In this short review we report selected examples from recent literature to show the potential of natural-derived, low molecular weight polyphenols as antitumor agents. The two major groups of polyphenol analogues have been reviewed here, namely flavonoids and stilbenoids. Notwithstanding these limitations, we listed 75 compounds, many of them representing only the most potent member in a library. In addition, many studies afforded useful SARs which may be the basis for future optimization. In this regard, it is worth highlighting the close structural relationships connecting some families of tubulin inhibitors, namely analogues of chalcones, combretastatin A-4, and resveratrol. Some interesting hybrid molecules have already been obtained, such as chalcone-combretastatin and chalcone-resveratrol hybrids. The optimization of natural polyphenols reputed to be anticarcinogenic has also been addressed to improve their metabolic stability and a number of analogues, which are more stable to metabolic conversion and display comparable or higher antitumor activity than the parent compound, have been obtained. In some cases analogues with higher lipophilicity showed higher activity than the parent compound, in particular stilbenoids, flavanols, and flavone derivatives. Table 1 summarizes the main biological data on the natural-derived polyphenols cited within this review.
As a whole, this survey of recently reported, natural-derived polyphenols, though not exhaustive, clearly indicates that intensive research is being carried out in the area of antitumor polyphenol analogues and suggests that in the near future some polyphenolic leads may become useful anticancer drugs or adjuvants in cancer therapy.