Oncolytic adenovirus modified to increase its infectivity for gastrointestinal cancer

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Adenovirus (Ad) has a strong cytotoxic activity and the E1A protein, one of the early transcriptional products, has a pivotal role in viral replication in the infected cells. Ad modified to control the E1A gene expression with a putative tumor promoter can thereby be oncolytic. We examined the regulatory regions of the genes which were predominantly expressed in tumors with the luciferase assay and found that a 500 bp and a 600 bp upstream regions of the survivin and midkine genes, respectively, were responsible for the transcriptional control. The cellular receptors of the Ad type 5 is CAR (Coxsackievirus and Adenovirus Receptor) and the expression is often downregulated in gastrointestinal tumors. In contrast, the expression of CD46, which is a receptor of Ad type 35, is rather upregulated in the tumors and consequently, the Ad bearing CD46 binding sites can increase the infectivity to the tumors. We thereby constructed a vector system consisting of vector DNA that could activate the E1A and E1B genes with an exogenous regulatory region and another vector that contained the rest of the whole Ad sequences, in which the fiber-knob region was replaced with the Ad type 35-derived one. In vitro ligation of the vectors enables the construction of the Ad bearing the type 35 fiber-knob structure in the E3 region. The oncolytic Ad with the type 35 fiber-knob can be produced with easy compared with conventional methods that required in vivo recombination. The chimeric oncolytic Ad prepared with our vector system was more cytotoxic to CAR-low human tumors than conventional type 5 oncolytic Ad and was as cytotoxic as the type 5 Ad to CAR-high tumors.