Abstract 767: Oncogenic mutant KRAS modulates EZH2 expression through MEK-ERK and PI3K/AKT signaling in NSCLC: differential effects of different KRAS mutations and increased efficacy of inhibition combined with EZH2 targeted therapy
Authors: Riquelme Erick M. , Shen Li , Wang Jing , Behrens Carmen , Simon George , Papadimitrakopoulou Vassiliki , Minna John D. , Wistuba Ignacio I. 
Published: August 2015

Background. EZH2 overexpression occurs in lung cancer and is associated with poor outcome. The mechanism(s) driving EZH2 expression in lung cancer are not fully understood and their identification would likely lead to new therapeutic targets in addition to drugs directly inhibiting EZH2 function. In this study, we investigated the mechanisms of EZH2 expression associated with oncogenic KRAS activation and whether pharmacological disruption of MEK-ERK and PI3K/AKT signaling pathways would affect EZH2 expression in a panel of NSCLC cell lines. Moreover, we investigated the efficacy of inhibition of MEK-ERK and PI3K/AKT with combined with direct EZH2 inhibition in KRAS mutant NSCLC cell lines.

Methods. NSCLC cell lines were treated with different doses of MEK-ERK inhibitor AZD6244 and PI3K/AKT inhibitor MK2206 and the expression of EZH2, MEK, MAPK and AKT were determined by Western-blotting. We knockdown KRAS expression using small interfering RNA (siRNA). EZH2 expression was correlated with KRAS mutation status in NSCLC tumor samples. Tumor cell inhibition (IC50 values) by AZD6244, MK2206 and drug combination with EZH2 inhibitor 3-deazaneplanocin A (DZNep) (AZD6244+DZNep and MK2206+DZNep) was determined by MTS assay.

Results. In NSCLC tissues we found that the expression of EZH2 was higher in tumors with a KRAS G12C mutation compared with the other types of KRAS amino acid substitutions. Knockdown of KRAS down-regulated EZH2 expression in cell lines harboring KRAS G12C and G12D mutations, but not in cells having other types of KRAS mutations. Pharmacological disruption of signaling MEK-ERK pathway with AZD6244 decreased EZH2 expression, and this effect correlated with the type of KRAS mutation, with a higher reduction occurring in NSCLCs harboring KRAS G12C mutation compared with the other types of mutations. By contrast, MK2206 strongly decreased EZH2 expression in NSCLCs with KRAS G12D mutation compared with the other type of KRAS mutations. Interestingly, the combination of MEK-ERK with EZH2 inhibitors enhanced the sensitivity to AZD6244 in KRAS G12C mutant cell lines compared to the other mutations. The combination of PI3K/AKT with EZH2 inhibitors enhanced the sensitivity to MK2206 in NSCLC cell lines with KRAS G12D mutation compared with other types of KRAS mutations.Conclusions. Our findings suggest that: 1. oncogenic KRAS G12C and G12D mutations differentially modulate EZH2 expression through MEK-ERK and PI3K/AKT signaling respectively - indicating the need for specific KRAS mutation guided therapy; 2. Inhibition of MEK-ERK and PI3K/AKT in combination with an EZH2 inhibitor should result in a significant increased sensitivity to MEK-ERK and PI3K/AKT targeted therapy in KRAS mutant lung cancers. (Grant support: 5 R01 CA155196 and P50CA70907)

Citation Format: Erick M. Riquelme, Li Shen, Jing Wang, Carmen Behrens, George Simon, Vassiliki Papadimitrakopoulou, John D. Minna, Ignacio I. Wistuba. Oncogenic mutant KRAS modulates EZH2 expression through MEK-ERK and PI3K/AKT signaling in NSCLC: differential effects of different KRAS mutations and increased efficacy of inhibition combined with EZH2 targeted therapy. [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 767. doi:10.1158/1538-7445.AM2015-767