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.

Non-small cell lung cancers (NSCLCs) harboring KEAP1 mutations are often resistant to immunotherapy. Here, we show that KEAP1 targets EMSY for ubiquitin-mediated degradation to regulate homologous recombination repair (HRR) and anti-tumor immunity. Loss of KEAP1 in NSCLC induces stabilization of EMSY, producing a BRCAness phenotype, i.e., HRR defects and sensitivity to PARP inhibitors. Defective HRR contributes to a high tumor mutational burden that, in turn, is expected to prompt an innate immune response. Notably, EMSY accumulation suppresses the type I interferon response and impairs innate immune signaling, fostering cancer immune evasion. Activation of the type I interferon response in the tumor microenvironment using a STING agonist results in the engagement of innate and adaptive immune signaling and impairs the growth of KEAP1-mutant tumors. Our results suggest that targeting PARP and STING pathways, individually or in combination, represents a therapeutic strategy in NSCLC patients harboring alterations in KEAP1.

Although deregulation of transfer RNA (tRNA) biogenesis promotes the translation of pro-tumorigenic mRNAs in cancers^1,2, the mechanisms and consequences of tRNA deregulation in tumorigenesis are poorly understood. Here we use a CRISPR-Cas9 screen to focus on genes that have been implicated in tRNA biogenesis, and identify a mechanism by which altered valine tRNA biogenesis enhances mitochondrial bioenergetics in T cell acute lymphoblastic leukaemia (T-ALL). Expression of valine aminoacyl tRNA synthetase is transcriptionally upregulated by NOTCH1, a key oncogene in T-ALL, underlining a role for oncogenic transcriptional programs in coordinating tRNA supply and demand. Limiting valine bioavailability through restriction of dietary valine intake disrupted this balance in mice, resulting in decreased leukaemic burden and increased survival in vivo. Mechanistically, valine restriction reduced translation rates of mRNAs that encode subunits of mitochondrial complex I, leading to defective assembly of complex I and impaired oxidative phosphorylation. Finally, a genome-wide CRISPR-Cas9 loss-of-function screen in differential valine conditions identified several genes, including SLC7A5 and BCL2, whose genetic ablation or pharmacological inhibition synergized with valine restriction to reduce T-ALL growth. Our findings identify tRNA deregulation as a critical adaptation in the pathogenesis of T-ALL and provide a molecular basis for the use of dietary approaches to target tRNA biogenesis in blood malignancies.

Small cell lung cancer (SCLC) has limited therapeutic options and an exceptionally poor prognosis. Understanding the oncogenic drivers of SCLC may help define novel therapeutic targets. Recurrent genomic rearrangements have been identified in SCLC, most notably an in-frame gene fusion between RLF and MYCL found in up to 7% of the predominant ASCL1-expressing subtype. To explore the role of this fusion in oncogenesis and tumor progression, we used CRISPR/Cas9 somatic editing to generate a Rlf-Mycl-driven mouse model of SCLC. Rlf-Mycl fusion accelerated transformation and proliferation of murine SCLC and increased metastatic dissemination and the diversity of metastatic sites. Tumors from the Rlf-Mycl genetically engineered mouse model displayed gene expression similarities with human Rlf-Mycl SCLC. Together, our studies support Rlf-Mycl as the first demonstrated fusion oncogenic driver in SCLC and provide a new preclinical mouse model for the study of this subtype of SCLC. SIGNIFICANCE: The biological and therapeutic implications of gene fusions in SCLC, an aggressive metastatic lung cancer, are unknown. Our study investigates the functional significance of the in-frame Rlf-Mycl gene fusion by developing a Rlf-Mycl-driven genetically engineered mouse model and defining the impact on tumor growth and metastasis.

[Figure: see text].

Introduction: The KEAP1/NRF2 pathway is mutationally activated in approximately 20-25% of NSCLC patients. NRF2 activation protects against oxidative stress and promotes tumor growth and survival. KEAP1/NRF2 mutations in advanced NSCLC are associated w/ dramatically shorter survival and poor outcomes following standard-of-care therapy. These tumors have heightened dependency on glutaminase-mediated conversion of glutamine to glutamate due to upregulation of NRF2 target genes involved in glutamine metabolism, which support a massive increase in glutathione synthesis. Telaglenastat (CB-839) is an investigational, first-in-class, potent, oral glutaminase inhibitor which has demonstrated activity in KEAP1/NRF2-mutated NSCLC cell lines and xenograft models. This study will evaluate the safety and efficacy of telaglenastat + standard-of-care pembrolizumab (pembro) and chemotherapy as 1L therapy in patients with KEAP1/NRF2-mutated non-squamous metastatic NSCLC (NCT04265534; Skoulidis et al. ASCO 2020).
Method(s): This phase 2, randomized, multicenter, double-blind study will enroll ~120 patients with histologically or cytologically documented stage IV non-squamous NSCLC with KEAP1 or NRF2 mutations, no prior systemic therapy for metastatic NSCLC, measurable disease (RECIST v1.1), ECOG PS 0-1, and no EGFR, ALK, ROS, or other actionable mutation w/ available approved therapy in the1L setting. KEAP1 or NRF2 mutations will be determined by next-generation sequencing (NGS); and study-provided liquid biopsy NGS will be available. Patients will be randomized 1:1 to receive telaglenastat (800 mg BID PO) or placebo, plus pembro, carboplatin, and pemetrexed at standard doses on day 1 of each 21-day cycle. Patients will be stratified by STK11/LKB1 mutational status and M stage of cancer (M1a-b vs M1c). The study includes an initial safety run-in period (1 cycle). The co-primary endpoints are safety and investigator-assessed progression-free survival (RECIST v1.1). Secondary endpoints include overall response rate, duration of response, and overall survival, as well as performing efficacy analyses in the subgroup of patients w/ biochemical confirmation of KEAP1/NRF2 pathway activation. Findings of this novel biomarker-selected study will inform the efficacy and safety profile of telaglenastat + standard-of-care chemoimmunotherapy in previously untreated patients with KEAP1/NRF2-mutated, non-squamous metastatic NSCLC. A separate screening protocol (NCT04698681) is also available to assess KEAP1or NRF2 mutational status based on liquid biopsy NGS, which may be used to determine KEAPSAKE trial eligibility of patients whose mutational status is unknown.
Result(s):
Conclusion(s): Keywords: glutaminase, KEAPSAKE, telaglenastat
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Oncogenic mutations in KRAS drive common metabolic programmes that facilitate tumour survival, growth and immune evasion in colorectal carcinoma, non-small-cell lung cancer and pancreatic ductal adenocarcinoma. However, the impacts of mutant KRAS signalling on malignant cell programmes and tumour properties are also dictated by tumour suppressor losses and physiological features specific to the cell and tissue of origin. Here we review convergent and disparate metabolic networks regulated by oncogenic mutant KRAS in colon, lung and pancreas tumours, with an emphasis on co-occurring mutations and the role of the tumour microenvironment. Furthermore, we explore how these networks can be exploited for therapeutic gain.

In a recent article published in Molecular Cell, Dai et al. demonstrate that energy stress induced by a ketogenic diet or fasting can enhance checkpoint blockade therapy. Energy stress promotes lysosome-mediated degradation of the immunoinhibitory ligand programmed death-ligand 1 (PDL1) and upregulation of tumor interferon (IFN) responses.