Abstract Background Auger electron-emitting radionuclides have potential in targeted treatment of small tumors. Thallium-201 (201Tl), a gamma-emitting radionuclide used in myocardial perfusion scintigraphy, decays by electron capture, releasing around 37 Auger and Coster–Kronig electrons per decay. However, its therapeutic and toxic effects in cancer cells remain largely unexplored. Here, we assess 201Tl in vitro kinetics, radiotoxicity and potential for targeted molecular radionuclide therapy, and aim to test the hypothesis that 201Tl is radiotoxic only when internalized. Methods Breast cancer MDA-MB-231 and prostate cancer DU145 cells were incubated with 200–8000 kBq/mL [201Tl]TlCl. Potassium concentration varied between 0 and 25 mM to modulate cellular uptake of 201Tl. Cell uptake and efflux rates of 201Tl were measured by gamma counting. Clonogenic assays were used to assess cell survival after 90 min incubation with 201Tl. Nuclear DNA damage was measured with γH2AX fluorescence imaging. Controls included untreated cells and cells treated with decayed [201Tl]TlCl. Results 201Tl uptake in both cell lines reached equilibrium within 90 min and washed out exponentially (t 1/2 15 min) after the radioactive medium was exchanged for fresh medium. Cellular uptake of 201Tl in DU145 cells ranged between 1.6 (25 mM potassium) and 25.9% (0 mM potassium). Colony formation by both cell lines decreased significantly as 201Tl activity in cells increased, whereas 201Tl excluded from cells by use of high potassium buffer caused no significant toxicity. Non-radioactive TlCl at comparable concentrations caused no toxicity. An estimated average 201Tl intracellular activity of 0.29 Bq/cell (DU145 cells) and 0.18 Bq/cell (MDA-MB-231 cells) during 90 min exposure time caused 90% reduction in clonogenicity. 201Tl at these levels caused on average 3.5–4.6 times more DNA damage per nucleus than control treatments. Conclusions 201Tl reduces clonogenic survival and increases nuclear DNA damage only when internalized. These findings justify further development and evaluation of 201Tl therapeutic radiopharmaceuticals.

Calcium minerals such as hydroxyapatite (HAp) can be detected noninvasively in vivo using nuclear imaging agents such as [18F]NaF (available from cyclotrons), for positron emission tomography (PET) and 99mTc-radiolabeled bisphosphonates (BP; available from 99mTc generators for single photon emission computed tomography (SPECT) or scintigraphy). These two types of imaging agents allow detection of bone metastases (based on the presence of HAp) and vascular calcification lesions (that contain HAp and other calcium minerals). With the aim of developing a cyclotron-independent PET radiotracer for these lesions, with broad calcium mineral affinity and simple one-step radiolabeling, we developed [68Ga]Ga-THP-Pam. Radiolabeling with 68Ga is achieved using a mild single-step kit (5 min, room temperature, pH 7) to high radiochemical yield and purity (>95%). NMR studies demonstrate that Ga binds via the THP chelator, leaving the BP free to bind to its biological target. [68Ga]Ga-THP-Pam shows high stability in human serum. The calcium mineral binding of [68Ga]Ga-THP-Pam was compared in vitro to two other 68Ga-BPs which have been successfully evaluated in humans, [68Ga]Ga-NO2APBP and [68Ga]Ga-BPAMD, as well as [18F]NaF. Interestingly, we found that all 68Ga-BPs have a high affinity for a broad range of calcium minerals implicated in vascular calcification disease, while [18F]NaF is selective for HAp. Using healthy young mice as a model of metabolically active growing calcium mineral in vivo, we compared the pharmacokinetics and biodistribution of [68Ga]Ga-THP-Pam with [18F]NaF as well as [68Ga]NO2APBP. These studies revealed that [68Ga]Ga-THP-Pam has high in vivo affinity for bone tissue (high bone/muscle and bone/blood ratios) and fast blood clearance (t1/2 < 10 min) comparable to both [68Ga]NO2APBP and [18F]NaF. Overall, [68Ga]Ga-THP-Pam shows high potential for clinical translation as a cyclotron-independent calcium mineral PET radiotracer, with simple and efficient radiochemistry that can be easily implemented in any radiopharmacy.

Purpose: Anion transport and accumulation by the human sodium/iodide symporter (hNIS) is an established target for molecular imaging and radionuclide therapy. Current radiotracers for PET imaging of hNIS expression are limited to [ 124 I]I - and [ 18 F]BF 4- . We sought to develop new 18 F-labeled hNIS substrates offering higher specific activity, higher affinity and simpler radiochemical synthesis than [ 18 F]BF 4- . Methods: The ability of a range of anions, some containing fluorine, to block [ 99m Tc]TcO 4-uptake in a hNIS-expressing cell line was measured. SO 3 F - emerged as a promising candidate. [ 18 F]SO 3 F - was synthesised by reaction of [ 18 F]F - with SO 3 -pyridine complex in MeCN and purified using alumina and QMA SPE cartridges. Chemical and radiochemical purity and stability in human serum were determined by radiochromatography. Radiotracer uptake and efflux in hNIS-transduced HCT116-C19 cells and the hNIS-negative parent cell line were evaluated in vitro in the presence and absence of a known substrate (NaClO 4 ) as a competitive inhibitor. PET/CT imaging and ex vivo biodistribution measurement were conducted in Balb/c mice, both with and without NaClO 4 inhibition. Results: The fluorosulfate anion was identified as a potent inhibitor of [ 99m Tc]TcO 4- uptake via hNIS in vitro (IC 50 0.55-0.56 µ M, cf. BF 4- 0.29-4.5, TcO 4- 0.07, I - 2.7-4.7 µ M). Radiolabeling to produce [ 18 F]SO 3 F - was simple to perform and afforded the desired radiotracer in high radiochemical purity, suitable for biological evaluation (RCP > 95%, decay corrected RCY = 31.6%, specific activity ≥ 48.5 GBq/µmol). Specific, blockable hNIS-mediated uptake in HCT116-C19 cells was observed in vitro , and PET/CT imaging in normal mice showed uptake in Conclusions: Fluorosulfate is a high-affinity hNIS substrate. [ 18 F]SO 3 F - is easily synthesized in high yield and very high specific activity and is a promising candidate for pre-clinical and clinical PET imaging of hNIS expression and thyroid-related disease; it is the first example of in vivo PET imaging with a tracer containing a S- 18 F bond.

Anion transport by the human sodium–iodide symporter (hNIS) is an established target for molecular imaging and radionuclide therapy. Current radiotracers for PET of hNIS expression are limited to 124I− and 18F-BF4−. We sought new 18F-labeled hNIS substrates offering higher specific activity, higher affinity, and simpler radiochemical synthesis than 18F-BF4−. Methods: The ability of a range of anions, some containing fluorine, to block 99mTcO4− uptake in hNIS-expressing cells was measured. SO3F− emerged as a promising candidate. 18F-SO3F− was synthesized by reaction of 18F− with SO3–pyridine complex in MeCN and purified using alumina and quaternary methyl ammonium solid-phase extraction cartridges. Chemical and radiochemical purity and serum stability were determined by radiochromatography. Radiotracer uptake and efflux in hNIS-transduced HCT116-C19 cells and the hNIS-negative parent cell line were evaluated in vitro in the presence and absence of a known competitive inhibitor (NaClO4). PET/CT imaging and ex vivo biodistribution measurement were conducted on BALB/c mice, with and without NaClO4 inhibition. Results: Fluorosulfate was identified as a potent inhibitor of 99mTcO4− uptake via hNIS in vitro (half-maximal inhibitory concentration, 0.55–0.56 μM (in comparison with 0.29–4.5 μM for BF4−, 0.07 μM for TcO4−, and 2.7–4.7 μM for I−). Radiolabeling to produce 18F-SO3F− was simple and afforded high radiochemical purity suitable for biologic evaluation (radiochemical purity > 95%, decay-corrected radiochemical yield = 31.6%, specific activity ≥ 48.5 GBq/μmol). Specific, blockable hNIS-mediated uptake in HCT116-C19 cells was observed in vitro, and PET/CT imaging of normal mice showed uptake in thyroid, salivary glands (percentage injected dose/g at 30 min, 563 ± 140 and 32 ± 9, respectively), and stomach (percentage injected dose/g at 90 min, 68 ± 21). Conclusion: Fluorosulfate is a high-affinity hNIS substrate. 18F-SO3F− is easily synthesized in high yield and very high specific activity and is a promising candidate for preclinical and clinical PET imaging of hNIS expression and thyroid-related disease; it is the first example of in vivo PET imaging with a tracer containing an S–18F bond.

SUV for the stomach in BALB/c mice estimated by ex vivo biodistribution and PET ROI analysis at varying doses of BF4 â . (PDF 9.33 KB).

[18F]BF4 −, the first 18F-labelled PET imaging agent for the sodium/iodide symporter (NIS), was produced by isotopic exchange yielding a product with limited specific activity (SA, ca. 1 GBq/μmol) posing a risk of sub-optimal target-to-background ratios (TBR) in PET images due to saturation of NIS in vivo. We sought to quantify this risk and to develop a method of production of [18F]BF4 − with higher SA.

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.

Tissue hypoxia is a feature of cancer, heart disease and stroke, and imaging it may become clinically important. Copper-ATSM (ATSMH(2) = 2,3-butanedione bis(N-methyl)thiosemicarb-azone), labelled With (CU)-C-60, (CU)-C-62 or (CU)-C-64, is selectively taken up in hypoxic cells in vitro and in vivo by a bioreductive mechanism, and is a prototype hypoxia. imaging agent amenable to improvement. In vitro studies with several differently alkylated analogues of CuATSM show that hypoxia. selectivity is a general property of complexes with two alkyl groups at the diketone backbone, offering a range of pharmacokinetic proper-ties while retaining hypoxia. selectivity. This pharmacokinetic control affords a route to development of second-generation hypoxia imaging agents With optimized properties for different clinical applications. Combinatorial synthesis of these analogues, including asymmetric ones, is possible by combining several diketones with several thiosemicarbazides and separating the products chromatographically. Copyright (c) 2007 John Wiley & Sons, Ltd.