Abstract 3546: DFMO based improvement in survival of pancreatic cancer-bearing mice is associated with modulation of immune suppression in the tumor microenvironment

Existing therapeutics have failed to improve pancreatic ductal adenocarcinoma (PDAC) patient outcomes, in part due to tumor associated immune suppression and upregulation of compensatory mechanisms. KRAS and c-MYC are important oncogenes in PDAC linked to tumor immune suppression. We describe the use of difluoromethylornithine (DFMO) and a c-RAF inhibitor (GW5074) to indirectly target c-MYC and KRAS, respectively. DFMO in combination with GW5074 was tested for ability to improve pancreatic cancer outcomes. Pancreatic cancer cells showed decreased cell viability and increased apoptosis in response to a combination of DFMO + GW5074. In vivo orthotopic models of pancreatic tumors had decreased tumor weight in DFMO + GW5074 treated mice, when compared to control group. However, only treatment with single agent DFMO resulted in improved survival of immunocompetent pancreatic tumor bearing mice with respect to control, in contrast to treatment with GW5074 alone or DFMO + GW5074. To understand why the in vivo data was contrary to in vitro results, immunohistochemical analysis of immune cells in the tumor microenvironment was used to reveal increased expression of markers associated with anti-tumor effects such as CD86, CD3, CD4 and CD8 in DFMO treated tumors. Tumors treated with DFMO also displayed decreased expression of MYC, suggesting that DFMO-associated MYC suppression could be linked to decreased immune suppression in the tumor microenvironment and improved survival. In contrast, GW5074 treatment maintained MYC expression in tumors. Overall, the present study points to DFMO being an immunomodulatory agent, and a need for further understanding of DFMO-based therapeutic strategies in PDAC.

Citation Format: Sai Preethi Nakkina, Sarah B. Gitto, Jordan M. Beardsley, Veethika Pandey, Michael M. Rohr, Jignesh Parikh, Otto Phanstiel, Deborah A. Altomare. DFMO based improvement in survival of pancreatic cancer-bearing mice is associated with modulation of immune suppression in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3546.

Induction of pancreatitis in mice with susceptibility to pancreatic cancer

Chronic inflammation is known to be associated with pancreatic cancer, however a complete picture regarding how these pathologies intersect is still being characterized. In vivo model systems are critical for the study of mechanisms underlying how inflammation accelerates neoplasia. Repeat injection of cerulein, a cholecystokinin (CCK) analog, is widely used to experimentally induce acute and chronic pancreatitis in vivo. Chronic cerulein administration into genetically engineered mouse models (GEMMs) with predisposition to pancreatic cancer can induce a pro-inflammatory immune response, pancreatic acinar cell damage, pancreatic stellate cell activation, and accelerate the onset of neoplasia. Here we provide a detailed protocol and insights into using cerulein to induce pancreatitis in GEMMs, and methods to experimentally assess inflammation and pancreatic neoplasia.

Identification of a novel IL-5 signaling pathway in chronic pancreatitis and crosstalk with pancreatic tumor cells

BACKGROUND

While inflammation is associated with pancreatic cancer, the underlying mechanisms leading to cancer initiation are still being delineated. Eosinophils may promote or inhibit tumor growth, although the specific role in pancreatic cancer has yet to be determined. Eosinophil-supporting cytokine interleukin-5 and receptor are likely to have a role, but the significance in the pancreatic cancer microenvironment is unknown.

METHODS

Genetically engineered Akt1^Myr/KRas^G12D and KRas^G12D mice were used to model changes induced by chronic inflammation. Tissue samples were collected to analyze the tumor microenvironment and infiltration of immune cells, whereas serum was collected to analyze cytokine and amylase activity in the inflammatory model. The expression of IL-5R and the effects of IL-5 were analyzed in human and murine tumor cells.

RESULTS

Compound Akt1^Myr/KRas^G12D mice, compared to single KRas^G12D or Akt1^Myr mice, exhibited increased tissue damage after repeat inductions of inflammation, and had accelerated tumor development and metastasis. M2 macrophages and newly identified eosinophils co-localized with fibrotic regions rather than infiltrating into tumors, consistent with immune cell privilege. The majority of eosinophils found in the pancreas of Akt1^Myr/KRas^G12D mice with chronic inflammation lacked the cytotoxic NKG2D marker. IL-5 expression was upregulated in pancreatic cells in response to inflammation, and then diminished in advanced lesions. Although not previously described in pancreatic tumors, IL-5Rα was increased during mouse pancreatic tumor progression and expressed in human pancreatic ductal adenocarcinomas (7 of 7 by immunohistochemistry). IL-5 stimulated tumor cell migration and activation through STAT5 signaling, thereby suggesting an unreported tumor-promoting role for IL-5Rα in pancreatic cancer.

CONCLUSIONS

Chronic inflammation induces increased pancreatic cancer progression and immune cells such as eosinophils are attracted to areas of fibrosis. Results suggest that IL-5 in the pancreatic compartment stimulates increased IL-5Rα on ductal tumor cells to increase pancreatic tumor motility. Collectively, IL-5/IL-5Rα signaling in the mouse and human pancreatic tumors microenvironment is a novel mechanism to facilitate tumor progression. Additional file 1: Video Abstract.

PRIMARY CARCINOMA OF THE LUNG IN A CHILD

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