Abstract 4080: Analysis of murine stromal components in patient-derived xenograft (PDX) models of pancreatic cancer

Proceedings: AACR 107th Annual Meeting 2016; April 16-20, 2016; New Orleans, LA Pancreatic cancer remains a lethal disease with only 3 - 8% of patients surviving 5 years after initial diagnosis (WHO, 2012). Reasons for this poor situation are advanced and inoperable tumor stages at time of diagnosis and resistance to conventional therapies. One bottleneck in the development of novel therapies is the restricted availability of preclinical models of high clinical relevance. Since the desmoplastic stroma has impact on the progression and treatment of pancreatic cancer, we investigated the attributes of the murine stroma in patient-derived xenografts that completely replaced the human surrounding tissue within a few months after primary transplantation. We elucidated the functionality of murine tumor microenvironment for growth and therapeutic response in a cohort of well-characterized pancreatic cancer (PDAC) PDX. PDX are a valuable tool for the prediction of therapy response, the identification of new biomarkers and therapeutic targets or pancreatic cancer specific pathways. In this study, 57 patient tumors were collected and immediately transplanted into immunodeficient mice. So far, 14 out of 57 samples were established as passageable pancreatic cancer xenografts (PDX). All engrafted PDX are poorly or moderately differentiated adenocarcinomas. Global gene expression analysis and determination of cancer associated mutations revealed K-ras mutations in 13 and additionally p53 mutations in 9 out of 14 PDX. Furthermore, chemosensitivity to standard of care (SoC) drugs was determined by using clinically relevant and optimized schedules and doses. The testing revealed that the response to Gemcitabine (1/10 responder) was moderate within the PDX panel, while the most efficient drug was Abraxane with 5 out of 10 responders. In general, the response profile of all PDX closely reflected patient's situation in the clinic. Cryo- and formalin-preserved tumor tissues of these chemosensitivity studies were investigated for markers of desmoplastic stroma (SPARC, alpha-SMA, FAP and collagen I). Immunohistochemistry and real-time PCR revealed, that even the replacing murine stroma is characterized by a distinct reactivate nature. Semi-quantitative analysis of stromal components showed that the tumor surrounding tissue mass was not significantly reduced due to therapeutic intervention. Though the tumor burden was diminished under SoC, the mRNA expression level of SPARC and FAP was unaffected in corresponding samples of the treatment groups compared to vehicle-treated control. The same effect was found for alpha-SMA and collagen I in immunohistochemically stained specimens. In summary, this study revealed a functional tumor environment of murine origin in patient-derived xenografts of pancreatic cancer and furthermore an apparently inherent resistance of this stromal tissue towards conventional therapy. Thus, targeting the tumor microenvironment should be implicated into clinical decisions. Citation Format: Diana Behrens, Ulrike Pfohl, Britta Buttner, Jens Hoffmann, Wolfgang Walther, Iduna Fichtner. Analysis of murine stromal components in patient-derived xenograft (PDX) models of pancreatic cancer. [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 4080.