Natural cancer drug available from soaking soybeans

A group of plant scientists at the University of Missouri have discovered a new, inexpensive approach to extracting an powerful anticancer chemical from soybeans. The incidence of a number of common cancers (breast, colorectal, prostate, bladder, lymphoma, and oral cancers) is lower in Japan by a factor of two to ten times than in North America or Western Europe (GLOBOCAN 2008). The medical profession is edging toward a conclusion that a significant portion of the reduction in alimentary system cancers and breast cancer is associated with the importance of the humble soybean to Japanese diets.

Researchers have considered the medical benefits of the soybean for centuries. However, the modern level of interest began with the identification of the Bowman-Birk Protease Inhibitor (BBI) in 1963.

This small protein (molecular weight of about 8,000 Daltons) has demonstrated strong cancer chemoprotective and anticancer treatment properties. It has been found effective against breast, colon, liver, lung, esophageal, and oral cancers. The studies are so impressive that BBI has been an FDA Investigational New Drug since 1992.

Unfortunately, BBI has also been very expensive (~US$2,000/gram at Sigma/Aldrich) owing to the very complex extraction sequence developed during its discovery. Early studies showed that BBI is found primarily in the soybean hulls (seed coats), which are generally removed before processing raw soybeans for the produce and fermentation markets. As a result, the hulls are extremely inexpensive at about $0.10 per kilogram. Ten percent of soybean hulls extracts as sugary solids with a protease inhibitor activity equivalent to about 70 mg/gram of solids, so that protease inhibitors make up about 7 mg/gram of the raw hulls.

Protease is any enzyme which starts the digestion of proteins by breaking peptide bonds in proteins. The extract of protease inhibitors consists of two main inhibitors, the Kunitz trypsin inhibitor and the Bowman-Birk protease inhibitor (BBI), which make up about 6 percent of the total protein of soybeans. However, the fraction with the largest level of protease inhibition is that containing BBI, a substance known to possess chemopreventive activity against a range of cancers.
BBI is traditionally purified by ammonium sulfate precipitation, organic solvent extraction, centrifugation, gel filtration, column chromatography, or high performance liquid chromatography. Each of these procedures is time-consuming, involves a variety of hazardous materials, and results in limited amounts of purified material. The result is, as mentioned earlier, an extremely expensive substance.

The Missouri plant scientists have invented a green procedure for extracting BBI from soybean hulls. They found that soybean hulls soaked in water at 122ºF (50ºC) for about four hours naturally release large amounts of BBI that can easily be harvested from the water. Higher extraction temperatures yield less BBI activity – apparently the protein will denature with very long exposures to 50ºC water. When the chemoprotective anticancer properties of the extracted BBI were tested, the extract proved capable of stopping the dividing of in-vitro breast cancer cell division.

There remains considerable research and testing to be carried out on soybean-extracted BBI. However, it provides another tempting and relatively harmless approach to fighting a wide range of cancers.