Are Quercetin Effective in Treating Cancer?

Quercetin (3,4,5,7-pentahydroxylflavone) is a common chemical pigment in the rinds and barks of a wide variety of plants. It is found in many plants and foods, such as red wine, apples, onions, green tea,  berries, St. John’s wort, ginkgo biloba. Animal-based and test tube studies suggest that flavonoids do have anti cancer effects. Quercetin and other flavonoids have been shown in studies to inhibit the growth of cancer cells from prostate, colon, breast, lung, ovarian, and endometrial, tumors.

Quercetin Cancer Prevention and Treatment

Epidemiological studies suggest elevated quercetin consumption is associated with reduced risk of  various types of cancer. In vitro studies shown that the way quercetin inhibits cancer cell proliferation is by causing cell death and/or stopping the cells from growing at some point in the cellular reproductive cycle. In a animal study looked at the effect of quercetin on mice bearing abdominal tumors derived from a human pharyngeal squamous cell carcinoma line. The mice were given a daily intraperitoneal injection of quercetin. All doses analyzed (20-, 200-, 400- 800 mg/kg) showed significant inhibition of  tumor growth. The 20 mg/kg dose had an effect only slightly less than that seen with 800 mg/kg.  The researchers concluded that quercetin appears to be a selective inhibitor of tumor cell growth.

An early Phase I clinical trial of quercetin in patients with different cancer types showed a diminution in activity of enzymes required for tumor growth in nine of eleven patients studied. In a study reported in Carcinogenesis in 1991 found that quercetin reduced the incidence of colonic neoplasia in rodent models of mutagen-induced colon cancer. One clinical trial of individuals with a potent inherited tendency to develop colorectal cancer found that the combination of curcumin and quercetin  reduction the number and size of precancerous rectal tumors. Cleveland Clinic oncologists investigated quercetin in patients who had familial adenomatous polyposis. They combined the quercetin with curcumin, in 5 patients, treating and following them for 6 months. All patients had a diminution in both size (60%) and number of polyps (51%) over the course of therapy.

A 2005 study in the  Drug Metabolism and Disposition found that quercetin, halts the growth and induces apoptosis, of lung tumor cells in lab settings. The June, 2009 edition of  the Journal of  Experimental and Clinical Cancer Research demonstrated that quercetin is found to be protecting against the formation of  liver cancer cells, mainly due to its role as an antioxidant. In a article reported in Nutrition and Cancer in 2011, scientists found that quercetin blocks the ability of a carcinogenic chemical to induce cancerous changes in the liver cells of lab animals. Co-ingestion of quercetin with other flavonoids such as catechins can increase quercetin bioactive effects. Investigators from Rutgers University have reported the result of a study in the journal “Food and Function” that explains a synergistic relationship when green tea and quercetin are provided through. The study found that combining catechins with quercetin increased the cellular adsorption of  Epigallocatechin Gallate (EGCG) 2 times in kidney cancer cells and 4 times in lung cancer cells significantly increasing the effectiveness of this cancer fighting compound in vivo.

Quercetin has been shown to enhance the medicinal efficacy of cisplatin both in vivo and in vitro. In mice bearing human tumor xenografts, intraperitoneal therapy with a combination of 20 mg/kg quercetin and 3 mg/ kg cisplatin led to a significantly reduced tumor growth compared to therapy with either medication. An in vitro study demonstrated quercetin works synergistically with busulfan against human leukemia cell lines. Quercetin has been found to stop the angiogenesis of  the breast cancer cells, in those which have been resistant to medication tamoxifen, according to a research reported in Nov 2010 edition of  Food and Chemical Toxicity. Also, Quercetin has been shown in vitro to increase the cytotoxic effect of cyclophosphamide, and to lessen resistance to topotecan and gemcitabine.

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