Abstract 936: KRAS mutational subtypes and copy number variations are predictive of response of human pancreatic cancer cell lines to MEK162 in vitro.

Abstract

Abstract Background: Activating mutations in KRAS have been observed in over 90% of pancreatic tumors and are thought to be a major mechanism of oncogenesis in pancreatic cancer. The EGFR signaling pathway serves as a potential target for cancer therapies. Although targeting KRAS itself has been difficult, targeting the downstream effector MEK1/2, a dual specific kinase required for activation of ERK1/2 has proven to be worthy in both preclinical cell lines and animal studies. MEK162 (ARRY-438192) is a potent, selective, ATP-uncompetitive inhibitor of MEK1/2 and was found to be effective at inhibiting growth in a cohort of solid tumors. The objective of this preclinical study was to assess the antitumor activity of MEK162 in pancreatic cancer comprehensively using a panel of 29 pancreatic cancer cell lines. Methods: MEK162 sensitivity in 29 pancreatic cancer cell lines was examined using a five day proliferation assay to assess growth inhibition in vitro. Array-comparative genomic hybridization (array-CGH) was performed on each cell line to determine genomic copy number variation (CNV). KRAS mutational status at codon 12 and 13 was determined by PCR. Results: Sensitivity of pancreatic cancer cell lines to MEK162 varied. There were 15 cell lines with IC50 values less than 500nm and 14 cell lines with IC50s greater than 500nM and 1 cell line (PATU8988T) in which the IC50 was not achieved at the maximum dose of 10uM. Although significant CNV was observed in many genes, only KRAS CNV was found to be significantly associated with sensitivity to MEK162 (p =0.007). In 15 cell lines with IC50 <500nM (sensitive lines), only 2 had detectable KRAS copy number gains (cell lines SU 86.86 had amplification and PSN-1 had high amplification) and 13 had normal levels of KRAS copy number. In the 14 cell lines with IC50 >500nM (resistant lines), 10 had detectable KRAS copy number variations (gains and losses), and 4 had normal levels of KRAS. KRAS mutational subtypes were also associated with sensitivity. Although, the average IC50 of cells with wildtype KRAS (n=4) was not statistically different from those with mutant KRAS (n=25), those cell lines with a KRAS(V12) mutation (n=12) were significantly more resistant to MEK 162 than those with wildtype (n=4) or KRAS(D12) mutations (n=10). Activating mutations resulting in a polar amino acid [KRAS(D12), KRAS(R12) or KRAS(C12)] were more sensitive to MEK162 than nonpolar amino acids [KRAS(V12) (p-value=0.01466)]. Finally, we showed that cells with a KRAS CNV and KRAS(V12) mutation (n=7) were less sensitive than cells having neither KRAS CNV or KRAS(V12) mutation (n=14) (p-value=0.0007). The remaining 8 cell lines had moderate sensitivity to MEK inhibition. Conclusions: Our study has established that MEK162 sensitivity in pancreatic cancer cells lines is associated with KRAS CNV and mutational subtype. Clinical validation of these markers is required. Citation Format: Habib R. Hamidi, Richard Finn, Lee Anderson, Ming Lu, Marlena Fejzo, Charles Ginther, Ronald Linnartz, Angela Zubel. KRAS mutational subtypes and copy number variations are predictive of response of human pancreatic cancer cell lines to MEK162 in vitro. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 936. doi:10.1158/1538-7445.AM2013-936