Endocrine-Exocrine Signaling Drives Obesity-Associated Pancreatic Ductal Adenocarcinoma

Obesity is a major modifiable risk factor for pancreatic ductal adenocarcinoma (PDAC), yet how and when obesity contributes to PDAC progression is not well understood. Leveraging an autochthonous mouse model, we demonstrate a causal and reversible role for obesity in early PDAC progression, showing that obesity markedly enhances tumorigenesis, while genetic or dietary induction of weight loss intercepts cancer development. Molecular analyses of human and murine samples define microenvironmental consequences of obesity that foster tumorigenesis rather than new driver gene mutations, including significant pancreatic islet cell adaptation in obesity-associated tumors. Specifically, we identify aberrant beta cell expression of the peptide hormone cholecystokinin (Cck) in response to obesity and show that islet Cck promotes oncogenic Kras-driven pancreatic ductal tumorigenesis. Our studies argue that PDAC progression is driven by local obesity-associated changes in the tumor microenvironment and implicate endocrine-exocrine signaling beyond insulin in PDAC development.

Abstract A35: Microenvironmental adaptations drive obesity-associated pancreatic cancer

Obesity is a major modifiable risk factor for pancreatic ductal adenocarcinoma (PDAC), yet how obesity contributes to pancreatic cancer development is not well understood. Moreover, whether and at what point weight loss or other obesity-related interventions may impact PDAC progression remains largely unexplored, with significant implications for prevention and treatment. Leveraging an autochthonous genetically engineered model of PDAC, we demonstrate that obesity plays a stage-specific causal and reversible role in early PDAC progression. Molecular and histologic analyses reveal prominent microenvironmental alterations in tumors from obese mice, including increased inflammation and fibrosis and evidence for marked pancreatic islet cell adaptation. In particular, we identify aberrant expression of the peptide hormone cholecystokinin (CCK) in pancreatic islets in tumors as an adaptive response to obesity and show that islet CCK expression promotes oncogenic Kras-driven pancreatic ductal tumorigenesis. Together, these studies link obesity, changes in the local microenvironment, and tumorigenesis and implicate islet-derived hormones beyond insulin in PDAC development. Furthermore, the reversible nature of these adaptations supports the potential of antiobesity strategies to intercept PDAC early during progression.

Citation Format: Katherine Minjee Chung, Jaffarguribal Singh, Lauren Lawres, Kimberly Judith Dorans, Rebecca Robbins, Arjun Bhutkar, Ana Babic, Sara A. Vayrynen, Andressa D. Costa, Jonathan A. Nowak, Daniel T. Chang, Richard F. Dunne, Aram F. Hezel, Albert C. Koong, Joshua J. Wilhelm, Melena D. Bellin, Vibe Nylander, Anna L. Gloyn, Mark I. McCarthy, Brian M. Wolpin, Tyler Jacks, Charles S. Fuchs, Mandar Deepak Muzumdar. Microenvironmental adaptations drive obesity-associated pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A35.

Abstract A05: Investigating mechanisms of obesity-mediated pancreatic cancer progression

Genetically engineered mouse models (GEMMs) that faithfully recapitulate the genetics and histology of human tumors are an underutilized tool to understand how modifiable risk factors influence tumor development. Prospective cohort studies have shown that obesity is associated with an increased risk of developing pancreatic cancer, more advanced disease at diagnosis, and worse survival, though the precise mechanisms behind which obesity contributes to cancer progression remain elusive. We crossed mice harboring loss-of-function mutations in the leptin gene (ob/ob) with Pdx1-Cre; LSL-KrasG12D (KC) mice predisposed to initiate pancreatic cancers. KC; ob/ob mice are obese and exhibit markedly shortened survival (~4 months vs. ~1 year), increased primary tumor burden, and enhanced progression to adenocarcinoma compared to nonobese KC mice. Interestingly, early correction of leptin deficiency using an adeno-associated virus (AAV)-based approach induces rapid normalization of body weight and hyperglycemia and completely prevents the emergence of enhanced tumor burden. In contrast, late leptin restoration following tumor progression does not impact survival. These data suggest a causal and reversible role for obesity in early pancreatic cancer progression. Furthermore, by evaluating the degree by which alternative interventions phenocopy the effects of leptin restoration, we have developed a model to rapidly interrogate mechanisms of obesity-mediated tumor progression. As a proof of principle, we have tested the ability of immunomodulatory (aspirin) and antidiabetic (metformin) agents, observed to impact pancreatic cancer risk and survival in human cohorts, to intercept cancer progression in this model. Finally, combined molecular and biochemical analyses of tumors reveal increased immune cell activation and fibrosis in KC; ob/ob mice compared to nonobese KC and KC; p53 mutant mice and provide specific molecular targets to evaluate for pancreatic cancer therapy and prevention.

Citation Format: Mandar Deepak Muzumdar, Kimberly Judith Dorans, Katherine Minjee Chung, Arjun Bhutkar, Charles Fuchs, Tyler Jacks. Investigating mechanisms of obesity-mediated pancreatic cancer progression [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A05.

Adaptive and Reversible Resistance to Kras Inhibition in Pancreatic Cancer Cells

Activating mutations in KRAS are the hallmark genetic alterations in pancreatic ductal adenocarcinoma (PDAC) and the key drivers of its initiation and progression. Longstanding efforts to develop novel KRAS inhibitors have been based on the assumption that PDAC cells are addicted to activated KRAS, but this assumption remains controversial. In this study, we analyzed the requirement of endogenous Kras to maintain survival of murine PDAC cells, using an inducible shRNA-based system that enables temporal control of Kras expression. We found that the majority of murine PDAC cells analyzed tolerated acute and sustained Kras silencing by adapting to a reversible cell state characterized by differences in cell morphology, proliferative kinetics, and tumor-initiating capacity. While we observed no significant mutational or transcriptional changes in the Kras-inhibited state, global phosphoproteomic profiling revealed significant alterations in cell signaling, including increased phosphorylation of focal adhesion pathway components. Accordingly, Kras-inhibited cells displayed prominent focal adhesion plaque structures, enhanced adherence properties, and increased dependency on adhesion for viability in vitro Overall, our results call into question the degree to which PDAC cells are addicted to activated KRAS, by illustrating adaptive nongenetic and nontranscriptional mechanisms of resistance to Kras blockade. However, by identifying these mechanisms, our work also provides mechanistic directions to develop combination strategies that can help enforce the efficacy of KRAS inhibitors.Significance: These results call into question the degree to which pancreatic cancers are addicted to KRAS by illustrating adaptive nongenetic and nontranscriptional mechanisms of resistance to Kras blockade, with implications for the development of KRAS inhibitors for PDAC treatment. Cancer Res; 78(4); 985-1002. ©2017 AACR.

Clonal dynamics following p53 loss of heterozygosity in Kras-driven cancers

Although it has become increasingly clear that cancers display extensive cellular heterogeneity, the spatial growth dynamics of genetically distinct clones within developing solid tumours remain poorly understood. Here we leverage mosaic analysis with double markers (MADM) to trace subclonal populations retaining or lacking p53 within oncogenic Kras-initiated lung and pancreatic tumours. In both models, p53 constrains progression to advanced adenocarcinomas. Comparison of lineage-related p53 knockout and wild-type clones reveals a minor role of p53 in suppressing cell expansion in lung adenomas. In contrast, p53 loss promotes both the initiation and expansion of low-grade pancreatic intraepithelial neoplasia (PanINs), likely through differential expression of the p53 regulator p19ARF. Strikingly, lineage-related cells are often dispersed in lung adenomas and PanINs, contrasting with more contiguous growth of advanced subclones. Together, these results support cancer type-specific suppressive roles of p53 in early tumour progression and offer insights into clonal growth patterns during tumour development.

Using mosaic analysis with double markers to label genetically-distinct clones in established tumors, the authors studied the effects of p53 loss in lung and pancreatic cancers. They find that loss of p53 enhances progression in both models but only influences initiation in the pancreas.