A novel pan-RAS inhibitor for luminal B breast cancer.

Abstract

e13132 Background: Luminal B breast cancer makes up between 10-20% of cases and is among the most lethal forms of breast cancer. Prognosis is little better than that of the notorious Triple Negative disease. There is currently no effective treatment for Luminal B breast cancer. Recently it has been found that, although mutations in the RAS oncogene are rare in Luminal B, hyper activation of the wild type RAS protein is common due to inactivation of key negative regulators of RAS such as DAB2IP and RASAL. Therefore, targeting RAS is a logical novel approach to developing enhanced therapy for this disease. There are three main isoforms of RAS and there are no currently approved pan-RAS inhibitors. We have developed a small molecule pan-RAS inhibitor which binds directly to all forms of RAS. It acts to block the ability of RAS and to bind and signal through its effectors by disrupting the RAS effector domain. It is active in vitro and in vivo against models of Luminal B breast cancer. Methods: In silico screening of a virtual compound library was performed to identify an initial candidate inhibitor. Iterative rounds of Medicinal Chemistry informed by structural modeling and bioassay in 3D vs 2D growth assays were performed to identify an enhanced activity derivative. Target binding was confirmed by Microscale Thermophoresis and NMR. RAS/RAF complex status was measured by co-immunoprecipitation of the endogenous proteins. Ras signaling was assayed by Western analysis of Phospho-ERK and RAL-GTP pull down assays. In vitro activity was measured using 3D soft agar assays. In vivo activity was measured by ip or po administration against a Luminal B breast cancer cell line. Results: The current lead, designated RAS-F binds all three main isoforms of RAS at low uM kd and modulates the RAS effector domain in NMR studies. It suppresses RAS signaling pathways in transient assays and suppresses Luminal B tumor cell tumor cell growth in soft agar and in vivo. Conclusions: We have developed a pre-clinical pan-RAS inhibitor that is active in vitro and in vivo against Luminal B breast cancer models. The agent also has potential uses against other tumor types partially driven by deregulated wild type RAS such as triple negative breast cancer.