Terpenoids: natural products for cancer therapy.

INTRODUCTION: Terpenoids constitute the largest class of natural products and are a rich reservoir of candidate compounds for drug discovery. Recent efforts into the research and development of anti-cancer drugs derived from natural products have led to the identification of a variety of terpenoids that inhibit cancer cell proliferation and metastasis via various mechanisms. Despite the increasing number of research reports, there lacks a comprehensive review of anti-cancer activity of terpenoids. AREAS COVERED: The present article provides an overview of the recent progress in the anti-cancer studies on terpenoids. Over a dozen naturally originated terpenoid compounds, in particular those derived from traditional Chinese medicine, were classified into five categories according to the structures, namely monoterpenoids, sesquiterpenoids, diterpenoids, triterpenoids and tetraterpenoids. The anti-cancer activities and relevant mechanistic insights of these compounds are discussed in this review. EXPERT OPINION: The anti-cancer activity of terpenoids appears promising and will potentially open more opportunities for cancer therapy. However, current studies are restricted to descriptive findings and lack mechanistic insights and systematic structure-activity relationship (SAR) studies. Future efforts into the systematic identification of the targets of terpenoids are believed to increase chances of gaining breakthrough insights in the field.