Pifithrin-alpha (PFT) is an inhibitor of p53 and is known to protect against a variety of p53-mediated
genotoxic agents. In this report, we examined the inhibitory effects of PFT against docosahexaenoic acid
(DHA)-induced cytotoxicity in the human hepatocellular carcinoma (HCC) cell line HepG2. PFT
significantly abrogated DHA-induced cytotoxicity in wild-type HepG2 cells (normal expression of p53)
and after p53-knockdown by siRNA, as well as in Hep3B (p53 null) and Huh7 (p53 mutant) cells. DHAinduced
cytotoxicity is mediated by induction of oxidative stress, and PFT inhibited this event, but it does
not exert antioxidant effects. PFT significantly suppressed the release of cytochrome c from mitochondria
to cytosol, as well as changes in the mitochondrial membrane potential (DCM) by DHA. Therefore,
protection of mitochondria by PFT is crucial for its inhibition of DHA-induced cytotoxicity. Although it has
been reported that PFT is able to block p53 function, our data suggest that PFT also has a p53-independent
inhibition mechanism. This work provided insights into the mechanisms of PFT action on DHA-induced
cytotoxicity in HCC.