Abstract #850: Cytotoxic activity of two pleurocidin-like cationic antimicrobial peptides against human breast cancer cells

Cationic antimicrobial peptides are small peptides that constitute an important defense against microbial pathogens and, in some cases, also exhibit potent cytotoxic activity against cancer cells. Atlantic pleuronectid flatfish are a particularly rich source of cationic antimicrobial peptides, including NRC-03 and NRC-07, which are pleurocidin-like peptides derived from winter and yellowtail flounder, respectively. The purpose of this investigation was to evaluate the potential of NRC-03 and NRC-07 as novel cytotoxic agents for the treatment of breast cancer. Colorimetric MTT and LDH-release assays showed that NRC-03 and NRC-07 rapidly killed MDA-MB-231, MDA-MB-468, MCF-7 and T47D human breast cancer cells in a time- and dose-dependent manner. Additionally, NRC-03 and NRC-07 were cytotoxic towards cisplatin-resistant human ovarian cancer cell lines. Colorimetric hemolytic assays revealed that neither NRC-03 nor NRC-07 possessed hemolytic activity. Human fibroblasts and umbilical vein endothelial cells were not harmed by NRC-03 or NRC-07; however, high concentrations of NRC-03 and NRC-07 were lytic for human T cells and mammary epithelial cells, suggesting that both peptides require modification to enhance breast cancer cell selectivity. Fluorescent microscopy revealed that fluorochrome-labeled NRC-03 and NRC-07 rapidly bound to the surface of breast cancer cells, but not human dermal fibroblasts, suggesting that peptide binding was required for cell death. Propidium iodide staining, as well as scanning electron microscopy, showed that NRC-03 and NRC-07 rapidly caused pore formation in the cellular membrane of breast cancer cells, suggesting that cell death was mediated by membrane lysis. However, flow cytometric analysis of dihydroethidium- or DiOC 6 -stained breast cancer cells revealed that NRC-03- and NRC-07-mediated cytotoxicity was also associated with reactive oxygen species production and mitochondrial membrane destabilization, respectively. Nevertheless, the pan-caspase inhibitor BOC-D-FMK did not prevent NRC-03- and NRC-07-induced cytotoxicity, supporting the hypothesis that NRC-03 and NRC-07 act primarily through a membrane-lytic mechanism. We conclude that NRC-03 and NRC-07 warrant further investigation as novel therapeutic agents for the treatment of breast cancer. Supported by Natural Science and Engineering Research Council of Canada, the Cancer Research Training Program, and the Canadian Breast Cancer Foundation - Atlantic Region Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 850.