magnolia and canecrThe magnolia tree is not just beautiful—it’s also the source of a potentially potent cancer-fighting drug. Researchers at the University of Pittsburgh have discovered that honokiol, a substance extracted from the root and stem bark of one species of magnolia tree, may help treat—or even prevent—prostate cancer.

Honokiol has been an important component of traditional Japanese and Chinese medicine because of its anti-inflammatory, anti-bacterial, and anti-allergic properties. A few studies have found that honokiol also can interfere with several processes that help cancer cells multiply and spread.

A recent study in the journal Clinical Cancer Research looked at the effects of honokiol on different types of prostate cancer cells. Two types of cell—PC-3 and C4-2—do not depend on male hormones (androgens) to grow. Another type of prostate cancer cell—LNCaP—does respond to androgens.

In one part of the study, researchers gave male nude mice 1, 2, or 3 milligrams of honokiol three times a week by mouth. Giving the drug this way has an advantage over injections, according to lead author Shivendra Singh, MD, PhD, Director for Basic Research and professor of Pharmacology and Urology at the University of Pittsburgh. “Orally active agents are highly desirable since they do not require supervised administration,” says Dr. Singh.

The researchers then implanted PC-3 prostate cancer tumor cells into the mice, and began to measure tumor growth. In mice given the 2-milligram dose of honokiol, the tumors were significantly smaller than tumors in mice that had not received the drug.

Treatment with honokiol halted prostate cancer cell growth in several ways: it decreased cell reproduction, led to a form of programmed cell death called apoptosis, and blocked the formation of blood vessels that feed tumors, according to the researchers. What’s more, mice treated with honokiol didn’t show any side effects.

The authors also looked at the effects of honokiol on PC-3 and C4-2 cells in the laboratory. They found that the drug inhibited growth and apoptosis in these types of prostate cancer cells, as well.

This was the first study to show the effects of oral honokiol on PC-3 prostate cancer cells, and the first to show that this treatment increases cell death and decreases cell reproduction in prostate cancer cells, regardless of whether they are androgen responsive. The results indicate that honokiol has great promise as a prostate cancer therapy, Dr. Singh says.

The authors refer to honokiol as a “promiscuous” drug because it has so many different biological effects. It also appears to be effective for lung cancer, colorectal cancer, and other types of cancers.

More research is needed to confirm honokiol’s effects on prostate cancer and other types of cancer cells. “We are thinking about doing a combination study with other bioactive compounds,” Dr. Singh says. “Ultimately, we want to conduct a human study.”

Hahm ER, Arlotti JA, Marynowski SW, Singh SV. Honokiol, a constituent of oriental medicinal herb Magnolia officinalis, inhibits growth of PC-3 xenografts in vivo in association with apoptosis induction. Clin Cancer Res. 2008;14:1248-1257.

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