Abstract 392: Combined targeting of MET and PI3K improves efficacy in breast cancer models with concurrent MET/PI3K aberrations
Authors: Liu Shuying , Ueno Naoto T. , Wang Bailiang , Gagea Mihai , Ram Prahlad T. , Merchant Mark , Mendelsohn John , Tripathy Debasish , Mills Gordon B. , Gonzalez-Angulo Ana M. 
Published: July 2016

Abstract
Introduction: Detailed understanding of the genetic abnormalities that drive subsets of cancer has led to the development of highly specific inhibitors targeting key oncogenic pathways. Growing evidence implicates aberrations of both mesenchymal epithelial transition receptor (MET) and its key downstream phosphatidylinositol 3-kinase (PI3K) signaling with poorer prognosis in breast cancer. Co-targeting MET/PI3K and identifying mechanisms of response and resistance could ultimately inform a novel therapeutic strategy for breast cancer treatment. Based on these finding, we hypothesized that concurrent aberrations in PI3K and MET will render breast cancers resistant to therapies targeting each pathway, and that combination therapy targeting the PI3K and MET pathway will improve the efficacy by preventing the acquisition of resistance.
Methods: We established cell models that stably express human wild type (WT) MET or MET-T1010I, a functional germline single nucleotide polymorphism, or mutant PI3K-H1047R alone, or variable concurrent aberrations in PI3K and MET using MCF-10A, a non-transformed mammary epithelial cell line, and HCC1954, a breast cancer cell line with an endogenous PI3KCA-H1047R mutation. Cell behaviors, including survival, invasion and response to MET one arm monoclonal antibody onartuzumab (MetMAb, Genentech Inc) and/or pan class I PI3K inhibitor GDC 941 (pictilisib, Genentech Inc), were detected. HCC1954 expressing WT MET or MET-T1010I along with PI3K-H1047R were transplanted into the mammary fat pad of hepatocyte growth factor-transgenic mice on a severe combined immunodeficiency background. Statistical analyses were carried out using the ANOVA and the Student t test.
Result: Expression WT MET or MET-T1010I act coordinately with PI3K-H1047R to increase colony formation (P &lt; 0.01, respectively). Concurrent MET-T1010I, but not WT MET, acts coordinately with PI3K-H1047R to increase cell invasion (P &lt; 0.0001). Expression MET-T1010I or WT MET induced cells resistance to GDC941, with MET-T1010I stronger than WT MET. Combined targeting MET with onartuzumab and targeting PI3K with GDC941 significantly inhibited cell growth in matrigel, dose dependently than each monotherapy (P &lt; 0.0001, respectively). Invasion assay showed similar pattern. Combined onartuzumab and GDC941 significantly inhibited invasion, dose dependently (P &lt; 0.001). The effects were confirmed using PI3K/mTOR inhibitor, GDC980. Consistently, combination of onartuzumab/GDC941 significantly inhibited tumor growth (P &lt; 0.01 versus GDC941; P &lt; 0.0001 versus onartuzumab alone).
Conclusions: Concurrent aberrations of MET and PI3K render breast cancer cells resistant to therapies blocking either pathway. Targeting both MET and PI3K increases inhibitory efficacy.
Citation Format: Shuying Liu, Naoto T. Ueno, Bailiang Wang, Mihai Gagea, Prahlad T. Ram, Mark Merchant, John Mendelsohn, Debasish Tripathy, Gordon B. Mills, Ana M. Gonzalez-Angulo. Combined targeting of MET and PI3K improves efficacy in breast cancer models with concurrent MET/PI3K aberrations. [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 392.