The AKT protein family plays an important role in cellular survival by inhibiting apoptotic processes and is one of the major downstream targets of the phosphatidylinositol 3-kinase (PI3K) pathway. Mammalian target of rapamycin (mTOR) is a key kinase acting downstream of the activation of PI3K. Several chemotherapeutic agents target this pathway 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 chemotherapetuic agent. The Mosaic Blue assay is a soft agar, ex vivo tumor response assay that utilized non-expanded patient cancer cells.

Human tumors with matched fresh tissue and 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 PI3K pathway. Samples were classified as resistant or sensitive. The corresponding FFPE tissue block was stained by immunohistochemistry for several phosphorylated proteins, which included AKT, PRAS40, 4EBP1, S6 kinase, S6 ribosomal protein, and PTEN in accordance with validated protocols. Additional fresh cells were also treated with inhibitors, harvested, and phophorylated proteins were evaluated in the pre and post-dose tumor cells. Results were compared the chemosensitivity results and 2 relationships were identified. First, biomarker status of the archival tissue was evaluated in order to understand the intrinsic chemosensitivity. Second, biomarker status upon treatment 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 Format: Lisa Dauffenbach, Patricia A. Cash, Gela C. Sia, Sherif K. Girees, Ryan S. Lim, Jianping Zheng, Eric P. Olsen, Christopher A. Kerfoot. Evaluation of PI3K Inhibitor chemosensitivity in human tumor explants using the Mosaic Blue assay and relationship to biomarkers by immunohistochemistry. [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 3510. doi:10.1158/1538-7445.AM2013-3510