Soy Protein Extract (SPE) Exhibits Differential In Vitro Cell Proliferation Effects in Oral Cancer and Normal Cell Lines

ABSTRACT

Prior research has demonstrated that specific isoflavones derived from soy may exhibit antitumor effects against many cancers, including oral cancer. Most of this prior research involved isolation and testing of individual soy components, such as genistein, daidzein, and glycitein, which exhibit cytotoxicity against cancerous cells but may also have residual cytotoxic effects on normal cells. Few studies have evaluated whole soy extract, containing a combination of these isoflavones, and other bioreactive compounds, which may function synergistically and more effectively against oral cancers. This study compared the antiproliferative effects of whole soy protein extract (SPE) on CAL 27 and SCC25 oral cancer cell lines in vitro. Administration of SPE significantly inhibited oral cancer growth and exerted these effects at lower concentrations compared with another class of flavonoids (proanthocyanidins) that were previously tested on these cell lines. This SPE-induced growth inhibition correlated with down-regulated mRNA expression in the oral cancer cell-cycle promoter ornithine decarboxylase (ODC), as well as upregulation of caspase-2 and caspase-8, initiators and effectors of apoptosis. These results suggest that SPE may represent a potential chemopreventive or chemotherapeutic option for oral cancer. Moreover, SPE may be more effective than other flavonoids currently used and may be effective at lower concentrations that approximate physiologic serum levels (0–2 μmol/l). This study may help to explain why diets rich in fruits, vegetables, and soy protein are associated with protection against development and progression of oral cancers, although further study is needed to develop specific public health recommendations for oral cancer treatment and prevention.

KEYWORDS. :

• soy protein extract
• oral cancer
• in vitro
• apoptosis

ABOUT THE AUTHORS

Karl Kingsley, Ph.D., is affiliated with the Department of Biomedical Sciences, School of Dental Medicine, University of Nevada, Las Vegas, Nevada, USA. Khanh Truong, Erik Low, and Charles K. Hill, DMD, are affiliated with the Department of Clinical Sciences, School of Dental Medicine, University of Nevada, Las Vegas, Nevada, USA. Shruti B. Chokshi is affiliated with the College of Sciences, School of Life Sciences, University of Nevada, Las Vegas, USA. Don Phipps is affiliated with the College of Sciences, School of Life Sciences, University of Nevada, Las Vegas, USA, and the College of Life Sciences, Brigham Young University, Provo, Utah, USA. M. Abigail West is affiliated with the Las Vegas Academy, Las Vegas, USA. Mark A. Keiserman is affiliated with the Department of Nutritional Sciences, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, USA. Christine J. Bergman, Ph.D., is affiliated with the Department of Food and Beverage, Harrah Hotel College, University of Nevada, Las Vegas, USA.