Correspondence mk@tum.de In BriefSecretin, a gut hormone secreted while eating a meal, stimulates brown fat thermogenesis and induction of satiation in mice and humans.

In recent years, implementation of 68 Ga-radiometalated peptides for PET imaging of cancer has attracted the attention of clinicians. Herein, we propose the use of 44 Sc (half-life 5 3.97 h, average b 1 energy [Eb 1 av ] 5 632 keV) as a valuable alternative to 68 Ga (half-life 5 68 min, Eb 1 av 5 830 keV) for imaging and dosimetry before 177 Lu-based radionuclide therapy. The aim of the study was the preclinical evaluation of a folate conjugate labeled with cyclotronproduced 44 Sc and its in vitro and in vivo comparison with the 177 Lulabeled pendant. Methods: 44 Sc was produced via the 44 Ca(p,n) 44 Sc nuclear reaction at a cyclotron (17.6 6 1.8 MeV, 50 mA, 30 min) using an enriched 44 Ca target (10 mg 44 CaCO 3 , 97.00%). Separation from the target material was performed by a semiautomated process using extraction chromatography and cation exchange chromatography. Radiolabeling of a DOTA-folate conjugate (cm09) was performed at 95°C within 10 min. The stability of 44 Sc-cm09 was tested in human plasma. 44 Sc-cm09 was investigated in vitro using folate receptor-positive KB tumor cells and in vivo by PET/CT imaging of tumor-bearing mice Results: Under the given irradiation conditions, 44 Sc was obtained in a maximum yield of 350 MBq at high radionuclide purity (.99%). Semiautomated isolation of 44 Sc from 44 Ca targets allowed formulation of up to 300 MBq of 44 Sc in a volume of 200-400 mL of ammonium acetate/HCl solution (1 M, pH 3.5-4.0) within 10 min. Radiolabeling of cm09 was achieved with a radiochemical yield of greater than 96% at a specific activity of 5.2 MBq/nmol. In vitro, 44 Sc-cm09 was stable in human plasma over the whole time of investigation and showed folate receptor-specific binding to KB tumor cells. PET/CT images of mice injected with 44 Sc-cm09 allowed excellent visualization of tumor xenografts. Comparison of cm09 labeled with 44 Sc and 177 Lu revealed almost identical pharmacokinetics. Conclusion: This study presents a highyield production and efficient separation method of 44 Sc at a quality suitable for radiolabeling of DOTA-functionalized biomolecules. An in vivo proof-of-concept study using a DOTA-folate conjugate demonstrated the excellent features of 44 Sc for PET imaging. Thus, 44 Sc is a valid alternative to 68 Ga for imaging and dosimetry before 177 Luradionuclide tumor therapy. In the past decade, applications of radiometal-based PET have rapidly increased, particularly for oncologic imaging purposes (1). Clinical implementation of 68 Ga-labeled somatostatin analogs (e.g., 68 Ga-DOTATATE, 68 Ga-DOTATOC) for imaging of neuroendocrine tumors has raised attention because of the excellent imaging quality that can be achieved and the on-site availability of 68 Ga (half-life [T 1/2 ] 5 68 min, average b 1 energy [Eb 1 av ] 5 830 keV, intensity 5 89%) by the 68 Ge/ 68 Ga generator (2-6). Somatostatin receptor-targeted PET is currently used for dosimetry before application of 177 Lu-based radionuclide therapy (7). These facts have established the basis of a new era of PET applicat...

Metabolism is a fundamental process of life. However, non-invasive measurement of local tissue metabolism is limited today by a deficiency in adequate tools for in vivo observations. We designed a multi-modular platform that explored the relation between local tissue oxygen consumption, determined by label-free optoacoustic measurements of hemoglobin, and concurrent indirect calorimetry obtained during metabolic activation of brown adipose tissue (BAT). By studying mice and humans, we show how video-rate handheld multi-spectral optoacoustic tomography (MSOT) in the 700-970 nm spectral range enables non-invasive imaging of BAT activation, consistent with positron emission tomography findings. Moreover, we observe BAT composition differences between healthy and diabetic tissues. The study consolidates hemoglobin as a principal label-free biomarker for longitudinal non-invasive imaging of BAT morphology and bioenergetics in situ. We also resolve water and fat components in volunteers, and contrast MSOT readouts with magnetic resonance imaging data.

The folate receptor (FR) is upregulated in various cancer types (FR-α isoform) and in activated macrophages (FR-β isoform) which are involved in inflammatory and autoimmune diseases, but its expression in healthy tissues and organs is highly restricted to only a few sites (e.g kidneys). Therefore, the FR is a promising target for imaging and therapy of cancer and inflammation using folate-based radiopharmaceuticals. Herein, we report the synthesis and evaluation of a novel folic acid conjugate with improved properties suitable for positron emission tomography (PET). [(18)F]-fluoro-deoxy-glucose folate ([(18)F]3) was synthesized based on the click chemistry approach using 2-deoxy-2-[(18)F]fluoroglucopyranosyl azide and a folate alkyne derivative. The novel radiotracer [(18)F]3 was produced in good radiochemical yields (25% d.c.) and high specific radioactivity (90 GBq/μmol). Compared to previously published (18)F-folic acid derivatives, an increase in hydrophilicity was achieved by using a glucose entity as a prosthetic group. Biodistribution and PET imaging studies in KB tumor-bearing mice showed a high and specific uptake of the radiotracer in FR-positive tumors (10.03 ± 1.12%ID/g, 60 min p.i.) and kidneys (42.94 ± 2.04%ID/g, 60 min p.i.). FR-unspecific accumulation of radioactivity was only found in the liver (9.49 ± 1.13%ID/g, 60 min p.i.) and gallbladder (17.59 ± 7.22%ID/g, 60 min p.i.). No radiometabolites were detected in blood, urine, and liver tissue up to 30 min after injection of [(18)F]3. [(18)F]-fluoro-deoxy-glucose-folate ([(18)F]3) is thus a promising PET radioligand for imaging FR-positive tumors.