PEG-Citrate dendrimer second generation: is this a good carrier for imaging agents In Vitro and In Vivo?

While cancer is the leading cause of human's deaths worldwide, finding an imaging agent which can detect cancer tumours is needed for cancer diagnosis. In the present study, PEG-citrate dendrimer-G2 was used as a nano-carrier of FITC dye and Iohexol to help passive targeting and uptake of both imaging agents in cancer cells/tumour in vitro and in vivo. Dendrimer was synthesisedand the product characterised using LC-MS, FT-IR, DLS, ELS, AFM, and 1HNMR. After FITC loading into dendrimer, MTT was performed to determine the cytotoxicity of formulation on HEK-293 and MCF-7 cells. In vitro imaging using dendrimer-FITC was done via fluorescent microscope thereafter. Moreover, CT imaging using Iohexol was employed to show the targeting nature and ability of the complex to use as imaging agent in vivo. Data yielded in this study corroborate the notion that the promised dendrimer was synthesised properly and had no toxicity along with FITC on normal cell. Furthermore, CT and fluorescent images showed the targeting nature and imaging ability of Iohexol/FITC loaded dendrimer in vitro and in vivo. Overall, results showed promising characteristics of the novel complexes using dendrimer-G2 both in vitro and in vivo.

Production of 68Ga-citrate Based on a SnO2 Generator for Short-Term Turpentine Oil-Induced Inflammation Imaging in Rats.

INTRODUCTION: Gallium-68 citrate has been successfully applied in the PET imaging of infections and inflammation in some centers; however further evaluation of the tracer in inflammation models is of great importance. METHODS: 68Ga-citrate prepared from [68Ga]GaCl3 (eluted form an SnO2 based 68Ge/68Ga generator) and sodium citrate at optimized conditions followed by quality control tests was injected to normal and turpentine-oil induced rats PET/CT imaging studies up to 290 min. RESULTS: 68Ga-citrate was prepared with acceptable radiochemical purity (>99 ITLC, >99% HPLC), specific activity (28-30 GBq/mM), chemical purity (Sn, Fe <0.3 ppm; Zn<0.2 ppm) in 15 min at 50°C. PET/CT imaging of the tracer demonstrated early detection of inflamed site in animal models in 60-80 min. CONCLUSION: This study demonstrated possible early detection of inflammation foci in vivo using 68Ga-citrate prepared using commercially available 68Ge/68Ga generators for PET imaging.

Chemical Synthesis of Staphyloferrin B Affords Insight into the Molecular Structure, Iron Chelation, and Biological Activity of a Polycarboxylate Siderophore Deployed by the Human Pathogen Staphylococcus aureus.

Staphyloferrin B (SB) is a citrate-based polycarboxylate siderophore produced and utilized by the human pathogen Staphylococcus aureus for acquiring iron when colonizing the vertebrate host. The first chemical synthesis of SB is reported, which enables further molecular and biological characterization and provides access to structural analogues of the siderophore. Under conditions of iron limitation, addition of synthetic SB to bacterial growth medium recovered the growth of the antibiotic resistant community isolate S. aureus USA300 JE2. Two structural analogues of SB, epiSB and SBimide, were also synthesized and employed to investigate how epimerization of the citric acid moiety or imide formation influence its function as a siderophore. Epimerization of the citric acid stereocenter perturbed the iron-binding properties and siderophore function of SB as evidenced by experimental and computational modeling studies. Although epiSB provided growth recovery to S. aureus USA300 JE2 cultured in iron-deficient medium, the effect was attenuated relative to that of SB. Moreover, SB more effectively sequestered the Fe(III) bound to human holo-transferrin, an iron source of S. aureus, than epiSB. SBimide is an imide analogous to the imide forms of other citric acid siderophores that are often observed when these molecules are isolated from natural sources. Here, SBimide is shown to be unstable, converting to native SB at physiological pH. SB is considered to be a virulence factor of S. aureus, a pathogen that poses a particular threat to public health because of the number of drug-resistant strains emerging in hospital and community settings. Iron acquisition by S. aureus is important for its ability to colonize the human host and cause disease, and new chemical insights into the structure and function of SB will inform the search for new therapeutic strategies for combating S. aureus infections.

A modified technique for efficient radiolabeling of 68Ga-citrate from a SnO2-based 68Ge/68Ga generator for better infection imaging.

Our aim was to develop a practical method to prepare 68Ga-citrate using a SnO2-based 68Ge/68Ga generator and evaluate its use in infection imaging. 68Ga-citrate synthesis was performed in a straight forward, quantitative, one-step-aseptic procedure; an amended labeling method was applied using ACD-A buffered citrate as a precursor. Study participants were imaged on a Siemens Biograph 40 PET/CT scanner 60 min post intravenous injection. Our results showed: 90%-95% 68Ga-yield was obtained and subsequently used at 324-527 MBq to perform three to four parallel 68Ga-citrate syntheses. 68Ga-citrate of 96%-99% was yielded after 10 min incubation. The radiochemical purity was >99% with a pH value of 4.0-4.5. All other quality control requirements were met. The 68Ga-citrate stability was >96%. The final product was sterile, pyrogen and solvent-free, with very low 68Ge-levels, with 191±33 MBq in 6.6±2.8 mL. High quality images were obtained at 60 min post injection of 185 MBq of 68Ga-citrate. In conclusion, a fast, direct and cheap method with a quantitative preparation of 68Ga-citrate was described. We reported on the adaptations needed when using a SnO2-based 68Ge/68Ga generator and ACD-A buffered citrate as a precursor. This method allowed for multiple patient productions from one generator elution, with 300 MBq/patient of 68Ga-citrate produced in less than 30 min and excellent labeling reproducibility for routine infection imaging.

Synthesis and biological evaluation of new citrate-based siderophores as potential probes for the mechanism of iron uptake in mycobacteria.

Several iron chelators containing alpha,beta-unsaturated hydroxamic acid motifs appended to a citric acid platform were synthesized. Mycobacterium paratuberculosis was then challenged to grow in the presence of a panel of siderophores (mycobactin J, deferrioxamine B, acinetoferrin, and nannochelin A) and the new synthetic agents. Of the structures tested, those containing the trans 2-octenoyl motif were preferred over those with trans cinnamoyl groups. In addition, derivatives containing longer tether lengths between the iron binding ligands (C5) were more efficacious and led to higher growth index values. Perhaps most remarkable was the finding that at 2.4 microM a trans 2-octenoylated, citrate-containing imide 6 was nearly 5-fold more effective in stimulating growth than the native chelator, mycobactin J. In this regard, new structural elements were identified (e.g., an imide motif or 2-octenoyl side chain), whose presence stimulated mycobacterial growth.

Synthesis, pH-dependent structural characterization, and solution behavior of aqueous aluminum and gallium citrate complexes.

Reactions of Al(III) and Ga(III) with citric acid in aqueous solutions, yielded the complexes (NH(4))(5)[M(C(6)H(4)O(7))(2)].2H(2)O (M(III) = Al (1), Ga (2)) at alkaline pH, and the complexes (Cat)(4)[M(C(6)H(5)O(7))(C(6)H(4)O(7))].nH(2)O (M(III) = Al (3), Ga (4), Cat. = NH(4)(+), n = 3; M(III) = Al (5), Ga (6), Cat. = K(+), n = 4) at acidic pH. All compounds were characterized by spectroscopic (FT-IR, (1)H, (13)C, and (27)Al NMR, (13)C-MAS NMR) and X-ray techniques. Complex 1 crystallizes in space group P1, with a = 9.638(5) A, b = 9.715(5) A, c = 7.237(4) A, alpha = 90.96(1) degrees, beta = 105.72(1) degrees, gamma = 119.74(1) degrees, V = 557.1(3) A(3), and Z = 1. Complex 2 crystallizes in space group P1, with a = 9.659(6) A, b = 9.762(7) A, c = 7.258(5) A, alpha = 90.95(2) degrees, beta = 105.86(2) degrees, gamma = 119.28(1) degrees, V = 564.9(7) A(3), and Z = 1. Complex 3 crystallizes in space group I2/a, with a = 19.347(3) A, b = 9.857(1) A, c = 23.412(4) A, beta = 100.549(5) degrees, V = 4389(1) A(3), and Z = 8. Complex 4 crystallizes in space group I2/a, with a = 19.275(1) A, b = 9.9697(6) A, c = 23.476(1) A, beta = 100.694(2) degrees, V = 4432.8(5) A(3), and Z = 8. Complex 5 crystallizes in space group P1, with a = 7.316(1) A, b = 9.454(2) A, c = 9.569(2) A, alpha = 64.218(4) degrees, beta = 69.872(3) degrees, gamma = 69.985(4) degrees, V = 544.9(2) A(3), and Z = 1. Complex 6 crystallizes in space group P1, with a = 7.3242(2) A, b = 9.4363(5) A, c = 9.6435(5) A, alpha = 63.751(2) degrees, beta = 70.091(2) degrees, gamma = 69.941(2) degrees, V = 547.22(4) A(3), and Z = 1. The crystal structures of 1-6 reveal mononuclear octahedral complexes of Al(III) (or Ga(III)) bound to two citrates. Solution NMR, on both 4- and 5- species, reveals rapid intramolecular exchange of the bound and unbound terminal carboxylates. Upon dissolution in water, the complexes, through a complicated reaction cascade, transform to oligonuclear 1:1 species that, in agreement with previous studies, represent the thermodynamically stable state in solution. The data provide, for the first time, structural details of low MW, mononuclear complexes of Al(III) (or Ga(III)) with citrate that are dictated, among other factors, by pH. The properties of 1-6 may provide clues relevant to their biological association with humans.