Preparation of an 18 F-Labeled Hydrocyanine Dye as a Multimodal Probe for Reactive Oxygen Species.

Hydrocyanine dyes are sensitive "turn-on" type optical probes that can detect reactive oxygen species (ROS). We have developed a method to prepare an 18 F-labeled hydrocyanine dye as a multi-modal PET and optical "turn-on" probe. A commercially available near infrared (NIR) dye was modified with a fluorinated prosthetic group that did not alter its ROS sensing properties in the presence of superoxide and hydroxyl radicals. The 18 F-labeled analogue was produced using a single-step terminal fluorination procedure. Positron emission tomography (PET) imaging and quantitative in vivo biodistribution studies indicated this novel probe had remarkably different pharmacokinetics compared to the oxidized cyanine analogue. The chemistry reported enables the use of quantitative and dynamic PET imaging for the in vivo study of hydrocyanine dyes as ROS probes.

Imidazole-based [2 + 1] Re(I)/99mTc(I) complexes as isostructural nuclear and optical probes.

The synthesis, stability, and photophysical properties of [2 + 1] Re(I)/Tc(I) complexes derived from bipyridine and a series of imidazole derivatives were investigated as a means of identifying complexes suitable for creating targeted isostructural optical/nuclear molecular imaging probes. To prepare the desired complexes, [Re(CO)3(H2O)3]Br was combined with 2,2'-bipyridine (bipy) to give [Re(CO)3(bipy)Br], which in turn was converted to the desired complexes by treatment with functionalized imidazoles, yielding crystal structures of two new Re complexes. The corresponding (99m)Tc complexes [(99m)Tc(CO)3(bipy)(L)](+) (L = imidazole derivatives) were prepared by combining [(99m)Tc(CO)3(bipy)(H2O)]Cl with the same series of ligands and heating at 40 or 60 °C for 30 min. Quantitative transformation to the final products was confirmed in all cases by HPLC, and the nature of the complexes was verified by comparison to the authentic Re standards. Incubation in saline and plasma, and amino acid challenge experiments showed that N-substituted imidazole derivatives, bearing electron donating groups, exhibited superior stability to analogous metal complexes derived from less basic ligands. Imaging studies in mice revealed that with the appropriate choice of monodentate ligand, it is possible to prepare robust [2 + 1] Tc complexes that can be used as the basis for preparing targeted isostructural optical and nuclear probes.

Isostructural nuclear and luminescent probes derived from stabilized [2 + 1] rhenium(I)/technetium(I) organometallic complexes.

A convenient method to prepare (99m)Tc analogues of a class of rhenium(I) luminophores was developed, creating isostructural pairs of nuclear and optical probes. A two-step procedure and a new one-pot procedure were used to produce a series of [2 + 1] complexes of the type [Tc(CO)3(bipy)L](+) in greater than 80% yield. The plasma stability of the reported compounds was evaluated, where the basicity of the monodentate pyridine type ligand (L) has a significant impact with half-lives ranging from 2 to 20 h. The ability to generate the radioactive complexes makes it possible to quantitate cell uptake of Re luminophores, which was demonstrated in MCF-7 breast cancer cells using (99m)Tc analogues of two Re(I)-based mitochondrial targeting dyes.

Imidazole fused phenanthroline (PIP) ligands for the preparation of multimodal Re(I) and 99mTc(I) probes.

A small library of [2 + 1] 99mTc(i) complexes based on phenyl-imidazole-fused phenanthroline (PIP) ligands were synthesized and evaluated as multimodal molecular imaging probes. Using either a two-step or a one-pot synthesis method, 99mTc-PIP complexes containing N-methylimidazole as the monodentate ligand were prepared and isolated in good (54 to 89%) radiochemical yield, with the exception of one derivative bearing a strongly electron-withdrawing substituent. The stability of the [2 + 1] complexes was assessed in saline and in cysteine and histidine challenge studies, showing 6 hours stability, making them suitable for in vivo studies. In parallel, the Re(i) analogues were prepared as reference standards to verify the structure of the 99mTc complexes. The optical properties were consistent with other previously reported [2 + 1] type Re(i) complexes that have been used as cellular dyes and sensors. To facilitate the development of targeted derivatives, a tetrazine-PIP ligand was also synthesized. The 99mTc complex of the tetrazine PIP ligand effectively coupled to compounds containing a trans-cyclooctene (TCO) group including a TCO-albumin derivative, which was prepared as a model targeting molecule. An added benefit of the Re-PIP-Tz construct is that the emission from the metal complex was quenched by the presence of the tetrazine. Following the addition of TCO, there was a 70-fold increase in fluorescence emission, which can in future be leveraged during in vitro studies to reduce background signal.

Preparation and Evaluation of Radiolabeled Antibody Recruiting Small Molecules That Target Prostate-Specific Membrane Antigen for Combined Radiotherapy and Immunotherapy.

The feasibility of developing a single agent that can deliver radioactive iodine and also direct cellular immune function by engaging endogenous antibodies as an antibody-recruiting small molecule (ARM) was determined. A library of new prostate-specific membrane antigen (PSMA)-binding ligands that contained antibody-recruiting 2,4-dinitrophenyl (DNP) groups and iodine were synthesized and screened in vitro and in vivo. A lead compound (9b) showed high affinity for PSMA and the ability to bind anti-DNP antibodies. Biodistribution studies of the iodine-125 analogue showed 3% ID/g in LNCaP xenograft tumors at 1 h postinjection with tumor-to-blood and tumor-to-muscle ratios of 10:1 and 44:1, respectively. The radiolabeled analogue was bound and internalized by LNCaP cells, with both functions blocked using a known PSMA inhibitor. A second candidate showed high tumor uptake (>10% ID/g) but had minimal binding to anti-DNP antibodies. The compounds reported represent the first examples of small molecules developed specifically for combination immunotherapy and radiotherapy for prostate cancer.

Irradiation of rainbow trout at early life stages results in legacy effects in adults.

PURPOSE: Communication of signals from irradiated to non-irradiated fish has been demonstrated by our group for adults. Major questions are however, whether the effects persist for significant lengths of time (meaning there are memories or legacies of the exposure) and whether they are induced in young animals or very early stages in the life cycle. METHODS: To address these questions we used a reporter cell clonogenic bioassay to detect the effects of radiation exposure and of 'bystander' signals, emitted from irradiated fish, on non-irradiated fish. The legacy of radiation exposure or receipt of bystander signals was investigated in rainbow trout irradiated as eggs at 48 h, eyed eggs at one month, yolk sac larvae (YSL) at two months and juveniles at three months after fertilisation. The irradiated and bystander fish together with shams and unhandled husbandry controls were grown on in a hatchery and examined as they reached each of the remaining life stages. They were also re-examined as one-year-olds with and without further irradiation and finally examined as sexually mature two-year-olds. RESULTS: The data indicate a clear legacy effect of irradiation at any early life stage in the adult fish. CONCLUSION: The data suggest that bystander signals can be transmitted in vivo and once induced are persistent during the animals' lifespan.