Lead Optimisation of a Novel Small Molecule Notch Inhibitor

Notch signalling represents a form of cell-to-cell communication that plays a pivotal role for cellular organisation during embryonic and postnatal development, as well as in the homeostasis of adult organs and tissues. Malfunction of this signalling pathway leads to aberrant regulation of the activities of the cells and may result in the loss of their integrity. The consequences include developmental defects, inherited disease syndromes as well as cancer. Accordingly, the discovery of Notch signalling regulating agents is highly desirable in order to extend the possibilities of clinical treatments providing benefits to patients suffering from Notch-associated diseases. In the frame of the present thesis, the initial steps in the lead optimisation of a novel small molecule Notch inhibitor were investigated. This compound, herein referred to as CB103, had been recently discovered in our laboratory by means of phenotypic high-throughput screenings of small molecule libraries for Notch regulators. CB103 turned out to exhibit an unconventional mode of action within the scope of known small molecule Notch inhibitors, due to its ability to block the NICD-mediated, thus activated form of the signalling pathway. However, the concrete cellular targets remained unknown. The aims of the present thesis comprised the structural optimisation and the concomitant retrospective identification of the cellular target molecules of CB103. This was pursued by implementing a repetitive cycle of the redesign of derivatives, their synthesis and their bioactivity assessment, leading to a comprehensive library of direct CB103 analogues. These investigations resulted not only in the identification of additional Notch inhibiting derivatives with in vivo activity, but surprisingly also in the discovery of molecules that appear to enhance Notch signalling. Moreover, the detailed knowledge about the structure-activity relationship was used to develop tagged versions of CB103 for target identification experiments entailing pull-down assays and yeast-three-hybrid (Y3H) screens. In this context, the Y3H system identified the enzyme soluble epoxide hydrolase (sEH) as a true cellular interaction partner of CB103. Additional interesting protein candidates were revealed by the diverse pull-down approaches and are currently under further investigation.