oa Editorial [Hot topic: Current Topics in the Development of Radioligands for Positron-Emission Tomography Imaging (Guest Editors: Andrew G. Horti and Robert F. Dannals)]

Medicinal radiochemistry involves design, synthesis and evaluation of radiotracers for emission tomography imaging. The development of new radiotracers is based on the structure-imaging properties relationships, suitability for radiolabeling and safety properties. Medicinal radiochemistry emerged over the last three decades mainly as a result of the rapid advances in positron-emission tomography (PET) and single photon emission computed tomography (SPECT). Nowadays most medicinal chemistry journals publish PET radiochemistry papers and there are also a number of specialized journals available. Initially we planned to publish a single special issue in 2010 on recent advances in the development of in vivo radiotracers, but, because the enthusiastic response of the authors substantially exceeded the space of a single issue, we divided the articles between two issues. In special issue # 15 entitled “Recent advances in the medicinal radiochemistry of radioligands for cerebral in vivo imaging” there is a discussion of positron emission tomography radioligands for several receptors of central nervous system. In special issue # 16 entitled “Current topics in the development of radioligands for positron-emission tomography imaging”, recent progress in the radioprobes for in vivo imaging of various non-central targets and advances in synthetic methodologies of PET radioligands is presented. Current Topics in the Development of Radioligands for Positron-Emission Tomography Imaging The paper from Mathews and Szabo presents the current status of PET radioligands for imaging of the angiotensin II subtype 1 receptor (AT1R). These radioligands may be vital to the development of more potent and specific drugs for the treatment of hypertension. Imaging studies using radiolabeled AT1R ligands have revealed the role of AT1R in angiogenesis as well as in various disease states beyond hypertension. In the next four reviews, progress in radioprobe development for imaging of cancer is presented. The paper from Mease reviews radionuclide based imaging agents for planar, single photon emission computed tomography (SPECT), and positron emission tomography (PET) imaging currently used in the clinic and those under development for prostate cancer. Alauddin et al. summarizes the present status of radiolabeled nucleoside analogues for PET imaging of HSV1-tk gene expression which is important for optimization of the clinical gene therapy protocols. The article by Roesch and Riss provides a very comprehensive overview of development of 68Ga-labeled PET agents for broad cancer imaging applications with emphasis on the 68Ge/68Ga generator systems. Another important aspect of PET radiochemistry for tumor imaging is reviewed in the Olberg's and Hjelstuen's paper that describes labeling strategies of peptides with 18F. The latest synthetic methods of 18F-labeled peptides may be a basis for preparation of the previously not available radioimaging probes. The last article of this issue written by Roeda and Dollé highlights the radiochemistry of [11C]phosgene, an important synthon for a number of PET radiochemistry applications including of synthesis of 11C-labeled carbamates, carbonates, heterocycles and C-11C-bond formation.