Abstract 899: Combination of PI3K and MEK inhibitor chemosensitivity in human tumor explants and cell lines using the Mosaic Blue assay and relationship to biomarkers by immunohistochemistry

Abstract

Abstract The PI3K and MEK pathways promote tumor cell survival through a variety of downstream signals and are commonly explored in cancer research. Many agents are in clinical development and new evidence suggests that a combination of these inhibitors may be required to achieve optimal anti-tumor activity. Twenty-one viable colorectal and non-small cell lung cancer tissue explants with matched formalin-fixed, paraffin embedded (FFPE) tissue and 8 cell lines (A431, AGS, HCT-116, HT-29, MCF-7, MDA-MB-468, MKN45, and T47D) were used for this study. Fresh tissues were disaggregated into single cells and exposed to GDC-0941, a PI3K inhibitor, and AZD6244, a MEK inhibitor, both as single agents and in combination in the Mosaic Blue assay. Combination results were compared to single agent results. Samples were classified as resistant or sensitive. Matched FFPE tissues and cells were stained with the following biomarkers to identify predictive relationships: pAKT, p4EBP1, pPRAS40, ppS6 kinase, pS6 ribosomal protein, pERK, PTEN, cMET, EGFR, HER3, Ki-67, and p53. To assess pharmacodynamics changes, the 8 cell lines were also exposed to 1 concentration of each inhibitor both as single agents and in combination. The cells were fixed and paraffin embedded for IHC staining of the following biomarkers to identify pharmacodynamic relationships: pAKT, p4EBP1, pPRAS40, ppS6 kinase, pS6 ribosomal protein, pEGFR, pHER3, pMET, pERK, and Ki-67. The combination of inhibitors demonstrated additive growth inhibition in the explants and cell lines. The average combination IC50 was more potent than single agents, with greater additivity demonstrated in colorectal cancer compared to lung cancer. Predictive and pharmacodynamic biomarkers were identified with both single agent and combination treatments, and differences were observed between the two inhibitors. In summary, this study demonstrated that the Mosaic Blue assay is a useful tool for classifying sensitive and resistant tumor explants and cell lines and also confirmed that dual targeting of PI3K and MEK pathways is a valuable approach to achieving higher therapeutic activity in vitro. Evaluation of biomarker profiles revealed predictive and pharmacodynamic relationships in this setting. Citation Format: Lisa M. Dauffenbach, Gela C. Sia, Patricia A. Cash, Sherif K. Girees, Ryan S. Lim, Jianping Zheng, Eric P. Olsen, Christopher A. Kerfoot. Combination of PI3K and MEK inhibitor chemosensitivity in human tumor explants and cell lines using the Mosaic Blue assay and relationship to biomarkers by immunohistochemistry. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 899. doi:10.1158/1538-7445.AM2014-899