The efficacy of indoximod upon stimulation with pro-inflammatory cytokines in triple-negative breast cancer cells

Abstract

Background

Indoleamine 2,3-dioxygenase (IDO) inhibition has received much attention in cancer immunotherapy due to its role in immune escape in cancer cells. Additionally, changes in the pro-inflammatory cytokine levels can affect tumor growth and metastasis as well as the effectiveness of immunotherapy. The purpose of this study was for the first time to determine the effects of indoximod as an IDO inhibitor on triple-negative breast cancer (TNBC) and to assess the link between the efficacy of indoximod and IFN-γ or TNF-α stimulation.

Methods

The cytotoxic and apoptotic effects of indoximod alone or IFN-γ or TNF-α induction to mimic an inflammatory environment were evaluated by WST-1, Annexin V, cell cycle analysis, and acridine orange (AO)/ethidium bromide (EtBr) staining. Furthermore, the expression levels of IDO1 and PD-L1 expression were analyzed by RT-PCR.

Results

Our results demonstrated that indoximod significantly decreased the TNBC cell viability through apoptotic cell death (p < .05). The combination of indoximod and TNF-α was more effective than indoximod and IFN-γ stimulation or indoximod alone in TNBC cells. Additionally, PD-L1 expression level was significantly up-regulated after treatment with indoximod and TNF-α or IFN-γ combinations (p < .05).

Conclusions

Indoximod exhibited a therapeutic potential in TNBC cells and pro-inflammatory cytokines could affect the effectiveness of indoximod. However, further studies are required to identify the role of the IDO-associated signaling pathways, the molecular mechanisms of indoximod induced apoptotic cell death, and the relationship between IDO inhibition by IDO inhibitors and pro-inflammatory cytokine levels.

Keywords:

• Triple-negative breast cancer
• indoleamine 2,3-dioxygenase (IDO)
• indoximod
• pro-inflammatory cytokines

Ethical approval

This study does not require ethical approval.

Disclosure statement

The authors declare that they have no conflict of interest.

Author contributions

GGE and CB conceived and designed research. GGE conducted experiments. GGE and CB analyzed data and wrote the manuscript. All authors read and approved the manuscript and all data were generated in-house and that no paper mill was used.

Data availability statement

All data generated or analyzed during this study are included in this published article.

Additional information

Funding

This work was supported by grants from the Scientific Research Projects Foundation of the Sakarya University in Turkey [Project No: 2018-3-12-243].