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Milk thistle
Silymarin marianum
Specific evidence for the role of silibinin in prostate cancer
treatment
Research suggests that the lower incidence of prostate cancer
among Asians living in Asia (compared with Asians living in the
United States and eating a standard Western diet) may be related
to a dietary lowering of biologically active androgen. Further
evidence to support this concept comes from the observation that
more than 75% of prostate cancers are androgen-dependent at initial
diagnosis. Prostate specific antigen (PSA), an important androgen-regulated
gene in both normal and cancerous prostate cells, has been shown
to be a particularly sensitive marker in the diagnosis and treatment
of the disease. The present study investigated the possible role
of the flavonoid antioxidant silibinin, a component of milk thistle,
in the regulation of this gene. Like other phytoestrogens, silibinin
is thought to have the potential to affect the progression of
hormone-dependent cancers. In this laboratory study, silibinin
was effective in decreasing intracellular and secreted levels
of PSA under serum- and androgen-induced conditions while retarding
cell growth by arresting the G1 phase of the growth
cycle. Silibinin treatment resulted in significant neuroendocrine
differentiation of the cancer cells, but not apoptosis. Further,
silibinin did not exert any apparent effects on normal cells,
only cancer cells. Decreased PSA levels caused by silibinin may
be attributable either to an inhibitory effect by silibinin against
PSA protein expression or by a direct inhibition of androgen receptor-mediated
PSA expression.
Zi X, Agarwal R. Silibinin decreases prostate-specific antigen
with cell growth inhibition via G1 arrest, leading
to differentiation of prostate carcinoma cells: implications for
prostate cancer intervention. Proc Natl Acad Sci USA 1999;
96: 7490-7495.
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