ABSTRACT
PURPOSE: Tumor cells have increased turnover of nicotinamide adenine dinucleotide (NAD⁺), the main coenzyme in processes including adenosine diphosphate-ribosylation, deacetylation, and calcium mobilization. NAD⁺ is predominantly synthesized in human cells via the salvage pathway, with the first component being nicotinamide. Nicotinamide phosphoribosyltransferase (NAMPT) is the key enzyme in this pathway, and its chemical inhibition by FK866 has elicited antitumor effects in several preclinical models of solid and hematologic cancers. However, its efficacy in estrogen receptor (ER)-positive and human epidermal growth factor receptor 2-positive breast cancer cells has not been previously investigated. In this study, we aimed to deplete the NAD⁺ content of MCF-7 cells, a model cell line for ER-positive breast cancer, by inhibiting NAMPT in order to evaluate downstream effects on p53 and its acetylation, p21 and Bcl-2-associated X protein (BAX) expression, and finally, apoptosis in MCF-7 breast cancer cells. METHODS: MCF-7 cells were cultured and treated with FK866. NAD⁺ levels in cells were determined colorimetrically. Levels of p53 and its acetylated form were determined by Western blotting. Expression of p21 and BAX was determined by real-time polymerase chain reaction. Finally, levels of apoptosis were assessed by flow cytometry using markers for annexin V and propidium iodide. RESULTS: FK866 treatment was able to increase p53 levels and acetylation, upregulate BAX and p21 expression, and induce apoptosis in MCF-7 cells. Addition of exogenous NAD⁺ to cells reversed these effects, suggesting that FK866 exerted its effects by depleting NAD⁺ levels. CONCLUSION: Results showed that FK866 could effectively inhibit NAD⁺ biosynthesis and induce programmed cell death in MCF-7 cells, suggesting that NAMPT inhibitors may be useful for the treatment of ER-positive breast cancers.