Abstract LB-280: SOX2 functions as a molecular rheostat to control the growth, tumorigenicity, and chemosensitivity of pancreatic ductal adenocarcinoma cells

Pancreatic ductal adenocarcinoma (PDAC) is a highly deadly cancer. The transcription factor SOX2 is expressed in ∼20 different cancers, and implicated in chemoresistance in many of these tumors. SOX2 increases as PDAC progresses to advanced stages. Thus, it is important to determine whether elevation of SOX2 during advanced PDAC affects the tumor growth, as well as their responses to chemotherapeutics. This study tested the hypothesis that modulating the levels of SOX2 in PDAC cells alters their growth, tumorigenicity, and responses to drugs currently being tested in PDAC clinical trials. To determine the effects of altered SOX2 levels on the tumorigenicity and drug response of PDAC cells, three PDAC cells lines were stably transduced with two lentiviral vectors that allow doxycycline (Dox) inducible expression of SOX2 (i-SOX2-T3M4, i-SOX2-BxPC3, and i-SOX2-HPAF-II). We also engineered two inducible SOX2-knockdown PDAC cell lines (i-KdSOX2-T3M4, i-KdSOX2-L3.6). Overexpression of SOX2 (∼5-fold) in all three SOX2-overexpresssing cell lines decreased cell growth 20-45%. Similarly, lowering SOX2 levels (∼50%) led to >50% reduction in cell growth in both engineered knockdown PDAC cell lines. We also examined the tumorigenicity of i-SOX2-T3M4 and i-KdSOX2-T3M4 cells by subcutaneous engraftment and subsequent treatment in vivo with Dox. We determined that both inducible elevation of SOX2, as well as inducible knockdown of SOX2, reduces the subcutaneous growth of PDAC tumors by ∼70% and ∼75%, respectively. Thus, small changes in the levels of SOX2 lead to growth inhibition, both in vitro and in vivo. The majority (>90%) of PDAC possess mutations in KRAS leading to strong activation of a number of pathways, including but not limited to RAF/MEK/ERK and AKT signaling axes. As a consequence, MEK and AKT inhibitors are being tested in clinical trials for patients with PDAC. We assessed how altered levels of SOX2 affect the growth of PDAC cells treated with MEK and AKT inhibitors. For all three SOX2-overexpressing PDAC cell lines, we observed significant decreases in clonal growth when the cells were treated with trametinib or MK-2206 at their EC50s. However, simultaneous treatment of all three cell lines with Dox (to elevate SOX2) partially reversed the growth inhibitory effects of trametinib as well as MK-2206. Importantly, knockdown of SOX2 in i-KdSOX2-T3M4 and i-KdSOX2-L3.6 cells further reduced the growth of cells treated with trametinib or MK-2206. Thus, altered levels of SOX2 modify the drug sensitivity of PDAC cells to drugs currently being tested in PDAC clinical trials. Our studies demonstrate that the levels of SOX2 must be carefully controlled in PDAC to maximize cell growth and tumorigenicity. Moreover, our studies argue that the efficacy of drugs currently being tested in PDAC clinical trials, specifically MEK and AKT inhibitors, is influenced by the levels of SOX2. Citation Format: Erin L. Wuebben, Phillip J. Wilder, Angie Rizzino. SOX2 functions as a molecular rheostat to control the growth, tumorigenicity, and chemosensitivity of pancreatic ductal adenocarcinoma cells. [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 LB-280.