Due to its frequent overexpression in a variety of solid tumors the epidermal growth factor receptor (EGFR) is a well-established target for therapeutic interventions in epithelial cancers. In order to target EGFR in head and neck cancer, we have generated a ribonuclease (RNase) fusion protein comprising a humanized anti-EGFR antibody single-chain Fv fragment (scFv) and Ranpirnase, an RNase from Rana pipiens. Fusion of Ranpirnase to the N-terminus of the scFv via a flexible glycine-serine linker (G4S)3 resulted in very poor cytotoxicity of the fusion protein. As endosomal accumulation and lysosomal degradation have been reported to diminish the antitumor efficacy of ribonuclease or toxin-based immunoagents, we explored a fusion peptide from dengue virus that has been reported to be involved in the endosomal escape of the virus. This peptide was introduced as a linker between Ranpirnase and the scFv moiety. The modified immunoRNase exhibited exceptionally high cytotoxicity toward EGFR-expressing head and neck cell lines without affecting specificity. These results indicate that endosomal entrapment needs to be considered for Ranpirnase-based immunoagents and might be overcome by the use of tailored transduction domains from viral proteins.
Keywords: EGFR; Ranpirnase; dengue virus; endosomal escape; immunoRNase.
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