Early onset of tumorigenesis in an oral-specific K-ras and p53 two hit model of carcinogenesis

ANA R. RAIMONDI, J. SILVIO GUTKIND

San Diego, Estados Unidos

Congreso; Reunion Anual de la Asociacion Americana para Investigacion en Cancer (AACR); 2008

American Association for Cancer Research

Head and neck squamous cell carcinoma (HNSCC), the majority of which occurs in the oral cavity, remains a significant cause of morbidity and mortality worldwide. In spite of the recent advances in the prevention and treatment of other types of cancers, the five-year survival rate after diagnosis for HNSCC is still low. A major limitation in this area of research has been the limited availability of animal models to test the validity of current genetic paradigms of tumorigenesis, and to explore the effectiveness of treatment modalities or chemopreventive strategies. Here, we have developed an inducible oral-specific animal tumor model system enabling the study of K-ras induced transformation in the oral cavity. This system consists in the expression of a tamoxifen-inducible Cre recombinase (CreERTAM) under the control of the cytokeratin 14 (K14) promoter (K14-CreERTAM mice), and the use of LSL-K-rasG12D mice, in which the endogenous K-ras locus is conditionally targeted, and endogenous levels of oncogenic K-RasG12D protein are expressed following removal of a floxed Stop element.  Initially, by using the K14-CreERTAM/Rosa26 reporter mouse in which b-galactosidase is expressed after Cre-mediated excision of the Stop cassette, we observed scattered b-galactosidase positives cells throughout the skin and the epithelium of the tongue and oral mucosa. Surprisingly, these K14-CreERTAM/LSL-K-rasG12D mice developed papillomas exclusively in the oral mucosa, as early as 1 month after the tamoxifen treatment. These lesions were highly proliferative, well differentiated, as judged by the strong expression of cytokeratin (CK) 1 and the weak expression of CK 5, and never progressed to carcinoma even after prolonged observation. Indeed, these papillomas retained the expression of the tumor suppressor protein p16 and did not harbor p53 mutations. However, when K14Cre-ERTAM/LSL-K-rasG12D mice were crossed with p53 conditional knock out mice (where loxP sites flank introns 1 and 10 of p53 gene, Trp53flox mice), these compound mice developed carcinomas on the tongue as early as 2 weeks after induction. Interestingly, we observed a distinct susceptibility of tumor progression between the tongue and the oral mucosa. This K14Cre-ERTAM/LSL-K-rasG12D/Trp53flox two-hit animal model system recapitulates oral cancer progression in humans. Thus, this model may represent a suitable platform for exploring the underlying molecular mechanisms and the susceptibility to malignant progression of tumoral lesions arising from distinct stratified epithelia of the oral cavity. These efforts may also facilitate exploring new treatment strategies and preventive modalities for oral cancers that harbor ras mutations.