Plenary Lecture 2

Title: Activity-based probes and bioorthogonal chemistry: novel tools
for chemical biology and drug discovery.

Professor Koen Augustyns

University of Antwerp, Belgium

Lecture Summary:
Covalent drugs have proven to be successful therapies for various indications, but are often not considered in drug discovery programs due to safety concerns. However, recently a resurgence of covalent drugs together with a recognition of the importance of drug-target residence time is observed.

Diarylphosphonates are known as irreversible inhibitors of serine proteases by phosphorylation of the active site serine alcohol. The synthesis of these molecules and their mechanism of enzyme inhibition will be described. Their potential as research tools for target validation and as lead molecules will be illustrated with examples from our own research in the field of trypsin-like serine proteases.1,2

Diarylphosphonates can also be converted to activity-based probes that are able to covalently label the active fraction of a serine protease. A clickable handle allows for the versatile derivatisation with reporter or visualisation tags. Hence, these probes will find applications in the identification of target and off-target binding partners, quantification of the active fraction of a protein with applications in biomarker analysis, visualisation and bioimaging of targets in cells and organisms.

Activity-based imaging probes targeting urokinase plasminogen activator (uPA) and their application in in vivo imaging will be demonstrated in oncology models. Examples will be presented for fluorescence-, PET- and SPECT imaging.3

Another interesting and recent development in molecular imaging is the use of bioorthogonal chemistry based on the Inverse Electron-Demand Diels-Alder (IEDDA) cycloaddition between 1,2,4,5-tetrazines and trans-cyclooctene (TCO) analogues. Until now, antibodies (Abs) were tagged with TCO and after pretargeting were reacted with tetrazines substituted with reporters. However, TCO tags have the tendency to degrade under physiological conditions, and due to their hydrophobic nature bury within the protein. This results in loss of reactivity and a low Ab functional loading.

To circumvent these problems, we reported for the first time an approach in which tetrazines are used as tags for antibody (Ab) modification, and TCO as imaging agent. We developed a new Ab-tetrazine conjugate which displays high functional loading, good stability and reactivity. We utilized this immunoconjugate for live-cell imaging together with novel TCO probes, resulting in the selective and rapid labeling of SKOV-3 cells.4


Acknowledgments: This work was supported by grants of the University of Antwerp (BOF-GOA), the Research Foundation – Flanders (FWO) and the Agency for Innovation by Science and Technology (IWT).


References: [1]Joossens, J.; Ali, O. M.; El-Sayed, I.; Surpateanu, G.; Van der Veken, P.; Lambeir, A. M.; Setyono-Han, B.; Foekens, J. A.; Schneider, A.; Schmalix, W.; Haemers, A.; Augustyns, K.J. Med. Chem.2007,50, 6638-6646.

2Van Soom, J.; Crucitti, G. C.; Gladysz, R.; van der Veken, P.; Di Santo, R.; Stuyver, I.; Buck, V.; Lambeir, A.-M.; Magdolen, V.; Joossens, J.; Augustyns, K. MedChemComm 2015, 6, 1954-1958.

3Vangestel, C.; Thomae, D.; Van Soom, J.; Ides, J.; wyffels, L.; Pauwels, P.; Stroobants, S.; Van der Veken, P.; Magdolen, V.; Joossens, J.; Augustyns, K.; Staelens, S. Contrast Media Mol. Imaging2016, DOI: 10.1002/cmmi.1706

4 Maggi, A.; Ruivo, E.; Fissers, J.; Vangestel, C.; Chatterjee, S.; Joossens, J.; Sobott, F.; Staelens, S.; Stroobants, S.; Van der Veken, P.; wyffels, L.; Augustyns, K. Org. Biomol. Chem. 2016, 14, 7544-7551.