Radioimmunotherapy of experimental head and neck squamous cell carcinoma (HNSCC) with E6-specific antibody using a novel HPV-16 positive HNSCC cell line

Abstract. Background: Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide with a poor prognosis. Human papilloma virus (HPV) infection is associated with 20% HNSCC, and 50% of oropharyngeal carcinoma. HPV16 type is detected in 90% of all HPV+ HNSCC. Recently we suggested a fundamentally different approach to treatment of cancers of viral origin by targeting viral antigens on cancer cells with radiolabeled antibodies (mAbs) which promises exquisite specificity of treatment. We aimed at extending this approach to HPV-related head and neck cancer by performing radioimmunotherapy (RIT) targeting E6 and E7 oncogenes with radiolabeled mAbs. Methods. We first aimed at developing HPV16+ cell line and animal model for RIT of HNSCC as at present there are no commercially available HPV16+ HNSCC cell lines and there is only one HPV+ cell line among the collection maintained by Dusseldorf, Michigan and Turku groups. Commercially available HNSCC cell line FaDu was transfected with pLXSN16E6E7 vector containing HPV16 E6 and E7 genes. Generated novel cell lines were evaluated by PCR and western blot and the tumorigenecity was assessed in nude mice. Proof of principle RIT targeting E6 oncoprotein in 2A3 tumor-bearing nude mice was conducted using unlabeled or 188-Rhenium (¹⁸⁸Re)-labeled C1P5 mAb to E6. Results: Novel HPV16+ 2A3 cell line reliably expressed E6 oncoprotein. E6 expression was modifiable with proteasome inhibitor MG132 in a dose-dependent manner. The levels of E6 expression in 2A3 cell line were estimated to be around 200 HPV copies per cell. The HPV16+ 2A3 cell line preserved 100% tumorigenicity of parent FaDu cells in nude mice. During RIT of 2A3 tumors in nude mice the relatively low dose of 200 μCi ¹⁸⁸Re-C1P5 mAb was effective in decreasing the tumor growth in comparison with untreated controls. Unlabeled C1P5 mAb also caused some decrease in tumor progression, however, much less pronounced than ¹⁸⁸Re-C1P5 mAb. Conclusions: We describe a proof-of-principle RIT study targeting HPV16 E6 oncoprotein with radiolabeled mAb to E6 in a stably transformed HPV16+ HNSCC cell line and tumor model in nude mice, and demonstrate potential utility of RIT as a novel molecular targeted therapy for HNSCC.