OBJECTIVES One of the characteristics of malignant cells is a constitutively increased expression of nuclear respiratory factor-2 (NRF2), a transcription factor which increases expression of genes of the mechanisms of antioxidant protection as well as other detoxification and protective mechanisms. Therefore, selective reduction of NRF2 expression in malignant cells is a modern concept of developing new therapeutic strategies in the treatment of oncological patients. The main objective of this in vitro study is to study the effect of bile acid, ursodeoxycholic acid (UDCA) on the cytotoxic activity of doxorubicin as well as the impact on the expression of NRF2 and antioxidant enzymes at the transcription level in breast human breast adenocarcinoma cells.

METHODS Human breast adenocarcinoma cells (MCF-7) were incubated in a medium containing doxorubicin (0,25nM) and a non-toxic concentration of UDCA (50 uM). After incubation for 24 h, cytotoxicity was determined using the MTT assay, whereas gene expression was determined using RT-qPCR method.

RESULTS Incubation of MCF-7 cells with doxorubicin and UDCA resulted in an increase in cytotoxicity compared to the group of cells incubated with doxorubicin only (p=0.005). Treatment of cells with doxorubicin significantly reduced the expression of NRF2, SOD, and GR compared to the control group (p<0.001; p<0.001; p=0.002, respectively). In the co-treated cells, the expression of NRF2 was also significantly reduced (p=0.004), however, the expression of SOD and GR was highly statistically significantly reduced (p<0.001) compared to the group of cells incubated with doxorubicin only.

CONCLUSIONS Results of this in vitro study indicate that UDCA has the potential to modify the response of malignant cells to doxorubicin-induced oxidative stress at the gene expression level, thereby increasing the cytotoxic activity of doxorubicin towards MCF-7 cell line. Acknowledgment:Supported by HORIZON2020 MEDLEM project No.690876, Project for Scientific Development of Vojvodina No. 114-451-2072-/2016-02, and project III41012 of Ministry of Education of Republic of Serbia.