Development of Carborane-Based Ligands for PET and SPECT Imaging

The early detection of diseases like Alzheimer, Parkinson or cancer have gained importance over the last decade, since they are still the cause of death of millions of people worldwide.[1] To screen patients for disease markers, non-invasive imaging techniques like Positron Emission Tomography (PET) and Single-photon Emission Computed Tomography (SPECT) are suitable methods for diagnostics.[2]
Radiopharmaceuticals with ligands of high affinity and selectivity towards the targets involved in the maladies, like the cannabinoid receptor type 2 (CB2R) or cyclooxygenase 2 (COX-2) have to be developed. In addition to high affinity and selectivity, other requirements are also high metabolic stability or balanced hydrophobicity.[2,3]
The development of such radioligands is a challenge; for example, no CB2R radioligand is available for routine clinical applications so far. To overcome the lack in metabolic stability and increase the selectivity of suitable ligands, closo-dicarbadodecaboranes (carboranes) are employed. The hydrophobic carborane can be introduced as a replacement for phenyl, cyclohexyl or adamantyl groups, to name but a few.[4]
A new class of ligands based on (metalla)carboranes for application in PET and SPECT imaging for investigation of CB2R and COX-2 have been synthesized and in part biologically evaluated. These results will be presented and discussed in detail.