In vitro actions on human cancer cells and the liquid chromatography-mass spectrometry/mass spectrometry fingerprint of phytochemicals in rice protein isolate

Rice protein isolate (RPI) has been reported to reduce the incidence of 7,12-dimethylbenz[a]anthracene- induced mammary tumors in rats. To determine the potential role of phytochemicals associated with the RPI, we studied in vitro antitumor activities of an ether fraction from RPI using human tumor cell lines, including two human breast carcinoma cell lines (MDA-MB-453 and MCF-7) and two myeloma cell lines (RPMI-8226 and IM-9). Concentration-dependent antiproliferative effects of the ether fraction were observed in all cell lines using the standard 3-[4,5-dimethylthiazol-2-yl]2,5- diphenyltetrazolium bromide assay. Fraction-induced apoptosis (P < 0.05) was detected in all cell lines, and this was associated with the induction of proapoptotic bax protein and cdk inhibitors (p21) and the suppression of cdk4 and cyclin D1 activity. Liquid chromatography-mass spectrometry/ mass spectrometry (LC-MS/MS) with both positive and negative modes was used to analyze the phytochemicals in the ether fraction from RPI. Fifty-seven phytochemicals were identified or characterized by their diagnostic fragmentation patterns and direct comparison with the authentic standards on the basis of electrospray ionization-MS/MS data. The major components bound to RPI were lysoglycerophospholipids, fatty acids, and fatty acid 3-[2-(2,3-dihydroxy-propoxycarbonyl)-2hydroxy-ethoxy]-2-hydroxy-propyl esters.