p53 (TP53) is the most frequently mutated gene in squamous cell carcinomas (SCCs) of the skin and head and neck. Certain p53 mutations are oncogenic and promote invasion and metastasis in SCCs. However, it is unclear how the oncogenic function of mutant p53 is modulated by other molecular alterations that co-exist in SCCs. Here, we show that deletion of the p53 gene and activation of an endogenous p53(R172H) gain-of-function mutation in the skin induce carcinomas with similar kinetics and penetrance. Deletion of p53 induced primarily well-differentiated SCCs. However, most of the tumours induced by p53(R172H) were poorly differentiated SCCs, the only metastatic tumours in this model. These tumours expressed higher levels of cyclin D1 than the well-differentiated SCCs and spindle carcinomas that developed in these mice. Unexpectedly, metastasis was not observed in mice that developed spindle carcinomas, which expressed high levels of the tumour suppressors p16(Ink4a) and p19(Arf) , encoded by Cdkn2a, a gene frequently deleted in human SCCs. Remarkably, deletion of the Cdkn2a gene in p53(R172H) -induced SCCs promoted a dramatic increase in metastasis rates and a shorter survival in mice that developed these tumours, compared with those observed in mice with tumours in which Cdkn2a was deleted in the presence of a p53 loss-of-function mutation or wild-type p53. Accordingly, the survival of patients with head and neck SCCs bearing co-occurring high-risk p53 mutations and CDKN2A homozygous deletions was much shorter than that of patients with tumours in which high-risk p53 mutations did not contain CDKN2A homozygous deletions, or that of patients with tumours in which homozygous CDKN2A deletions co-existed with either low-risk p53 mutations or potential loss-of-function mutations in p53. These findings genetically identify a population of SCC patients with worst outcomes and will help to predict outcomes according to the p53 status and alterations in CDKN2A. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Most of the squamous cell carcinomas (SCCs) of the skin and head and neck contain p53 mutations. The presence of p53 mutations in premalignant lesions suggests that they represent early events during tumor progression and additional alterations may be required for SCC development. Here we show that co-deletion of the p53 and αv integrin genes in mouse stratified epithelia induced SCCs in 100% of the mice, more frequently and with much shorter latency than deletion of either gene alone. The SCCs that lacked p53 and αv in the epithelial tumor cells exhibited high Akt activity, lacked multiple types of infiltrating immune cells, contained a defective vasculature, and grew slower than tumors that expressed p53 or αv. These results reveal that loss of αv in epithelial cells that lack p53 promotes SCC development, but also prevents remodeling of the tumor microenvironment and delays tumor growth. We observed that Akt inactivation in SCC cells that lack p53 and αv promoted anoikis. Thus, tumors may arise in these mice as a result of the increased cell survival induced by Akt activation triggered by loss of αv and p53, and by the defective recruitment of immune cells to these tumors, which may allow immune evasion. However, the defective vasculature and lack of a supportive stroma create a restrictive microenvironment in these SCCs that slows their growth. These mechanisms may underlie the rapid onset and slow growth of SCCs that lack p53 and αv.

Oral squamous cell carcinoma (OSCC) develops through the multistep malignant progression of squamous epithelium. This process can be prevented by PD-1 blockade in a mouse model for oral carcinogenesis. OSCCs exhibit a high incidence of p53 mutations that confer oncogenic gain-of-function (GOF) activities that promote resistance to standard therapies and poor clinical outcomes. To determine whether epithelial p53 mutations modulate anti-PD-1-mediated oral cancer immunoprevention, we generated mouse models for oral carcinogenesis by exposing mice carrying epithelial-specific p53 mutations to the carcinogen 4NQO. Consistent with the oncogenic functions of mutant p53, mice with OSCCs expressing the p53R172H GOF mutation developed higher metastasis rates than mice with loss-of-function (LOF) p53 deletion or with wild-type p53. Throughout oral cancer progression, pre-invasive and invasive lesions showed a gradual increase in T-cell infiltration, recruitment of immunosuppressive regulatory T-cells (Tregs), and induction of PD-1/PD-L1 immune checkpoint proteins. Notably, while PD-1 blockade prevented the development of OSCCs in mice with wild-type p53 or p53 deletion, GOF p53R172H abrogated the immunopreventive effects of anti-PD-1, associated with upregulation of IL17 signaling and depletion of exhausted CD8 cells in the microenvironment of the p53R172H tumors. These findings sustain a potential role for p53 profiling in personalized oral cancer immunoprevention.

Oral squamous cell carcinomas (OSCC) tend to develop from oral premalignant lesions (OPLs) through the accumulation of genetic alterations. Therefore, effective prevention strategies designed to block the malignant progression of OPLs are expected to contain the development of aggressive carcinomas. Our previous studies showed that immune checkpoint blockade can prevent the progression of OPLs to OSCC, in a mouse model for oral carcinogenesis. However, a subset of the lesions continued to progress even after treatment with anti-PD1 antibodies. Mutations that accumulate in the epithelial cells of the oral lesions may shape the immune microenvironment of the oral lesions and impact the response to immunotherapies. The p53 gene (TP53) is the most frequently mutated gene in OSCCs, as over 80% of the OSCCs contain p53 mutations. Most p53 mutations found in human cancers are missense mutations that encode mutant forms of p53, some of which are associated with poor clinical outcomes and can transform cells as a result of their gain-of-function (GOF) activities. To assess the role of p53 mutations in the response to anti-PD-1 immunoprevention, we generated mouse models in which oral tumors were induced by the carcinogen 4NQO in genetically engineered mice in which the p53 GOF mutation p53R172H or deletion of p53, a loss-of-function (LOF) mutation, were activated in oral epithelial cells. Therefore, the OPLs that developed in these mice differed in their p53 status. We found that the oral lesions that developed in these mice showed a gradual increase in T-cell infiltration during oral cancer progression, the recruitment of immunosuppressive regulatory T-cells (Tregs), and induction of PD-1/PD-L1 immune checkpoint proteins. Remarkably, while PD-1 blockade prevented the development of SCCs in mice with wild-type p53 or p53 deletion, the GOF mutant p53R172H abrogated the immunopreventive effects of anti-PD-1 antibodies, associated with depletion of exhausted CD8 cells in the microenvironment of the p53R172H tumors. Overall, these findings indicate that mutant p53R172H promotes the development of an immune microenvironment that prevents the efficacy of PD-1 inhibitors. These studies suggest that p53 profiling may help to predict the response to oral cancer immunoprevention, and patients with OPLs containing wild-type p53 or p53 LOF mutations may benefit from the immunopreventive effects of anti-PD1 antibodies. Citation Format: Jin Wang, Yuan Hu, Cassandra Gonzalez, Lin Tang, Bingbing Wang, Adel El-Naggar, Jeffrey Myers, Carlos Caulin. The p53R172H gain-of-function mutation promotes resistance to oral cancer immunoprevention [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr A14.