KEAP1/NRF2 (NFE2L2) mutations in NSCLC – Fuel for a superresistant phenotype?

doi:10.1016/j.lungcan.2021.07.006

Lung Cancer

Volume 159, September 2021, Pages 10-17

https://doi.org/10.1016/j.lungcan.2021.07.006 Get rights and content

Abstract

The transcription factor NRF2 (nuclear factor E2-related factor 2) (also known as nuclear factor, erythroid 2 like 2 [NFE2L2]) is the master regulator of cellular antioxidant responses. NRF2 is repressed by interaction with a redox-sensitive protein KEAP1 (Kelch-like ECH-associated protein 1). Dysregulation of KEAP1/NRF2 transcriptional activity has been associated with the pathogenesis of multiple diseases, and the KEAP1/NRF2 axis has emerged to be the most important modulator of cellular homeostasis. Oxidative stress plays an important role in the initiation and progression of many chronic diseases, including diabetes, cancer, and neurodegenerative diseases. Although its role in immunotherapy is still somewhat controversial, it is well documented from clinical studies that KEAP1/NRF2 mutations in NSCLCs are associated with resistance to various cancer treatments including chemotherapy, X-irradiation, TKI treatment, and a shorter OS and currently available results from clinical trials suggest that KEAP1/NRF2 mutations can be used as a prognostic biomarker (poorer prognosis) for determining prognosis following immunotherapy and a predictive marker for chemo-, radio-, immunotherapy- and TKI-resistance. Despite overwhelming enthusiasm about the various KEAP1/NRF2 inhibitors that have been described during the last decades, none of these inhibitors are currently explored in clinical trials or in clinical applications which clearly add weight to the proposal that the development of these inhibitors remains challenging, but will be beneficial for novel treatment approaches in NSCLC in the near future. In this review we highlight the molecular features, the key components, and possible inhibitors of the KEAP1/NRF2 pathway, its role as prognostic and predictive biomarker, and the resulting clinical implications in NSCLC patients.

Introduction

Dysregulation of KEAP1/NRF2 transcriptional activity has been associated with the pathogenesis of multiple diseases, and the KEAP1/NRF2 axis has emerged to be the most important modulator of cellular homeostasis. NRF2 is highly sensitive to oxidative and electrophilic products, including reactive oxygen species (ROS) and reactive nitrogen species (RNS). In the cell nucleus, NRF2 activates various antioxidant and related genes by binding to antioxidant-responsive elements (AREs) or electrophile-responsive elements (EpREs) (consensus sequence: 5‘-TGACNNNGC-3′). NRF2 then in turn activates genes that regulate redox homeostasis, drug metabolism and excretion, energetic metabolism, iron metabolism, amino acid metabolism, survival, proliferation, autophagy, proteasomal degradation, DNA repair, and mitochondrial physiology [3].

Oxidative stress plays an important role in the initiation and progression of many chronic diseases, including diabetes, cancer, and neurodegenerative diseases [4], [5], [6], [7], and regulation of cytoprotective gene expression by KEAP1/NRF2 is the principal inducible defense mechanism against oxidative and electrophilic cellular stresses [8], [9] (Fig. 1).

The KEAP1/NRF2 axis has also been recognized as a central cornerstone for a cross-talk of cellular defense and survival pathways. NRF2 has been found to control expression of over 1,000 protective genes [12], [13], which comprise more than 1% of the human genome [14]. In addition, KEAP1 is a well-conserved protein, sharing around 95% of sequence homology between species [15] underpinning its important role in cellular defense mechanisms. Of note, in normal unstressed conditions, cellular NRF2 levels are very low (turnover: 20–30 min) [1], but are dramatically increased upon exposure to different stress levels of electrophilic chemicals, RNS, or ROS (concentration-dependent effects: cytostatic → tumorigenic → cytotoxic) [16].

Several lines of evidence have added further weight to the proposal that the KEAP1/NRF2 pathway is the key driver of cancer progression, metastasis, and resistance to tumor therapy. Interestingly, recent research has revealed that the KEAP1/NRF2 axis may have a contradictory role in cancers. Although this pathway is the main component of drug detoxification in normal cells, it also can be hijacked by malignant cells to evade the efficacy of various cancer treatments [2].

In this review we highlight the molecular features, the key components, and possible inhibitors of the KEAP1/NRF2 pathway, its role as prognostic and predictive biomarker, and the resulting clinical implications in NSCLC patients.

Section snippets

Molecular biology

Under normal conditions, NRF2 interacts with two KEAP1 molecules through the ETGE and DLG motifs in its Neh2 domain to activate the cullin 3 (Cul3)-based E3 ligase complex-mediated NRF2 ubiquitination reaction [2]. Cul3 serves as a scaffold for the E3 ligase RBX1. After NRF2 is ubiquitinated, it is rapidly degraded by 26S proteasome and maintained at a very low level in the cytoplasm [1].

Once cells are exposed to oxidative stress or chemo preventive compounds, electro-philes and ROS react with

KEAP1/NRF2 mutations in NSCLCs: A distinct clinical phenotype

Several lines of clinical research have provided evidence that NSCLC patients harboring KEAP1/NRF2 mutation exert a distinct clinicopathological phenotype [30], [55]. Mutations in the KEAP1/NRF2 complex occur in 23% of lung adenocarcinomas [54] and in 34% of squamous cell carcinomas [57]. They are the most often observed NSCLC mutations behind p53 and K-ras. In addition, mutations are generally mutually exclusive and only in a minor proportion of patients other druggable targets can be

KEAP1/NRF2 inhibitors

Developing of KEAP1/NRF2 inhibitors has become one of the most attractive strategies for anticancer therapies during the past 10 years, but has sent many pharmaceutical companies to the graveyard in the last decade. The characterization of the crystal structure of KEAP1 in complex with the Neh2 domain of NRF2 has now offered new opportunities to design molecules that specially and selectively interfere with the binding of the KEAP1/NRF2 complex [59], but NRF2 has a very short half-life, even

Conclusion

The KEAP1/NRF2 system appears to be a very promising intracellular pathway to target common pathologic mechanisms of many chronic diseases and cancers including NSCLC. In this regard inhibitors of KEAP1 and/or NRF2 are expected to function as anticancer drugs. However, it needs to be taken into account that the role of NRF2 activation in cancer is paradoxical and does require further exploration as NRF2 inducers act to protect normal cells from carcinogens, whereas NRF2 inhibitors act to

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors are indebted to Alwin Hierl (Munich, Germany) for preparing the art work.

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¹: Both authors contributed equally to the paper.

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KEAP1/NRF2 (NFE2L2) mutations in NSCLC – Fuel for a superresistant phenotype?

Abstract

Introduction

Section snippets

Molecular biology

KEAP1/NRF2 mutations in NSCLCs: A distinct clinical phenotype

KEAP1/NRF2 inhibitors

Conclusion

Declaration of Competing Interest

Acknowledgement

Trends Pharmacol Sci

Free Radic. Biol. Med.

Biochem. Biophys. Res. Commun.

J. Thorac. Oncol.

Lung Cancer

J. Thorac. Oncol.

J. Thorac. Oncol.

J. Thorac. Oncol.

Lung Cancer

Ann. Oncol.

Lung Cancer

Clin. Lung Cancer

Mol. Cell.

Mol. Cell

J. Biol. Chem.

Mol. Cell.

J Thorac. Oncol

Redox Biol.

The KEAP1-NRF2 system in cancer

Front. Oncol.

Nrf2 in cancers: a double-edged sword

Cancer Med.

NRF2 and the hallmarks of cancer

Cancer Cell

Oxidative stress

Annu. Rev. Biochem.

Modulation of oxidative stress as an anticancer strategy

Nat. Rev. Drug Discov.

Neurodegenerative diseases and oxidative stress

Nat. Rev. Drug Discov.

Keap1-Nrf2 signaling pathway in angiogenesis and vascular diseases

J. Tissue Eng. Med.

The KEAP1-NRF2 system: a thiol-based sensor-effector apparatus for maintaining redox homeostasis

Physiol. Rev.

The molecular mechanisms regulating the KEAP1-NRF2 pathway

Mol Cell. Biol.

Global mapping of binding sites for Nrf2 identifies novel targets in cell survival response through ChIP-Seq profiling and network analysis

Nucl. Acid. Res.

Regulatory flexibility in the Nrf2-mediated stress response is conferred by conformational cycling of the Keap1-Nrf2 protein complex

Proc. Natl. Acad USA

Identification of the interactive interface and phylogenic conservation of the Nrf2-Keap1 system

Genes Cells

SCF/β-TrCP promotes glycogen synthase kinase 3-dependent degradation of the Nrf2 transcription factor in a Keap1-independent manner

Mol. Cell. Biol.