Direct inhibition of the NOTCH transcription factor complex

Abstract

Direct inhibition of transcription factor complexes remains a central challenge in the discipline of ligand discovery. In general, these proteins lack surface involutions suitable for high-affinity binding by small molecules. Here we report the design of synthetic, cell-permeable, stabilized α-helical peptides that target a critical protein–protein interface in the NOTCH transactivation complex. We demonstrate that direct, high-affinity binding of the hydrocarbon-stapled peptide SAHM1 prevents assembly of the active transcriptional complex. Inappropriate NOTCH activation is directly implicated in the pathogenesis of several disease states, including T-cell acute lymphoblastic leukaemia (T-ALL). The treatment of leukaemic cells with SAHM1 results in genome-wide suppression of NOTCH-activated genes. Direct antagonism of the NOTCH transcriptional program causes potent, NOTCH-specific anti-proliferative effects in cultured cells and in a mouse model of NOTCH1-driven T-ALL. The NOTCH complex is of tremendous interest because of its role as a master developmental regulator of gene transcription, a substrate for γ-secretase and an oncogene inappropriately activated in many cancers including T-cell leukaemias. Like the majority of transcription factors, NOTCH was thought to be untargetable by synthetic cell-permeable molecules. But now a promising NOTCH antagonist has been designed, and found to be effective in reducing leukaemia growth in a mouse model. The hydrocarbon-stapled peptide SAHM1 acts by preventing assembly of the active transcriptional complex, providing a potentially valuable tool for studies of the role of NOTCH and a starting point for therapeutic agents. In addition, the direct targeting of transactivation complexes may be applicable to several other transcription factor complexes previously considered untargetable. It is notoriously difficult to target transcription factors with aberrant activity in cancer. Inappropriate activation of the NOTCH complex of transcription factors is directly implicated in the pathogenesis of several disease states, including T-cell acute lymphoblastic leukaemia. The design of synthetic, cell-permeable, stabilized α-helical peptides that disrupt protein–protein interactions in NOTCH is now described.