Characterization of infectivity of knob-modified adenoviral vectors in glioma

Abstract

Malignant gliomas have been a major target for gene therapy and virotherapy, because of their current lack of effective treatment. These approaches remain hampered by lack of significant infectivity of glioma cells by viral vectors, in particular for vectors derived from serotype 5 adenoviruses (Ad5). This has been shown to result from a relative paucity of cell surface expression of the native adenovirus receptor, coxsackie-adenovirus-receptor (CAR), on primary tumor cells. Thus, targeting strategies applying adenovirus capsid modifications to enhance viral infectivity via CAR-independent pathways have been developed. All these capsid modifications (such as RGD, polylysine fiber modification……) have previously been shown to enhance viral infectivity (to different levels) in a variety of tumor types, including human glioma. Recently, we extended these infectivity enhancements to the development of “xenotype” knobs, whereby canine adenovirus types 1 and 2 knobs were switched with adenovirus type 5 knob to achieve enhanced transduction in low-CAR containing human tumors. In this study, we tested human adenoviral vectors that carry a luciferase reporter gene (driven by the CMV promoter) with five different xenotype Ad knobs, including those derived from murine, ovine, porcine and canine species, in four human glioma cell lines (U87MG, U118MG, U251MG and D65MG) and in primary glioma tumor cells from four different patients. Adenovirus vectors carrying either canine type 1 or porcine knob had the highest luciferase levels in both tumor cell lines and primary tumor cells. The correlation between the viral infectivity of modified adenovirus vectors and expression of human CAR and CD46 (an adenovirus type B receptor) on the surfaces of tumor cells was also analyzed. Taken together, human adenovirus vectors modified with either canine type 1 or porcine knob should be excellent candidates to target human glioma as they demonstrate enhanced viral infectivity at the transductional level.