Calcium Channel Blockers as Novel Therapeutic Agents for Triple-Negative Breast Cancer

Abstract

<b>Abstract ID 21157</b> <b>Poster Board 447</b> Breast cancer is a prevalent disease among women in the U.S. One of the most aggressive subtypes of breast cancer is triple-negative breast cancer (TNBC) and is predominantly seen in young African American (AA) women. TNBC is characterized by the lack of three receptors: estrogen, progesterone, and human epidermal growth factor receptor 2. Current treatment includes surgery, chemotherapy, and radiation, none of which are successful against TNBC. A signature for the disease is high levels of intracellular calcium. Therefore, components that regulate calcium could be a potential target for developing novel treatment. Calcium signaling is immensely complex and maintenance of calcium homeostasis is strictly regulated. Calcium enters the intracellular space via voltage-gated calcium channels. Intracellular calcium is regulated by the gamma-butyrobetaine hydroxylase 1 (BBOX1) 1,4,5-inositol trisphosphate receptor 3 (IP3R3) complex on the endoplasmic reticulum (ER) and the store operated calcium entry (SOCE) mechanism. Binding of BBOX1 prevents IP3R3 ubiquitination. IP3R3 is responsible for protein stabilization, calcium homeostasis, and cellular bioenergetics. IP3R3 sends calcium from the ER to the mitochondria for mitochondrial function and glycolysis, ultimately leading to cell survival. This depletion of calcium in the ER activates the ER stromal interaction molecule 1 (STIM1) sensor to signal SOCE channels for calcium restoration back to the ER. Based on this information, this study hypothesizes that calcium channel blockers (CCBs) also exert their effects intracellularly by acting as a BBOX1 antagonist. By blocking BBOX1, this causes protease degradation of IP3R3 and blocks mitochondrial function and glycolysis, ultimately leading to cell apoptosis. TNBC cells from AA and European American (EA) women were treated with CCBs in a dose-dependent and time-dependent manner. Cell viability assessment was performed to test the efficacy of drug treatment. Western blots and RT-PCR were performed for analysis of protein and RNA expression. Reactive oxygen species assay was used to test for oxidative stress. Our data has shown that various CCBs decrease cell proliferation in TNBC cells in a dose-dependent and time-dependent manner. In addition, ethnic differences were shown to be dependent on drug treatment. Therefore, this study presents CCBs as novel therapeutic agents for TNBC. Support/Funding Information: NIH/NCI; HU/Georgetown Collaborative Partnership in Cancer Research (5P20CA242611-03)