Abstract
Cyclic nucleotide phosphodiesterases (PDEs) represent one of the key targets in the research field of intracellular signaling related to the second messenger molecules cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP). Hence, non-invasive imaging of this enzyme class by positron emission tomography (PET) using appropriate isoform-selective PDE radioligands is gaining importance. This methodology enables the in vivo diagnosis and staging of numerous diseases associated with altered PDE density or activity in the periphery and the central nervous system as well as the translational evaluation of novel PDE inhibitors as therapeutics. In this follow-up review, we summarize the efforts in the development of novel PDE radioligands and highlight (pre-)clinical insights from PET studies using already known PDE radioligands since 2016.
Highlights
This follow-up of our first review in 2016 [1] aims to report on (I) novel radioligands for imaging of cyclic nucleotide phosphodiesterases (PDEs) with positron emission tomography (PET) and (II) recentclinical insights from PET studies using already known PDE radioligands
A considerable number of pre-clinical and clinical PET studies using already known and well-established radioligands have been published for the PDE isoforms 2A, 4 (B,D)
For the isoforms PDE4 (B,D) and PDE10A, a lot of new insights have been reported regarding the complex relationship between altered enzyme density or activity and the pathophysiology of diseases of the central nervous system
Summary
This follow-up of our first review in 2016 [1] aims to report on (I) novel radioligands for imaging of cyclic nucleotide phosphodiesterases (PDEs) with positron emission tomography (PET) and (II) recent (pre-)clinical insights from PET studies using already known PDE radioligands. PDEs are a class of intracellular enzymes that are expressed throughout the body. They are encoded by 21 genes and divided into 11 families that are subdivided into various subfamilies with different isoforms. Their central role is to hydrolyze the second messenger molecules, cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP) and, to regulate the intracellular levels as well as the signaling cascades of these cyclic nucleotides. In vivo imaging and quantification of PDEs with appropriate radioligands for PET is commended as an important research and translational tool in related (pre-)clinical investigations. We will review novel radioligands as well as current results from (pre-)clinical PET studies related to the PDEs 1, 2A, 4, 5, 7 and 10A.
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