Sulfurous agent in cruciferous vegetables mimics the anti-cancer mechanism of plant-derived chemotherapy drugs
by Craig Weatherby
Judging by the results of new research, broccoli and its “cruciferous” botanical cousins richly deserve their reputation as deterrents to breast cancer.
Population studies worldwide show that diets high in cruciferous vegetables reduce the risk of cancers of the breast, endometrium, lung, colon, liver, colon, and cervix
The botanical name of this plant family—Cruciferae—derives from the cross-like marking on the flower-buds of some of its members, which include broccoli, kale, cauliflower, cabbage, bok choy, kale, kohlrabi, Brussels sprouts, horseradish, mustard, capers, cress, rutabaga, arugula, and turnips.
The anti-cancer powers of cruciferous vegetables are attributed to a class of compounds called glucosinolates, which our bodies break down into byproducts called isothiocyanates.
Broccoli family's anti-cancer actions had been ill-defined
Glucosinolates and isothiocyanates boost the body's antioxidant status, inhibit cell proliferation, and induce detoxification enzymes that help eliminate cancer-promoting toxins.
But the mechanism(s) by which cruciferous vegetables' anti-cancer glucosinolates inhibit cell proliferation—a key anti-cancer effect—was uncertain until now.
Lead author Olga Azarenko, from the University of California at Santa Barbara, made these comments in a press release (UC 2008):
“Breast cancer, the second leading cause of cancer deaths in women, can be protected against by eating cruciferous vegetables… [which] contain compounds called isothiocyanates we believe to be responsible for the cancer-preventive and anti-carcinogenic activities in these vegetables. Broccoli and broccoli sprouts have the highest amount of the isothiocyanates.”
She went on to say, “Our paper focuses on the anti-cancer activity of one of these compounds, called sulforaphane, or SFN. It has already been shown to reduce the incidence and rate of chemically induced mammary tumors in animals. It inhibits the growth of cultured human breast cancer cells, leading to cell death.”
Broccoli sprouts are the richest sources of SFN, and the results of a recent pilot clinical study show that eating broccoli sprouts raises the levels of SFN in women's breast tissue (Cornblatt BS et al. 2007).
It also appears that cooking tends to reduce the bioavailability of the SFN in cruciferous veggies, so it is better to cook broccoli and its cousins as lightly as is possible and palatable (Rungapamestry V et al. 2007).
Broccoli compound apes action of chemotherapy drugs
Scientists at UC Santa Barbara have discovered how the deterrent power of these vegetables works at the cellular level (Azarenko O et al. 2008).
Ms. Azarenko's team made the surprising discovery that SFN inhibits the proliferation of human tumor cells by a mechanism similar to the way that the anti-cancer drugs taxol and vincristine inhibit cell division during mitosis: the process during which the duplicated DNA in chromosomes is distributed to the two daughter cells when a cell divides.
Like many chemotherapy drugs, taxol and vincristine are derived from plants, with taxol isolated from the Pacific yew tree (Taxus brevifolia), and vincristine isolated from the Madagascar periwinkle (Catharanthus roseus).
Hundreds of tiny tube-like structures, called microtubules, make up the machinery that cells use to separate the chromosomes.
Like taxol and vincristine, SFN interferes with microtubule functioning during mitosis in a similar manner.
However SFN is much weaker than these other plant-based drugs, and thus much less toxic. (Taxol and vincristine affect all rapidly dividing cell types, including cancer cells, but also intestinal epithelium and bone marrow.)
These exciting findings open the possibility that SFN could be combined with taxol and similar drugs, to kill tumor cells with lower drug doses and reduced side effects.
- Azarenko O, Okouneva T, Singletary KW, Jordan MA, Wilson L. Suppression of microtubule dynamic instability and turnover in MCF7 breast cancer cells by sulforaphane. Carcinogenesis. 2008 Dec;29(12):2360-8. Epub 2008 Oct 23.
- Cornblatt BS, Ye L, Dinkova-Kostova AT, Erb M, Fahey JW, Singh NK, Chen MS, Stierer T, Garrett-Mayer E, Argani P, Davidson NE, Talalay P, Kensler TW, Visvanathan K. Preclinical and clinical evaluation of sulforaphane for chemoprevention in the breast. Carcinogenesis. 2007 Jul;28(7):1485-90. Epub 2007 Mar 7.
- Fahey JW, Zhang Y, Talalay P. Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens. Proc Natl Acad Sci U S A. 1997 Sep 16;94(19):10367-72.
- Rungapamestry V, Duncan AJ, Fuller Z, Ratcliffe B. Effect of cooking brassica vegetables on the subsequent hydrolysis and metabolic fate of glucosinolates. Proc Nutr Soc. 2007 Feb;66(1):69-81. Review.
- Shapiro TA, Fahey JW, Dinkova-Kostova AT, Holtzclaw WD, Stephenson KK, Wade KL, Ye L, Talalay P. Safety, tolerance, and metabolism of broccoli sprout glucosinolates and isothiocyanates: a clinical phase I study. Nutr Cancer. 2006;55(1):53-62.
- University of California / Santa Barbara (UC). UCSB Scientists Show How Certain Vegetables Combat Cancer. December 23, 2008. Accessed online December 27, 2008 at http://www.ia.ucsb.edu/pa/display.aspx?pkey=1902