| Summary: | 碩士 === 國立成功大學 === 口腔醫學研究所 === 94 === Efficient targeted retroviral gene delivery remains an important goal in gene therapy. The host range of retroviruses is determined primarily by the interaction between the retroviral envelope glycoproteins and specific proteins of the host cell surface that act as retroviral receptors. The variable proline-rich region (PRR) in the retroviral envelope glycoprotein (gp70) has been reported to tolerate a small insertion of peptides, which does not affect the stability of viral particles. The modification of the PRR might redirect binding of the retroviral envelope protein to a new cell surface receptor. We modified the variable PRR of the ecotropic MMLV (Moloney murine leukemia virus) by constructing these peptides (DG-1, DG-2, or F56) to the variable PRR. Peptide DG-1 and DG-2 are composed of 9 amino acids and can specifically bind to neuropilin-1 (NRP-1), a new VEGF receptor, which is expressed by endothelial cells and tumor cells. VEGFR-1/Flt-1 plays important roles during the neovascularization under pathological conditions including tumor. Peptide F56 can specifically bind to VEGF receptor Flt-1 and almost abolished VEGF binding to receptor Flt-1 in vitro. Retroviral vector particles containing such chimeric envelope proteins achieved a wild-type titer on NIH3T3 cells, but the modified retroviruses could not change the tropism to infect non-murine cell lines, such as human lung cancer cells. Therefore, modifications of the envelope on the retroviral vectors might have not redirected the tropism of the retrovirus. Nevertheless, we investigated the functions of these peptides on the modified retroviruses. We found that the DG-1-, DG-2-, or F56-modified retroviruses could inhibit the cell migration and affect the signal transduction of their targeted cells. The modified retroviruses might confer specific binding to the cells and interfere with the functions of targeted receptors. A major obstacle in cancer gene therapy is the limited efficiency of in vivo gene transfer by replication-defective retrovirus vectors in current use. We had also developed replication-competent retroviral (RCR) vectors, derived from the ecotropic MMLV, with DG-1-, DG-2-, or F56-modified envelope. These RCR vectors could stably retain over multiple replication cycles in culture. Finally, these RCR vectors had the antitumor effects in animal tumor models. These result suggested that RCRs with modified envelopes had therapeutic potential for tumors.
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