Soy Peptide Increases Effectiveness of Colon Cancer Chemotherapy

A peptide isolated from soybeans was found to be a potent inhibitor of metastasis when tested together with the chemotherapeutic drug oxaliplatin in a mouse colon cancer model.

Investigators at the University of Illinois (Urbana, USA) examined the effect of the 43 amino acid soy peptide lunasin on three human colon cancer-cell lines in vitro and a liver metastasis model of colon cancer in vivo. Lunasin was administered either alone or in conjunction with the chemotherapeutic drug oxaliplatin. In previous clinical studies, oxaliplatin by itself had demonstrated only modest activity against advanced colorectal cancer. It has been extensively studied in combination with fluorouracil and folinic acid (a combination known as FOLFOX).

In the current study, a population of immunocompromised mice that had been infected with human colon cancer cells was divided into four groups: a control group that received no treatment; a group that was injected daily with lunasin; a group injected with the chemo drug oxaliplatin; and a group that received both lunasin and oxaliplatin. After 28 days, the mice were examined to learn the extent of cancer's involvement in the liver.

Results published in the September 10, 2011, online edition of the journal Cancer Letters revealed that the group that received lunasin alone (the dosage was the equivalent of 25 daily grams of soy protein) had 50% percent fewer metastatic sites than the controls. When lunasin was given together with oxaliplatin, spread of tumors was reduced by 82%.

At the molecular level, lunasin inhibited metastasis of human colon cancer cells by direct binding with alpha5beta1 integrin, which suppressed FAK/ERK/NF-kappaB signaling, and potentiated the effect of oxaliplatin in preventing the outgrowth of metastasis.

“When lunasin was used in combination with the chemotherapy drug oxaliplatin, we saw a sixfold reduction in the number of new tumor sites,” said senior author Dr. Elvira Gonzalez de Mejia, associate professor of food chemistry and food toxicology at the University of Illinois. “Two glasses of soymilk a day generally provide half the amount of lunasin used in our study," said Dr. de Mejia. “It certainly seems feasible to create a lunasin-enriched product that people could consume in a preventive way.”

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