, we selected the chelator with longer arms, AAZTHAG, as the best complexing agent for 89Zr presenting a stability of 86.4 ± 5.5% in human serum (HS) for at least 72 h. Small animal PET/CT static scans acquired at different time points (up to 24 h) and ex vivo organ distribution studies were then carried out in healthy nude mice (n = 3) to investigate the stability and biodistribution in vivo of this new 89Zr-based complex. High stability in vivo, with low accumulation of free 89Zr in bones and kidneys, was measured. Furthermore, an activated ester functionalized version of AAZTHAG was synthesized to allow the conjugation with biomolecules such as antibodies. The bifunctional chelator was then conjugated to the human anti-HER2 monoclonal antibody Trastuzumab (Tz) as a proof of principle test of conjugation to biologically active molecules. The final 89Zr labeled compound was characterized via radio-HPLC and SDS-PAGE followed by autoradiography, and its stability in different solutions was assessed for at least 4 days. [ABSTRACT FROM AUTHOR]

It is known that phenylboronic acid (PBA) can target tumor tissues by binding to sialic acid, a substrate overexpressed by cancer cells. This capability has previously been explored in the design of targeting diagnostic probes such as Gd- and 68Ga-DOTA-EN-PBA, two contrast agents for magnetic resonance imaging (MRI) and positron emission tomography (PET), respectively, whose potential has already been demonstrated through in vivo experiments. In addition to its high resolution, the intrinsic low sensitivity of MRI stimulates the search for more effective contrast agents, which, in the case of small-molecular probes, basically narrows down to either increased tumbling time of the entire molecule or elevated local concentration of the paramagnetic ions, both strategies resulting in enhanced relaxivity, and consequently, a higher MRI contrast. The latter strategy can be achieved by the design of multimeric GdIII complexes. Based on the monomeric PBA-containing probes described recently, herein, we report the synthesis and characterization of the dimeric analogues (GdIII-DOTA-EN)2-PBA and (GdIII-DOTA-EN)2F2PBA. The presence of two Gd ions in one molecule clearly contributes to the improved biological performance, as demonstrated by the relaxometric study and cell-binding investigations. [ABSTRACT FROM AUTHOR]

Increasing the length of the carboxyamide arm of a GdDOTA monoamide (DOTA = 1,4,7,10-tetraaza-1,4,7,10-tetrakis(carboxymethyl)cyclododecane) complex from acetic to propionic accelerates the water exchange rate (kex) by nearly two orders of magnitude; the 1H relaxivity of the corresponding macromolecular derivatives may then be remarkably enhanced in MRI-based molecular imaging applications, as exemplified in the case of micellar systems. [ABSTRACT FROM AUTHOR]

Evaluates the crystal structure of zinc-lithium complex of bisaminoethyl triazacyclononane acetate. Hydrogen bond; Diffraction quality colorless crystals of the compound; Atom numbering scheme; Selected geometric parameters.

In the last three decades, high-relaxivity Magnetic Resonance Imaging (MRI) contrast agents (CAs) have been intensively sought, aiming at a reduction in the clinically injected dose while maintaining the safety of the CA and obtaining the same pathological information. Thus, four new Gd(III) complexes based on modified 10-(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (HP-DO3A) macrocyclic structure were designed and synthesized by introducing further polar and protic functional groups (amides, phosphonates, and diols) adjacent to the metal-coordinated hydroxyl group. A detailed 1H NMR relaxometric analysis allowed us to investigate the effect of these functional groups on the relaxivity, which showed a 20–60% increase (at 0.5 T, 298 K, and pH 7.4) with respect to that of clinically approved CAs. The contribution of the water molecules H-bonded to these peripheral functional groups on the relaxivity was evaluated in terms of the second sphere effect or prototropic exchange of labile protons. [ABSTRACT FROM AUTHOR]

In this paper, we describe the synthesis and gas adsorption properties of a porous carbonaceous material, obtained from commercial expanded polystyrene. The first step consists of the Friedel-Craft reaction of the dissolved polystyrene chains with a bridging agent to form a highly-crosslinked polymer, with permanent porosity of 0.7 cm3/g; then, this polymer is treated with potassium hydroxide at a high temperature to produce a carbon material with a porous volume larger than 1.4 cm3/g and a distribution of ultramicro-, micro-, and mesopores. After characterization of the porous carbon and determination of the bulk density, the methane uptake was measured using a volumetric apparatus to pressures up to 30 bar. The equilibrium adsorption isotherm obtained is among the highest ever reported for this kind of material. The interest of this product lies both in its excellent performance and in the virtually costless starting material. [ABSTRACT FROM AUTHOR]

The preparation of porous carbons by post-synthesis treatment of hypercrosslinked polymers is described, with a careful physico-chemical characterization, to obtain new materials for gas storage and separation. Different procedures, based on chemical and thermal activations, are considered; they include thermal treatment at 380 °C, and chemical activation with KOH followed by thermal treatment at 750 or 800 °C; the resulting materials are carefully characterized in their structural and textural properties. The thermal treatment at temperature below decomposition (380 °C) maintains the polymer structure, removing the side-products of the polymerization entrapped in the pores and improving the textural properties. On the other hand, the carbonization leads to a different material, enhancing both surface area and total pore volume—the textural properties of the final porous carbons are affected by the activation procedure and by the starting polymer. Different chemical activation methods and temperatures lead to different carbons with BET surface area ranging between 2318 and 2975 m2/g and pore volume up to 1.30 cc/g. The wise choice of the carbonization treatment allows the final textural properties to be finely tuned by increasing either the narrow pore fraction or the micro- and mesoporous volume. High pressure gas adsorption measurements of methane, hydrogen, and carbon dioxide of the most promising material are investigated, and the storage capacity for methane is measured and discussed. [ABSTRACT FROM AUTHOR]

Three different 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide (DOTAM) derivatives bearing as amide N-substituents phenyl, p-methoxyphenyl and p-ethylbenzoate groups were synthesized and the 1H and 17O NMR relaxometric behaviour of the Gd(III)-chelates and chemical exchange saturation transfer (CEST) effect of the Eu(III) complexes were evaluated. The electronic properties of the substituents were shown to strongly influence the coordinated water exchange rate (kex), resulting in five times faster kex for the electron donating phenylmethoxy group compared to the electron withdrawing ethylbenzoate group. [ABSTRACT FROM AUTHOR]

Kinetic inertness of Mn(II)‐based MRI contrast agents can be improved by increasing the rigidity of the polydentate ligand that tightly coordinate the metal ion. Taking inspiration from the remarkable increase in kinetic inertness of [Mn(CDTA)]2− compared to [Mn(EDTA)]2− due to the cyclohexyl backbone rigidity, we devised that bicyclic ligands would further improve the kinetic inertness of the Mn(II) complexes. The length of the alkyl bridge on the cyclohexane ring was varied from methylene (BCH‐DTA), ethylene (BCO‐DTA) to propylene (BCN‐DTA) to evaluate the influence of the different trans‐diaminotetraacetate ligands on relaxometric, thermodynamic and kinetic properties of the Mn(II) complexes. 1H and 17O NMR relaxometric studies showed a slight increase in relaxivity and a faster water exchange rate in these Mn(II)‐complexes with respect to [Mn(CDTA)]2−. Solution studies revealed that the conditional stability (pMn) and dissociation half‐life (t1/2) at pH 7.4 follow the order [Mn(BCH‐DTA)]2−<[Mn(BCO‐DTA)]2−<[Mn(BCN‐DTA)]2− highlighting the effect of the bridge length on the overall stability of the Mn(II) complexes. Remarkably, [Mn(BCN‐DTA)]2− shows an improved pMn value and a 7‐times higher kinetic inertness than [Mn(CDTA)]2−. NMR studies on the Zn(II) analogues confirm the rigidity of the bicyclic complexes with an isomerization process at >313 K for the smaller bridged complex [Zn(BCH‐DTA)]2−. [ABSTRACT FROM AUTHOR]

The article presents a study that examines the use of DOTA-like GdIII chelates in the high relaxivity enhancement of micelles and liposomes. It states that four complexes were synthesized and alkylated through alkyl bromide. It mentions that amphiphilic complexes such as GdDOTAGAC12 and GdDOTA(GAC12)2 were yielded. It reveals that the GdDOTA derivative enables to incorporate micelles into liposomes which reflects unprecedented relaxivity enhancement.

Al(III) complexes have been recently investigated for their potential use in imaging with positron emission tomography (PET) by formation of ternary complexes with the radioisotope fluorine-18 (18F). Although the derivatives of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) are the most applied chelators for [Al18F]2+ labelling and (pre)clinical PET imaging, non-macrocyclic, semi-rigid pentadentate chelators having two N- and three O-donor atoms such as RESCA1 and AMPDA-HB have been proposed with the aim to allow room temperature labelling of temperature-sensitive biomolecules. The paucity of stability data on Al(III) complexes used for PET imaging instigated a complete thermodynamic and kinetic solution study on Al(III) complexes with aminomethylpiperidine (AMP) derivatives AMPTA and AMPDA-HB and the comparison with a RESCA1-like chelator CD3A-Bn (trans-1,2-diaminocyclohexane-N-benzyl-N,N′,N′-triacetic acid). The stability constant of [Al(AMPDA-HB)] is about four orders of magnitude higher than that of [Al(AMPTA)] and [Al(CD3A-Bn)], highlighting the greater affinity of phenolates with respect to acetate O-donors. On the other hand, the kinetic inertness of the complexes, determined by following the Cu2+-mediated transmetallation reactions in the 7.5–10.5 pH range, resulted in a spontaneous and hydroxide-assisted dissociation slightly faster for [Al(AMPTA)] than for the other two complexes (t1/2 = 4.5 h for [Al(AMPTA)], 12.4 h for [Al(AMPDA-HB)], and 24.1 h for [Al(CD3A-Bn)] at pH 7.4 and 25 °C). Finally, the [AlF]2+ ternary complexes were prepared and their stability in reconstituted human serum was determined by 19F NMR experiments. [ABSTRACT FROM AUTHOR]

The introduction of a phenolate pendant arm in place of an acetate on AAZTA‐ and DATA‐like ligands resulted in hepta‐ and hexadentate chelators able to form Ga(III) complexes with thermodynamic stability and kinetic inertness higher than that of other Ga(III) complexes based on the parent 6‐amino‐6‐methylperhydro‐1,4‐diazepine scaffold. In particular, the heptadentate AAZ3A‐endoHB with a phenolate arm on an endocyclic N‐atom shows a logKGaL of 27.35 and a remarkable resistance to hydroxide coordination up to basic pH (pH>9). This behaviour allows to also improve the kinetic inertness of the complex showing a dissociation half‐life (t1/2) at pH 7.4 of 76 h. Although also the hexadentate AAZ2A‐exoHB chelator forms a stable (logKGaL=24.69) and inert (t1/2=33 h at pH 7.4) Ga(III) complex, the 68Ga labelling showed a better radiochemical yield with AAZ3A‐endoHB, especially at room temperature. Thus, a bifunctional chelator of AAZ3A‐endoHB was synthesized bearing an isothiocyanate group that was conjugated to the N‐terminus of a c(RGD) peptide for integrin receptor targeting. Finally, the conjugate was successfully labelled with 68Ga isotope, and the resulting radiotracer tested for its stability in human serum and then in vivo for targeting B16‐F10 tumours with miniPET imaging. [ABSTRACT FROM AUTHOR]

A dimeric GdAAZTA-like complex (AAZTA is 6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) bearing an adamantyl group (Gd L1) able to form strong supramolecular adducts with specific hosts such as β-cyclodextrin (β-CD), poly-β-CD, and human serum albumin (HSA) is reported. The relaxometric properties of Gd L1 were investigated in aqueous solution by measuring the H relaxivity as a function of pH, temperature, and magnetic field strength. The relaxivity of Gd L1 (per Gd atom) at 40 MHz and 298 K is 17.6 mM s, a value that remains almost constant at higher fields owing to the great compactness and rigidity of the bimetallic chelate, resulting in an ideal value for the rotational correlation time for high-field MRI applications (1.5-3.0 T). The noncovalent interaction of Gd L1 with β-CD, poly-β-CD, and HSA and the relaxometric properties of the resulting host-guest adducts were investigated using H relaxometric methods. Relaxivity enhancements of 29 and 108 % were found for Gd L1-β-CD and Gd L1-poly-β-CD, respectively. Binding of Gd L1 to HSA ( K = 1.2 × 10 M) results in a remarkable relaxivity of 41.4 mM s for the bound form (+248 %). The relaxivity is only limited by the local rotation of the complex within the binding site, which decreases on passing from Gd L1-β-CD to Gd L1-HSA. Finally, the applicability of Gd L1 as tumor-targeting agent through passive accumulation of the HSA-bound adduct was evaluated via acquisition of magnetic resonance images at 1 T of B16-tumor-bearing mice. These experiments indicate a considerable signal enhancement (+160 %) in tumor after 60 min from the injection and a very low hepatic accumulation. [ABSTRACT FROM AUTHOR]

Abstract: We developed and examined the applicability of two multimodal paramagnetic contrast agents for the longitudinal in vivo investigations of the brain projections. The classical dextran based neuroanatomical tracer was conjugated with mono- and bimetal Gd3+ complexes and an optical reporter. Relaxometric studies of both tracer molecules were performed in vitro followed by in cellulo MR and microscopy investigations. Finally, tracers were injected into the motor cortex of the rat brain; uptake and transporting properties were compared by MRI. The advantage of the multimodal approach was taken and histological studies were performed on the same animals. The histology results confirm the MRI studies demonstrating that the applied tracers labelled anterogradely the regions known for their connections with the motor cortex of the rat brain. [Copyright &y& Elsevier]

The phenotypic and molecular diversity of tumor-associated vasculature provides a basis for the development of targeted diagnostics and therapeutics. In the present study, we have developed a peptide-based targeting of human tumor endothelial cells (TEC) derived from renal carcinomas. We used a murine model of human tumor angiogenesis, in which TEC injected subcutaneously in severe combined immunodeficiency (SCID) mice organized in vascular structures connected with the mouse circulation, to screen in vivo a phage display library of random peptides. Using this approach, we identified cyclic peptides showing specific binding to TEC and not to normal human endothelial cells or to murine tumor endothelial cells. In particular, the peptide CVGNDNSSC (BB1) bound to TEC in vitro and in vivo. Using BB1 peptide conjugated with the ribosome-inactivating toxin saporin, we targeted TEC in vivo. Injection of BB1-saporin but not saporin alone or control modified BB-1ala saporin induced a selective cell apoptosis and disruption of the TEC vessel network. No increase in cell apoptosis was found in other murine organs. In conclusion, the identification of peptide sequences able to bind selectively human tumor-derived endothelial cells may represent a tool to deliver antiangiogenic or antitumor agents within the neoplastic vessels. [ABSTRACT FROM AUTHOR]