Methioninase cancer gene therapy with selenomethionine as suicide prodrug substrate.

In this study, we report a novel approach to gene-directed enzyme prodrug therapy for cancer. This gene therapy strategy exploits the toxic pro-oxidant property of methylselenol, which is released from selenomethionine (SeMET) by cancer cells with the adenoviral-delivered methionine alpha,gamma-lyase (MET) gene cloned from Pseudomonas putida. In MET-transduced tumor cells, the cytotoxicity of SeMET is increased up to 1000-fold compared with nontransduced cells. A strong bystander effect occurred because of methylselenol release from MET gene-transduced cells and uptake by surrounding tumor cells. Methylselenol damaged the mitochondria via oxidative stress and caused cytochrome c release into the cytosol, thereby activating the caspase cascade and apoptosis. Adenoviral MET-gene/SeMET treatment also inhibited tumor growth in rodents and significantly prolonged their survival. Recombinant adenovirus-encoding MET gene-SeMET treatment thereby offers a new paradigm for cancer gene therapy.