Advanced stages of cancer are highly associated with short overall survival in patients due to the lack of long-term treatment options following the standard form of care. New options for cancer therapy are needed to improve the survival of cancer patients without disease recurrence. Auranofin is a clinically approved agent against rheumatoid arthritis that is currently enrolled in clinical trials for potential repurposing against cancer. Auranofin mainly targets the anti-oxidative system catalyzed by thioredoxin reductase (TrxR), which protects the cell from oxidative stress and death in the cytoplasm and the mitochondria. TrxR is over-expressed in many cancers as an adaptive mechanism for cancer cell proliferation, rendering it an attractive target for cancer therapy, and auranofin as a potential therapeutic agent for cancer. Inhibiting TrxR dysregulates the intracellular redox state causing increased intracellular reactive oxygen species levels, and stimulates cellular demise. An alternate mechanism of action of auranofin is to mimic proteasomal inhibition by blocking the ubiquitin–proteasome system (UPS), which is critically important in cancer cells to prevent cell death when compared to non-cancer cells, because of its role on cell cycle regulation, protein degradation, gene expression, and DNA repair. This article provides new perspectives on the potential mechanisms used by auranofin alone, in combination with diverse other compounds, or in combination with platinating agents and/or immune checkpoint inhibitors to combat cancer cells, while assessing the feasibility for its repurposing in the clinical setting.

Auranofin (AF) is a gold compound approved in 1985 as a main treatment against rheumatoid arthritis. However, as new anti-rheumatoid agents displaced the use of AF, there have been studies aiming to repurpose the drug to treat other diseases, including cancer. In this study, we investigated the potentiality of AF to impair the growth of high-grade serous ovarian cancer (HGSOC) cells regardless of platinum (CDDP) sensitivity. Preliminary studies utilizing a colorimetric proliferation assay revealed that HGSOC cells that are clinically sensitive (PEO1) or resistant (PEO4) to CDDP-based chemotherapy are both equally sensitive to the growth inhibition induced by AF. The resistant factor estimated for AF-defined as the ratio between IC50 values calculated for the resistant cells and for the sensitive ones—was close to one, suggesting that CDDP-resistant PEO4 cells are equally sensitive to AF than CDDP-sensitive PEO1 cells. As expected, the resistant factor for CDDP was 12-fold higher in PEO4 compared to PEO1. The toxicity of AF against HGSOC cells was further studied exposing PEO1 to various concentrations of AF and assessing cell number, cell viability, and cell cycle traverse after 72 h. Results showed that AF, in a dose-dependent manner, blocked cell proliferation and caused accumulation of cells with hypo-diploid DNA content, suggesting that AF-induced cytotoxicity was associated not only with inhibition of cell proliferation but also with cell death likely driven via apoptosis. We further studied the long-term or residual toxicity of AF by exposing PEO1 cells that were alive, after 72 h treatment with AF, to a clonogenic survival assay. The results clearly demonstrated that even if not dying within 72 h, the cells were affected in a manner not compatible with long-term cell cycle progression as demonstrated by the formation of ‘abortive' colonies (i.e. colonies with few cells that show abnormal phenotypes). Finally, as AF is a pro-oxidant agent, we evaluated whether AF-induced cell death was mediated by oxidative stress by incubating PEO1 cells with AF in the presence or absence of the anti-oxidant N-acetyl-cysteine (NAC). PEO1 cells treated with AF and NAC showed no decrease in cell viability and cell number in comparison to PEO1 cells treated with AF alone. This data reveals that AF most likely induces cell death in a reactive oxygen species (ROS)-dependent manner. In conclusion, our results suggest that AF can equally impair the growth of CDDP-sensitive or -resistant HGSOC cells, and that its toxicity is likely mediated by oxidative stress. Citation Format: Farah H. Abdalbari, Alicia A. Goyeneche, Elvis Martinez-Jaramillo, Siham Sabri, Carlos M. Telleria. Repurposing the anti-rheumatic gold compound auranofin for high-grade serous ovarian cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1014.

High-grade serous ovarian cancer (HGSOC) is the 11th most common cancer-causing death in women. HGSOC is treated with platinum (Pt)-based chemotherapy, to which patients develop resistance over time, leaving them with very limited therapeutic options. Thus, new treatments are needed for these patients. In the present work, we provide evidence for the in vitro anti-HGSOC efficacy of the gold complex auranofin (AUF), a compound approved in the clinic in the 1980’s as an anti-rheumatic agent. AUF targets thioredoxin reductase 1 (TrxR1), which is overexpressed in many cancers, including ovarian cancer. Using the Kaplan-Meir plotter database we analyzed that high expression of TrxR1 predicted poor overall survival, suggesting that TrxR1 plays an important role in ovarian cancer progression. We show that AUF impairs the growth of HGSOC cells regardless of Pt sensitivity. HGSOC cells obtained from the same patient when it was clinically sensitive (PEO1) or resistant (PEO4) to Pt-based chemotherapy, were both equally sensitive to the growth inhibition induced by the gold complex in a concentration-dependent manner when using an MTT reduction assay. The toxicity of AUF against HGSOC cells was further studied exposing PEO1 cells to the compound and assessing cell number, cell viability, and cell cycle traverse. Results showed that AUF blocked cell proliferation, reduced viability, and caused accumulation of cells with hypo-diploid DNA content, suggesting a likely apoptosis-mediated cell death mechanism. We confirmed that AUF-triggered lethality was driven by apoptosis by measuring the accumulation of Annexin V positive/7-AAD negative cells via flow cytometry. We also found out that the lethality of AUF required the induction of oxidative stress because the effect was prevented by the presence of the reactive oxygen species (ROS) scavenger N-acetyl-cysteine. We further show that AUF-induced ROS production is associated with the generation of DNA damage as denoted by the increase in the phosphorylation of the Ser-139 residue of the histone variant H2AX by western blotting thus signaling a genotoxic endpoint. Finally, we generated evidence that the combination of AUF and the Pt agent cisplatin (CDDP) is more potent than either drug alone in inducing lethality in PEO4 cells isolated from a patient when Pt-resistant. In summary, we provide proof-of-principle that the TrxR1 inhibitor AUF impairs the survival capacity of HGSOC cells regardless of their Pt sensitivities, triggering a program of apoptosis induced by oxidative stress that is associated with DNA damage; such toxicity is enhanced when AUF is combined with CDDP. The novelty of this work for cancer research in general and HGSOC in particular is that, as AUF is clinically approved to treat arthritis-related conditions, the compound can be rapidly repositioned as a consolidation therapy following Pt-based standard of care and/or overcome Pt resistant disease. Citation Format: Farah H. Abdalbari, Alicia A. Goyeneche, Elvis M. Jaramillo, Siham Sabri, Carlos M. Telleria. Anticancer effects of the gold complex auranofin on high-grade serous ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4066.