Development of a caspase-3 selective activity-based probe for PET imaging of apoptosis

Apoptosis or programmed cell death plays a key role not only in normal tissue homeostasis but also in the etiology, progression and even treatment of a plethora of diseases including neurodegenerative disorders, cardiovascular disease, sepsis and cancer. Caspase-3 is a cysteine-aspartate protease which plays a central role in the cell death process. Selective in vivo imaging of caspase-3 activity could aid in further elucidating the role of apoptosis and more specifically caspase-3 in a range of diseases and could stimulate and improve drug discovery. Furthermore, in vivo imaging of treatment induced apoptosis would allow to early after onset of a therapy evaluate its effectiveness. Positron Emission Tomography (PET) is a highly sensitive molecular imaging modality that allows non-invasive in vivo imaging of cell death by using radiolabelled probes or radiotracers that specifically target hallmarks of the apoptosis process like caspase-3 activation. Existing PET probes for caspase-3 imaging are based upon caspase-3 substrates and inhibitors. Alternatively, activity-based probes or ABPs could be used. ABPs contain a tag for visualisation and a peptide recognition sequence linked to a reactive functional group or 'warhead' which will covalently modify the active site of the enzyme. For caspase-3 activity-based probes as well as substrate-based probes typically DEVD is used as the recognition sequence. DEVD however lacks selectivity for caspase-3 over other caspases. A recent study showed that by introduction of unnatural amino acids in the DEVD sequence probes can be developed that selectively target caspase-3. The aim of the current study is therefore to develop an 18F-labeled activity-based probe bearing an unnatural amino acid sequence for selective PET imaging of caspase-3 activity. In vitro caspase-3 binding will be evaluated and the pharmacokinetic profile will be studied in normal nude mice. The in vivo apoptosis targeting properties of the probe will be evaluated in mouse models of treated non-small-cell lung cancer and colorectal cancer and compared to a substrate-based and an activity-based PET probe bearing the classical DEVD sequence.

Keywords:MOLECULAR IMAGING, APOPTOSIS

Disciplines:Medical imaging and therapy, Biomarker discovery and evaluation, Drug discovery and development, Medicinal products, Pharmaceutics, Pharmacognosy and phytochemistry, Pharmacology, Pharmacotherapy, Toxicology and toxinology, Other pharmaceutical sciences