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Mining a Cancer-Fighting Soy Protein

Lunasin is a peptide in soybean seeds that’s been shown to inhibit the growth of certain cancerous cells in laboratory tests. It’s also being investigated for anti-inflammatory properties that might prove helpful in the battle against some chronic diseases.

Unfortunately, obtaining sufficient amounts of this prospective cancer-fighter has been a costly, time-consuming, and laborious affair. This, in turn, has impeded lunasin’s investigation in large-scale animal and human clinical trials.

Now, however, a team of Agricultural Research Service scientists has devised a fast new procedure for extracting lunasin in amounts suitable for conducting these trials.

“We have developed an alternative strategy that focuses on isolation of soy protein extract that is highly enriched in lunasin and protease inhibitors—proteins with well-established roles in cancer prevention,” write Hari Krishnan and Thomas Wang in the January 2015 online version of Food Chemistry. Krishnan, a molecular biologist, is in ARS’s Plant Genetics Research Unit in Columbia, Missouri. Wang is research leader of the agency’s Diet, Genomics, and Immunology Laboratory in Beltsville, Maryland.

Using the new procedure, they produced 3.2 grams of a concentrated form of lunasin, along with two protease inhibitors, from 100 grams of soybean flour. The actual extraction is done with a 30 percent solution of ethanol, followed by centrifuging steps and the addition of calcium chloride to further purify the concentrate.

According to Krishnan, the entire process takes less than 2 hours and yields far more lunasin and protease inhibitor concentrate than other methods that have been tried, including sophisticated chromatography procedures and live cultures of genetically modified yeast or bacteria. Besides being faster, the new method can also be easily scaled-up to yield much larger amounts.

Test-tube experiments conducted by Wang in Beltsville also demonstrated the extract’s biological activity, inhibiting the production of inflammation-causing cytokines by human leukemia cells derived from a line called THP-1, which is commonly used in biomedical research.

The team’s research comes at a time when breast cancer is the second leading cause of cancer-related deaths in American women and more scientific attention is being given to the preventive role that consuming soy or soy products can play in reducing that and other cancers, including colon and prostate.

Lunasin may work by turning off genes that enable cancerous cells to divide and spread to new sites. In 2013, University of Illinois researchers published the results of a USDA-funded study in which feeding cancer-injected mice 20 milligrams lunasin daily per kilogram of body weight reduced the number of tumors in the rodents’ livers by 94 percent. Trials with a larger sampling of mice are needed to better analyze those results, the researchers caution.—By Jan Suszkiw, Agricultural Research Service Information Staff.

“Mining a Cancer-Fighting Soy Protein” was published in the July 2015  issue of AgResearch Magazine.

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Key Facts

  • A soybean protein called “lunasin” has anticancer activity.
  • The protein is difficult to produce and purify until recently.
  • A new method yields 3.2 grams lunasin and other compounds from 100 grams soy flour.
  • The new method can be scaled up for higher yields.

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