The ß-TrCP-Mediated Pathway Cooperates with the Keap1-Mediated Pathway in Nrf2 Degradation In Vivo.

Nrf2 activates cytoprotective gene expression, and Nrf2 activity is regulated through at least two protein degradation pathways: the Keap1-mediated and ß-TrCP-mediated pathways. To address the relative contributions of these pathways, we generated knock-in mouse lines expressing an Nrf2SA mutant that harbored two substitution mutations of serine residues interacting with ß-TrCP. The homozygous (Nrf2SA/SA) mice grew normally, with Nrf2 levels comparable to those of wild-type (WT) mice under unstressed conditions. However, when Keap1 activity was suppressed, high levels of Nrf2 accumulated in Nrf2SA/SA macrophages compared with that in WT macrophages. We crossed Nrf2SA/SA mice with mice in which Keap1 was knocked down to two different levels. We found that the Nrf2SA/SA mutation induced higher Nrf2 activity when the Keap1 level was strongly reduced, and these mice showed severe growth retardation. However, activation and growth retardation were not evident when Keap1 was moderately suppressed. These increases in Nrf2 activity induced by the Nrf2SA mutation caused severe hyperplasia and hyperkeratosis in the esophageal epithelium but did not cause abnormalities in the other tissues/organs examined. These results indicate that the ß-TrCP-mediated pathway cooperates with the Keap1-mediated pathway to regulate Nrf2 activity, which is apparent when the Keap1-mediated pathway is profoundly suppressed.

Halofuginone micelle nanoparticles eradicate Nrf2-activated lung adenocarcinoma without systemic toxicity.

The Keap1-Nrf2 system is the master regulator of the cellular response against oxidative and xenobiotic stresses. Constitutive activation of Nrf2 is frequently observed in various types of cancers. Nrf2 hyperactivation induces metabolic reprogramming in cancer cells, which supports the increased energy demand required for rapid proliferation and confers high-level resistance against anticancer radio/chemotherapy. Hence, Nrf2 inhibition has emerged as an attractive therapeutic strategy to counter such acquired resistance in Nrf2-activated tumors. We previously identified Halofuginone (HF) as a promising Nrf2 inhibitor. In this study, we pursued preclinical characterization of HF and found that while HF markedly reduced the viability of cancer cells, it also caused severe hematopoietic and immune cell suppression in a dose-dependent manner. Hence, to overcome this toxicity, we decided to employ a nanomedicine approach to HF. We found that encapsulation of HF into a polymeric micelle (HF micelle; HFm) largely relieved the systemic toxicity exhibited by free HF while maintaining the tumor-suppressive properties of HF. LC-MS/MS analysis revealed that the reduction in the magnitude of adverse effects was the result of the ability to release HF from the HFm core in a slow and sustained manner. These results thus support the contention that HFm will potentially counteract Nrf2-activated cancers in the clinical settings.

Multifaceted Roles of the KEAP1-NRF2 System in Cancer and Inflammatory Disease Milieu.

In a multicellular environment, many different types of cells interact with each other. The KEAP1-NRF2 system defends against electrophilic and oxidative stresses in various types of cells. However, the KEAP1-NRF2 system also regulates the expression of genes involved in cell proliferation and inflammation, indicating that the system plays cell type-specific roles. In this review, we introduce the multifarious roles of the KEAP1-NRF2 system in various types of cells, especially focusing on cancer and inflammatory diseases. Cancer cells frequently hijack the KEAP1-NRF2 system, and NRF2 activation confers cancer cells with a proliferative advantage and therapeutic resistance. In contrast, the activation of NRF2 in immune cells, especially in myeloid cells, suppresses tumor development. In chronic inflammatory diseases, such as sickle cell disease, NRF2 activation in myeloid and endothelial cells represses the expression of proinflammatory cytokine and adherent molecule genes, mitigating inflammation and organ damage. Based on these cell-specific roles played by the KEAP1-NRF2 system, NRF2 inducers have been utilized for the treatment of inflammatory diseases. In addition, the use of NRF2 inducers and/or inhibitors with canonical antineoplastic drugs is an emerging approach to cancer treatment.

Microenvironmental Activation of Nrf2 Restricts the Progression of Nrf2-Activated Malignant Tumors.

The transcription factor Nrf2 activates transcription of cytoprotective genes during oxidative and electrophilic insults. Nrf2 activity is regulated by Keap1 in a stress-dependent manner in normal cells, and somatic loss-of-function mutations of Keap1 are known to induce constitutive Nrf2 activation, especially in lung adenocarcinomas, conferring survival and proliferative benefits to tumors. Therefore, several therapeutic strategies that aim to inhibit Nrf2 in tumors have been developed for the treatment of Nrf2-activated cancers. Here we addressed whether targeting Nrf2 activation in the microenvironment can suppress the progression of Nrf2-activated tumors. We combined two types of Keap1-flox mice expressing variable levels of Keap1 with a Kras-driven adenocarcinoma model to generate Keap1-deficient lung tumors surrounded by normal or Keap1-knockdown host cells. In this model system, activation of Nrf2 in the microenvironment prolonged the survival of Nrf2-activated tumor-bearing mice. The Nrf2-activated microenvironment suppressed tumor burden; in particular, preinvasive lesion formation was significantly suppressed. Notably, loss of Nrf2 in bone marrow-derived cells in Nrf2-activated host cells appeared to counteract the suppression of Nrf2-activated cancer progression. Thus, these results demonstrate that microenvironmental Nrf2 activation suppresses the progression of malignant Nrf2-activated tumors and that Nrf2 activation in immune cells at least partially contributes to these suppressive effects. SIGNIFICANCE: This study clarifies the importance of Nrf2 activation in the tumor microenvironment and in the host for the suppression of malignant Nrf2-activated cancers and proposes new cancer therapies utilizing inducers of Nrf2.

Dietary supplementation with sulforaphane attenuates liver damage and heme overload in a sickle cell disease murine model.

Sickle cell disease (SCD) is a recessively inherited blood disorder caused by abnormal ß-globin production. The ß-globin mutation changes erythrocyte morphology into a sickle shape and increases erythrocyte vulnerability to hemolysis. Oxidative stress and concomitant inflammation eventually result in damage to multiple organs. Nrf2 is a master regulator of the oxidative stress response, homeostasis, and metabolism. Keap1 modulates Nrf2 protein levels; Nrf2 inducers alter nuclear Nrf2 levels by interacting with Keap1. Genetic modification of Keap1 helps to reduce inflammation and tissue damage in SCD model mice through Nrf2 induction. Here, we investigated the benefits of a mild and safe Nrf2 agonist, sulforaphane (SFN), in ameliorating SCD pathology in a murine model. SFN is a phytochemical and is found in cruciferous vegetables as its inert precursor, glucoraphanin. We found that dietary SFN administration for 14 days or 2 months increased the expression of Nrf2-dependent cytoprotective genes, but SFN uptake did not have deleterious effects on the food consumption and growth of SCD model mice. SFN ameliorated the liver damage of SCD mice, which could be validated by the rescue of liver function and the significantly reduced liver necrotic area. SFN administration also helped to eliminate heme released from lysed sickle cells. These results indicate that dietary supplementation with SFN relieves SCD symptoms by inducing Nrf2 and support our contention that SFN is a potential drug for the long-term treatment of children with SCD.

Nrf2 activation in myeloid cells and endothelial cells differentially mitigates sickle cell disease pathology in mice.

Sickle cell disease (SCD) is caused by a monogenic mutation of the ß-globin gene and affects millions of people worldwide. SCD is associated with sustained hemolytic anemia, vasoocclusion, ischemia-reperfusion injury, oxidative tissue damage, inflammatory cell activation, and systemic endothelial dysfunction. The transcription factor Nrf2 coordinates the expression of a wide variety of genes encoding antioxidant, detoxification, and metabolic enzymes. Nrf2 participates in suppressing proinflammatory cytokines and organ protection in SCD. However, little is known regarding the mechanisms by which Nrf2 ameliorates SCD pathology or how some cells respond to Nrf2 stimuli to alleviate SCD pathology. Here, we asked whether monocytes/granulocytes and/or endothelial cells are particularly critical in alleviating the pathology of SCD. By targeting these cells with a Cre recombinase system, we generated SCD::Keap1F/F::LysM-Cre and Tie1-Cre mice with constitutive Nrf2 activation in monocytes/granulocytes and endothelial cells, respectively. Analyses of SCD::Keap1F/F::LysM-Cre and SCD::Keap1F/F::Tie1-Cre mice revealed significantly reduced inflammation, along with decreased white blood cell counts and lower Tnfα and Il1ß expression in the lungs. Notably, SCD::Keap1F/F::LysM-Cre mice exhibited reduced heme distribution in the liver, consistent with a decrease in the damaged areas. Vascular function in SCD::Keap1F/F::Tie1-Cre mice was significantly improved, with a 50% decrease in vascular leakage and low expression of the adhesion molecules Vcam1 and P-selectin. Thus, Nrf2 activation in monocytes/granulocytes and endothelial cells contributes differentially and cooperatively to the improvement of SCD pathology.