The Role of HIF2 in Pancreatic Ductal Adenocarcinoma

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PROJECT SUMMARY/ABSTRACT Pancreatic ductal adenocarcinoma (PDAC) contains a desmoplastic stroma that limits blood perfusion and thus the delivery of nutrients, oxygen, and therapeutics, creating a hypoxic microenvironment that is able to resist nearly all forms of treatment, including immunomodulating therapy. Cancer-associated fibroblasts (CAFs) are the main components and producers of stroma in PDAC. The hypoxia-inducible factors-1 (HIF1) and -2 (HIF2) are stabilized in low oxygen and have been hypothesized to mediate therapeutic resistance and aggressive growth of PDAC, but deletion of HIF1 or HIF2 in the pancreatic epithelial compartment produced no obvious phenotype in PDAC. Thus, we reasoned that HIF may instead be supporting PDAC pathobiology through its functions in cancer-associated fibroblasts (CAFs), which are the other major cellular component in pancreatic tumors. Since little was known about the role of HIF in the stromal compartment, we created a mouse model that exploits two recombinases enabling us complete spatiotemporal control of tumor growth and HIF ablation in CAFs. Using this model, we found that the abrogation of HIF2 in CAFs decreased tumor growth and doubled the median survival of animals with pancreatic cancer. The loss of HIF2 in CAFs correlated with fewer intratumoral M2 macrophages and regulatory T cells. Furthermore, conditioned media from hypoxic CAFs produced similar effects in ex vivo assays even after boiling. These preliminary data suggested a HIF2- dependent crosstalk between CAF and the immune compartment that may be critical to the ability of PDAC to evade the immune system. Building on this preliminary data, we propose to identify the molecular mechanisms that allow hypoxic CAFs to modulate the immune microenvironment of pancreatic cancer through three aims. In Aim 1, we will determine the molecular mediators of HIF2-dependent crosstalk between CAFs and macrophages. We will use mass spectrometry to identify the HIF2 dependent factor secreted from CAFs capable of inducing M2 polarization in macrophages and determine how this factor is produce in CAFs and how it alters macrophage function. Aim 2 will define the HIF2-dependent relationships between CAFs and T lymphocytes. We will explore how CD8+ suppression and Treg conversion is regulated by HIF2 signaling in CAFs using mouse models and co-culture methods. Lastly, in Aim 3, we will repurpose HIF2 inhibitors from their current indications in renal cell carcinoma to pancreatic cancer as a drug to enhance immunotherapy responses. The proposed research is significant because pancreatic cancer does not respond to immunotherapy, and our data suggests that HIF2 inhibition may greatly improve immune responses. This research is innovative because we will provide the first description of the immune-targeting molecular pathways activated by hypoxic microenvironment in PDAC. Further, we will offer the first mechanistic evaluation of a potential therapeutic combination using a HIF2 inhibitor along with immune checkpoint blockade as the first steps towards clinical translation.