Abstract by Tobias Nørby Hansen

The lysine deacylase enzyme family consists of 18 enzymes, the eleven Zn²⁺ dependent HDACs (HDAC1-11) along with the seven NAD⁺ dependent sirtuins (SIRT1-7). These enzymes all catalyse the removal of ε-N-acyl modifications on lysine residues in the cell. The 18 enzymes have both different subcellular localization and preference for different substrates. Together these enzymes regulate a range of cellular processes including gene transcription, DNA repair, and metabolism. Dysregulation of these enzymes is related to a wide range of diseases including neurodegenerative diseases, cancers, and metabolic disorders. This makes them interesting drug targets, and where the HDACs are validated targets with multiple drugs approved in the clinic, the sirtuins are still being investigated as promising therapeutic targets. This thesis investigates SIRT5 and 7 with a focus on developing novel inhibitors and chemical tools to investigate these enzymes. Furthermore, the thesis also covers the development of new chemical methods for the rapid generation of compound libraries, which were utilized to develop isozyme-selective HDAC inhibitors.

The first part of the thesis covers the investigation of SIRT5 inhibition by the screening of an elaborate library of carboxylic acid isosteres. Through kinetic studies, we identified novel slow-tight binding inhibitors, which were further transformed into cell-permeable prodrugs that showed potent targeting of SIRT5 in cells. This prodrug also showed cytotoxicity toward SIRT5-addicted leukaemia cells. Next, we envisioned that further development of these compounds could give SIRT5 inhibitors with improved pharmacokinetic properties. We here investigated the incorporation of polar amino acid residues, with retained potency towards SIRT5. Furthermore, initial efforts were made to transform the inhibitors into compounds suitable for targeted protein degradation, where preliminary results showed some degree of SIRT5 degradation.

The second part of the thesis investigates a series of cyclic peptides binder of SIRT7 identified from mRNA-display. By first re-synthesizing the hits and screening these for the inhibition of SIRT7 we identified the first potent and selective inhibitor of SIRT7. This was also shown to target SIRT7 in cells and we further found it to upregulate acetylation at SIRT7-dependent histone sites.

In the final part of the thesis, a novel approach for on-resin sulfur(VI) fluoride exchange has been developed and utilized to synthesize a library of novel HDAC inhibitors. Here novel isozyme selective inhibitors were discovered.