To facilitate drug discovery activities targeting KRAS/MAPK pathway, we have produced the full spectrum of pathway proteins including kinases, wild type, and mutated KRAS, exchange factors, and effectors. This presentation will summarize our most recent assay development efforts for biochemical, biophysical, and cell-based assays for these targets. 

Revolution Medicines is developing novel RAS(ON) Inhibitors based on our proprietary tri-complex technology platform, enabling a highly differentiated approach to inhibiting the active, GTP-bound form of RAS (RAS(ON)). We will discuss a portfolio of compounds that we believe are the first RAS(ON) inhibitors to use this mechanism of action. RMC-6291, our inhibitor targeting KRASG12C/NRASG12C(ON), and RMC-6236, our inhibitor of multiple RAS variants (RASMULTI(ON)), are in IND-enabling preclinical development.

This presentation will discuss the history of targeting KRAS in the clinic, advances to directly target KRAS G12C, and clinical progress of KRAS G12C inhibitors (eg, adagrasib) in the clinic. I will also discuss future questions and directions for targeting KRAS G12C, including biomarkers and combination strategies.

Active RAS interacts with effectors to link extracellular signals to downstream signaling pathways. Structures of RAS in complex with various effectors have shown that the switch-I region of RAS plays a major role in RAS-effector interactions. Our recent structural work on RAS in complex with effectors has provided new insights into the role of other regions in RAS forming key interactions with effector proteins.

Son of Sevenless (SOS) facilitates the exchange of GDP-bound Ras with GTP. Native ion mobility-mass spectrometry is used to monitor the assembly of the catalytic domain of SOS (SOScat) with KRas. We discover different molecular assemblies and distinct conformers of SOScat engaging KRas. We also find KRasG13D exhibits high affinity for SOScat, a potent allosteric modulator of SOS activity, and small-molecule Ras•SOS disruptors fail to dissociate KRasG13D•SOScat complexes.

The protein-tyrosine phosphatase SHP2 plays a key positive role in signaling from receptor tyrosine kinases, cytokine receptors, immune receptors and integrins. SHP2 function is required for RTK-evoked RAS activation, acting upstream of SOS. Consequently, SHP2 inhibitors (SHP2i) have a potential role for tumors with "cycling" KRAS mutants. I will discuss the use of these inhibitors alone and in combination with other targeted and immune therapies.

Inhibitors of key RAS effector signaling pathways, particularly of the RAF-MEK-ERK MAPK cascade and the PI3K-AKT-mTOR pathway, have become part of the armamentarium for RAS-driven cancers. Yet de novo and acquired resistance mechanisms in response to both indirect and the new direct RAS inhibitors commonly include reactivation of these crucial networks. Therefore, effective blockade of RAS downstream signaling remains of paramount importance. We discuss strategies to address this ongoing need.

Nearly 30% of tumors harbor mutations in one of the RAS genes. Nevertheless, more effective therapies are still needed for nearly all RAS-mutant malignancies. I will discuss several strategies that we have employed to identify new therapeutic targets and develop promising combination therapies for KRAS mutant lung and pancreatic cancer, as well as NRAS mutant melanoma.

Using our PPI-disruption identifying platform, ToRPPIDO, we have discovered new compounds that disrupt the Ras-Raf1 interaction. One set of hits exerts its disruptive effect allosterically by binding Raf1 in a new pocket distal to its Ras Binding Domain. STX201, a cell-permeable member of this set, exhibits selective growth inhibition activity against a variety of mutant Ras cancer lines but not against mutant BRAF-driven or WT Ras lines. Mechanistic characterization suggests that this cytotoxic activity of STX201 is independent of the kinase activity of Raf1 and impinges on actin. Another program focused on oncogenic Ras “GAPs," STX300,  will be briefly discussed.

Screening of combinatorial peptide libraries followed by a medicinal chemistry campaign led to the discovery of a metabolically stable and cell-permeable bicyclic peptide, B4-27, as a potent pan-Ras inhibitor. B4-27 inhibits Ras signaling by blocking Ras-effector interactions and induces apoptosis of cancer cells carrying different K-, H-, and N-Ras mutations. In mouse xenograft models, B4-27 prevented tumor growth at 1-5 mg/kg/day (iv).