Inhibition of Thioredoxin/Thioredoxin Reductase Induces Synthetic Lethality in Lung Cancers with Compromised Glutathione Homeostasis

Abstract

Glutathione (GSH)/GSH reductase (GSR) and thioredoxin/ thioredoxin reductase (TXNRD) are two major compensating thiol-dependent antioxidant pathways that maintain protein dithiol/disulfide balance. We hypothesized that functional deficiency in one of these systems would render cells dependent on compensation by the other system for survival, providing a mechanism-based synthetic lethality approach for treatment of cancers. The human GSR gene is located on chromosome 8p12, a region frequently lost in human cancers. GSR deletion was detected in about 6% of lung adenocarcinomas in The Cancer Genome Atlas database. To test whether loss of GSR sensitizes cancer cells to TXNRD inhibition, we knocked out or knocked down the GSR gene in human lung cancer cells and evaluated their response to the TXNRD inhibitor auranofin. GSR deficiency sensitized lung cancer cells to this agent. Analysis of a panel of 129 non-small cell lung cancer (NSCLC) cell lines revealed that auranofin sensitivity correlated with the expression levels of the GSR, glutamatecysteine ligase catalytic subunit (GCLC), and NAD(P)H quinone dehydrogenase 1 (NQO1) genes. In NSCLC patientderived xenografts with reduced expression of GSR and/or GCLC, growth was significantly suppressed by treatment with auranofin. Together, these results provide a proof of concept that cancers with compromised expression of enzymes required for GSH homeostasis or with chromosome 8p deletions that include the GSR gene may be targeted by a synthetic lethality strategy with inhibitors of TXNRD.Significance: These findings demonstrate that lung cancers with compromised expression of enzymes required for glutathione homeostasis, including reduced GSR gene expression, may be targeted by thioredoxin/thioredoxin reductase inhibitors.

Therapeutic cooperation between auranofin, a thioredoxin reductase inhibitor and anti‐PD‐L1 antibody for treatment of triple‐negative breast cancer

“…AF is known to induce a significant anticancer activity in vivo in some cancers, however, responses in vivo vary considerably and did not achieve complete tumor regression . Consistently, in our study, AF transiently reduced in vivo tumor growth in a murine 4T1.2 syngeneic model, human MDA‐MB‐231 xenograft and TNBC PDX model by inhibiting intracellular TrxR1 redox activity in primary tumors (Fig.…”

“…). Similar to lung cancer, TNBC cells with higher TrxR1 activity were susceptible to AF‐induced cell death as observed by reduced cell proliferation, PARP1 cleavage, γ H2AX accumulation and decreased clonogenic survival compared to non‐TNBC cells following AF treatment (Fig. ).…”

“…Inhibition of the Trx system by targeting the TrxR1 enzyme inhibits tumor cell proliferation and induces apoptosis in multiple cancer types . To decipher the role of the Trx system in TNBC cells and to assess their survival dependency on the Trx system, we used an FDA‐approved gold‐based TrxR1 inhibitor AF.…”

“…These two systems compensate for each other functionally in the absence of antioxidant activity . In lung cancer cells, downregulation of the GSH system upregulates the Trx system leaving these cells functionally dependent on Trx …”

Tumor characteristics associated with engraftment of patient‐derived non–small cell lung cancer xenografts in immunocompromised mice

“…[18][19][20] Although several groups have devoted efforts to generating and characterizing NSCLC PDXs, the overall PDX engraftment rates for NSCLC range from 25% to 40%, 2,[20][21][22] which is lower than the engraftment rates reported for colorectal cancer 23 and melanoma PDXs. Some of these PDX models have been used for the preclinical evaluation of anticancer agents [25][26][27] and are available to the cancer research community through the National Cancer Institute's PDXNet program (www.pdxfi nder.org). 16 The engraftment rate rose to approximately 35% when NOD SCID mice with null mutations of the gene encoding for the interleukin 2 receptor-γ (NOD scid gamma [NSG] mice) were used for PDX generation.…”