Abstract 6501: Development and characterization of covalent inhibitors of the RAS-PIK3CA interaction
Authors: Klebba Joseph , Tamiya Junko , Wang Jinwei , Miao Hui , Lamb Kelsey , Snead Aaron , Esparza-Oros Antonio , Lin Richard , Yue Chanyu , Grabow Stephanie , Bernard Steffen , Liu Yongsheng , Horning Benjamin , Hoffman Melissa , Pariollaud Marie , Wyrick Taylor , Parker Holly , Sigler John , Pastuszka Martha , Weinstein David , Kinsella Todd , Patricelli Matt 
Published: March 2024

Abstract
RAS proteins are membrane bound GTPases that when hyperactivated, act as oncogenes through activation of the MAPK & PI3K pathways. Each of these pathways has oncogenic potential, as exemplified by the high frequency of BRAF mutations in melanoma and PIK3CA and PTEN mutations in breast and gynecological cancers. Simultaneous activation of these pathways, as occurs in RAS driven cancers, generates aggressive cancers that present a significant clinical challenge. KRAS, the most commonly mutated RAS isoform, is also the most frequently mutated oncogene in cancer. While treatment options have improved for a subset of these patients due to the accelerated approval of KRAS-G12C inhibitors, the rapid development of resistance highlights the continued need for effective treatments. In RAS driven cell and animal models, dual inhibition of the MAPK &PI3K pathways has shown superior efficacy relative to targeting the individual pathways, however dose limiting toxicities in humans have prevented this combination strategy from finding clinical success. While physiological activation of the MAPK pathway is RAS dependent, the interaction between RAS and the catalytic subunit of PI3Kα, PIK3CA, serves as an amplifier but not a primary activator of this pathway. This interaction is particularly important in cancerous cells as it serves to amplify basal PI3K activity and support tumor progression. Conversely, in healthy cells, RAS independent activation of PI3K by upstream signaling factors is sufficient for maintaining physiological homeostasis. Unfortunately, traditional strategies of targeting the PI3K pathway have been unable to capitalize on this therapeutic opportunity as they do not discriminate between RAS dependent and RAS independent signaling. This leads to on-target dose-limiting toxicities, most commonly hyperglycemia and rash. We have discovered small molecules that disrupt the RAS:PIK3CA interaction through covalent ligation of C242, in the RAS binding domain, adjacent to the RAS binding interface. Using a Nanobit system to measure the RAS:PIK3CA interaction and signaling assays in “RAS active” cells, we have optimized molecules that disrupt the RAS:PIK3CA interaction and inhibit RAS mediated activation of PIK3CA. These molecules show robust inhibition of PIK3CA signaling, and tumor growth inhibition in cancer models, but unlike PIK3CA active site inhibitors, they do not impact glucose handling. Profound efficacy is seen when these RAS:PIK3CA inhibitors are used in combination with an agent targeting the MAPK pathway or with a therapy directly targeting mutant KRAS. Finally, we found that ligation of C242 on PIK3CA blocks HER2/3 driven activation of PI3Kα in a RAS independent manner. Overall, our data supports the clinical investigation of these molecules, particularly in combination with rationally chosen therapies where they may provide a tolerable and efficacious means of blocking the PI3K pathway.
Citation Format: Joseph Klebba, Junko Tamiya, Jinwei Wang, Hui Miao, Kelsey Lamb, Aaron Snead, Antonio Esparza-Oros, Richard Lin, Chanyu Yue, Stephanie Grabow, Steffen Bernard, Yongsheng Liu, Benjamin Horning, Melissa Hoffman, Marie Pariollaud, Taylor Wyrick, Holly Parker, John Sigler, Martha Pastuszka, David Weinstein, Todd Kinsella, Matt Patricelli. Development and characterization of covalent inhibitors of the RAS-PIK3CA interaction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6501.