2-methoxyestradiol sensitizes tamoxifen-resistant MCF-7 breast cancer cells via downregulating HIF-1α

The clinical studies for breast cancer (BC) are now assessing the efficacy of 2-Methoxyestradiol (2-ME), a naturally occurring derivative of estradiol. Our study aimed to explore the potential of combining the 2-ME and tamoxifen (TAM) on sensitization of TAM-resistant cells using LCC2 the TAM-resistant cells as a model and comparing the results to the sensitive cells MCF-7. Sulphorhodamine-B (SRB) assay is used to examine the 2-ME chemo-sensitizing impact on the cytotoxicity of TAM on LCC2 cells. Colorimetric assay kits were used to assess the level of the apoptosis-related markers caspases 3, Bcl2, and Bax in cell lysate. Hypoxia-inducible factor 1 alpha (HIF-1α) expression was measured using western blotting. Total cholesterol and triglyceride (TG) levels were examined colorimetrically, using the BIOLABO kit. The use of 2-ME enhanced the cytotoxic effects of TAM and effectively reversed TAM resistance. This was achieved by inhibiting the expression of HIF-1α, while concurrently increasing the levels of apoptotic marker caspase-3, as well as the pro-apoptotic protein Bax. Additionally, there was a reduction in the levels of Bcl2, an anti-apoptotic protein. Furthermore, a reduction in TG and cholesterol levels was noted. Our findings show that HIF-1α plays an important role in TAM resistance and that suppression of HIF-1α by 2-ME-mediated sensitization of BC-resistant cells to TAM. Therefore, the concurrent administration of TAM/2-ME might potentially serve as a viable therapeutic approach to address TAM resistance and enhance the overall therapy efficacy for patients with BC.