Capsid modifications overcome low heterogeneous expression of heparan sulfate proteoglycan that limits AAV2-mediated gene transfer and therapeutic efficacy in human ovarian carcinoma.

OBJECTIVES Capsid-modified AAV vectors can mediate enhanced gene transfer to neoplasms characterized by low AAV receptor expression. Here we sought to determine the therapeutic potential of a capsid-modified AAV vector for gene therapy of ovarian carcinoma (OvCa). METHODS We tested a panel of OvCa cell lines for AAV2-mediated gene transduction and for sensitivity to ganciclovir (GCV) following AAVHSVtk administration. Levels of AAV internalization and attachment receptor were assessed by flow cytometry and immunohistochemistry. The role of receptors in AAV-mediated gene transfer was assessed by competition assays. Finally, we examined the ability of a modified vector with an integrin-binding RGD motif inserted into the AAV capsid to improve gene delivery to OvCa and enhance AAVHSVtk/GCV-mediated killing by cytotoxicity assay. RESULTS All OvCa cell lines were poorly transduced with AAV2 vectors and showed variably sensitive to AAVHSVtk/GCV. While OvCa cell lines expressed AAV2 internalization receptors (alphav integrins), expression of the AAV2 attachment receptor, HSPG, was variable and not detected on many lines. Analysis of archived clinical specimens showed no detectable HSPG expression on approximately 45% of primary human tumors. Gene transfer to OvCa was increased several fold using the RGD-modified vector. Gene transfer was independent of HSPG and specific to the targeted receptor. Importantly, the RGD-modified capsid markedly increased the ability of the AAVHSVtk to kill OvCa cells in the presence of GCV. CONCLUSIONS The development of AAV vectors targeted to cell surface receptors other than HSPG will be critical to the advancement of AAV-mediated gene therapy for treating OvCa.