Development of Oncolytic Adenovirus Armed with a Fusion of Soluble Transforming Growth Factor-β Receptor II and Human Immunoglobulin Fc for Breast Cancer Therapy

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Abstract
We have developed an approach to cancer gene therapy in which the oncolytic effects of an adenoviral vector have been combined with selective expression of a soluble form of transforming growth factor (TGF)-β receptor II fused with Fc (sTGFβRIIFc). We chose to use adenoviral dl01/07 mutant because it can replicate in all cancer cells regardless of their genetic defects. An oncolytic adenovirus expressing sTGFβRIIFc (Ad.sTβRFc) was constructed by homologous recombination. Infection of MDA-MB-231 and MCF-7 human breast cancer cells with Ad.sTβRFc produced sTGFβRIIFc, which was released into the media. The conditioned media containing sTGFβRIIFc could bind with TGF-β1 and inhibited TGF-β-dependent transcription in target cells. Infection of MDA-MB-231, MCF-7, and 76NE human breast cancer cells with Ad.sTβRFc resulted in high levels of viral replication, comparable to that of a wild-type dl309 virus. Although some viral replication was observed in actively dividing normal human lung fibroblasts, there was no replication in nonproliferating normal cells. Direct injection of Ad.sTβRFc into MDA-MB-231 human breast xenograft tumors grown in nude mice resulted in a significant inhibition of tumor growth, causing tumor regression in more than 85% of the animals. These results indicate that it is possible to construct an oncolytic virus expressing sTGFβRIIFc in which both viral replication and transgene expression remain intact, and the recombinant adenovirus is oncolytic in a human tumor xenograft model. On the basis of these results we believe that it may be feasible to develop a cancer gene therapy approach using Ad.sTβRFc as an antitumor agent.