Al(OH)(3) facilitated synthesis of water-soluble, magnetic, radiolabelled and fluorescent hydroxyapatite nanoparticles

Magnetic and fluorescent hydroxyapatite nanoparticles were synthesised using Al(OH)3-stabilised MnFe2O4 or Fe3O4 nanoparticles as precursors. They were readily and efficiently radiolabelled with 18F. Bisphosphonate polyethylene glycol polymers were utilised to endow the nanoparticles with excellent colloidal stability in water and to incorporate cyclam for high affinity labelling with 64Cu

Re-assessing gallium-67 as a therapeutic radionuclide

INTRODUCTION: Despite its desirable half-life and low energy Auger electrons that travel further than for other radionuclides, (67)Ga has been neglected as a therapeutic radionuclide. Here, (67)Ga is compared with Auger electron emitter (111)In as a potential therapeutic radionuclide. METHODS: Plasmid pBR322 studies allowed direct comparison between (67)Ga and (111)In (1 MBq) in causing DNA damage, including the effect of chelators (EDTA and DTPA) and the effects of a free radical scavenger (DMSO). The cytotoxicity of internalized (by means of delivery in the form of oxine complexes) and non-internalized (67)Ga and (111)In was measured in DU145 prostate cancer cells after a one-hour incubation using cell viability (trypan blue) and clonogenic studies. MDA-MB-231 and HCC1954 cells were also used. RESULTS: Plasmid DNA damage was caused by (67)Ga and was comparable to that caused by (111)In; it was reduced in the presence of EDTA, DTPA and DMSO. The A(50) values (internalized activity of oxine complexes per cell required to kill 50% of cells) as determined by trypan blue staining was 1.0 Bq/cell for both (67)Ga and (111)In; the A(50) values determined by clonogenic assay were 0.7 Bq/cell and 0.3 Bq/cell for (111)In and (67)Ga respectively. At the concentrations required to achieve these uptake levels, non-internalized (67)Ga and (111)In caused no cellular toxicity. Qualitatively similar results were found for MDA-MB-231 and HCC1954 cells. CONCLUSION: (67)Ga causes as much damage as (111)In to plasmid DNA in solution and shows similar toxicity as (111)In at equivalent internalized activity per cell. (67)Ga therefore deserves further evaluation for radionuclide therapy. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: The data presented here is at the basic level of science. If future in vivo and clinical studies are successful, (67)Ga could become a useful radionuclide with little healthy tissue toxicity in the arsenal of weapons for treating cancer

Hydrazinonicotinic acid (HYNIC) - Coordination chemistry and applications in radiopharmaceutical chemistry

HYNIC (hydrazinonicotinamide) is an efficient bifunctional chelator for Tc-99m used for labelling biomolecules for molecular imaging. Developments and enhancements to improve its efficacy and versatility, including applications beyond Tc-99m labelling, include designs to allow site specificity, availability of amino acid building blocks, improved protecting groups, and a varied choice of co-ligands. In this review, these enhancements are summarised, along with an assessment of the opportunities afforded and problems posed by the use of HYNIC, a discussion of its coordination mode, and the prospects for improving its use and overcoming some of the limitations. There is now an opportunity to exploit the excellent labelling kinetics associated with the tricine-HYNIC system with better co-ligand design to enable both efficient production of labelled proteins and peptides and better specific activity and in vivo properties. In summary, HYNIC represents a well-established way to exploit the highly reactive hydrazine group, to generate bioconjugate chemistry with a degree of bioorthogonality offering the possibility for highly efficient and site specific modification of biomolecules for imaging. © 2010 Elsevier B.V. All rights reserved

Synthesis and evaluation of analogues of HYNIC as bifunctional chelators for technetium

6-Hydrazinonicotinic acid (HYNIC, 1) is a well-established bifunctional technetium-binding ligand often used to synthesise bioconjugates for radiolabelling with Tc-99m. It is capable of efficient capture of technetium at extremely low concentrations, but the structure of the labelled complexes is heterogeneous and incompletely understood. In particular, it is of interest to determine whether, at the no-carrier-added level, it acts in a chelating or non-chelating mode. Here we report two new isomers of HYNIC: 2-hydrazinonicotinic acid (2-HYNIC, 2), which (like 1) is capable of chelation through the mutually ortho hydrazine and pyridine nitrogens and 4-hydrazinonicotinic acid (4-HYNIC, 3), which is not (due to the para-relationship of the hydrazine and pyridine nitrogens). LC-MS shows that the coordination chemistry of 2 with technetium closely parallels that of conventional 1, and no advantages of one over the other in terms of potential labelling efficiency or isomerism were discernable. Both 1 and 2 formed complexes with the loss of 5 protons from the ligand set, whether the co-ligand was tricine or EDDA. Ligand 3, however, failed to complex technetium except at very high ligand concentration: the marked contrast with 1 and 2 suggests that chelation, rather than nonchelating coordination, is a key feature of technetium coordination by HYNIC. Two further new HYNIC analogues, 2-chloro-6- hydrazinonicotinic acid (2-chloro-HYNIC, 4a) and 2,6-dihydrazinonicotinic acid (diHYNIC, 5) were also synthesised. The coordination chemistry of 4a with technetium was broadly parallel to that of 1 and 2 although it was a less efficient chelator, while 5 also behaved as an efficient chelator of technetium, but its coordination chemistry remains poorly defined and requires further investigation before it can sensibly be adopted for 99mTc-labelling. The new analogues 4a and 5 present an opportunity to develop trifunctional HYNIC analogues for more complex bioconjugate synthesis. © 2011 The Royal Society of Chemistry

Inorganic approaches for radiolabelling biomolecules with fluorine-18 for imaging with Positron Emission Tomography

Conventional methods for radiolabelling biomolecules such as proteins and peptides with fluorine-18 for PET imaging rely on carbon-fluorine bond formation and are complex and inefficient. Several non-carbon elements form strong bonds (i.e. with high bond enthalpy) with fluorine, but with lower activation energy for their formation compared to carbon-fluorine bonds, whilst preserving a relatively high kinetic stability. In particular, by incorporating boron-, aluminium- and silicon-containing prosthetic groups into biomolecules, promising results have recently been achieved in the radiolabelling with F-18-fluoride under mild aqueous conditions, affording a level of convenience, efficiency and specific activity potentially superior to those offered by conventional C-F bond formation methods. The promise already shown by these early studies heralds a new branch of bioconjugate radiochemistry involving a wider range of "fluoridephilic" elements for synthesis of PET molecular imaging agents. © 2011 The Royal Society of Chemistry

Technetium-binding in labelled HYNIC-peptide conjugates: Role of coordinating amino acids

Electrospray mass spectrometry (ESMS) of certain peptides labelled with 99mTc via hydrazinonicotinamide (HYNIC) with tricine as co-ligand shows one Tc-bound tricine, whereas typically two are observed. We speculated that this was due to coordination of a neighbouring histidine (His) or glutamate (Glu). To investigate this possibility, several short peptides incorporating lysine (HYNIC), with and without His and Glu at different positions in the sequence, were radiolabelled with 99mTc, using tricine, ethylenediaminediacetic acid (EDDA) and nicotinic acid as co-ligands. The products were examined by HPLC-ESMS, cysteine challenge and bovine serum albumin (BSA) challenge. Peptides with His nearby on either side of lysine (HYNIC) contained only one tricine and showed markedly enhanced structural homogeneity and stability to cysteine challenge and BSA binding, except those with His located at the N-terminus. Peptides without His, or with neighbouring N-terminal His, contained two tricines and were less stable to cysteine challenge and BSA binding. Glu participated in Tc-binding but did not enhance stability. We conclude that neighbouring His or Glu side chains coordinate to Tc and this could alter peptide or protein conformation. Inclusion of His in a neighbouring position to lysine (HYNIC) enhances stability, improves homogeneity and reduces the demand of the metal center for binding to additional co-ligands. © 2009 Elsevier Inc. All rights reserved

Trifluoroacetyl as a protecting group for HYNIC: stability in the presence of electrophiles and application in the synthesis of 99mTc-radiolabelled peptides

TrifluoroacetylHYNIC-peptides have recently been shown to label directly with 99mTc as efficiently as their non-trifluoroacetylated analogs. In this work, the trifluoroacetyl (Tfa) moiety has been evaluated as a protecting group for HYNIC against reaction with strong electrophiles. Fmoc-(trifluoroacetylHYNIC)-lysine, the chosen model starting material, was found to be resistant against acetaldehyde and benzylchloroformate challenges, at 1 mol equiv and a 1000 M excess, respectively. In contrast, the Fmoc-(HYNIC)-lysine derivative, with a free hydrazine group, was quantitatively converted to the corresponding hydrazone after a 1 h incubation with acetaldehyde. Fmoc-(trifluoroacetylHYNIC)-lysine was also found to be stable over a wide pH range (3.6-10) to the acetaldehyde challenge. High efficiency 99mTc-radiolabelling (99%) was achieved in the presence of acetaldehyde using Fmoc-(trifluoroacetylHYNIC)-lysine, as compared to a poor radiolabelling yield (34%) obtained with the non-trifluoroacetylated analog. These findings firmly establish the trifluoroacetyl group as a convenient and effective protecting group for HYNIC, and as a promising alternative to currently available labelling strategies. © 2010 Elsevier Ltd. All rights reserved