Keith Singletary and colleagues at the University of Illinois at Urbana-Champaign exposed cultures of malignant human breast cancer cells to sulphoraphane. Within hours, it had blocked cell division and disrupted microtubules, which are long, slender cylinders made up of tubulin (protein), that are essential for the separation of duplicated chromosomes during cell division.
"This is the first report to show how the naturally occurring plant chemical sulforaphane can block late stages of the cancer process by disrupting components of the cell called microtubules," said Singletary, a professor in the department of food science and human nutrition. "We were surprised and pleased to find that SUL could block the growth of breast cells that were already cancerous."
Sulphoraphane is abundant in vegetables like broccoli, brussels sprouts and kale, and when these vegetables are chewed, they release the anti-cancer compound. More than 125 scientific papers have been published on sulphoraphane, broccoli and broccoli sprouts, with many of them focusing on sulphoraphane's anti-cancer activity, as well as its benefits for heart health.
Since its discovery by a John Hopkins team in 1992, a company called called Brassica Protection Products has been marketing patented concentrated forms of broccoli sprouts - three-day-old broccoli plants said to provide 20 times the concentration of sulphoraphane glucosinolate as found in adult broccoli.
They are currently sold in the US, Japan - where business is already robust - and New Zealand as a vegetable, and the company is looking for partners for use of the ingredient in other applications. It has recently been added to a tea.
However the products do not carry health claims and the new trial, published in the September issue of the Journal of Nutrition (134:2229-2236), lends further scientific support to potential claims in the future.
"It is not yet clear whether the doses required to produce inhibition of tubulin polymerization are higher than those achievable via dietary intakes," write Jackson and Singletary. "However, the results show that tubulin disruption may be an important explanation for SUL's antiproliferative action."
"These findings are significant since SUL's actions appear similar to a group of anticancer drugs currently in use, such as Taxol," added Singletary.
Sulphoraphane works as an 'indirect antioxidant', helping to boost the body's natural Phase 2 enzyme antioxidant defense systems and detoxifying carcinogens before they can damage cells. Typical direct antioxidant molecules, such as vitamins C and E, scavenge one free radical or other oxidant molecule at a time. But this means that once a direct antioxidant molecule binds to a free radical molecule, rendering it harmless, the antioxidant is consumed and is no longer active. They then have to be regenerated.
Sulphoraphane does not work directly on free radicals but up-regulates the defence system, letting the body itself fight free radicals.
The new findings may be helpful in the development of new breast cancer prevention and treatment strategies, according to Singletary. "For example, it may be possible that ingesting SUL in combination with certain natural compounds or drugs could enhance their anticancer effectiveness and reduce side effects."
According to the National Cancer Institute about one in eight women in the United States (approximately 13.3 percent) will develop breast cancer during her lifetime.
While improvements in treatments such as chemotherapy have improved the survival rate, some current chemotherapy drugs have side effects and researchers are seeking new strategies that combine chemotherapy drugs with other treatments to potentially lessen the toxic effects.
More research is however needed to assess SUL's potential in countering breast cancer development.
"What we do not know is how specific SUL and other similar phytochemicals are toward cancer cells compared to normal cells," said Singletary. "We also do not know against which cancers SUL's microtubule-targeting actions are most effective."