The cytotoxic activity of the phage E protein suppress the growth of murine B16 melanomas in vitro and in vivo.

Novel treatment modalities, including gene therapy, are needed for patients with advanced melanoma. The E gene from the phage varphiX174 encodes a 91-aa protein which lyses Escherichia coli by formation of a transmembrane tunnel structure. To evaluate whether this E gene has a cytotoxic impact on melanoma cells in vitro and in vivo, and could therefore be used as a new therapeutic strategy for this tumor type, we selected the B16-F10 murine melanoma cell line as a model. We used a nonviral gene delivery approach (pcDNA3.1/E plasmid) to study the inhibition of melanoma cells' proliferation in vitro and direct intratumoral injection of pcDNA3.1/E complexed with jetPEI to deliver E cDNA to rapidly growing murine melanomas, and found that the E gene has both a strong antiproliferative effect in B16-F10 cells in vitro and induces an efficient decrease in melanoma tumor volume in vivo (90% in 15 days). Interestingly, the GFP-E fusion protein expressed in melanoma cells was located in the mitochondria. In vitro and in vivo analysis demonstrated significant functional and morphological mitochondrial alterations accompanied by a significant increase of cytochrome c and active caspase-3 and -9 in transfected cells, which suggests that tumoral cell death is mediated by the mitochondrial apoptotic pathway. These results show that E gene expression in melanoma cells has an extraordinary antitumor effect, which means it may be a new candidate for an effective strategy for melanoma treatment.