Chemoprevention of Aflatoxin B1‐Induced Cytokine Storm and Tumor Dormancy Escape via Dual COX‐2/sEH Inhibition

Abstract

Inflammation plays a critical role in stimulating tumor growth, invasion and metastasis. Hepatocellular carcinoma (HCC), the most common primary liver malignancy worldwide is usually resistant to treatment and arises most frequently in the setting of chronic inflammation. A critical underlying cause of HCC other tumor‐types includes exposure to toxic environmental carcinogens. Aflatoxin B1 (AFB1), a mycotoxin produced by Aspergillus fungi, is a contaminant in a large portion of the world’s food supply. While AFB1 causes cancer presumably via genotoxic mechanisms by inducing DNA adducts, potential non‐genotoxic mechanisms of aflatoxin‐induced cancer remain poorly characterized. Cytotoxic drugs generate apoptotic cell death (“debris”), which may promote the growth of residual surviving cancer cells via inflammation. The cytotoxic aflatoxins stimulate apoptosis of multiple cell types including hepatocytes, thymocytes, and epithelial cells via increased apoptotic caspases and pro‐inflammatory cytokines (e.g. TNF‐α). As over 30–90% of individuals harbor dormant microscopic tumors, we hypothesized that AFB1 generated debris may stimulate tumor dormancy escape via pro‐inflammatory and pro‐angiogenic cytokines. Here we demonstrate that hepatocellular cancer and non‐cancer debris generated by AFB1 accelerates tumor dormancy escape by stimulating a macrophage‐derived “storm” of pro‐inflammatory cytokines and bioactive lipids. Targeting multiple inflammatory mediators simultaneously is a desired therapeutic strategy but is challenging to achieve. CYP450‐derived epoxyeicosatrienoic acids (EETs) promote the clearance of cellular debris by local macrophages and activate anti‐inflammatory programs. EETs are rapidly metabolized in the body by soluble epoxide hydrolase (sEH), but inhibition of sEH can stabilize EETs and promote the resolution of inflammation. Combined pharmacological abrogation of the cyclooxygenase‐2 (COX‐2) and soluble epoxide hydrolase (sEH) pathways (e.g. PTUPB) prevented the debris‐induced storm of both cytokines and lipid mediators. Dual COX2/sEH inhibition also stimulated macrophage phagocytosis of AFB1‐generated cell debris. AFB1 debris induced oxidative stress and reactive oxygen species were counter‐regulated by dual COX2/sEH inhibition. In animal models, the dual COX‐2/sEH inhibitor PTUPB prevented the onset of debris‐stimulated liver cancer tumor growth leading to sustained survival. Thus, carcinogen generated tumor cell debris triggers a “cytokine storm” providing a potential mechanism whereby environmental substances harbor the potential to stimulate or induce tumor initiation, growth, and/or metastasis. Enhancing clearance of cell debris via dual COX2/sEH inhibition represents a novel approach to prevent carcinogen‐induced tumor growth and recurrence.