Abstract 987: Nrf2-dependent HO-1 positive macrophages accumulate in murine models of KRAS-mutated pancreatic cancer and promote tumorigenesis
Authors: Leal Ana S. Mendes , Liby Karen T. 
Published: September 2020

The Nrf2 (NF-E2-related factor-2) transcription factor regulates oxidative/xenobiotic stress responses and can drive cancer progression, metastasis and chemoresistance. Nrf2 also attenuates inflammation through elimination of reactive oxygen species (ROS) and regulation of macrophage specific genes involved in oxidative/stress responses. The tumor microenvironment in pancreatic cancer is rich in macrophages that promote cancer progression and chemoresistance. Recent studies suggest that HO-1 positive macrophages are immunosuppressive, however the role of these macrophages in tumor progression and metastasis is not known. We hypothesized that the activation of Nrf2-dependent macrophages expressing HO-1 in the pancreas is essential for tumor development and metastasis.Heme-oxygenase 1 (HO-1) is an inducible enzyme, classical expressed by anti-inflammatory macrophages, to degrade heme. HO-1 expression is dependent on the translocation of NRF2 to the nucleus and activation of redox-electrophilic stress genes. In RAW 267.4 cells or bone marrow derived macrophages stimulated with conditioned media from murine pancreatic cancer cells, HO-1 protein levels increased. In contrast, HO-1 expression in macrophages was not affected when these cells were treated with classical macrophage activators such as IL-6 and IL-4. Increased HO-1 protein expression was associated with higher NRF2 expression in the nuclear fraction.Pancreatitis, or inflammation of the pancreas, is a known risk factor for pancreatic cancer, as hereditary pancreatitis increases the lifetime risk of developing cancer by 40-50%. In mice, chronic or acute pancreatitis promotes mutant Kras-mediated development of pancreatic cancer. LSL-KrasG12D/+;Pdx-1-Cre (KC) and Nrf2 whole body knockout (KO) mice were stimulated with cerulean (75 ug/kg injected intra peritoneally, every hour for 8 hours for 2 consecutive days) to induce pancreatitis. Pancreatitis, human and murine, is associated with an increased infiltration of macrophages to the pancreas during the acute phase of the disease. After 72 hours post-cerulean stimulation, macrophage infiltration into the pancreas was analyzed by flow cytometry. KC mice showed a significantly (P&lt;0.05) higher infiltration of macrophages when compared with Nrf2 KO or wild type mice (51.1% vs 10.7% vs 21.5% of all immune cells in the pancreas). Additionally, pancreas of KC mice expressed higher levels of HO-1 protein when compared with NRF2 KO and wild-type mice. KrasG12D/+; Trp53R172H/+; Pdx-1-Cre (KPC) mice will succumb to pancreatic cancer at an average of 23 weeks of age. At 12 weeks of age, the levels of HO-1 in the pancreas are increased, promoting tumorigenesis. Additionally, the levels of HO-1 in the liver, one of the primary sites for metastasis, are increased at 20 weeks, surrounding early lesions. These studies suggest that Nrf2 activation in macrophages, which elevates HO-1 expression, is hijacked by Kras-mutated epithelial cells in order to promote tumorigenesis and metastasis.

Citation Format: Ana S. Mendes Leal, Karen T. Liby. Nrf2-dependent HO-1 positive macrophages accumulate in murine models of KRAS-mutated pancreatic cancer and promote tumorigenesis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 987.