Abstract A35: Evaluation of MEK inhibitor chemosensitivity in human tumor explants using the Mosaic Blue Assay and relationship to biomarkers by immunohistochemistry.
Authors: Dauffenbach Lisa M. , Cash Patricia A. , Sia Gela C. , Girees Sherif K. , Lim Ryan S. , Zheng Jianping , Olsen Eric P. , Kerfoot Christopher A. 
Published: August 2014

Abstract
The MEK pathway is activated in most cancers. Several chemotherapeutic agents target this pathway through inhibition of MEK, ERK or upstream receptor tyrosine kinases and are in clinical trials to treat patients with solid tumors. The use of chemosensitivity testing using human cancer explants is very useful in identifying biomarkers that relate to the intrinsic sensitivity of the tumor to a chemotherapeutic agent. The Mosaic Blue assay is a soft agar, ex vivo tumor response assay that utilizes non-expanded patient cancer cells. Viable colorectal and non-small cell lung cancer tissues with matched formalin-fixed, paraffin embedded (FFPE) tissue were used for this study. Fresh tissues were disaggregated into single cells and exposed to various inhibitors of the MEK pathway, specifically AZD6244 and GSK1120212. Samples were classified as resistant or sensitive. The inhibitors demonstrated different resistance and sensitivity profiles in the human tumors and samples demonstrated a higher frequency of resistance to AZD6244 than to GSK1120212 at similar concentrations. The corresponding FFPE tissue block was stained by immunohistochemistry for phosphorylated AKT, PRAS40, 4EBP1, S6 kinase, S6 ribosomal protein as well as PTEN, EGFR, cMET, HER3, and Ki-67 in accordance with validated protocols. In addition to analysis of primary cancer samples, the MDA-MB-468, MKN45, and T47D cell lines were also treated with AZD6244 and GSK1120212, harvested, and phosphorylated proteins were evaluated in the pre and post-dose tumor cells. Immunohistochemistry results were compared to chemosensitivity results and 2 relationships were identified. First, biomarker status of the archival tissue was evaluated in order to understand the intrinsic chemosensitivity. Resistant tissues demonstrated higher expression of EGFR, cMET, and HER3 and lower expression of phosphorylated S6 ribosomal protein (S240/244 and S235/236) and phosphorylated PRAS40 compared to sensitive tissues. Second, biomarker status upon treatment in cell lines was evaluated to understand modulation of proteins due to therapy. In summary, use of soft agar ex vivo tumor response assays such as the Mosaic Blue assay is a useful tool to predict relative sensitivity across tumor types and allow investigation of potential biomarkers.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A35.
Citation Format: Lisa M. Dauffenbach, Patricia A. Cash, Gela C. Sia, Sherif K. Girees, Ryan S. Lim, Jianping Zheng, Eric P. Olsen, Christopher A. Kerfoot. Evaluation of MEK inhibitor chemosensitivity in human tumor explants using the Mosaic Blue Assay and relationship to biomarkers by immunohistochemistry. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A35.