ATR and tongue cancer: A later study by Chen and colleagues [150] showed that 40 μM emodin induced DNA damage (tested by comet assay) after long-term treatment (24 h) in human tongue cancer (SCC-4) cells and inhibited mRNA expression of genes associated with DNA damage and repair, such as the checkpoint kinases ATM (ataxia telangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3-related), which are central regulators of DNA damage response.