Identifying a Novel Ferrocene Derivative as a K-Ras Inhibitor
Abstract
Ras proteins are small GTPases that regulate cell proliferation, differentiation and survival at the plasma membrane (PM). There are three Ras isoforms ubiquitously expressed in mammalian cells: H-, N- and K-Ras. Constitutively active Ras mutations are found in ~19% of all human cancers, with ~75% of those being in K-Ras. There are K-Ras inhibitors in clinic but they only target the oncogenic K-RasG12C mutant, which only makes up a small sub-set of K-Ras-driven cancers. Thus, there still exists a need for a pan anti-K-Ras drug. Ferrocene derivatives are a class of compounds that have been shown to inhibit the growth of a lung cancer cell line harboring an oncogenic mutant K-Ras via their elevation of cellular reactive oxygen species (ROS). Given that lung cancer cells harboring an oncogenic mutant K-Ras require K-Ras signaling for their survival, the effect of a novel ferrocene derivative, C16H20FeClNO, on K-Ras signaling was tested. C16H20FeClNO was found to specifically disrupt the K-Ras/MAPK signaling pathway and inhibit the growth of K-Ras-dependent human pancreatic and lung cancer cell lines. Given that localization to the PM is essential for K-Ras signaling, the effect of C16H20FeClNO on K-Ras PM localization was tested. C16H20FeClNO was found to dissociate K-Ras, but not other Ras isoforms, from the PM. Furthermore, other ROS-elevating drugs had a similar effect on K-Ras PM localization and K-Ras signal output. C16H20FeClNO was shown to elevate cellular ROS levels and supplementation of N-acetylcysteine (NAC), a general antioxidant, reversed these effects, suggesting that C16H20FeClNO disrupts K-Ras PM localization and K-Ras signaling through an ROS-mediated mechanism. Lastly, K-Ras histidine 95 (His95) residue in the G-domain was identified as the oxidative residue involved in C16H20FeClNO-induced K-Ras dissociation from the PM. Overall, C16H20FeClNO disrupts K-Ras PM localization and signal output through oxidation of His95. Taken together, this dissertation identifies C16H20FeClNO as a novel K-Ras inhibitor and provides the groundwork for C16H20FeClNO to be developed into an anti-cancer drug.