Abstract 3139: Innate immune cells expressing myeloperoxidase directly inhibit tumor NF-κB transcriptional activation during tumor initiation

Abstract

Abstract Neutrophils are considered the primary defenders of the innate immune system. However, in the context of cancer, the role of neutrophils is complex where they can be host protecting or pro-tumorigenic. For example, myeloperoxidase (MPO), the major protein in neutrophils, produces reactive oxygen species (ROS); ROS can lead to tumor regression from cell cytotoxicity or cause DNA-damage resulting in genetic mutations triggering tumor initiation/progression. Using the melanoma cell lines, B16F10, stably expressing a NF-κB-driven Firefly luciferase (FLuc) reporter or an IκBα-FLuc fusion reporter gene, co-culture studies in vitro with bone marrow-isolated-neutrophils from C57BL/6 animals demonstrated inhibition of NF-κB transcriptional activation in a MPO activity-dependent manner. Using bioluminescence imaging with luminol, neutrophils pre-stimulated with 50uM phorbol myristate acetate (PMA) demonstrated an increase in MPO activity by 20.3 ± 2.4 fold over unstimulated neutrophils. When B16F10 reporter cells were co-cultured with PMA pre-stimulated neutrophils, we observed inhibition of IκBα degradation by 33.0% ± 11.9%, resulting in a decrease in NF-κB transcriptional activation compared to co-culture studies with unstimulated neutrophils. The role of neutrophils during B16F10 tumor initiation and growth was compared in C57BL/6 and syngeneic MPO-null mice. Utilizing intravital imaging with skinfold window chamber animal models and imaging reporters, we evaluated in real-time, the recruitment of MPO-expressing cells and tumor NF-κB activation in vivo. Mean NF-κB transcriptional activation within the tumor compartment in MPO-null mice was 42.2% ± 1.6% greater compared to wild type animals. Tumor growth and survival curves demonstrated that B16F10 tumors grew slower in wild-type animals (mean survival of 26.8 days) compared to MPO-null animals (mean survival time of 23.4 days). Using an MPO inhibitor, 4-aminobenzoic acid hydrazide (4-ABAH), we pharmacologically mimicked the MPO-null phenotype in C57BL/6 animals (40mg/kg intraperitoneal injection twice daily). B16F10 tumors grew slower in C57BL/6 animals treated with 4-ABAH (mean survival of 23.8 days) compared to wild type animals. Taken together, these data demonstrated that MPO-expressing cells contribute to host protection during tumor initiation in a NF-κB-dependent manner. Citation Format: Tracy W. Liu, Seth T. Gammon, David Piwnica-Worms. Innate immune cells expressing myeloperoxidase directly inhibit tumor NF-κB transcriptional activation during tumor initiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3139.