See also G Proteins
Introduction:
The RAS gene plays a central role in controlling how cells grow and divide, but mutations in this gene occur in about 1 in 5 cancers. When mutated, RAS becomes permanently active, continually senidng signals that push cells to keep growing and multiplying. Insdie the cell, RAS sits on the embrane and acts as the starting signal in a chain of grwoth processses. Completely shutting down RAS or the enzymes it controls has proven difficult becasue these same pathways are essential for normal cell function. For example, one of the enzymes linked to RAS, PI3K, also helps regulate blood sugar through insulin.
The Ras family of small guanine-nucleotide binding proteins plays a pivotal role in many intracellular signal transduction pathways, including those which regulate cellular growth and differentiation and those which contribute to cell activation (Bourne et al., Nature 348:125-132 (1990); Marshall, FASEB J. 9:1311-1318 (1995)). Moreover, many different receptors expressed on the surface of diverse cell types can result in the activation of signal transduction pathways that are importantly influenced by Ras, and these pathways in turn determine whether, and to what extent, these cells respond to such cell surface receptor-dependent activation by proliferating, differentiating (i.e., developing new functional characteristics), and/or expressing specific functions.
Depending on the circumstances, these “down-stream” consequences of the activation of Ras-dependent signal transduction pathways can have either adaptive (physiological) or maladaptive (pathological) consequences. For example, controlled Ras-dependent cellular proliferation is required for wound healing, whereas poorly regulated Ras-dependent cellular proliferation can result in the development of cancer and other neoplasms. Similarly, appropriate Ras-dependent cell secretion of histamine, serotonin, cytokines and other mediators can be important for host defense against parasites and other pathogens, whereas the inappropriate activation of these same pathways, for example, by a reaction to a bee-sting in patients who are allergic to components of bee venom, can lead to fatal anaphylaxis. Thus, Ras represents a major regulator of many of the most fundamental biological processes involved in both health and disease. (Tam US 6500942 B1)
The mechanism by which Ras regulates such processes, through interactions with other intracellular molecules, is quite complex. Ras proteins are membrane-associated proteins that cycle between an active GTP-bound form and an inactive GDP-bound form. Evidence is accumulating for the existence of many different classes of positive or negative regulators of Ras and positive or negative Ras signaling effectors, all of which, by definition, are thought to interact directly with the active GTP-bound form of Ras to influence cellular signaling for growth, differentiation and expression of function (Boguski and McCormick, Nature 366:643-654 (1993); Marshall, FASEB J. 9:1311-1318 (1995); Marshall, Curr. Opin. Cell Biol 8:197-204 (1996)).
Ras Family Members:
Introduction:
RAS (KRAS, NRAS, HRAS) proteins regulate cell growth and other cellular functions by converting between a guanosine triphosphate (GTP)-bound “on” state (“RAS(ON)”) and a guanosine diphosphate (GDP)-bound “off” state (“RAS(OFF)”). The active state of RAS is bound to GTP, which is hydrolyzed to the GDP-bound inactive state. RAS proteins have a slow intrinsic hydrolysis rate (Westover et al., Mol Cancer Res (2015) 13 (9): 1325-1335), which is enhanced in the presence of RAS GTPase-activating proteins (GAPs).
KRAS is a small GTPase protein which cycles between GDP-bound inactive & GTP-bound active states to regulate cellular signaling cascades and promote cell proliferation and survival. KRAS is frequently mutated in cancer with gain-of-function missense mutations clustering in hotspots, e.g., at codon 12, 13 and 61. Oncogenic mutations at these residues can disrupt intrinsic and GAP-mediated GTP hydrolysis increasing levels of GTP-bound active KRAS, thereby leading to inappropriate activation of cellular signaling cascades which can drive the progression of cancers.
Ras Effectors:
In contrast to Ras regulators, which function primarily by influencing the amount of Ras which is in the GTP-bound active, as opposed to the GDP-bound inactive, form, Ras effectors are thought to influence the ability of active, GTP-bound Ras to initiate signaling. In the case of many Ras-interacting proteins which can influence the intensity of Ras-dependent signaling, it is not yet clear to what extent they function as effectors as opposed to regulators; such proteins can therefore be called Ras regulators/effectors (Boguski and McCormick, Nature 366:643-54 (1993); Han and Colicelli, Mol. Cell. Biol. 15:1318-1323 (1995); Marshall, FASEB J. 9:1311-1318 (1995); Marshall, Curr. Opin. Cell. Biol. 8:197-204 (1996)).
RAS Regulators:
Some of the best-characterized Ras regulators include the GTPase activating proteins (GAPs) and guanine nucleotide exchange factors (Boguski and McCormick, Nature 366:643-654 (1993)). The GAPs represent a family of Ras-binding proteins which stimulate the intrinsic rate of Ras GTP hydrolysis and thus negatively regulate the Ras-induced signaling by accelerating the conversion of active GTP-bound form of Ras to the inactive GDP-bound form. Recent studies have identified several GAPs specific for Ras proteins, which include p120-Ras GAP, neurofibromin (the protein encoded by the neurofibromatosis type 1 (NF1) gene), Gap1, Ral-GDS, Rsbs 1, 2, and 4, Rin1, MEKK-1, and phosphatidylinositol-3-OH kinase (P13K) (Boguski and McCormick, Nature 366:643-654 (1993)).
Ras Inhibitors:
Introduction:
It has been well established in literature that Ras proteins (K-Ras, H-Ras, and N-Ras) play an essential role in various human cancers and are therefore appropriate targets for anticancer therapy. Indeed, mutations in Ras proteins account for approximately 30% of all human cancers in the United States, many of which are fatal. Dysregulation of RAS proteins by activating mutations, overexpression or upstream activation is common in human tumors, and activating mutations in RAS are frequently found in human cancer. For example, activating mutations at codon 12 in RAS proteins function by inhibiting both GTPase-activating protein (GAP)-dependent and intrinsic hydrolysis rates of GTP, significantly skewing the population of RAS mutant proteins to the “on” (GTP-bound) state (RAS(ON)), leading to oncogenic MAPK signaling. Notably, RAS exhibits a picomolar affinity for GTP, enabling RAS to be activated even in the presence of low concentrations of this nucleotide. Mutations at codons 13 (e.g., G13C) and 61 (e.g., Q61K) of RAS are also responsible for oncogenic activity in some cancers. (Jian, US 20250375445)
RAS(ON) mutant-selective inhibitors:
Clinical data from RAS(ON) mutant-selective inhibitors, such as elironrasib (RMC-6291), a
RAS(ON) G12C-selective inhibitor (NCT05462717), and zoldonrasib (RMC-9805), a RAS(ON) G12Dselective inhibitor (NCT06040541), have shown well-tolerated safety profiles. As of April 7, 2025, the most common reported treatment-related adverse events (TRAEs) for elironrasib were QTc prolongation and Gl-related toxicities that were primarily Grade 1 or 2 in severity. As of December 2, 2024, the most common TRAEs for zoldonrasib occurring in at least 10% of patients were GI-related toxicities and rash which were primarily Grade 1 or 2 in severity. (MEYEROWITZ, WO 2025/265060 A1)
—RMC-6236 (daraxonrasib):
Clinical data from the Phase I study of RMC-6236 (daraxonrasib) (NCT05379985), a RAS(ON) multi-selective inhibitor, have demonstrated an acceptable safety profile and encouraging antitumor activity in patients with RAS mutant NSCLC or PDAC. The most common treatment-related adverse events (TRAEs) observed were rash and GI-related toxicities, which are consistent with the known on-target toxicities in normal tissues reported from other RAS pathway inhibitors. These data supported the initiation of Phase 3 studies of RMC-6236 in patients with PDAC (NCT06625320) or NSCLC (NCT06881784). (Jian, US 20250375445)
KRAS mutations are present in up to 25% of cancers, wherein the oncogenic variants have different prevalence rates in different cancers (see Box 1 of Mullard, Nature reviews DRUG DISCOVERY Vol. 18, December 2019:887-891).
Small Molecules:
The vast majority of small molecule drugs act by binding a functionally important pocket on a target protein, thereby modulating the activity of that protein. For example, cholesterol-lowering drugs known as statins bind the enzyme active site of HMG-CoA reductase, thus preventing the enzyme from engaging with its substrates. Dysregulation of Ras proteins by activating mutations, overexpression or upstream activation is common in human tumors, and activating mutations in Ras are frequently found in human cancer. For example, activating mutations at codon 12 in Ras proteins function by inhibiting both GTPase-activating protein (GAP)-dependent and intrinsic hydrolysis rates of GTP, significantly skewing the population of Ras mutant proteins to the “on” (GTP-bound) state (Ras(ON)), leading to oncogenic MAPK signaling. Notably, Ras exhibits a picomolar affinity for GTP, enabling Ras to be activated even in the presence of low concentrations of this nucleotide. (Liu, US 20260152514)
Researchers at Vividion Therapeutics identified a set of small molecules that attach to the surface of PI3K near the spot where RAS would normally bind. These compounds successfully blocked the RAS-PI3K interaction but still allowed PI3K to perform its other roles. In a lung tumor model, the treatment stopped tumor growth but no elevted blood sugar levles. (Particelli, “Covalent inhibitors of the PI3Kalpha RAS binding domain impair tumor growh driven by RAS and HER2” Science, 2025).
Revolution Medicines are developing RAS inhibitors using structure guided design. Its RAS(ON) inhibitors are designed to suppress diverse oncogenic variants of RAS proteins. Granted FDA breathrough therapy designation in previously treated metastatic pancreatic cancer with KRAS G12 mutaitons, Daroxonrasib, a RAS(ON) mlti-selective inhibtor, is active agaisnt diverse RAS driver mutaitons and multiple drug resistance mechanisms. Two Phase III trails are ognoing. (MEYEROWITZ, WO 2025/265060 A1)
Side-Effects:
–rash and mucositis:
Due to their ability to inhibit both mutant and wild-type RAS isoforms, RAS(ON) multi-selective
inhibitors offer broad therapeutic potential. However, inhibition of wild-type RAS in non-tumor tissues (e.g., skin and mucosa) may lead to TRAEs, such as rash and mucositis, as observed in the Phase 1 clinical studies of daraxonrasib (RMC-6236) (NCT05379985), a RAS(ON) multi-selective inhibitor (data utoff of September 30, 2024). These TRAEs are consistent with the known on-target toxicities in normal tissues reported from other RAS pathway inhibitors. The encouraging Phase 1 data supported the initiation of Phase 3 studies of daraxonrasib in patients with PDAC (NCT06625320) or NSCLC (NCT06881784). (MEYEROWITZ, WO 2025/265060 A1)
discloses administration of a CypA-binding compound (e.g., cyclosporin A, sanglifehrin A, and analogs or derivatives thereof) to a normal tissue can compete for binding with the RAS(ON) inhibitor to CypA in that tissue. This competitive interaction reduces formation of the RAS-inhibitory tri complex in the treated area, thereby decreasing RAS pathway inhibition locally. In tumor tissues, for example, where no such competition occurs, the RAS(ON) inhibitor remains active and forms the tri-complex with CypA and RAS, thereby maintaining antitumor efficacy. (MEYEROWITZ, WO 2025/265060 A1)