A new strategy of selective Notch receptor targeting in multiple myeloma based on small molecules

Multiple myeloma (MM) is a hematological cancer characterized by MM cells accumulation in the bone marrow (BM) that promotes tumor survival and drug resistance rendering this disease incurable. The oncogenic Notch signaling consists of 4 receptors (Notch1-4) and their 5 ligands (Jag1 and 2, Dll1,3 and 4) and plays a crucial role in the pathological interaction between MM and BM cells. In particular, aberrant Notch2 activation and Jag2 overexpression in MM cells play an important role in MM progression by stimulating osteoclast differentiation, release of pro-tumor cytokines by BM niche cells and MM cell self-renewal. Therefore uncoupling the interaction between Notch2 receptor and Jag2 ligand is critical to affect not only MM cells growth, but also their interaction with the BM niche. These lines of evidence prompt us to develop a therapeutic tool to selectively inhibit Notch2 signaling triggered by Jag2 using an unprecedented approach based on druglike small molecules. We applied in silico protein-protein docking and virtual high-throughput screening (HTS) of a chemoteque to select druglike small molecules. Firstly, we selected and characterized in vitro two candidate compounds that is according to our in silico predictions interfere with Notch2 receptor/ligand binding. Indeed, biological assays showed that they inhibited Notch2 signaling activation and showed an anti-proliferative efficacy, however they were not selective only for Notch2::Jagged2 binding but also affect Notch2:Dll interaction. To identify more selective small molecules, we refined the previous strategy and set-up a new strategy to exclusively uncouple Notch2::Jag2, leaving unaltered the interaction of Notch2 with Dll. A new approach based on the differences in the surfaces of Notch2::Jag2 and Notch2::Dll4 complexes. This allowed us to select in silico 100 top-scoring compounds supposed to be exclusively directed to Notch2::Jag2 surface by HTS of the chemoteque of druglike small molecules. Preliminary, 2 of 100 compounds were validated in vitro. A Notch responsive reporter assay on HEK293T cells showed that compounds were able to significantly reduce Notch2 transcriptional activity. A viability assay of MM cell lines showed a dose-dependent cell growth inhibition in the presence of the compounds. Notch reporter assay of co-culture systems to measure Notch2 activation triggered either by Dll4 or Jag2 ligands detected that one of two compounds specifically inhibited Notch2::Jag2 but not Notch2::Dll4 interactions. Overall, our data indicate that identified compounds directly and selectively antagonize Notch activation and this provide a basis for the development of entirely novel drugs to inhibit Notch signaling in cancer.