Estrogen Receptor Is Required for Metformin-Induced Apoptosis in Breast Cancer Cells Under Hyperglycemic Conditions.

ABSTRACT

Backgrounds About 25% to 30% of estrogen receptor (ER)-positive breast cancer patients develop resistance to endocrine therapy. Human epidermal growth factor receptor 2 (HER2) has been shown to cooperate with several growth factors that regulate cellular energy metabolism, including the insulin-like growth factor 1 receptor (IGF-1R). Objective: As the first-line therapy for type 2 diabetes mellitus (T2DM) patients, metformin is widely known to inhibit the metabolic reprogramming of cancer cells. This study aims to investigate metformin's efficacy in inhibiting endocrine resistance related to genes regulating energy metabolism in both ER-positive and ER-negative breast cancer cell lines under hyperglycemic conditions. Design and methods: MDA-MB-361 (ER-positive, HER2-positive) and SKBR3 (ER-negative, HER2-positive) cancer cell lines were used to represent ER status. Cell viability and cell survival rate were measured using the colorimetric assay of Cell Counting Kit-8. All mRNA levels were quantified using real-time quantitative polymerase chain reaction preceded by reverse transcription. A P value of <.05 was considered statistically significant. Results: Unlike MDA-MB-361, SKBR3 were found to acquire resistance upon metformin treatment in hyperglycemic conditions. Moreover, the mRNA expression of IGF-1R and its downstream signaling, such as the mammalian target of rapamycin (mTOR), was not affected by metformin. Meanwhile, the mRNA expression level of ribosomal S6 kinase 1 (S6K1) was upregulated, whereas forkhead box O1 (FOXO1) was downregulated after metformin treatment in hyperglycemic conditions. Conclusions: This preliminary study suggests that an alternative pathway of metformin resistance may exist in the absence of ERα. Therefore, relying solely on metformin may be inadequate to inhibit the aggressiveness of breast cancer cells.

Navigating metformin's impact on breast cancer insights into resistance, alternative pathways, and the crucial role of estrogen receptor under high-glucose conditions Around 25% to 30% of breast cancer patients with estrogen receptor (ER)-positive tumors become resistant to hormone therapy. This study explores whether metformin, a drug commonly used for type 2 diabetes, can counteract this resistance by affecting genes linked to energy metabolism. The research focused on both ER-positive (MDA-MB-361) and ER-negative (SKBR3) breast cancer cell lines under high-glucose conditions. Results showed that although metformin inhibited the growth of ER-positive cells, it surprisingly promoted resistance in ER-negative cells. The expression of insulin-like growth factor 1 receptor (IGF-1R) and its downstream signals like mammalian target of rapamycin (mTOR) remained unaffected by metformin. However, metformin did alter the expression of other genes related to energy metabolism, suggesting that a different resistance pathway might exist in ER-negative cases. In conclusion, this early study implies that relying solely on metformin might not be sufficient to combat the aggressiveness of breast cancer cells, particularly in cases lacking ERα. More research is needed to understand alternative pathways and develop more effective strategies against resistance.