Identification of small molecules uncoupling the Notch::Jagged interaction through an integrated high-throughput screening

Notch signaling plays an important role in several cellular functions including growth, differentiation, cell fate determination and stemness. Increased Notch activity has been linked to several types of cancers. Activation of Notch signaling is triggered by the interaction of Notch receptors (Notch1-4) with 5 different ligands (Jagged1-2 and Dll1-3-4) expressed on the neighbouring cells. Currently, indirect approaches to inhibit Notch signalling are based on the inhibition of the key step of Notch activation catalyzed by the γ-Secretase and thereby affect several different γ-Secretase substrates; conversely direct strategies get advantage of antibody-based drugs. The evidence that Jagged-mediated Notch activation plays a key role in cancer cell biology and the interplay with the surrounding microenvironment prompted us to develop a strategy to directly inhibit Notch activation by uncoupling its interaction with the Jagged, using an unprecedented approach based on small molecules. We set-up a screening strategy based on: protein::protein docking of crystallographic structures of Notch1 with Jagged1; comparative modelling of the Notch2:Jagged2 complex, based on the Notch1::Jagged1 complex; in silico high-throughput screening directed to Notch2 interaction surface of a virtual chemical library containing a large variety of molecules commercially available. The predicted pharmacological activity of the selected compounds was validated i n vitro by a gene reporter and a viability assay. This approach led to the successful identification of two candidates with different anti-proliferative potency and efficacy. This represents the first step towards the rational identification of candidate molecules for the development of entirely novel drugs directed to inhibit Notch signaling in cancer.