A review of propolis antitumour action in vivo and in vitro
Epidemiologic findings strongly suggest that cancer rates are influenced by environmental factors that can be mitigated to a great extent, for example by a diet rich in polyphenolic/flavonoid compounds. Among natural products, honeybee propolis has been applied for centuries in traditional medicine as well as in diets and supplementary nutrition. Honeybee propolis and its polyphenolic/flavonoid compounds have been known to exhibit biological activity including immunopotentiation, chemopreventive and antitumour effects. In this review we consider the inhibition of tumour growth by honeybee propolis and their polyphenolic/flavonoid compounds as well as the mechanisms involved based on in vivo and in vitro studies. Results have shown that propolis and its polyphenolic compounds exerted an anti-metastatic and antitumour effect in mice and rats and considerable cytotoxicity without cross-resistance in both wild-type and chemoresistant human tumour cell lines. These findings suggest that propolis and their polyphenolic/flavonoid components may serve as a potent adjunct to chemotherapy and radiotherapy in the treatment of cancers. However, further in-depth studies including clinical trials are needed to fully evaluate the value of flavonoids in combination with chemotherapeutic agents for the treatment of human cancers.