Objectives: The clinical applicability of adenovirus-mediated gene therapy is limited by the lack of tumor-targeted strategies. Ubiquitous expression of the coxsackie-adenovirus receptor, the native binding site for adenovirus, broadens viral tropism and increases systemic toxicity. Adenoviruses can be genetically engineered to target tumor-specific cell surface biomarkers. Here, we present a novel recombinant adenovirus vector (Ad5-Flag-LDS) that demonstrated a marked targeting bias against Hsp47, a biomarker for head and neck squamous cell carcinoma (HNSCC).
Methods: Cell surface expression of Hsp47 was determined in six human HNSCC cell lines and in negative and positive control cells. Colocalization of LDS and Hsp47 was assessed by immunocytochemistry in Ad5-Flag-LDS-transfected cells, and subsequent transgene expression was determined. The contribution of the Hsp47 biomarker in mediating targeted gene transfer was evaluated with a blocking assay. Ad5-Flag-LDS-targeting efficacy in a mixed cell population was determined by immunofluorescence.
Results: HNSCC cells had significantly higher Hsp47 biomarker density than control cell lines. After Ad5-Flag-LDS transfection, significant colocalization was found between the LDS peptide and Hsp47 biomarker, indicating that viral entry occurred via Hsp47-LDS binding. This unique tumor-targeted entry feature significantly enhanced gene transfer relative to an untargeted adenoviral vector. Blockade of Hsp47 biomarkers abrogated transgene expression, indicating that Hsp47 has a dominant role in Ad5-Flag-LDS targeting. Ad5-Flag-LDS-targeting selectivity was maintained in a cell mixture, producing greater transgene expression in Hsp47-expressing cells.
Conclusions: The enhanced targeting achieved with Ad5-Flag-LDS highlights a potential strategy for clinically applicable targeted gene therapy against HNSCC or any tumor type expressing Hsp47.