Faculty Bibliography

The Kelch-like ECH-associated protein 1 (KEAP1)/nuclear factor erythroid 2-related factor 2 (NRF2) pathway plays a physiologic protective role against xenobiotics and reactive oxygen species. However, activation of NRF2 provides a powerful selective advantage for tumors by rewiring metabolism to enhance proliferation, suppress various forms of stress, and promote immune evasion. Genetic, epigenetic, and posttranslational alterations that activate the KEAP1/NRF2 pathway are found in multiple solid tumors. Emerging clinical data highlight that alterations in this pathway result in resistance to multiple therapies. Here, we provide an overview of how dysregulation of the KEAP1/NRF2 pathway in cancer contributes to several hallmarks of cancer that promote tumorigenesis and lead to treatment resistance. SIGNIFICANCE: Alterations in the KEAP1/NRF2 pathway are found in multiple cancer types. Activation of NRF2 leads to metabolic rewiring of tumors that promote tumor initiation and progression. Here we present the known alterations that lead to NRF2 activation in cancer, the mechanisms in which NRF2 activation promotes tumors, and the therapeutic implications of NRF2 activation.

Approximately 30% of human lung cancers acquire mutations in either Keap1 or Nfe2l2, resulting in the stabilization of Nrf2, the Nfe2l2 gene product, which controls oxidative homeostasis. Here, we show that heme triggers the degradation of Bach1, a pro-metastatic transcription factor, by promoting its interaction with the ubiquitin ligase Fbxo22. Nrf2 accumulation in lung cancers causes the stabilization of Bach1 by inducing Ho1, the enzyme catabolizing heme. In mouse models of lung cancers, loss of Keap1 or Fbxo22 induces metastasis in a Bach1-dependent manner. Pharmacological inhibition of Ho1 suppresses metastasis in a Fbxo22-dependent manner. Human metastatic lung cancer display high levels of Ho1 and Bach1. Bach1 transcriptional signature is associated with poor survival and metastasis in lung cancer patients. We propose that Nrf2 activates a metastatic program by inhibiting the heme- and Fbxo22-mediated degradation of Bach1, and that Ho1 inhibitors represent an effective therapeutic strategy to prevent lung cancer metastasis.

Rewiring of metabolic pathways is a hallmark of tumorigenesis as cancer cells acquire novel nutrient dependencies to support oncogenic growth. A major genetic subtype of lung adenocarcinoma with KEAP1/NRF2 mutations, which activates the endogenous oxidative stress response, undergoes significant metabolic rewiring to support enhanced antioxidant production. We demonstrate that cancers with high antioxidant capacity exhibit a general dependency on exogenous non-essential amino acids (NEAAs) that is driven by the Nrf2-dependent secretion of glutamate through system x_c^- (XCT), which limits intracellular glutamate pools that are required for NEAA synthesis. This dependency can be therapeutically targeted by dietary restriction or enzymatic depletion of individual NEAAs. Importantly, limiting endogenous glutamate levels by glutaminase inhibition can sensitize tumors without alterations in the Keap1/Nrf2 pathway to dietary restriction of NEAAs. Our findings identify a metabolic strategy to therapeutically target cancers with genetic or pharmacologic activation of the Nrf2 antioxidant response pathway by restricting exogenous sources of NEAAs.

The unregulated proliferative capacity of many tumors is dependent on dysfunctional nutrient utilization and ROS (reactive oxygen species) signaling to sustain a deranged metabolic state. Although it is clear that cancers broadly rely on these survival and signaling pathways, how they achieve these aims varies dramatically. Mutations in the KEAP1/NRF2 pathway represent a potent cancer adaptation to exploit native cytoprotective pathways that involve both nutrient metabolism and ROS regulation. Despite activating these advantageous processes, mutations within KEAP1/NRF2 are not universally selected for across cancers and instead appear to interact with particular tumor driver mutations and tissues of origin. Here, we highlight the relationship between the KEAP1/NRF2 signaling axis and tumor biology with a focus on genetic mutation, metabolism, immune regulation, and treatment implications and opportunities. Understanding the dysregulation of KEAP1 and NRF2 provides not only insight into a commonly mutated tumor suppressor pathway but also a window into the factors dictating the development and evolution of many cancers.
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Treating KRAS-mutant lung adenocarcinoma (LUAD) remains a major challenge in cancer treatment given the difficulties associated with directly inhibiting the KRAS oncoprotein. One approach to addressing this challenge is to define mutations that frequently co-occur with those in KRAS, which themselves may lead to therapeutic vulnerabilities in tumors. Approximately 20% of KRAS-mutant LUAD tumors carry loss-of-function mutations in the KEAP1 gene encoding Kelch-like ECH-associated protein 1 (refs. 2, 3, 4), a negative regulator of nuclear factor erythroid 2-like 2 (NFE2L2; hereafter NRF2), which is the master transcriptional regulator of the endogenous antioxidant response. The high frequency of mutations in KEAP1 suggests an important role for the oxidative stress response in lung tumorigenesis. Using a CRISPR-Cas9-based approach in a mouse model of KRAS-driven LUAD, we examined the effects of Keap1 loss in lung cancer progression. We show that loss of Keap1 hyperactivates NRF2 and promotes KRAS-driven LUAD in mice. Through a combination of CRISPR-Cas9-based genetic screening and metabolomic analyses, we show that Keap1- or Nrf2-mutant cancers are dependent on increased glutaminolysis, and this property can be therapeutically exploited through the pharmacological inhibition of glutaminase. Finally, we provide a rationale for stratification of human patients with lung cancer harboring KRAS/KEAP1- or KRAS/NRF2-mutant lung tumors as likely to respond to glutaminase inhibition.

The circadian clock controls metabolic and physiological processes through finely tuned molecular mechanisms. The clock is remarkably plastic and adapts to exogenous "zeitgebers," such as light and nutrition. How a pathological condition in a given tissue influences systemic circadian homeostasis in other tissues remains an unanswered question of conceptual and biomedical importance. Here, we show that lung adenocarcinoma operates as an endogenous reorganizer of circadian metabolism. High-throughput transcriptomics and metabolomics revealed unique signatures of transcripts and metabolites cycling exclusively in livers of tumor-bearing mice. Remarkably, lung cancer has no effect on the core clock but rather reprograms hepatic metabolism through altered pro-inflammatory response via the STAT3-Socs3 pathway. This results in disruption of AKT, AMPK, and SREBP signaling, leading to altered insulin, glucose, and lipid metabolism. Thus, lung adenocarcinoma functions as a potent endogenous circadian organizer (ECO), which rewires the pathophysiological dimension of a distal tissue such as the liver. PAPERCLIP.

Loss-of-function mutations in KEAP1 frequently occur in lung cancer and are associated with poor prognosis and resistance to standard of care treatment, highlighting the need for the development of targeted therapies. We previously showed that KEAP1 mutant tumors consume glutamine to support the metabolic rewiring associated with NRF2-dependent antioxidant production. Here, using preclinical patient-derived xenograft models and antigenic orthotopic lung cancer models, we show that the glutamine antagonist prodrug DRP-104 impairs the growth of KEAP1 mutant tumors. We find that DRP-104 suppresses KEAP1 mutant tumors by inhibiting glutamine-dependent nucleotide synthesis and promoting antitumor T cell responses. Using multimodal single-cell sequencing and ex vivo functional assays, we demonstrate that DRP-104 reverses T cell exhaustion, decreases T_regs, and enhances the function of CD4 and CD8 T cells, culminating in an improved response to anti-PD1 therapy. Our preclinical findings provide compelling evidence that DRP-104, currently in clinical trials, offers a promising therapeutic approach for treating patients with KEAP1 mutant lung cancer.

Cellular redox homeostasis is an essential, dynamic process that ensures the balance between reducing and oxidizing reactions within cells and thus has implications across all areas of biology. Changes in levels of reactive oxygen species can disrupt redox homeostasis, leading to oxidative or reductive stress that contributes to the pathogenesis of many malignancies, including cancer. From transformation and tumor initiation to metastatic dissemination, increasing reactive oxygen species in cancer cells can paradoxically promote or suppress the tumorigenic process, depending on the extent of redox stress, its spatiotemporal characteristics and the tumor microenvironment. Here we review how redox regulation influences tumorigenesis, highlighting therapeutic opportunities enabled by redox-related alterations in cancer cells.