Astatine (At) is the rarest naturally occurring element on Earth, exhibiting only short-lived radioisotopes. One of them, 211At, decays with a half-life of 7.2 h by emission of a highly energetic alpha particle, making it one of the rare alpha emitters suitable for targeted alpha therapy (TAT) of cancers, if bound to an appropriate cancer targeting molecule. Because the number of cyclotrons able to produce it has seen a significant rise in the past years, it is expected that 211At will become more accessible and play a major role in the development of TAT.
Astatine belongs to the halogen elements, and despite more than 80 years since its discovery, many chemical properties remain to be discovered. This lack of knowledge is due to the absence of stable isotopes and the availability in minute amounts that preclude the use of standard analytical methods. Yet, research has shown that At behaves similarly to metals but also to halogens, forming bonds similar to its closest homologue, iodine, such as the carbon-At bond. This carbon-At strategy is the main approach currently available to develop 211At-labeled radiopharmaceuticals. Yet, a lack of in vivo stability of the C-At bond is often observed, resulting in the release of 211At before it reaches its target and leading to irradiation of healthy tissues. Improving this stability is therefore a major challenge that remains to be overcome in order to unleash the potential of 211At in cancer treatments.
In this context the objective of the SAt-Radio project is to explore alternative bonding modalities to the C-At bond in order to develop novel radiolabeling approaches with improved in vivo stability. The strategies developed will exploit both the halogen and the metallic character of At, using analytical and computational approaches that have recently become available and making possible to elucidate the chemistry of this enigmatic elements at the trace concentration it is available.
