Direct inhibition of oncogenic KRAS by hydrocarbon-stapled SOS1 helices

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-02, Vol.112 (6), p.1761-1766
• Main Authors: Leshchiner, Elizaveta S., Parkhitko, Andrey, Bird, Gregory H., Luccarelli, James, Bellairs, Joseph A., Escudero, Silvia, Opoku-Nsiah, Kwadwo, Godes, Marina, Perrimon, Norbert, Walensky, Loren D.
• Format: Article
• Language: English
• Subjects: Animals; Biological Sciences; Blotting, Western; Cancer; Cell Line, Tumor; Chromatography, Gel; Drosophila melanogaster; Drosophila Proteins - metabolism; Escherichia coli; Fluorescence; Gene Expression Regulation, Enzymologic - physiology; Humans; Insects; Magnetic Resonance Spectroscopy; MAP Kinase Signaling System - genetics; MAP Kinase Signaling System - physiology; Microfluidics; Mutation; Mutation - genetics; Oncology; Pathogenesis; Peptides; Peptides - genetics; Peptides - metabolism; Peptides - pharmacology; Protein Binding; Protein Structure, Secondary - genetics; Proto-Oncogene Proteins - antagonists & inhibitors; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins p21(ras); ras Proteins - antagonists & inhibitors; ras Proteins - genetics; ras Proteins - metabolism; SOS1 Protein - genetics; SOS1 Protein - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1413185112

Significance KRAS is one of the most prevalent and vicious oncogenic proteins, yet no drugs are available to inhibit its pathologic activity in patients. We report that KRAS-targeting stapled peptides, modeled after the native son of sevenless 1 (SOS1) helical domain, engage wild-type and clinically relevant KRAS mutant proteins with nanomolar affinity. To our knowledge, these compounds represent the highest affinity and broadest spectrum binders of KRAS mutants reported to date. The stapled peptides disrupt the SOS1/KRAS protein interaction and directly inhibit nucleotide association to wild-type and mutant KRAS proteins. We correlate functional binding activity with SAH-SOS1 cytotoxicity across a 13-member panel of KRAS-driven cancer cells and demonstrate sequence- and dose-dependent inhibition of the ERK-MAP kinase phosphosignaling cascade downstream of KRAS in vitro and in vivo. Activating mutations in the Kirsten rat sarcoma viral oncogene homolog (KRAS) underlie the pathogenesis and chemoresistance of ∼30% of all human tumors, yet the development of high-affinity inhibitors that target the broad range of KRAS mutants remains a formidable challenge. Here, we report the development and validation of stabilized alpha helices of son of sevenless 1 (SAH-SOS1) as prototype therapeutics that directly inhibit wild-type and mutant forms of KRAS. SAH-SOS1 peptides bound in a sequence-specific manner to KRAS and its mutants, and dose-responsively blocked nucleotide association. Importantly, this functional binding activity correlated with SAH-SOS1 cytotoxicity in cancer cells expressing wild-type or mutant forms of KRAS. The mechanism of action of SAH-SOS1 peptides was demonstrated by sequence-specific down-regulation of the ERK-MAP kinase phosphosignaling cascade in KRAS-driven cancer cells and in a Drosophila melanogaster model of Ras85D ⱽ¹² activation. These studies provide evidence for the potential utility of SAH-SOS1 peptides in neutralizing oncogenic KRAS in human cancer.