Abstract 706: Inflammatory and stem-like colorectal cell lines show differential response to MEK-162 and neratinib in combination
Authors: Pal Rekha , Song Nan , Srinivasan Ashok , Jacobs Samuel A. , Paik Soonmyung , Pogue-Geile Katherine L. 
Published: August 2015

Abstract
Background: Improvement of colorectal cancer (CRC) treatment depends on finding new effective agents and associated biomarkers that can predict patient response to drugs. Recent cell culture experiments show that a combination of MEK and pan ERBB inhibitors may be efficacious in treating CRC (Sun et al 2014). The purpose of this study was to determine whether a cell line's response to targeted agents would correlate with its mutation profile and/or gene expression subtype.
Methods: K-RAS mutation status of 7 cell lines were identified and classified into stem-like or inflammatory subtypes using gene expression data from the cancer cell line encyclopedia and an algorithm described by Sadanandam et al. We tested 5 stem-like cell lines (SW480, SW620, HCT116, C2BBE1, HS675T) and 2 inflammatory cell lines (NCI-H747, SW837) for response to inhibitors of the RAS/RAF and PI3K pathways. MEK-162 and neratinib were tested as single agents and in combination, using cell viability and clonogenic assays.
Results: Cell lines varied in response to the drugs when used as single agents. All cell lines were resistant to the EGFR inhibitor (Gefitinib) at concentrations ≥5 μM. Two pan ERBB inhibitors (neratinib and afatinib) showed IC50 values at or &gt;4 μM and 2 MEK inhibitors (Selumetinib and MEK162) had IC50 values at or &gt;1μM. The inflammatory cell lines, SW837 and NCI-H747, had greater sensitivity to the MEK inhibitors (IC50 value 1μM) while the KRAS mutant stem-like cell lines were relatively more resistant (SW480, SW620) with IC50 values ≥4-5 μM. Stem-like cell lines with WT-KRAS (C2BBE1, HS675T) were even more resistant; IC50s were not achieved at concentrations of 5 μM. Similar results were obtained in clonogenic growth assay.
The MEK and pan ERBB inhibitor combinations were more effective at decreasing cell viability and inducing apoptosis in inflammatory cell lines than in stem-like cell lines. This combination effectively inhibited 60-70% of cell viability in inflammatory cell lines at a dose of 0.5 μM and 0.062 μM for neratinib and MEK-162 respectively. The lethality of this combination was the same even if the doses were reversed (0.5 μM MEK-162 and 0.062 μM neratinib). In contrast, we observed that this combination was not nearly as effective against stem-like cell lines irrespective of KRAS mutation status. Profiling of the phosphorylation status of proteins in the RAF-MEK-ERK signaling pathway after exposure to the MEK-162 plus neratinib combination showed a substantial inhibition of ERK phosphorylation in inflammatory cell lines but not in 4 of the 5 stem-like cell lines.
Conclusion: This study demonstrates that colon cancer cell lines classified as the inflammatory subtype are sensitive to the combination of MEK-162 plus neratinib at concentrations at which cell lines of the stem-like subtype are resistant.
The PA DOH disclaims responsibility for analysis, interpretations, or conclusions.
Citation Format: Rekha Pal, Nan Song, Ashok Srinivasan, Samuel A. Jacobs, Soonmyung Paik, Katherine L. Pogue-Geile. Inflammatory and stem-like colorectal cell lines show differential response to MEK-162 and neratinib in combination. [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 706. doi:10.1158/1538-7445.AM2015-706