Anticancer Potential of Soy Peptides

187 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008.Leukemia is the most common type of cancer in children. Various topoisomerase inhibitors are currently used in the treatment of leukemia. Epidemiological studies have associated soy consumption with lowering cancer risk. However, the anticancer potential and mechanism of soy peptides have not been fully understood. The objective of this research was to evaluate the anticancer potential of soy peptides and to elucidate the role of lunasin on an established cancer cell line. The anticancer potential was determined by the inhibitory activities of L1210 leukemia cells and human DNA topoisomerases. Bioactive peptides were isolated and identified by a co-immunoprecipitation approach coupled with nanoLC-Q-TOF-MS/MS. Soy protein hydrolysates produced by simulated gastrointestinal digestion induced L1210 cytotoxicity through apoptosis independent pathway, possibly through inducing p21 overexpression and G2/M cell cycle arrest and inhibiting topoisomerase II activities. Matrix proteins were important to the bioactivity, and beta-conglycinin produced more active peptides than glycinin after simulated gastrointestinal enzyme digestion. Three topoisomerase II inhibitory peptides, FEITPEKNPQ, IETWNPNNKP and VFDGEL, were identified. Their interaction energies with CTD enzyme domain ranged from -186 to -398 Kcal/mol, as determined by molecular docking, correlated with IC50 values (2.4 to 7.9 mM) (R 2 = 0.99). A naturally present peptide in soy, lunasin, inhibited 50% of L1210 leukemia cell at 14 muM, and caused a dose-dependent G2 cell cycle arrest. Treatment with 1 mg/mL of lunasin enriched flour (27% purity) for 18 h led to an increase in apoptotic cells from 1.9% to 39.7%. Compared with untreated cells, lunasin enriched soy flour (1 mg/mL) treatment induced caspases 8 and 9 expression by up to 6-fold and, as a later event, caspase 3 by 12-fold. The results for the first time demonstrated the cytotoxicity of lunasin on established cancer cell lines, and indicated the important role of caspase cascade in leukemia cell cytotoxicity. In conclusion, enzyme hydrolysis increased the anticancer potential of soy proteins by releasing bioactive peptides.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD