The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences Dissertations and Theses (Open Access)
The Role of the Hypoxia-Inducible Factor 2 in Pancreatic Cancer: Mechanisms of Tumor Immunosuppression and Intestinal Radioprotection
Author ORCID Identifier
Date of Graduation
Doctor of Philosophy (PhD)
Cullen M. Taniguchi, MD, PhD
Noah F. Shroyer, PhD
Jessica L. Bowser, PhD
Eduardo Vilar-Sánchez, MD, PhD
Jae-Il Park, PhD
Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with dismal prognosis. The only curative option for patients is surgery, but over 80% of patients are not surgical candidates. Unfortunately, PDAC is resistant to the three remaining options. PDAC is characterized by a profoundly hypoxic and immunosuppressive stroma, which contributes to its therapeutic recalcitrance. Alpha-smooth muscle actin+ (αSMA+) cancer-associated fibroblasts (CAFs) are the most abundant stromal component, as well as mediators of stromal deposition. The hypoxia-inducible factors (HIF1 and HIF2) coordinate responses to hypoxia, yet, despite their known association to poor patient outcomes, their functions within the PDAC tumor microenvironment (TME) remain unknown. This dissertation examines the roles of the HIFs in PDAC with the objective of exploiting this tumor’s profoundly hypoxic status to improve immunotherapy and radiotherapy.
We used a dual recombinase mouse model that developed autochthonous PDAC and restricted the deletion of HIFs to αSMA+ CAFs. Interestingly, CAF-specific deletion of Hif2a, but not Hif1a, suppressed tumor growth and significantly improved survival. Moreover, deletion of Hif2α in CAFs decreased the recruitment of immunosuppressive macrophages and regulatory T cells and increased the presence of effector immune cells in tumors. CAF treatment with PT2399, a clinically relevant HIF2 inhibitor, significantly reduced macrophage chemotaxis and M2 polarization, and improved responses to checkpoint immunotherapy in two syngeneic mouse models. Together, these data suggest that stromal HIF2 is an essential component of PDAC and is a druggable therapeutic target that could relieve TME immunosuppression and enhance immunotherapy responses in this disease.
Moreover, radiotherapy for PDAC is challenging because of its proximity to the exquisitely radiosensitive small intestine (SI). Our group previously showed that HIF2 stabilization protects against SI radiotoxicity in mice, but the mechanisms behind this remain elusive. Since PDAC displays maximal stabilization of the HIFs, we hypothesized that HIF2’s regenerative function in the SI can be exploited to reduce toxicities while optimizing radiotherapy. We overexpressed HIF2 in SI organoids and found that Wnt5a was among the top upregulated transcripts. Luciferase reporter assays showed that HIF2 directly activates the WNT5A promoter via a hypoxia response element. Furthermore, through knockout and rescue experiments, we found that Wnt5a is necessary and sufficient for SI radioprotection. Together, our results suggest that HIF2 radioprotects the SI, at least in part, by inducing Wnt5a expression.
Hypoxia, Pancreatic Cancer, Tumor Microenvironment, Cancer-Associated Fibroblasts, Tumor-Associated Macrophages, Immunotherapy, Intestinal Stem Cells, Wnt5a, Radiotherapy, Radiation Enteritis
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