Abstract 240: Functional significance of co-occurring mutations in PIK3CA and MAP3K1 in breast cancer

Abstract

Abstract PI3Kα signalling pathway is frequently hyper-activated in breast cancer (BrCa) with mutations of PIK3CA (∼45%) frequently found in luminal A BrCa samples. Genomic studies have also uncovered inactivating mutations in MAP3K1 (13-20%) and MAP2K4 (∼8%), two upstream kinases of the JNK apoptotic pathway in luminal A BrCa samples and co-occurring mutation of PIK3CA and MAP3K1 are found in ∼11% of PIK3CA mutants (TCGA). How these two alterations cooperate to promote tumorigenesis and impact the sensitivity to PI3Kα(AZD8835) and AKT (AZD5363) inhibitors is currently unknown. Using siRNA targeting and precise gene editing we have knocked down MAP3K1 in PIK3CA mutant cell lines to create in vitro models reflecting the mutational status of PIK3CA and MAP3K1 in BrCa patients. MAP3K1-deficient cells exhibited increased proliferation rate and decreased sensitivity to AZD8835 compared with parental control cells. In addition, mechanistic analysis revealed that siRNA mediated depletion of MAP3K1 enhances AKT phosphorylation and downstream signalling (i.e. pPRAS40, pFoxO1/FoxO3a) and provides resistance to AZD8835-mediated pathway inhibition. Using in vitro 3D-breast cancer organoid models we have found that MAP3K1 depletion increases overall acinar volume and counteracts AZD8835-mediated reduction of acinar growth. MAP3K1 deficient acini exhibited high pAKT levels in the presence of AZD8835 compared with control acini validating observations in 2D. Remarkably, whereas in control acini pAKT+ cells were restricted to the basal compartment, MAP3K1 deficient acini also exhibited pAKT+ cells in the luminal compartment suggesting anoikis resistance which is a hallmark in early stages of tumorigenesis. Elucidating the mechanistic basis for these clinically co-occurring mutations will provide insights into the mechanisms contributing to the oncogenic role of the PI3K pathway and future patient selection strategies. Citation Format: Alvaro Avivar-Valderas, Robert McEwen, Amir Taheri-Ghahfarokhi, Ambar Ahmed, Daniel Stetson, Brian Dougherty, Marcello Maresca, Kevin Hudson, Francisco Cruzalegui. Functional significance of co-occurring mutations in PIK3CA and MAP3K1 in breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 240.