The scientists tested turmeric, also known as curcumin, along with phenethyl isothiocyanate (PEITC), a naturally occurring substance particularly abundant in a group of vegetables that includes watercress, cabbage, winter cress, broccoli, Brussels sprouts, kale, cauliflower, kohlrabi and turnips. "The bottom line is that PEITC and curcumin, alone or in combination, demonstrate significant cancer-preventive qualities in laboratory mice, and the combination of PEITC and curcumin could be effective in treating established prostate cancers," said Ah-Ng Tony Kong, a professor of pharmaceutics at Rutgers, The State University of New Jersey.
The discovery was announced in the Jan. 15 issue of the journal Cancer Research by Kong and his colleagues at Rutgers' Ernest Mario School of Pharmacy.
Prostate cancer is the second leading cause of cancer death in men in the United States, with a half-million new cases appearing each year. The incidence and mortality of prostate cancer have not decreased in past decades despite tremendous efforts and resources devoted to treatment. This is because advanced prostate cancer cells are barely responsive even to high concentrations of chemotherapeutic agents or radiotherapy.
The authors noted that in contrast to the high incidence of prostate cancer in the United States, the incidence of this disease is very low in India. This has been attributed to the dietary consumption of large amounts of plant-based foods rich in phytochemicals – nonnutritive plant chemicals that have protective or disease-preventive properties.
Consequently, scientists have been investigating intervention options based on compounds found in edible and medicinal plants. They have had some success, and a majority of patients with prostate cancer are now combining the conventional therapies with these compounds as alternative, supplementary or complementary medications.
For Kong's study, researchers used mice bred so that their immune systems would not reject foreign biological material and injected the mice with cells from human prostate cancer cell lines to grow tumors against which the compounds could be tested.
"Despite convincing data from laboratory cell cultures, we knew little about how PEITC and curcumin would perform in live animals, especially on prostate cancer," Kong said. "So we undertook this study to evaluate how effective PEITC and curcumin might be – individually and in combination – to prevent and possibly treat prostate cancer."
The researchers injected the mice with curcumin or PEITC, alone or in combination, three times a week for four weeks, beginning a day before the introduction of the prostate cancer cells. They found the injections significantly retarded the growth of cancerous tumors. Using PEITC and curcumin in tandem produced even stronger effects.
The group went on to evaluate the therapeutic potential of curcumin and PEITC in mice with well-established tumors, and the results showed that PEITC or curcumin alone had little effect, whereas the combination of curcumin and PEITC significantly reduced tumor growth.
The paper, "Combined Inhibitory Effects of Curcumin and Phenethyl Isothiocyanate on the Growth of Human PC-3 Prostate Xenografts in Immunodeficient Mice," is available at cancerres.aacrjournals.org.
The authors are Tin Oo Khor, Young-Sam Keum, Wen Lin, Jung-Hwan Kim, Rong Hu, Guoxiang Shen, Changjiang Xu, Avanthika Gopalakrishnan, Bandaru Reddy, Xi Zheng, Allan H. Conney and Ah-Ng Tony Kong, all from Rutgers.