Abstract A06: ATM loss and KrasG12D cooperate to promote widely metastatic pancreatic ductal adenocarcinoma in mice
Authors: Drosos Yiannis , Roys Kathryn , Kuliyev Emin , McKinnon Peter , Sosa-Pineda Beatriz 
Published: October 2015

Invasive pancreatic adenocarcinoma (PDAC) is one of the most lethal solid malignancies. Mutational activation of Kras is nearly universal in preneoplastic pancreatic lesions (Pancreatic Intraepithelial Neoplasias-PanINs) and PDAC, whereas the progression of PanINs to PDAC is accompanied by both inactivating mutations in p16/CDKN2A, TP53, DPC4/SMAD4 and activating mutations in PI3K signaling. Although most PDAC cases represent a sporadic disease, about 5-10% of cases have a hereditary basis. Some of the loci responsible for inherited high-risk PDAC encode gene products implicated in DNA repair, such as BRCA2 and PALB2.

The kinase Ataxia-Telangiectasia Mutated (ATM) plays a critical role in DNA damage responses activated by double-strand breaks, by triggering cell cycle checkpoints that repair DNA or induce p53-dependent apoptosis or senescence. ATM was recently identified as a novel predisposition gene for PDAC because deleterious ATM mutations were found in some families with hereditary PDAC, as well as in ~8% of sporadic PDAC cases. Thus far, the role of ATM as an anti-cancer barrier – especially in pancreatic cancer biology – is poorly understood. Here we sought to address this crucial issue using 3 different mouse strains expressing both an oncogenic version of Kras (KrasG12D) and variable ATM genetic dosage in the pancreas: 1) KC mice, express wild-type ATM, 2) KC;ATMcHET mice, carry deletion of one ATM-allele; and 3) KC;ATMcKO mice, carry deletion of both ATM-alleles. Our preliminary analysis of KrasG12D-induced PanIN formation uncovered that these lesions form earlier in pancreatic tissues carrying one functional ATM allele or lacking ATM in comparison to KC pancreata. In addition, we determined that the median survival due to metastatic tumor burden is considerably shorter in both KC;ATMcKO mice (~6 months) and KC;ATMcHET mice (~9 months) compared to KC mice (~15 months).

We also began establishing primary cell lines from both PDAC and metastatic foci formed in KC, KC;ATMcKO and KC;ATMcHET mice. Preliminary analyses of 2 primary cell lines treated with ionizing radiation (IR) to induce DNA damage and processed for Western blot analysis showed lack of total ATM, phospho-ATM, phospho-KAP1 (an ATM-specific target), and phospho-p53 in ATM-deficient primary pancreatic cancer cells. In contrast, primary cell lines from KC;Cdkn2a+/- tumors and established human PDAC cell lines display functional ATM signaling after IR. In addition, primary cell lines from PDAC and liver metastases of KC;ATMcKO mice also exhibited genomic instability depicted by a high number of anaphase bridges. To complement the characterization of these primary cell lines, we will attempt to identify DNA repair pathway(s) compensating for the loss of ATM and exploit these findings to induce synthetic lethality. Likewise, additional signaling pathways that are activated or inactivated during PDAC progression in the context of ATM deficiency will be identified using both biased and unbiased approaches.

To our knowledge, these preliminary results provide the first evidence in vivo that ATM activity poses an intrinsic barrier to oncogenic transformation in the pancreas. A comprehensive characterization of pancreatic tumor formation in the context of ATM deficiency using our generated mouse models is currently underway, together with experiments in primary cell lines attempting to identify vulnerabilities that could be exploited to develop adequate tailored treatments.

Citation Format: Yiannis Drosos, Kathryn Roys, Emin Kuliyev, Peter McKinnon, Beatriz Sosa-Pineda. ATM loss and KrasG12D cooperate to promote widely metastatic pancreatic ductal adenocarcinoma in mice. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A06.