Influence of E3 region on conditionally replicative adenovirus mediated cytotoxicity in hepatocellular carcinoma cells.

Virotherapy employing conditionally replicative adenovirus (CRAd) represents a novel targeted strategy for the hepatocellular carcinoma (HCC) treatment. In this study, we explored the potential influence of E3 region, which encodes several TRAIL-inhibiting proteins (E3-6.7K, E3-10.4K/14.5K and E3-14.7K), on CRAd mediated cytotoxicity to HCC cells. Two E1B-55 kDa-deleted CRAds containing E3 region (Ad.DeltaE1B) or no E3 region (Ad.DeltaE1B.DeltaE3) were fabricated. Ad.DeltaE1B.DeltaE3 exhibited higher cytocidal potency than Ad.DeltaE1B in all tested HCC cells (Hep3B, BEL-7404, BEL-7402, HuH7, PLC/PRF/5 and HepG2), suggesting that Ad.DeltaE1B.DeltaE3 mediated cytotoxicity was partly attributed to the absence of E3 region encoding TRAIL-inhibiting proteins. In representative Hep3B cells, Ad.DeltaE1B.DeltaE3 led to more drop of mitochondrial membrane potential (MMP) and much lower ATP level than Ad.DeltaE1B. Moreover, Ad.DeltaE1B.DeltaE3 induced early apoptotic cells and the late apoptotic/necrotic cells for three and four times more than those infected by Ad.DeltaE1B. The cytotoxicity to all TRAIL endogenously expressing HCC cells and MMP drop of Hep3B cells induced by Ad.DeltaE1B.DeltaE3 but not Ad.DeltaE1B could be significantly inhibited by z-vad-fmk, a pan caspase inhibitor, suggesting that the endogenous TRAIL-mediated apoptotic pathway may be implicated in the cytocidal potency of Ad.DeltaE1B.DeltaE3 on HCC cells although other unknown mechanisms may be also involved. Our findings provided the first evidence that CRAd without E3 region might be a smart choice for the virotherapy of HCC.