Editors' ChoiceDRUG DESIGN

Blocking Notch

Science Signaling  17 Nov 2009:
Vol. 2, Issue 97, pp. ec369
DOI: 10.1126/scisignal.297ec369

Ligand binding to transmembrane Notch receptors leads to their proteolytic cleavage and the liberation of the Notch intracellular domain (NICD), which translocates to the nucleus to bind to the transcription factor CSL. Mastermind-like (MAML) coactivator proteins bind to a groove created by the NICD-CSL interface, leading to recruitment of the transcriptional machinery and activation of Notch target genes. Crucial to various developmental pathways, aberrant Notch signaling has been implicated in several cancers, including T cell acute lymphoblastic leukemia (T-ALL), and, like other transcription factors, its therapeutic targeting by small-molecule inhibitors has been challenging (see Arora and Ansari). Moellering et al. took another approach: Noting that a dominant-negative MAML fragment inhibits Notch signaling when expressed in T-ALL cells, they designed a series of peptides based on the α-helical MAML1 NICD-CSL interaction motif, using hydrocarbon “staples” to stabilize them in an α-helical conformation. Intriguingly, fluorescently labeled forms of some of these stapled α-helical peptides derived from MAML1 (SAHMs) penetrated cells and distributed throughout the cytoplasm and nucleus. The authors combined in vitro pull-down assays, fluorescence polarization spectroscopy, and surface plasmon resonance to show that the peptide SAHM1 bound to a complex of CSL and a fragment of NICD. SAHM1 competed with endogenous MAML1 in binding to NICD1-CSL in lysates of a human T-ALL cell line and inhibited the transcriptional activation of Notch1-dependent gene reporter, as well as the expression of Notch target genes. Indeed, SAHM1 elicited a global suppression of Notch-activated genes in T-ALL cells and inhibited the proliferation of T-ALL cell lines sensitive to inhibitors of γ-secretase (which block release of NICD). Moreover, in a bioluminescent mouse model of T-ALL, SAHM1 inhibited expression of Notch target genes, as well as leukemia progression. Thus, a stapled peptide based on the MAML1 NICD-CSL interaction motif appears to effectively inhibit Notch-dependent gene transcription.

R. E. Moellering, M. Cornejo, T. N. Davis, C. Del Bianco, J. C. Aster, S. C. Blacklow, A. L. Kung, D. G. Gilliland, G. L. Verdine, J. E. Bradner, Direct inhibition of the NOTCH transcription factor complex. Nature 462,182–188 (2009). [PubMed]

P. S. Arora, A. Z. Ansari, A Notch above other inhibitors. Nature 462,171–173 (2009). [PubMed]