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Published OnlineFirst November 6, 2018; DOI: 10.1158/0008-5472.CAN-18-1938 Cancer Molecular Cell Biology Research Inhibition of Thioredoxin/Thioredoxin Reductase Induces Synthetic Lethality in Lung Cancers with Compromised Glutathione Homeostasis Xiang Yan1,2, Xiaoshan Zhang1, Li Wang1, Ran Zhang1, Xingxiang Pu1, Shuhong Wu1, Lei Li3, Pan Tong4, Jing Wang4, Qing H. Meng5, Vanessa B. Jensen6, Luc Girard7, John D. Minna7, Jack A. Roth1, Stephen G. Swisher1, John V.Heymach8, and Bingliang Fang1 Abstract Glutathione (GSH)/GSH reductase (GSR) and thioredoxin/ cancer (NSCLC) cell lines revealed that auranofin sensitivity thioredoxin reductase (TXNRD) are two major compensating correlated with the expression levels of the GSR, glutamate- thiol-dependent antioxidant pathways that maintain protein cysteine ligase catalytic subunit (GCLC), and NAD(P)H qui- dithiol/disulfide balance. We hypothesized that functional none dehydrogenase 1 (NQO1) genes. In NSCLC patient- deficiency in one of these systems would render cells depen- derived xenografts with reduced expression of GSR and/or dent on compensation by the other system for survival, pro- GCLC, growth was significantly suppressed by treatment with viding a mechanism-based synthetic lethality approach for auranofin. Together, these results provide a proof of concept treatment of cancers. The human GSR gene is located on that cancers with compromised expression of enzymes chromosome 8p12, a region frequently lost in human cancers. required for GSH homeostasis or with chromosome 8p dele- GSR deletion was detected in about 6% of lung adenocarci- tions that include the GSR gene may be targeted by a synthetic nomas in The Cancer Genome Atlas database. To test whether lethality strategy with inhibitors of TXNRD. loss of GSR sensitizes cancer cells to TXNRD inhibition, we knocked out or knocked down the GSR gene in human lung Significance:Thesefindings demonstrate that lung cancers cancer cells and evaluated their response to the TXNRD inhib- with compromised expression of enzymes required for glutathi- itor auranofin. GSR deficiency sensitized lung cancer cells to one homeostasis, including reduced GSR gene expression, may this agent. Analysis of a panel of 129 non–small cell lung be targeted by thioredoxin/thioredoxin reductase inhibitors. Introduction maintain cellular thiol redox homeostasis and protein dithiol/ disulfide balance (1, 2). Both GSH and TXN catalyze the reduction Glutathione (GSH)/GSH reductase (GSR) and thioredoxin of disulfide bonds in proteins to dithiols, which is critical for (TXN)/thioredoxin reductase (TXNRD) are two parallel, compen- maintaining protein functions (Fig. 1A). Oxidized GSH (GSSG) sating thiol-dependent antioxidant pathways that regulate and and TXN generated during this catalytic process are converted to their reduced states by GSR and TXNRD, respectively, both using NADPH generated in the pentose phosphate cycle as the hydrogen 1Department of Thoracic and Cardiovascular Surgery, The University of Texas donor. Functional deficiency in one of these systems will render 2 MD Anderson Cancer Center, Houston, Texas. Department of Medical Oncol- cells dependent on compensation by the other system for survival. 3 ogy, Chinese PLA General Hospital, Beijing, China. Department of Experimental In GSR-deficient yeasts (3) and Drosophila (4), the TXN/TXNRD Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas. 4Department of Bioinformatics and Computational Biology, pathway is required for the reduction of GSSG to GSH. Similarly, The University of Texas MD Anderson Cancer Center, Houston, Texas. 5Depart- GSH acts as a backup for human TXNRD1 to reduce TXN, thereby ment of Laboratory Medicine, The University of Texas MD Anderson Cancer preventing cell death induced by gold compound–mediated Center, Houston, Texas. 6Department of Veterinary Medicine and Surgery, The TXNRD1 inhibition (5). Combined inhibition of the GSH and 7 University of Texas MD Anderson Cancer Center, Houston, Texas. Hamon TXN pathways has led to synergistic cancer cell death (6, 7). Center for Therapeutic Oncology, The Harold C. Simmons Comprehensive Because synthetic lethality interactions occur significantly more Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas. 8Department of Thoracic/Head and Neck Medical Oncology, The University of frequently among genes involved in similar biological processes, Texas MD Anderson Cancer Center, Houston, Texas. such as those in parallel or compensating pathways (8), we hypothesized that loss and/or reduced expression of enzymes Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). required for GSH homeostasis, including GSR and glutamate- cysteine ligase (the first rate-limiting enzyme of GSH synthesis), in X. Yan and X. Zhang contributed equally to this article. a subgroup of cancers predisposes them to vulnerability to treat- Corresponding Author: Bingliang Fang, The University of Texas MD Anderson ment with TXNRD inhibitors, providing a mechanism-based Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030. Phone: 713-563-9147; synthetic lethality therapy for these cancers. Fax: 713-794-4901; E-mail: [email protected] The human GSR gene is located on chromosome 8p12, a region doi: 10.1158/0008-5472.CAN-18-1938 frequently lost in lung cancers (9, 10) and other types of cancers, Ó2018 American Association for Cancer Research. including breast (11), head and neck (12), prostate (13), bladder www.aacrjournals.org 125 Downloaded from cancerres.aacrjournals.org on October 1, 2021. © 2019 American Association for Cancer Research. Published OnlineFirst November 6, 2018; DOI: 10.1158/0008-5472.CAN-18-1938 Yan et al. Figure 1. GSR gene deletions in human cancers from TCGA database. A, GSH/GSR and TXN/ TXNRD pathways in regulating protein dithiol/disulfide balance. Both GSH and TXN catalyze the reduction of disulfide bonds in proteins to dithiols, which is critical for maintaining protein functions. B, Alterations in GSR and other selected genes in lung adenocarcinomas. The mutation frequencies are shown on the left side of the graph. Deletions of the GRS gene overlap mostly with the deletion of TUSC3, a gene located in chromosome 8p22, indicating co- occurrence of GSR deletion and chromosome 8p loss. C, Frequencies of GSR gene deletions in different types of cancers. The data were obtained by using the cBioPortal for Cancer Genomics. (14), and gastric/colorectal (10) cancers and lymphoma (15). PCR Detection Kit (Sigma-Aldrich) and authenticated per rou- Accumulating evidence has shown that loss of chromosome 8p tine at our institution's Characterized Cell Line Core using a increases tumor invasiveness and metastasis potential (16–18) short tandem repeat DNA fingerprint assay with a PowerPlex 16 and confers resistance to chemotherapy and poor survival HS kit (Promega). in patients with cancer (13, 18). Targeted deletion of chromosome 8p yielded altered lipid metabolism and increased autophagy, Gene knockout and knockdown in lung cancer cells which trigger invasiveness and confer tumor growth under stress A549–GSR-knockout cells were generated by using the CRISPR/ conditions (18). Unfortunately, therapeutic strategies for cancers Cas9 genome editing system. Briefly, GSR-specific guide RNA with chromosome 8p loss have yet to be developed. Loss of (gRNA) expression vectors were generated as described (20). the GSR gene may offer a unique opportunity for treatment of LentiCas9-Blast (plasmid 52962) and gRNA cloning vector lenti- cancer in a subgroup of patients whose cancer has chromosome Guide-Puro (plasmid 52963) were obtained from Addgene. The 8p aberrations. CRISPR guide sequences targeting GSR were GATCATGCAT- To explore the concept of targeting cancers in which expression GAATTCAGAG (gRNA1) and GTGAGGGTAAATTCAATTGG of enzymes required for GSH homeostasis is reduced or lost, we (gRNA2). A549 cells were cotransfected with lentiCas9-Blast and searched The Cancer Genome Atlas (TCGA) database for genetic gRNA expression vectors. The transfected cells were selected using alterations and found that deep GSR deletion was detected in 6% puromycin (2 mg/mL) for 48 hours. Isolated single colonies were of lung adenocarcinomas, 3.5% of squamous cell lung cancers, analyzed by Western blot. The colonies without GSR expression and 4% to 9% of prostate, breast, liver, ovarian, and colon cancers, were subjected to detection of genomic mutations by DNA suggesting that loss of the GSR gene occurs in a subset of human sequencing. cancers. We then tested whether loss of GSR in cancer cells will For siRNA-mediated gene knockdown, scramble control siRNA result in their vulnerability to auranofin, a TXNRD inhibitor (19). or siRNA targeting the GSR or the glutamate-cysteine ligase Our results show that reduced expression of enzymes required for catalytic subunit (GCLC) gene (all, Sigma-Aldrich) was trans- GSH homeostasis sensitized cancer cells to TXNRD inhibitor fected into cells with oligofectamine (Sigma-Aldrich) according auranofin. to the manufacturer's instructions. Plasmids for lentiviral vectors expressing cDNA or short-hairpin RNA (shRNA) used in this study were obtained from Open Biosystems through our institution's Materials and Methods shRNA and ORFeome Core facility. Lentiviral vectors were pack- Cell lines and cell culture aged in 293 cells after cotransfection with lentiviral packaging Human non–smallcelllungcancer(NSCLC)celllines, plasmids by using Fugene 6 as