Abstract B54: Targeting constitutively active RAS signaling in high-grade serous ovarian carcinoma (HGSOC) with ADT-006, a novel small molecule that blocks RAS-effector interactions

Abstract

Abstract Gain-of-function mutations in RAS genes occur at high frequency in several types of cancer, including pancreatic, colorectal, and lung adenocarcinomas. Such driver mutations result in constitutive activation of RAS and its downstream signaling pathways, promoting tumor cell proliferation, survival, and metastasis. The development of drugs directly targeting RAS has been hindered due to the lack of suitable surfaces on the protein for small-molecule binding, as well as its high affinity for GTP binding. We recently identified a novel series of indene derivatives that showed highly selective growth inhibitory activity in tumor cells harboring constitutively active RAS versus tumor cells with low levels of active RAS. Chemical optimization resulted in series of compounds that potently and selectively inhibit RAS-dependent tumor cell growth by blocking RAS-effector interactions. High-grade serous ovarian carcinoma (HGSOC) is invariably characterized by the key driver mutation in TP53, but other mutational drivers, such as mutations or altered methylation of BRCA1 and BRCA2, cyclin E1, PIK3CA and AKT1/2 amplifications, and loss of NF1, RB1 and PTEN, are also commonly found. Conversely, RAS mutations are usually associated with low-grade serous ovarian carcinoma (LGSOC) and mucinous ovarian tumors. Here we show that 5 (OVCAR5, OVCAR8, ES2, KURAMOCHI, and IGROV1) out of 12 ovarian cancer cell lines tested have high levels of constitutive RAS activation as measured by the active RAS pull-down assay, comparable or higher than those of MIA PaCa-2 pancreatic cancer cells, which harbors the activating mutation G12C on KRAS. The 7 remainder cell lines tested (A2780, SKOV3ip, CAOV3, OVCAR4, OVCAR3, OVSAHO, and OV90) had levels of active RAS comparable or lower than BxPC-3 pancreatic cells, which lacks constitutively active RAS. Interestingly, most ovarian cancer cell lines were highly sensitive to ADT-006 (IC50 ~20 nM) in vitro, with the exception of OV-90 cells, which showed IC50 ~300 nM and the lowest level of active RAS measured by the pull-down assay. Treatment of intact SKOV3ip and OVCAR8 cells with ADT-006 inhibited RAF/MAPK and PI3K/AKT phosphorylation within the same concentration range as the growth inhibitory activity of this compound. Xenograft studies performed with SKOV3ip cells implanted intraperitoneally in athymic nude mice and treated twice daily with ADT-006 i.p. at the dose of 10 mg/kg for two weeks showed significant antitumor activity with no discernible toxicity. Our results demonstrate that ADT-006 inhibits HGSOC cell growth by blocking RAS-effector interactions, and supports further evaluation of our novel RAS inhibitors for the treatment of ovarian cancer. Citation Format: Luciana Madeira da Silva, Tyler E. Mattox, Adam B. Keeton, Bing Zhu, Kristy L. Berry, Alla Musiyenko, Elaine Gavin, Kevin Lee, Veronica Ramirez-Alcantara, Yulia Y. Maxuitenko, Xi Chen, Jacob Valiyaveettil, Michael R. Boyd, Jennifer Scalici, Rodney Rocconi, Gary A. Piazza. Targeting constitutively active RAS signaling in high-grade serous ovarian carcinoma (HGSOC) with ADT-006, a novel small molecule that blocks RAS-effector interactions [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr B54.