Suppressors of kRAS Activity Discovered Using a Fruit Fly-based In-vivo Screen

Period of Performance: 09/15/2017 - 08/31/2018


Phase 2 SBIR

Recipient Firm

Tosk, Inc.
Mountain View, CA 94043
Principal Investigator
Principal Investigator


Principal Investigator: Garland, WA ABSTRACT/SUMMARY kRAS is a GTPase which is the main mediator (on/off) of downstream signaling from the EGF receptor (EGF?R) on the surface of cells. kRAS controls major signaling systems such as the RAF/MEK1/2/ERK1/2 cell proliferation pathway and the PI3K/AKT/mTOR cell survival pathway. Somatic kRAS mutations, termed oncogenic kRAS, are common in many cancers: 90% incidence in pancreatic, 45% in colorectal, and 35% in lung cancer. Mutated kRAS allows the EGF?R system to bypass its natural controls and operate nearly continuously in a pro?growth mode. Wild?type kRAS is self?inactivating, while oncogenic kRAS is not. Consistent with this mechanism, the presence of G12V mutated kRAS blocks the efficacy of monoclonal antibody drugs against EGF?R, such as panitumumab (Vectibix®) and cetuximab (Erbitux®), which are used to treat colorectal cancer, head and neck, and other cancers. Tosk?s Phase I SBIR research used a proprietary, genetically modified Drosophila melanogaster strain that expresses G12V kRAS in its wings to identify two chemical scaffolds (?hits?) that suppress kRAS? related activity. In addition to phenotype reversal of anti?G12V activity in the mutant fly, the hits were tested in relevant cell culture, protein kinase, computational active site docking, RAF, and SOS pull down assays. Assessment of ERK activity, xenograft model studies, and short?term safety and PK studies were also performed. Information about the presence, location, and activity of the mutant kRAS gene was also obtained. The repeatability and reproducibility of the G12V fly screens were evaluated and confirmed. Although not conclusive, MOA studies, including knockout studies in the G12V?expressing fly, strongly suggest that the hits inhibit kRAS activity in the RAS/RAF/MEK/ERK pathway. Computational docking studies further suggest a direct interaction of the hits with kRAS, possibly leading to interference with the kRAS?RAF protein?protein interaction. The primary goals of this Phase II SBIR application are to: (1) perform additional screening using an improved version of the Phase I fly assay to discover new kRAS inhibitors, (2) optimize and further characterize the two inhibitors discovered in the SBIR Phase I and any newly discovered inhibitors from Phase II, and (3) use mechanism, efficacy, safety, and pharmacokinetic studies to select a candidate and one back?up ready for IND?enabling tests needed to file an IND for an inhibitor of mutant kRAS.