Flavonoids as Cancer Treatment Flavonoids are plant compounds known to have antioxidant properties in vitro and in vivo. Many of the thousands of flavonoids in nature have been studied for anti-cancer properties. Space does not permit a detailed discussion of this work. The most well characterized anti-tumor flavonoids are epigallocatechin gallate (from green tea),155 genistein (from soy and red clover),156,157 curcumin (from turmeric),158 silibinin (from milk thistle),159 and quercetin (from many yellow vegetables). The authors are presently preparing a review of the use of quercetin as cancer therapy. Flavonoids with Radiation Little is known about the effects of flavonoids on radiotherapy. An in vitro experiment showed post-treatment application of quercetin caused greater cell death in radiation-treated hepatoma cells than radiation alone. In the same experiment, genistein was showed to be associated with increased cell death from radiation when applied during or after treatment.160 Many different rutosides (flavonoids with similar structures to quercetin) were found to have neither a protective nor sensitizing effect on radiotherapy in experimental mouse tumors.161 There is not enough evidence currently to support or argue against the use of therapeutic doses of flavonoids together with radiation. Flavonoids with Chemotherapy Recent research has focused on the ability of flavonoids to increase the concentration of chemotherapeutics in tumor cells. Resistance to many chemotherapy agents is thought to be due to reduced accumulation in tumor cells.162 Oral administration of green tea in mice to increased the concentration of doxorubicin in two tumor types, but not in normal tissue. The anti-tumor activity of doxorubicin was enhanced 2.5 times.163 Another report confirmed this action of green tea, finding the tumor inhibition of doxorubicin increased from negligible to 62 percent. This report, however, determined the activity of green tea to be due to an amino acid, theanine, rather than its flavonoid content.164 Quercetin has been shown in vitro to increase the concentration of doxorubicin in multidrug-resistant human breast cancer cells.165 Conversely, quercetin decreased the concentration of doxorubicin in a resistant human colon cancer cell line.166 Quercetin and genistein both increased the concentration of daunorubicin in some multidrug-resistant cell lines, but had no effect in others.167 Genistein in vitro increased the concentration of cisplatin in resistant cell lines.168 Other than the green tea studies, none of these studies analyzed cell death due to flavonoid administration. In mice with transplanted human tumors, quercetin (20 mg/kg) given with cisplatin reduced tumor growth to a greater degree than cisplatin alone.169 In a separate experiment, quercetin enhanced the effect of cisplatin and busulfan in vitro and in vivo. No enhancement or reduction of the anti-tumor activity of doxorubicin or etoposide was seen.170 An in vitro study found quercetin increased the effect of doxorubicin against resistant breast cancer cells.165 It should be cautioned, however, that a recent study showed a potential adverse interaction. Tangeretin, a flavonoid found in citrus fruits, completely blocked the inhibitory effect of tamoxifen on mammary cancer in mice.171 One in vitro study suggests attenuation of tamoxifen may be a concern with genistein as well.172 Another in vitro study, however, shows tamoxifen and genistein synergistically inhibit the growth of estrogen receptor-negative breast cancer cells.173 Until the flavonoid-tamoxifen interactions are investigated more completely, it may be best to avoid using therapeutic doses of flavonoid compounds in breast cancer treated with tamoxifen. Alternative Medicine Reviews, 1999;4(5):304-329 Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.