Refinement Of Inhibitors Of The Kras-Signaling Naocluster Protein, Cnksr1, That Block Oncogenic Kras Signaling And Growth

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PAIntroduction: KRAS, the predominant form of mutated RAS (mut-KRAS), is found in ∼25% of patient tumors across many cancer types and plays a critical role in driving tumor growth and resistance to therapy. CNKSR1 (connector enhancer of kinase suppressor of Ras 1) a protein associated with KRAS in the RAS membrane signaling nanocluster and we have shown it is critical for mut-KRAS but not wild type (wt)-KRAS signaling and cell proliferation. CNKSR1 is a multi-domain protein with a pleckstrin homology (PH) domain, which we have exploited to discover inhibitors that selectively inhibit mut-KRAS tumor growth. The initial leads identified were found to inhibit mut-KRAS signaling and growth of mut-KRAS isogenic NSCLC cell lines (IC50 ∼ 30 μM) and compound refinement provided PHT-7390 and 7391 (IC50 5 to 10 μM). Importantly, they did not block the growth of wt-KRAS cell lines at concentrations up to 100 μM. In mice the agents had antitumor activity againsta mut-KRAS xenograft model and improved the activity of EGFR inhibitors without observable toxicity, but had poor pharmacokinetic properties.Methods: PHusis has used its in silico computational modeling of the PH-domain of CNK1 to optimize its lead inhibitors to improve potency and pharmacokinetic properties. In silico compound refinement has been paired with surface plasmon resonance spectroscopy (SPR) and in vitro cell line screening to provide the latest panel of highly potent CNK1 inhibitors that are moving toward late preclinical development.Results: A panel of analogues of PHT-7390 and 7391 were synthesized with the aim of improving potency and pharmacokinetic properties. This structural optimization yielded several analogues with up to 100 fold greater potency than PHT-7390 to mut-KRAS NSCLC lines (IC50 10-100 nM) while retaining the differential in effect against wt-KRAS lines without activity up to 100 μM. Target engagement studies have shown that the agents inhibit mut-KRAS signaling in similar fashion as KRAS knockdown with siRNA, confirming on target effects in cells. Pharmacokinetic properties were also improved and agents have moved to clinical candidate selection. Conclusion: Potent and specific inhibitors of CNK1 PH-domain with improved pharmacokinetics have been identified. These novel PH-domain inhibitors now provide a therapeutic potential for patients with oncogenic KRAS for which there is currently no effective therapy.Citation Format: D. Lynn Kirkpatrick, Martin Indarte, Mike Scott, Assael Madrigal, Geoffrey Grandjean, Garth Powis. Refinement of inhibitors of the KRAS-signaling naocluster protein, CNKSR1, that block oncogenic KRAS signaling and growth. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2583. doi:10.1158/1538-7445.AM2015-2583