Milk Thistle Compound Stops Lung Cancer

DENVER, Colo.--Silibinin, a flavanone derived from the primary milk thistle (Silybum marianum) flavonoid silymarin, curbed angiogenesis of urethane-induced tumors in mice lungs, according to a study published in the June 21 issue of the Journal of the National Cancer Institute (98, 12:846-55, 2006).

In the study, researchers from the University of Colorado, here, injected mice (groups of 15) with either saline or cancer-causing urethane, and fed them normal diets for two weeks. Then they fed some of the mice diets containing different doses of pure silibinin (zero- to one-percent, from Sigma Chemical) for 18 or 27 weeks. Immunohistochemistry and Western blot analysis were used to examine angiogenesis (formation of new blood vessels) and enzymatic markers of inflammation, proliferation and apoptosis.

The urethane-injected mice who also consumed silibinin had significantly reduced lung tumors compared to those not taking silibinin. In fact, the urethane mice taking one-percent silibinin for 18 weeks had 93-percent fewer large lung tumors than control mice. Also, lung tumors in the mice taking silibinin had 41- to 74-percent fewer cells positive for cell proliferation markers, proliferating cell nuclear antigen and cyclin D1 (a marker of proliferation and cancer). And, tumor microvessel density was reduced by 89 percent in the silibinin mice. Administration of the flavanones also seemed to decrease lung tumor expression of vascular endothelial growth factor (VEGF), as well as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), two enzymes that that promote lung tumor angiogenesis and progression (by inducing VEGF).

The scientists concluded silibinin inhibits lung tumor angiogenesis in an animal model and warrants further investigation as a chemopreventive agent for suppressing lung cancer progression. However, lead researcher Rana Singh, Ph.D., noted the study used pure silibinin in a diet prepared at room temperature and air dried. "We did not use milk thistle dietary supplements, which are available for human consumption," she cautioned. "We have been studying milk thistle components, silymarin and silibinin, to examine their efficacy and mechanisms against different...cancers for over a decade."