CASP9 and hepatocellular carcinoma: Calomelanone (DHC-1) exhibited cytotoxic properties in human hepatocellular carcinoma HepG2, human promyelocytic leukemic HL-60, and human monocytic leukemic U937 cells by inducing apoptosis/regulated cell death through the mitochondrial pathway with a loss of mitochondrial transmembrane potential and an increase in caspase-9 activity.