Characterization of infectivity of knob-modified adenoviral vectors in glioma

Malignant glioma continues to be a major target for gene therapy and virotherapy due to its aggressive growth and the current lack of effective treatment. However, these approaches have been hampered by inefficient infection of glioma cells by viral vectors, particularly vectors derived from serotype 5 adenoviruses (Ad5). This results from limited cell surface expression of the primary adenovirus receptor, coxsackie-adenovirus-receptor (CAR), on tumor cells. To circumvent this problem, Ad fiber pseudotyping, the genetic replacement of either the entire fiber or fiber knob domain with its structural counterpart from another human Ad serotype that recognizes a cellular receptor other than CAR, has been shown to enhance Ad infectivity in a variety of tumor types, including human glioma. Here, we have extended the paradigm of genetic pseudotyping to include fiber domains from non-human or "xenotype" Ads for infectivity enhancement of human glioma cell populations. In this study, we evaluated the gene transfer efficiency of a panel of Ad vectors which express one of five different "xenotype" fiber knob domains, including those derived from murine, ovine, porcine and canine species, in both human glioma cell lines as well as primary glioma tumor cells from patients. Adenovirus vectors displaying either canine Ad or porcine Ad fiber elements had the highest gene transfer to both glioma 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 "xenotype" fiber elements could be excellent candidates to target human glioma.