Abstract 3015: Selective inhibition of mutant KRAS cell and tumor growth by PHT-7.3, an inhibitor of the KRas signaling nanocluster protein Cnk1

Activating mutations of KRas is the most common proto-oncogenic event in human cancer but there remains no effective therapy for patients harboring mutated KRas (mut-KRas). Despite intense efforts, tight nucleotide binding, few defined pockets, and redundant localization signals have impeded the development of compounds that bind or inhibit KRas. We have identified connector enhancer of kinase suppressor of Ras 1 (Cnk1) as a critical mediator for growth driven by mut-KRas in human cancer cells. Cnk1 co-localizes with mutant KRas at the membrane and deletion of Cnk1 abrogates KRas activation and the activation of the Ras effectors Ral and Rho. Cnk1 deletion caused cells with mutant KRas to accumulate at the G1 checkpoint similar to selective deletion of mutant KRas itself. Following a screen and initial structural optimization a small molecule probe compound PHT-7.3 was identified and shown to bind selectively to the pleckstrin homology PH domain of Cnk1 preventing Cnk1 and mut-KRas co-localization. PHT-7.3 inhibited mut-KRas but not wt-KRas non small cell lung cancer (nsclc) cell growth, and selectively blocks mut-KRas downstream signaling in cells. PHT-7.3 exhibited cytostatic antitumor activity in the mut-KRas(G12S) A549 and mut-KRas(G12V) H441 nsclc xenografts, but not in the wt-KRas H1975 nsclc xenograft. Mut-KRas downstream signaling was inhibited by PHT-7.3 in the xenografts with downregulation of activated Rho and Ral signaling. PHT-7.3 showed further increased antitumor activity in A549 xenografts in combination with erlotinib or trametinib. Thus, the work identifies the PH domain of Cnk1 as a druggable target whose inhibition selectively blocks mutant-KRas activation, and PHT-7.3 as a lead agent in the development of therapies for KRas tumors. Citation Format: Roisin Delaney, Marco Maruggi, Martin Indarte, Robert Lemos, Geoff Grandjean, Lynn Kirkpatrick, Garth Powis. Selective inhibition of mutant KRAS cell and tumor growth by PHT-7.3, an inhibitor of the KRas signaling nanocluster protein Cnk1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3015. doi:10.1158/1538-7445.AM2017-3015