Adenovirus Gene Transfer to Amelogenesis Imperfecta Ameloblast-Like Cells

To explore gene therapy strategies for amelogenesis imperfecta (AI), a human ameloblast-like cell population was established from third molars of an AI-affected patient. These cells were characterized by expression of cytokeratin 14, major enamel proteins and alkaline phosphatase staining. Suboptimal transduction of the ameloblast-like cells by an adenovirus type 5 (Ad5) vector was consistent with lower levels of the coxsackie-and-adenovirus receptor (CAR) on those cells relative to CAR-positive A549 cells. To overcome CAR -deficiency, we evaluated capsid-modified Ad5 vectors with various genetic capsid modifications including “pK7” and/or “RGD” motif-containing short peptides incorporated in the capsid protein fiber as well as fiber chimera with the Ad serotype 3 (Ad3) fiber “knob” domain. All fiber modifications provided an augmented transduction of AI-ameloblasts, revealed following vector dose normalization in A549 cells with a superior effect (up to 404-fold) of pK7/RGD double modification. This robust infectivity enhancement occurred through vector binding to both αvβ3/αvβ5 integrins and heparan sulfate proteoglycans (HSPGs) highly expressed by AI-ameloblasts as revealed by gene transfer blocking experiments. This work thus not only pioneers establishment of human AI ameloblast-like cell population as a model for in vitro studies but also reveals an optimal infectivity-enhancement strategy for a potential Ad5 vector-mediated gene therapy for AI

3PO, a novel nonviral gene delivery system using engineered Ad5 penton proteins

This study describes the development of 3PO, a nonviral, protein-based gene delivery vector which utilizes the highly evolved cell-binding, cell-entry and intracellular transport functions of the adenovirus serotype 5 (Ad5) capsid penton protein. A penton fusion protein containing a polylysine sequence was produced by recombinant methods and tested for gene delivery capability. As the protein itself is known to bind integrins through a conserved consensus motif, the penton inherently possesses the ability to bind and enter cells through receptor-mediated internalization. The ability to lyse the cellular endosome encapsulating internalized receptors is also attributed to the penton. The recombinant protein gains the additional function of DNA binding and transport with the appendage of a polylysine motif. This protein retains the ability to form pentamers and mediates delivery of a reporter gene to cultured cells. Interference by oligopeptides bearing the integrin binding motif suggests that delivery is mediated specifically through integrin receptor binding and internalization. The addition of protamine to penton-DNA complexes allows gene delivery in the presence of serum