Retrovirus-mediated delivery of short hairpin RNA targeting human papillomavirus (HPV) 16 E6 and E7 oncogenes and induction of apoptosis in oropharyngeal squamous cell cancer (OSCC) cell line

6002 Background: Human papillomavirus type 16 is identified in almost 50% of the cases of OSCC. The E6 and E7 genes of HPVs encode oncoproteins that bind and degrade the tumor suppressor proteins p53 and Rb, respectively. We are exploring the potential use of short hairpin RNA (sh RNA) for gene therapy of HPV-positive OSCC. Methods: Small hairpin RNAs targeting E6 or E7 genes were delivered by a retrovirus vector to 93VU147T (bearing integrated HPV16 DNA) and 92VU040T (HPV negative) oropharyngeal cancer cell lines. Flow cytometry analysis was used to assess apoptosis after the retrovirus infection. The E6 and E7 mRNA downregulation was assessed by reverse transcription polymerase chain reaction (RT-PCR). At protein level p53 and Rb expression were evaluated with Western blotting analysis. Results: Apoptosis was seen in over 90% of 93VU147T cells 48 hours after infection whereas 92VU040T cells were not affected. RT-PCR demonstrated that HPV16 E6/E7 mRNA levels decreased significantly in infected 93VU147T cells. 93VU147T infected cells also showed a marked increase in p53 and Rb protein levels. Conclusions: Downregulation of E6/E7 gene expression in HPV16+ OSCC cells results in apoptosis and reactivation of p53 and Rb tumor suppression pathways. These results have significant implications in treating HPV-associated OSCC with HPV-targeted gene therapy. No significant financial relationships to disclose.