Sulfur compounds in broccoli stop creation of breast cancer stem cells; effect should extend to kale, cabbage, and broccoli's many "cruciferous" cousins
by Craig Weatherby
As a killer of women, breast cancer runs a distant second to cardiovascular disease... but that’s no comfort.
Some 94,280 Americans will be diagnosed with breast cancer this year and 40,610 will die from the disease, according to the American Cancer Society.
Sulforaphane (SFN) from broccoli killed a majority of cancer stem cells in mice, and stopped breast tumor growth.
The benefits of SFN were seen both in mice given human breast tumors and in isolated human breast cancer cells.
The mice received large amounts of SFN by injection… levels that cannot be achieved by eating broccoli or other cruciferous vegetables.
However, the researchers said the levels of SFN needed to impact cancer could be achieved by taking the broccoli extract from which they extracted the SFN.
New findings suggest that sulforaphane—a compound abundant in broccoli, broccoli sprouts, and other cruciferous veggies—might help prevent or treat breast cancer by blocking the creation of cancer stem cells.
A University of Michigan team reports that sulforaphane killed cancer stem cells and prevented new tumors from growing… both in mice implanted with human breast cancer cells, and in cultured breast cancer cells (Li Y et al. 2010).
—or SFN for short
—has been tested in various cancers, with mixed results.
Breast cancer has often been selected as a subject because of the link, seen in epidemiological studies, between eating more broccoli and being less likely to have pre-menopausal breast cancer.
Broccoli and its cousins versus cancer… the background
Two years ago, we summarized current research into the anti-cancer properties of “cruciferous” veggies, which abound in sulfur-based compounds called glucosinolates (see “Broccoli and Company vs. Cancer and Aging”).
A few months later, scientists at UC Santa Barbara reported intriguing findings about SFN… a key glucosinolate compound.
SFN had already been shown to reduce the incidence and rate of artificially induced mammary tumors in animals. And we know that it both inhibits the growth of cultured human breast cancer cells and leads them to undergo apoptosis… a sort of “cellular suicide”.
The UC Santa Barbara team found that SFN stops the spread of human tumor cells by blocking cancer-cell division… and it works in virtually the same way as the plant-derived anti-cancer drugs taxol and vincristine (Azarenko O et al. 2008; see “Broccoli Curbs Breast Cancer like Chemo Drugs”).
While SFN is much weaker than taxol or vincristine, results like those from the UC Santa Barbara study suggest that frequent enjoyment of cruciferous veggies may help deter or curb certain cancers.
The cruciferous family includes broccoli, kale, cabbage, cauliflower, collard greens, Brussels sprouts, kohlrabi, turnip, rutabaga, radish, daikon, horseradish, mustard (seeds and greens), wasabi, and more.
Cancer stem cells... the latest target of research
Recent studies indicate that cancer stem cells have the capacity to help tumors resist attacks and to promote recurrence of cancer.
Evidence is building for the idea that various kinds of cancer—including cancers of the breast—are driven and sustained by small amounts of cancer stem cells.
While the exact nature and role of cancer stem cells remain unclear, they seem a logical target for drug development… and for using foods to help prevent, kill, or cripple breast cancer.
The Michigan researchers note that because current chemotherapies can do little against advanced or metastatic breast cancer, we need new approaches… including ones that target cancer stem cells.
Now, encouraging results from the University of Michigan lend new support to anti-cancer hopes for broccoli and company… hopes that, while unproven, have become increasingly credible.
Importantly, the new research suggests that there is yet another way in which the SFN found in broccoli and its cruciferous cousins may curb breast cancer.
Study finds broccoli extract could stem breast cancer cells
The new studies—conducted both in mice implanted with human breast tumors and in isolated human breast cancer cells—come from researchers based at the University of Michigan’s College of Pharmacy (Li Y et al. 2010).
Mice implanted with human breast cancer were injected with varying concentrations of sulforaphane (SFN) derived from a concentrated commercial broccoli extract.
They used several methods to track the number of various kinds of cancer stem cells in the tumors, and any changes in those numbers.
The Michigan team reported that sulforaphane injections decreased certain cancer cell populations by 65 to 80 percent and reduced the size of “primary mammospheres” by eight to 125 times and cut their number by 45 to 75 percent.
(Primary mammospheres are incipient, potentially cancerous mammary glands.)
Daily injection with sulforaphane for two weeks reduced a key kind of cancer stem cell by more than 50 percent, in various kinds of implanted tumors.
Interestingly, in addition to eliminating all cancer stem cells in the mice, those animals’ tumor cells failed to grow when they were re-implanted into other mice.
The results also showed that sulforaphane “down-regulated” a tumor self-renewal pathway called Wnt/beta-catenin, making this known bodily mechanism one possible explanation for the compound’s efficacy.
A (mild) caution on cruciferous veggies
Cruciferous vegetables contain enzymes that interfere with the formation of thyroid hormone, but cooking for 30 minutes significantly reduces these compounds.
And, like grapefruit, cruciferous vegetables promote an enzyme (CYP1A2) that is responsible for the elimination of toxins … a class of compounds which, from the body’s perspective, includes most medical drugs.
Thus, a diet high in cruciferous vegetables could increase the rate at which drugs are metabolized, thereby reducing their efficacy.
These effects provide another rationale for developing drugs or supplements that are free of these agents.
Just don’t overdo consumption of members of the cruciferous family, and cook them when possible.
Critically, the researchers noted that the sulforaphane injections had little effect on the animals’ normal, healthy cells.
And in addition to its known anti-cancer actions, SFN possesses properties that make it a plausible food-borne cancer fighter.
As the authors of the new study wrote, “Sulforaphane from broccoli extracts is efficiently and rapidly absorbed in the human small intestine and distributed throughout the body” (Li Y et al. 2010).
Broccoli and its cruciferous cousins probably can’t kill existing cancer
The concentrations of SFN used in the study were higher than what can be achieved by eating broccoli, broccoli sprouts, or other cruciferous vegetables.
While prior research suggests that the levels of SFN needed to impact cancer can be absorbed by the body from the broccoli extract they used to obtain pure SFN, the supplement’s positive or adverse effects in people, if any, are unknown.
While broccoli extracts are available in capsule form, their composition and SFN levels may vary widely.
The Michigan team is developing a method to extract and preserve sulforaphane and hope to conduct a clinical trial to test it for the prevention and treatment of breast cancer.
According to lead researcher Max Wicha, M.D., “This research suggests a potential new treatment that could be combined with other compounds to target breast cancer stem cells. Developing treatments that effectively target the cancer stem cell population is essential for improving outcomes.”
You can say that again, doc… it’s long past time that medical research expanded its focus from trial-and-error development of synthetic drugs to include likely food-borne allies.
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