Search

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal malignancies with an alarming resistance to both chemotherapeutics and targeted therapy approaches. Genetically engineered mouse models (GEMM) of PDAC reflect molecularly and pathophysiologically the carcinogenesis and cancer progression observed in humans, thus being excellent tools for preclinical evaluation of new therapies. To successfully predict and characterize the effect of chemotherapies and targeted approaches in PDAC, we use a complex and highly aggressive GEMM of endogenous PDAC, Ptf1a +/Cre Kras +/LSL-G12D p53Lox/Lox (CKP) mice. To do so, we established a highly usable GEMM-based therapy platform including multi-parametric MR imaging using CKP mice, in which tumors develop within the first 6 weeks of age (Bardeesy et al, 2006). Animals receive a T2w scan on a 3T clinical MRI scanner for detection and staging of solid tumors for study enrolment at defined inclusion criteria (tumour volume 200-400 mm3). Mice get a weekly scan throughout the study until endpoint criteria are met. Upon reaching the endpoint criteria, mice are sacrificed and tumor material is processed for histopathological and RNA/Protein analysis, isolation and culturing of primary tumor cells. Tumors are assessed macro- and microscopically and graded. Proliferation, apoptosis and analysis of respective downstream effectors are characterized. Further comprehensive analysis depending on the respective phenotypical features is then carried out. Primary cell lines are generated for further functional and molecular characterization including but not limited to cell viability, drug sensitivity, expression and methylation profiling. Through this platform, we have successfully been able to target key signaling pathways and to identify promising novel chemotherapeutic and targeted combinations for PDAC. Here we want to highlight the vital need to develop improved preclinical tools to characterize individual tumors throughout the course of treatment. We propose that such a platform is highly relevant and usable for predicting responses to chemotherapeutic and targeted agents. Citation Format: Aayush Gupta, Marija Trajkovic-Arsic, Irina Heid, Nicole Teichman, Evdokia Kalederis, Rickmer Braren, Jens Siveke. Predictive value of genetically engineered endogenous mouse models in preclinical therapeutic studies. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B141.

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.