Emodin and shikonin are quinones that are commonly found in the roots of plant species of the families Polygonaceae and Boraginceae, respectively. They have a wide spectrum of bioactivities, including anti-cancer properties. This overview on the cytotoxic properties of emodin and shikonin is focused on lung cancer, the leading cause of cancer death in the world. In emodin, the −OH groups at C1 and C3 positions, while in shikonin, the −OH groups of the naphthazarin moiety and chiral side-chain, are important for their anti-tumour functions. Studies have shown that emodin and shikonin inhibit the growth of lung cancer cells by inducing apoptosis, autophagy, necrosis and early senescence, and by inhibiting proliferation, invasion, migration and metastasis. The cytotoxic activities are involved multiple molecular targets and signalling pathways. A clinical trial using shikonin to treat patients with late-stage lung cancer has been presented. Some future perspectives and research needs are suggested. Sources of information are from Google Scholar, PubMed, Science Direct, J-Stage, PubChem and CNKI.
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