Abstract 3594: Development of a TRPV1 inducible expression model in MCF-7 breast cancer cells and its potential role in the evaluation of calcium channels as viable therapeutic targets in cancer

Abstract

Abstract Calcium is an important intracellular messenger that regulates many physiological functions such as cellular differentiation, proliferation and apoptosis. Abnormal functioning of calcium signaling pathways may occur during tumorigenesis. Calcium signals are tightly controlled by calcium influx channels and many calcium channels, including those of the transient receptor potential (TRP) ion channel family have altered expression levels in specific cancer types, such as the upregulation of TRPM8 in some prostate cancers. Plasma membrane calcium channels belong to a protein class that can be effectively pharmacologically modulated. Pharmacological agents are available that modify specific TRP calcium channels and some voltage gated calcium channels, such as the inhibition of L-type calcium channels by the anti-hypertensive nifedipine. Both activators and inhibitors of calcium channels overexpressed in cancer cells are potential anti-cancer drugs. This is due to the duality of the calcium signal, whereby calcium can be both a promoter of proliferation but also an inducer of apoptosis. Therefore, calcium channels with increased expression and/or activity in cancer could potentially serve as anti-cancer therapeutic targets. To test this and to explore some of the likely issues related to calcium channels as drug targets in cancer, we have generated a Tet-Off inducible model system where the transient receptor potential vanilloid 1 (TRPV1) calcium channel is over-expressed in the MCF-7 Tet-Off breast cancer cell line. TRPV1 has been chosen in this model, due to the wide availability of selective inhibitors and activators to this channel. TRPV1 functional activity in the model system was measured by calcium influx using the Fluorescent Imaging Plate Reader (FLIPR) and the calcium sensitive probe Fluo-4. Capsaicin, a TRPV1 agonist had an EC50 of 2 × 10-7 M for increased cytosolic free calcium in the absence of doxycycline and an EC50 of 1 × 10-6 M in the presence of doxycycline (1µg/ml). In this same stable cell line, peak cytosolic responses were significantly higher in the absence of doxycycline compared to the presence of doxycycline. This suggests a tight regulation of TRPV1 expression in the Tet-Off system. Future studies will characterize the consequences of TRPV1 over-expression and TRPV1 pharmacological modulators on cellular proliferation and apoptosis pathways. This model system could be an important tool to address the feasibility of calcium channels as drug targets in cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3594.