Abstract 1845: Mutant p53 promotes progression and metastasis of mouse oral tumors induced by 4NQO, associated with specific immune infiltrates

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide. The vast majority of the human HNSCCs contain p53 mutations, some of which acquire oncogenic gain-of-function (GOF) activities. Previous mouse models in which either the p53 R172H GOF mutation or deletion of the p53 gene were co-activated with oncogenic K-ras showed that p53 R172H can predispose to oral tumor initiation, accelerate tumor growth and promote progression to SCC. However, the impact of p53 gain- and loss-of-function (LOF) mutations in metastasis could not be assessed because of the low rates of progression to SCC in that model. To overcome this limitation, we used the tobacco-surrogate 4NQO to induce oral lesions that may progress to advance carcinomas following stepwise changes that resemble the gradual accumulation of histological and molecular abnormalities observed during human oral cancer progression. To examine the role of p53 mutations during SCC malignant progression we applied 4NQO to mice in which the p53 R172H mutation or homozygous deletion of p53 were activated in oral epithelial cells. We observed that oral tumors appeared faster in the presence of p53 mutations than in mice with wtp53. No significant difference was observed between the p53 R172H mutation and p53 deletion. However, survival was shorter in mice expressing p53 R172H than in mice with loss of p53. Notably, regional and distant metastasis were only observed in mice with oral tumors expressing p53 R172H . Therefore, these mice are excellent tools for pre-clinical studies designed to target early stages of tumor development or latest stages of progression and metastasis. As immunotherapy is becoming adopted as part of the standard treatment for head and neck cancer patients, we conducted a detailed characterization of the immune infiltrates of the lesions that developed in these mice in order to assess their immunogenicity. We observed a progressive increase in T-cell infiltration from normal oral mucosa to oral premalignant lesions (OPL) to SCC, in the presence or absence of p53 mutations. Similarly, the expression of immune checkpoint proteins, including PD1, PDL1 and CTLA4 increased during oral tumor progression, regardless of the p53 status. Interestingly, we observed a sharp increase in the presence of immune infiltrates expressing the co-stimulatory OX40 in SCCs relative to premalignant lesions, with different extent depending on the nature of the p53 mutation. The significance of these observations is currently being analyzed. In summary, p53 R172H promotes metastasis in oral tumors induced by 4NQO. In addition, T-cell infiltration and activation of immune checkpoints during oral tumor progression suggest that this is an excellent model to test immunotherapy-based strategies. Furthermore, our findings suggest that OX40-based therapies may be tailored to patients according to their p53 status. Citation Format: Jin Wang, Yuanyuan Zhang, Bingbing Wang, Adel K. El-Naggar, Jeffrey N. Myers, Carlos Caulin. Mutant p53 promotes progression and metastasis of mouse oral tumors induced by 4NQO, associated with specific immune infiltrates [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1845. doi:10.1158/1538-7445.AM2017-1845