Characterizing a Novel HPV-driven GEMM of Oral Squamous Cell Carcinoma

Objectives: HPV-induced OSCC is steadily increasing and currently implicated in 60% of all oropharyngeal carcinomas. Whole genome, transcriptome, and proteome analyses have aided in identifying altered signaling pathways in HPV-induced OSCCs; however, additional tools such as tractable genetically engineered mouse models (GEMMs) are needed. Current HPV-induced oral cancer models do not accurately recapitulate the levels, stoichiometric ratios, or anatomic location of oncoprotein expression. Our aim was to develop a conditional and inducible GEMM that specifically develops oral cancer to enable longitudinal investigation of HPV-driven OSCCs in vivo.
Methods: We generated a GEMM that enables directed expression of the high-risk HPV16 E6 and E7 oncoproteins by introducing a transcriptional/translational STOP element flanked by LoxP sites upstream of an E7iresE6 cassette, and targeted to the ubiquitous Rosa26 locus (Rosa26-LSL-E7iresE6). Conditional and inducible activation of E6 and E7 in the basal epithelial layer of oral mucosa, a site of HPV infection in humans, was achieved by crossing these mice to tissue-specific, tamoxifen-inducible Cre recombinase (CreER^T2) driven by the keratin 14 promoter (KRT14-CreER^T2). In addition, we generated a GEMM for conditional and inducible expression of our LumiFluor (eGFP-NanoLuc) optical reporter (Rosa26-LSL-LumiFluor).
Results: We compared two versus three intra-lingual tamoxifen injections into the ventral surface of KRT14-CreER^T2;Rosa26-LSL-E7iresE6 cohort tongues to activate Cre-mediated recombination and STOP element removal leading to induced site-specific E6 and E7 expression. In agreement with previously reported HPV-induced abnormalities, E6 and E7 expression promotes tissue hyperplasia and dysplasia in our model compared to controls. Further characterization of targeted tamoxifen administration using our LumiFluor GEMM demonstrated higher induction with less tamoxifen in animals that received intra-lingual injections (1.5 mg) compared to conventional intra-peritoneal injections (5 mg).
Conclusions: Ongoing studies are evaluating cooperating mutations in driving OSCC development. Thus, we developed novel GEMMs for directed expression of E6, E7, and LumiFluor for establishing a tractable autochthonous model of HPV-driven OSCC.