Abstract A234: Targeting Ras-dependent pathways in murine models of pancreatic cancer
Authors: Heid Irina , Braren Rickmer , Einwächter Henrik , Gretzinger Manuela R. , Kosanke Yvonne , Rad Roland , Wildgruber Moritz , Meier Reinhard , Schmid Roland M. , Siveke Jens T. 
Published: June 2012

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a devastating human malignancy that is highly resistant to chemo- and radiation therapy. Lately our research group established a new mouse model of pancreatic cancer which recapitulates two of the most frequent genetic alterations in human PDAC: activation of oncogenic KrasG12D and EGFR signaling. These mice develop invasive and metastatic PDAC from both clinically most relevant preneoplastic lesions, so-called pancreatic intraepithelial neoplasia (PanIN) and intraductal mucinous papillary neoplasm (IPMN). The aim of this study was to characterize Ras-dependent pathways in cell lines isolated from KrasG12D and EGFR activated PDAC in order to develop and test new individual therapeutic strategies for treatment of pancreatic cancer. To evaluate promising candidates in vivo, a multimodal platform for noninvasive imaging was evaluated and used for preclinical studies.

Methods: Primary tumor cells isolated from PDAC of Ptf1a+/Cre;KrasG12D and Ptf1a+/Cre;KrasG12D;Ela-Tgf mice were characterized by genetic and biochemical analysis using array-CGH, gene sequencing, protein activation assays and western blotting. Moreover, the cellular response to known chemo therapeutics and selected signal transduction inhibitors were tested in vitro and some of them in vivo using endogenous and transplantation models. Spontaneous tumor progression and therapy response were monitored by multiparametric imaging using a combination of DCE-MRI, DWI and [18F]FDG-PET measurements.

Results: Similarly to human PDAC, most of the murine cell lines showed an inactivation of tumor suppressors such as p16Ink4a, p19Arf and Tp53. Furthermore, some of the cell lines showed amplification of Tgf /Egfr and Myc loci. Different levels of MAPK, STAT3 and AKT- phosphorylation as well as activation of Rac1 and cdc42 were observed. We found that, Gemcitabine was the most active agent of all tested in vitro. A combination of the Rac1 inhibitor NSC23766 and Gemcitabine led to a significant additive growth-inhibitory effect in most primary cell lines in vitro, while inhibition of other Ras-dependent pathways in combination with Gemcitabine showed no strong antiproliferative effect. In vivo, we observed a high heterogeneity of endogenous tumors in terms of perfusion, tumor composition and metabolic activity. Multimodal monitoring of Gemcitabine therapy in endogenous PDAC as well as different transplantation models showed resistance of tumors to treatment independent of the model used.

Conclusion: Our results reveal that mice with the same genetic background have different genetic and biochemical alterations during cancer progression, emphasizing the necessity for developing new individualized therapeutic strategies for pancreatic carcinoma. Here we developed a robust platform to study PDAC for further preclinical testing in endogenous mouse models, which closely mimics the human situation.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A234.