Polyphenols and Prostate Cancer Prevention

By Belle McCaleb ND, RN, MSS-C, BSN, RYT

 

Prostate cancer has a long latent period, tumour marker availability (PSA) and easily identifiable precancerous lesions and is therefore an ideal candidate for chemoprevention or the use of specific natural (dietary) agents to prevent, delay or slow the carcinogenic process.  According to the National Cancer Institute of the US about 400 different compounds have been listed as potential chemopreventative agents and about 40 are currently under clinical evaluation.  Polyphenols are one class of such agents and preclinical models of carcinogenesis have demonstrated notable efficacy of several polyphenols including epigallocatechin-3-gallate, curcumin, resveratrol, quercetin and genistein.

 

Epigallocatechin-3-gallate or EGCG is the major phenolic compound found in green tea and many epidemiological studies have found a correlation between increased green tea consumption and decreased development of and progression of prostate cancer. This may be due to its many anti-cancer actions including inhibition of cellular proliferation, induction of natural cell death (apoptosis) in cancer cells, induction of cellular detoxification and reduction of oxidative damage to DNA. In one study, a phenolic compound consisting of ECGC, green tea extract, black tea extract and theaflavins inhibited enzymes involved in angiogenesis and cancer spread. Another double blind placebo controlled trial of men with premalignant lesions found a 90% reduction in development of prostate cancer following the use of green tea in a capsule form.

 

Curcumin is a major chemical component of turmeric that has been used medicinally for centuries throughout Asia.  Over the past decade its anticarcingenic properties have been unequivocally substantiated in numerous studies.  The chemopreventative properties of curcumin are attributed to its effect on several molecular targets within cells leading to apoptosis in both androgen-dependent and independent cell lines.  Curcumin has been found to decrease hormone refractory prostate cancer proliferation and delay chemoresistance to the drug taxane. Curcumin has also been shown to enhance radiation- induced apoptosis via several mechanisms. No toxic effects have been reported in either humans or animals to date.

 

Resveratrol is a phenolic compound found in red grapes.  It has broad-spectrum health benefits via its antioxidant, anti-infective and cardioprotective properties. Its chemporeventative properties include an ability to modulate intracellular cancer targets affecting cell growth, inflammation, apoptosis, angiogenesis, invasion and metastasis.  Resveratrol has been found to inhibit hormone sensitive and androgen independent prostate cancer cells. It strongly inhibits oxidative stress within premalignant cells reducing the growth and spread of prostate cancer. Like curcumin, resveratrol can overcome chemoresistance in tumor cells via several mechanisms.

 

Querectin is a polyphenolic compound highly concentrated in onions, broccoli, apples, grapes and soybeans.  It has antioxidant, antiinflammatory and anti-proliferative effects. It has the capacity to induce apoptosis via multiple mechanisms and its ability to inhibit the onset/growth of prostate cancer is supported by both epidemiological studies and preliminary clinical data.  One study noted a 27% risk reduction for prostate cancer for those who consume at least 24 mcg of quercetin a day. Quercetin has also been shown to inhibit the activity of protease enzymes required for metastasis as well as suppress the function of androgen receptor.

 

And finally we come to genistein, a phenolic isoflavone found mainly in soybeans but also in peas, lentils and beans. In addition to many other health benefits, genistein has chemopreventative properties including the ability to inhibit growth of both androgen dependent and independent prostate cancer cells via multiple molecular targets including down regulation of the androgen receptor and several steroid metabolising enzymes.  Genistein’s strong antioxidant properties may also contribute to its anticarcinogenic and anti-metastatic properties. A randomised placebo-controlled, double blind phase 11 trial found PSA decreased by 7.8% in the genistein arm and increased by 4.4% in the placebo arm.

 

Reference

Cimino, Sebastiano et al, Polyphenols: Key Issues Involved in Chemoprevention of Prostate Cancer, Oxidative Medicine and Cellular Longevity Volume 2012, Article ID 632959