5'AMP-activated
protein kinase (AMPK) and the
mammalian target of rapamycin (mTOR) are two
serine/threonine protein kinases responsible for cellular energy homeostasis and translational control, respectively. Evidence suggests that these two kniases are potential targets for
cancer chemotherapy against
hepatocellular carcinoma (HCC).
Antroquinonol that is isolated from Antrodia camphorate, a well-known
Traditional Chinese Medicine for treatment of
liver diseases, displayed effective anticancer activity against both HBV
DNA-positive and -negative HCC cell lines. The rank order of potency against HCCs is HepG2>HepG2.2.15>Mahlavu>PLC/PRF/5>SK-Hep1>Hep3B.
Antroquinonol completely abolished cell-cycle progression released from double-
thymidine-block synchronization and caused a subsequent apoptosis. The data were supported by down-regulation and reduced nuclear translocation of G1-regulator
proteins, including
cyclin D1,
cyclin E, Cdk4 and Cdk2. Further analysis showed that the
mRNA expressions of the G1-regulator
proteins were not modified by
antroquinonol, indicating an inhibition of translational but not transcriptional levels.
Antroquinonol induced the assembly of
tuberous sclerosis complex (
TSC)-1/TSC2, leading to the blockade of cellular
protein synthesis through inhibition of
protein phosphorylation including mTOR (Ser(2448)), p70(S6K) (Thr(421)/Ser(424) and Thr(389)) and 4E-BP1 (Thr(37)/Thr(46) and Thr(70)). Furthermore, the AMPK activity was elevated by
antroquinonol. Compound C, a selective AMPK inhibitor, significantly reversed
antroquinonol-mediated effects suggesting the crucial role of AMPK. Besides, the loss of mitochondrial membrane potential and depletion of mitochondrial content indicated the mitochondrial stress caused by
antroquinonol. In summary, the data suggest that
antroquinonol displays anticancer activity against HCCs through AMPK activation and inhibition of mTOR translational pathway, leading to G1 arrest of the cell-cycle and subsequent cell apoptosis.