Oncogenic mutations in KEAP1 disturbing inhibitory Nrf2-Keap1 interaction: Activation of antioxidative pathway in papillary thyroid carcinoma

A NRF2 inhibitor selectively sensitizes KEAP1 mutant tumor cells to cisplatin and gefitinib by restoring NRF2-inhibitory function of KEAP1 mutants

NRF2 (nuclear factor erythroid 2-related factor 2) is a master regulator of protective responses in healthy tissues. However, when it is active in tumor cells, it can result in drug resistance. KEAP1, the endogenous NRF2 inhibitor, binds NRF2 and redirects it to proteasomal degradation, so the KEAP1/NRF2 interaction is critical for maintaining NRF2 at a basal level. A number of clinically relevant KEAP1 mutations were shown to disrupt this critical KEAP1/NRF2 interaction, leading to elevated NRF2 levels and drug resistance. Here, we describe a small-molecule NRF2 inhibitor, R16, that selectively binds KEAP1 mutants and restores their NRF2-inhibitory function by repairing the disrupted KEAP1/NRF2 interactions. R16 substantially sensitizes KEAP1-mutated tumor cells to cisplatin and gefitinib, but does not do so for wild-type KEAP1 cells, and sensitizes KEAP1 G333C-mutated xenograft to cisplatin. We developed a BRET2-based biosensor system to detect the KEAP1/NRF2 interaction and classify KEAP1 mutations. This strategy would identify drug-resistant KEAP1 somatic mutations in clinical molecular profiling of tumors.

Nrf2 as a novel diagnostic biomarker for papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most common thyroid malignancy. However, it is very difficult to distinguish PTC from benign carcinoma. Thus, specific diagnostic biomarkers are actively pursued. Previous studies observed that Nrf2 was highly expressed in PTC. Based on this research, we hypothesized that Nrf2 may serve as a novel specific diagnostic biomarker. A single-center retrospective study, including 60 patients with PTC and 60 patients with nodular goiter, who underwent thyroidectomy at the Central Theater General Hospital from 2018 to July 2020, was conducted. The clinical data of the patients were collected. Nrf2, BRAF V600E, CK-19, and Gal-3 proteins were compared from paraffin samples of the patients. Through this study, we obtained the following results: i) Nrf2 exhibits high abundance expression in PTC, but not in adjacent to PTC and nodular goiter; increased Nrf2 expression could serve as a valuable biomarker for PTC diagnosis; the sensitivity and specificity for the diagnosis of PTC were 96.70% and 89.40%, respectively. ii) Nrf2 also shows higher expression in PTC with lymph node metastasis, but not adjacent to PTC and nodular goiter, thus the increased Nrf2 expression might serve as a valuable predictor for lymph node metastasis in PTC patients; the sensitivity and specificity for the prediction in lymph node metastasis were 96.00% and 88.57%, respectively; excellent diagnostic agreements were found between Nrf2 and other routine parameters including HO-1, NQO1 and BRAF V600E. iii) The downstream molecular expression of Nrf2 including HO-1 and NQO1 consistently increased. In conclusion, Nrf2 displays a high abundance expression in human PTC, which leads to the higher expression of downstream transcriptional proteins: HO-1 and NQO1. Moreover, Nrf2 can be used as an extra biomarker for differential diagnosis of PTC and a predictive biomarker for lymph node metastasis of PTC.

Incidental Node Metastasis as an Independent Factor of Worse Disease-Free Survival in Patients with Papillary Thyroid Carcinoma

INTRODUCTION

Papillary thyroid carcinoma (PTC) have high node metastasis rates. Occasionally after thyroidectomy, the pathological report reveals node metastasis unintentionally resected. The present study aimed to evaluate the prognosis of these patients.

METHODS

A retrospective cohort of patients submitted to thyroidectomy with or without central compartment neck dissection (CCND) due to PTC with a minimum follow-up of five years.

RESULTS

A total of 698 patients were included: 320 Nx, 264 pN0-incidental, 37 pN1a-incidental, 32 pN0-CCND and 45 pN1a-CCND. Patients with node metastasis were younger, had larger tumors, higher rates of microscopic extra-thyroidal extension, and angiolymphatic invasion and most received radioiodine therapy. Treatment failure was higher in patients pN1a-incidental and pN1a-CCND (32% and 16%, respectively; p < 0.001-Chi-square test). Disease-free survival (DFS) was lower in patients pN1a-incidental compared to patients Nx and pN0-incidental (p < 0.001 vs. Nx and pN0-incidental and p = 0.005 vs. pN0-CCND) but similar when compared to patients pN1a-CCND (p = 0.091)-Log-Rank test. Multivariate analysis demonstrated as independent risk factors: pT4a (HR = 5.524; 95%CI: 1.380-22.113; p = 0.016), pN1a-incidental (HR = 3.691; 95%CI: 1.556-8.755; p = 0.003), microscopic extra-thyroidal extension (HR = 2.560; 95%CI: 1.303-5.030; p = 0.006) and angiolymphatic invasion (HR = 2.240; 95%CI: 1.077-4.510; p = 0.030).

CONCLUSION

Patients that were pN1a-incidental were independently associated with lower DFS.

The Knockdown of Nrf2 Suppressed Tumor Growth and Increased the Sensitivity to Lenvatinib in Anaplastic Thyroid Cancer

Papillary thyroid cancer can dedifferentiate into a much more aggressive form of thyroid cancer, namely into anaplastic thyroid cancer. Nrf2 is commonly activated in papillary thyroid cancer, whereas its role in anaplastic thyroid cancer has not been fully explored. In this study, we used two cell lines and an animal model to examine the function of Nrf2 in anaplastic thyroid cancer. The role of Nrf2 in anaplastic thyroid cancer was investigated by a series of functional studies in two anaplastic thyroid cancer cell lines, FRO and KAT-18, and further confirmed with an in vivo study. The impact of Nrf2 on the sensitivity of anaplastic thyroid cancer cells to lenvatinib was also investigated to evaluate its potential clinical implication. We found that the expression of Nrf2 was significantly higher in anaplastic thyroid cancer cell line cells than in papillary thyroid cancer cells or normal control cells. Knockdown of Nrf2 in anaplastic thyroid cancer cells inhibited their viability and clonogenicity, reduced their migration and invasion ability in vitro, and suppressed their tumorigenicity in vivo. Mechanistically, knockdown of Nrf2 decreased the expression of Notch1. Lastly, knockdown of Nrf2 increased the sensitivity of anaplastic thyroid cancer cells to lenvatinib. As knockdown of Nrf2 reduced the metastatic and invasive ability of anaplastic thyroid cancer cells by inhibiting the Notch 1 signaling pathway and increased the cancer cell sensitivity to lenvatinib, Nrf2 could be a promising therapeutic target for patients with anaplastic thyroid cancer.

Inhibition of the NRF2/KEAP1 Axis: A Promising Therapeutic Strategy to Alter Redox Balance of Cancer Cells

Significance: The nuclear factor erythroid 2-related factor 2/Kelch-like ECH-associated protein 1 (NRF2/KEAP1) pathway is a crucial and highly conserved defensive system that is required to maintain or restore the intracellular homeostasis in response to oxidative, electrophilic, and other types of stress conditions. The tight control of NRF2 function is maintained by a complex network of biological interactions between positive and negative regulators that ultimately ensure context-specific activation, culminating in the NRF2-driven transcription of cytoprotective genes. Recent Advances: Recent studies indicate that deregulated NRF2 activation is a frequent event in malignant tumors, wherein it is associated with metabolic reprogramming, increased antioxidant capacity, chemoresistance, and poor clinical outcome. On the other hand, the growing interest in the modulation of the cancer cells' redox balance identified NRF2 as an ideal therapeutic target. Critical Issues: For this reason, many efforts have been made to identify potent and selective NRF2 inhibitors that might be used as single agents or adjuvants of anticancer drugs with redox disrupting properties. Despite the lack of specific NRF2 inhibitors still represents a major clinical hurdle, the researchers have exploited alternative strategies to disrupt NRF2 signaling at different levels of its biological activation. Future Directions: Given its dualistic role in tumor initiation and progression, the identification of the appropriate biological context of NRF2 activation and the specific clinicopathological features of patients cohorts wherein its inactivation is expected to have clinical benefits, will represent a major goal in the field of cancer research. In this review, we will briefly describe the structure and function of the NRF2/ KEAP1 system and some of the most promising NRF2 inhibitors, with a particular emphasis on natural compounds and drug repurposing. Antioxid. Redox Signal. 34, 1428-1483.

Mice Hypomorphic for Keap1, a Negative Regulator of the Nrf2 Antioxidant Response, Show Age-Dependent Diffuse Goiter with Elevated Thyrotropin Levels

Background: Familial nontoxic multinodular goiter (MNG) is a rare disease. One of the associated genes is Kelch-like ECH-associated protein 1 (KEAP1), which encodes the main inhibitor of nuclear factor erythroid 2-related transcription factor 2 (Nrf2), a central mediator of antioxidant responses. The association of KEAP1 with familial MNG is based on only two loss-of-function mutations identified in two families, only one of which included proper phenotyping and adequate demonstration of co-segregation of the phenotype and the mutation. There is no experimental evidence from model organisms to support that decreased Keap1 levels can, indeed, cause goiter. This study used mice hypomorphic for Keap1 to test whether decreased Keap1 expression can cause goiter, and to characterize the activation status of Nrf2 in their thyroid. Methods: C57BL/6J Keap1flox/flox (Keap1 knock-down [Keap1KD]) mice were studied at 3 and 12 months of age. Plasma and thyroid glands were harvested for evaluation of thyroid function tests and for gene and protein expression by real-time polymerase chain reaction and immunoblotting, respectively. Results: Keap1KD mice showed diffuse goiter that began to develop in early adult life and became highly prominent and penetrant with age. The goiter was characterized by a markedly increased size of thyroid follicles, most notably of the colloid compartment, and by absence of thyroid nodules or hyperplasia. Keap1KD mice also showed decreased T4 levels in early adult life that were eventually well compensated over time by increased thyrotropin (TSH) levels. Nrf2 was activated in the thyroid of Keap1KD mice. Despite a known stimulatory effect of Nrf2 on thyroglobulin (Tg) gene transcription and Tg protein abundance, the expression levels were decreased in the thyroid of Keap1KD mice. No clear patterns were observed in the expression profiles of other thyroid hormone synthesis-specific factors, with the exception of Tg-processing and Tg-degrading cathepsins, including an increase in mature forms of cathepsins D, L, and S. Conclusions: Keap1KD mice develop age-dependent diffuse goiter with elevated TSH levels. The precise mechanism accounting for the thyroidal phenotype remains to be elucidated, but it may involve enhanced Tg solubilization and excessive lysosomal Tg degradation.

The Keap1/Nrf2 Signaling Pathway in the Thyroid-2020 Update

The thyroid gland has a special relationship with oxidative stress. On the one hand, like all other tissues, it must defend itself against reactive oxygen species (ROS). On the other hand, unlike most other tissues, it must also produce reactive oxygen species in order to synthesize its hormones that contribute to the homeostasis of other tissues. The thyroid must therefore also rely on antioxidant defense systems to maintain its own homeostasis in the face of continuous self-exposure to ROS. One of the main endogenous antioxidant systems is the pathway centered on the transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) and its cytoplasmic inhibitor Kelch-like ECH-associated protein 1 (Keap1). Over the last few years, multiple links have emerged between the Keap1/Nrf2 pathway and thyroid physiology, as well as various thyroid pathologies, including autoimmunity, goiter, hypothyroidism, hyperthyroidism, and cancer. In the present mini-review, we summarize recent studies shedding new light into the roles of Keap1/Nrf2 signaling in the thyroid.

Nuclear Factor Erythroid 2-Related Factor 2 in Regulating Cancer Metabolism

Significance: Nuclear factor erythroid 2 (NFE2)-related factor 2 (NFE2L2, or NRF2) is a transcription factor predominantly affecting the expression of antioxidant genes. NRF2 plays a significant role in the control of redox balance, which is crucial in cancer cells. NRF2 activation regulates numerous cancer hallmarks, including metabolism, cancer stem cell characteristics, tumor aggressiveness, invasion, and metastasis formation. We review the molecular characteristics of the NRF2 pathway and discuss its interactions with the cancer hallmarks previously listed. Recent Advances: The noncanonical activation of NRF2 was recently discovered, and members of this pathway are involved in carcinogenesis. Further, cancer-related changes (e.g., metabolic flexibility) that support cancer progression were found to be redox- and NRF2 dependent. Critical Issues: NRF2 undergoes Janus-faced behavior in cancers. The pro- or antineoplastic effects of NRF2 are context dependent and essentially based on the specific molecular characteristics of the cancer in question. Therefore, systematic investigation of NRF2 signaling is necessary to clarify its role in cancer etiology. The biggest challenge in the NRF2 field is to determine which cancers can be targeted for better clinical outcomes. Further, large-scale genomic and transcriptomic studies are missing to correlate the clinical outcome with the activity of the NRF2 system. Future Directions: To exploit NRF2 in a clinical setting in the future, the druggable members of the NRF2 pathway should be identified. In addition, it will be important to study how the modulation of the NRF2 system interferes with cytostatic drugs and their combinations.

Kopp P, Habeos I, Trougakos IP, Khoo NKH, Sykiotis GP. The Transcriptomic Response of the Murine Thyroid Gland to Iodide Overload and the Role of the Nrf2 Antioxidant System

Background: Thyroid follicular cells have physiologically high levels of reactive oxygen species because oxidation of iodide is essential for the iodination of thyroglobulin (Tg) during thyroid hormone synthesis. Thyroid follicles (the functional units of the thyroid) also utilize incompletely understood autoregulatory mechanisms to defend against exposure to excess iodide. To date, no transcriptomic studies have investigated these phenomena in vivo. Nuclear erythroid factor 2 like 2 (Nrf2 or Nfe2l2) is a transcription factor that regulates the expression of numerous antioxidant and other cytoprotective genes. We showed previously that the Nrf2 pathway regulates the antioxidant defense of follicular cells, as well as Tg transcription and Tg iodination. We, thus, hypothesized that Nrf2 might be involved in the transcriptional response to iodide overload. Methods: C57BL6/J wild-type (WT) or Nrf2 knockout (KO) male mice were administered regular water or water supplemented with 0.05% sodium iodide for seven days. RNA from their thyroids was prepared for next-generation RNA sequencing (RNA-Seq). Gene expression changes were assessed and pathway analyses were performed on the sets of differentially expressed genes. Results: Analysis of differentially expressed messenger RNAs (mRNAs) indicated that iodide overload upregulates inflammatory-, immune-, fibrosis- and oxidative stress-related pathways, including the Nrf2 pathway. Nrf2 KO mice showed a more pronounced inflammatory–autoimmune transcriptional response to iodide than WT mice. Compared to previously published datasets, the response patterns observed in WT mice had strong similarities with the patterns typical of Graves’ disease and papillary thyroid carcinoma (PTC). Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) also responded to iodide overload, with the latter targeting mRNAs that participate mainly in inflammation pathways. Conclusions: Iodide overload induces the Nrf2 cytoprotective response and upregulates inflammatory, immune, and fibrosis pathways similar to autoimmune hyperthyroidism (Graves’ disease) and PTC.

CRISPR/Cas9-Induced Loss of Keap1 Enhances Anti-oxidation in Rat Adipose-Derived Mesenchymal Stem Cells

Stem cells have become a powerful tool in the treatment of many diseases owing to their regenerative ability and rapid promotion of development in regenerative medicine such as in traumatic brain injury. However, the high level of oxidant micro-environment in lesion region leads to more than 99% cells into death. In this study, we used genetic methods to edit Keap1 gene in mesenchymal stem cells, we and observed their antioxidative ability. First, we disturbed the start codon and the 376th amino acid codon of Keap1 in adipose-derived mesenchymal stem cells (Ad-MSCs) with CRISPR/Cas9, respectively, to release Nrf2 from the binding of Keap1. As a result, Nrf2 was activated and localized into nuclei and regulated cellular anti-oxidation. We observed that the cells lacking Keap1 ATG codon showed obvious nuclear localization of Nrf2. Besides lower expression of Bax-1 and lower content of malondialdehyde (MDA) were detected after H₂O₂ treatment, we also found higher expression of Bcl-2 in Keap1 ATG codon knock-out cells, whereas a higher expression of PCNA was observed only in the Keap1 376th codon-edited cells, whose Bax-1 expression was lower than that in the control cells. Our study revealed that loss of Keap1 resulted in anti-oxidative ability in Ad-MSCs, suggesting that our strategy can hopefully increase the viability of mesenchymal stem cells after grafting. This study is also a frontier exploration to the application of CRISPR/Cas9 in Ad-MSCs.

Potential Applications of NRF2 Inhibitors in Cancer Therapy

The NRF2/KEAP1 pathway represents one of the most important cell defense mechanisms against exogenous or endogenous stressors. Indeed, by increasing the expression of several cytoprotective genes, the transcription factor NRF2 can shelter cells and tissues from multiple sources of damage including xenobiotic, electrophilic, metabolic, and oxidative stress. Importantly, the aberrant activation or accumulation of NRF2, a common event in many tumors, confers a selective advantage to cancer cells and is associated to malignant progression, therapy resistance, and poor prognosis. Hence, in the last years, NRF2 has emerged as a promising target in cancer treatment and many efforts have been made to identify therapeutic strategies aimed at disrupting its prooncogenic role. By summarizing the results from past and recent studies, in this review, we provide an overview concerning the NRF2/KEAP1 pathway, its biological impact in solid and hematologic malignancies, and the molecular mechanisms causing NRF2 hyperactivation in cancer cells. Finally, we also describe some of the most promising therapeutic approaches that have been successfully employed to counteract NRF2 activity in tumors, with a particular emphasis on the development of natural compounds and the adoption of drug repurposing strategies.

Keap1/Nrf2 Signaling: A New Player in Thyroid Pathophysiology and Thyroid Cancer

The Keap1/Nrf2 pathway is a key mediator of general redox and tissue-specific homeostasis. It also exerts a dual role in cancer, by preventing cell transformation of normal cells but promoting aggressiveness, and drug resistance of malignant ones. Although Nrf2 is well-studied in other tissues, its roles in the thyroid gland are only recently emerging. This review focuses on the involvement of Keap1/Nrf2 signaling in thyroid physiology, and pathophysiology in general, and particularly in thyroid cancer. Studies in mice and cultured follicular cells have shown that, under physiological conditions, Nrf2 coordinates antioxidant defenses, directly increases thyroglobulin production and inhibits its iodination. Increased Nrf2 pathway activation has been reported in two independent families with multinodular goiters due to germline loss-of-function mutations in KEAP1. Nrf2 pathway activation has also been documented in papillary thyroid carcinoma (PTC), due to somatic mutations, or epigenetic modifications in KEAP1, or other pathway components. In PTC, such Nrf2-activating KEAP1 mutations have been associated with tumor aggressiveness. Furthermore, polymorphisms in the prototypical Nrf2 target genes NQO1 and NQO2 have been associated with extra-thyroidal extension and metastasis. More recently, mutations in the Nrf2 pathway have also been found in Hürthle-cell (oncocytic) thyroid carcinoma. Finally, in in vitro, and in vivo models of poorly-differentiated, and undifferentiated (anaplastic) thyroid carcinoma, Nrf2 activation has been associated with resistance to experimental molecularly-targeted therapy. Thus, Keap1/Nrf2 signaling is involved in both benign and malignant thyroid conditions, where it might serve as a prognostic marker or therapeutic target.