title: Aromatase Inhibitor-Mediated Downregulation of INrf2 (Keap1) Leads to Increased Nrf2 and Resistance in Breast Cancer.
abstract: Aromatase inhibitors are effective drugs that reduce or eliminate hormone-sensitive breast cancer. However, despite their efficacy, resistance to these drugs can occur in some patients. The INrf2 (Keap1):Nrf2 complex serves as a sensor of drug/radiation-induced oxidative/electrophilic stress. INrf2 constitutively suppresses Nrf2 by functioning as an adapter protein for the Cul3/Rbx1-mediated ubiquitination/degradation of Nrf2. Upon stress, Nrf2 dissociates from INrf2, is stabilized, translocates to the nucleus, and coordinately induces a battery of cytoprotective gene expression. Current studies investigated the role of Nrf2 in aromatase inhibitor resistance. RT-PCR and immunoblot assays showed that aromatase inhibitor-resistant breast cancer LTLTCa and AnaR cells express lower INrf2 and higher Nrf2 protein levels, as compared with drug-sensitive MCF-7Ca and AC1 cells, respectively. The increase in Nrf2 was due to lower ubiquitination/degradation of Nrf2 in aromatase inhibitor-resistant cells. Higher Nrf2-mediated levels of biotransformation enzymes, drug transporters, and antiapoptotic proteins contributed to reduced efficacy of drugs and aversion to apoptosis that led to drug resistance. shRNA inhibition of Nrf2 in LTLTCa (LTLTCa-Nrf2KD) cells reduced resistance and sensitized cells to aromatase inhibitor exemestane. Interestingly, LTLTCa-Nrf2KD cells also showed reduced levels of aldehyde dehydrogenase, a marker of tumor-initiating cells and significantly decreased mammosphere formation, as compared with LTLTCa-Vector control cells. The results together suggest that persistent aromatase inhibitor treatment downregulated INrf2 leading to higher expression of Nrf2 and Nrf2-regulated cytoprotective proteins that resulted in increased aromatase inhibitor drug resistance. These findings provide a rationale for the development of Nrf2 inhibitors to overcome resistance and increase efficacy of aromatase inhibitors.
authors.affiliation: Department of Pharmacology and Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Raju
authors.initials: R
authors.lastname: Khatri
authors.affiliation: Department of Pharmacology and Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Preeti
authors.initials: P
authors.lastname: Shah
authors.affiliation: Department of Pharmacology and Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Rupa
authors.initials: R
authors.lastname: Guha
authors.affiliation: Department of Pharmacology and Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Feyruz V
authors.initials: FV
authors.lastname: Rassool
authors.affiliation: Department of Internal Medicine, University of New Mexico, Albuquerque, New Mexico.
authors.forename: Alan E
authors.initials: AE
authors.lastname: Tomkinson
authors.affiliation: Department of Pharmacology and Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Angela
authors.initials: A
authors.lastname: Brodie
authors.affiliation: Department of Pharmacology and Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland. ajaiswal@som.umaryland.edu.
authors.forename: Anil K
authors.initials: AK
authors.lastname: Jaiswal
mesh_terms: D000077384:Anastrozole; D000730:Androstadienes / Q000737:chemistry / Q000494:pharmacology; D047072:Aromatase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D000072019:Kelch-Like ECH-Associated Protein 1; D000077289:Letrozole; D061986:MCF-7 Cells; D015394:Molecular Structure; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D009570:Nitriles / Q000737:chemistry / Q000494:pharmacology; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014230:Triazoles / Q000737:chemistry / Q000494:pharmacology; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D000730:Androstadienes; D047072:Aromatase Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; C431364:KEAP1 protein, human; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D009570:Nitriles; D017382:Reactive Oxygen Species; D014230:Triazoles; D000077384:Anastrozole; D000077289:Letrozole; C056516:exemestane