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Adenoviral (Ad) vectors are good candidates for gene therapy in view of their high in vivo gene delivery efficiency. However, greater control over the tissue distribution of transgene expression is required to avoid potentially deleterious effects in non-target organs. In this regard, the liver is particularly at risk due to the high natural tropism of Ad for this organ, where dose limiting toxicity has been seen due to toxic transgene expression. We hypothesized that the cre/IoxP system could be utilized to reduce unintended transgene expression at this site. This concept was tested using an Ad vector (AdLCLLL) carrying a reporter gene cassette in which the promoter and luciferase gene were flanked by LoxP sequences. Co-administration of this vector with a second vector carrying the cre recombinase gene in vitro and in vivo resulted in specific down-regulation of transgene expression. This novel approach thus has the potential to improve the safety of gene therapy strategies that rely upon the defivery of genes which may be hepatotoxic. [ABSTRACT FROM AUTHOR]

In this study we analyzed two ways of retargeting of Advectors to human pancreatic carcinoma with the aim of enhancing the gene transfer efficiency. First, we analyzed the expression of the epidermal growth factor receptor (EGFR) on primary, as well as established pancreatic carcinoma cells by flow cytometry which revealed high expression levels of EGFR on the surface of these cells. We showed that EGFR-retargeted entry pathway using a bispecific fusion protein formed by a recombinant soluble form of truncated Coxsackie and Adenovirus Receptor (sCAR) genetically fused with human EGF (sCAR-EGF) redirects them to the EGFR leading to an enhanced gene transfer efficiency to pancreatic carcinoma cells. Since flow cytometry revealed absence of CAR expression, but the presence of at least one of both αv integrins on the pancreatic carcinoma cells, a second way of targeting was investigated using a genetically modified Ad vector which has an RGD (Arg-Gly-Asp)-containing peptide inserted into the HI-loop of the fiber knob. This RGD targeted Ad (AdlucRGD) revealed efficient CARindependent infection by allowing binding to cellular integrins resulting in a dramatic enhancement of gene transfer. These findings have direct relevance for Ad-vector based gene therapy strategies for pancreatic carcinoma. [ABSTRACT FROM AUTHOR]

The He fragment of tetanus toxin (He) retains the specific nerve ceil binding and transport properties of the holotoxin, but lacks any toxicity. We are investigating the potential for utilising its neurotropism for targeted gene delivery to the central nervous system. Previously we reported the use of He-polylysine conjugates for selective gene transfer into neuronal cells in vitro. However, as attempts to apply these constructs in vivo were not successful, we have extended these studies to modification of the tropism of adenoviral vectors. Either He-polylysine conjugates or the Fab fragment of a neutralising anti-knob antibody covalently bound to He were attached to the virus. Infection of neuronal and nonneuronal cell lines with retargeted virus showed highly increased neuronal cell selectivity, but no significant enhancement of gene delivery into these cells. High concentrations of free He blocked the infectivity of the retargeted vector efficiently. Intramuscular injection of retargeted virus into mouse tongues resulted in selective gene transfer to the neurons of the hypoglossal nucleus, where no pathological changes were observed. As differentiated neurons do not undergo cell division, appropriate vectors carrying a thymidine kinase gene, which allows selective elimination of dividing cells, may be exploitable for the treatment of tumours of the central nervous system. The demonstrated suitability of the He fragment of tetanus toxin as targeting moiety for viral vectors also indicates a potential for gene therapy of inherited neurodegenerative diseases such as spinal muscular atrophy. [ABSTRACT FROM AUTHOR]