Hydroxycitric acid reverses tamoxifen resistance through inhibition of ATP citrate lyase

Lipid metabolic reprogramming is involved in mediating tamoxifen (TAM) response in breast cancer cells. Published microarray data indicated that ATP citrate lyase (ACLY) is overexpressed in TAM-resistant BC cells. Hydroxycitric acid (HCA) is a powerful competitive inhibitor of the enzyme ACLY, which links carbohydrates and lipids metabolism. However, whether inhibition of ACLY could modulate TAM response in TAM-resistant BC cells remained unexplored. Thus the current study aimed to explore the effect of ACLY inhibition on TAM-resistant BC cells. The cytotoxicity of TAM and/or HCA on LCC2 and its TAM-sensitive counterpart MCF7 cells was evaluated. Also, the effect of TAM and/or HCA treatments on ACLY protein levels were investigated by western blotting. In addition, the effects of TAM and/or HCA on caspase-3, Bax, and Bcl2 levels were evaluated by ELISA.; besides, and flow cytometric analysis was performed for the detection of apoptosis. Moreover, cholesterol and triglyceride contents of LCC2 and MCF7 were quantified colorimetrically. Our results demonstrated that TAM/HCA co-treatment synergistically diminished LCC2 and MCF7 cell viability, with the effect being more significant on LCC2. Mechanistically, TAM/HCA co-treatment decreases the expression level of ACLY in LCC2 by 74 %, while in MCF7 by only 59 %. Moreover, apoptosis marker caspase-3 and Bax were increased, while the anti-apoptotic Bcl2 was decreased. Furthermore, the cholesterol and TG contents were increased in LCC2 than in MCF7. Our data revealed that ACLY plays a key role in TAM resistance and ACLY inhibition by HCA-mediated sensitization of BC-resistant cells to TAM.