Head and neck squamous cell carcinoma (HNSCC) is an aggressive disease with a poor prognosis if not detected and treated at the early stages. P53 inactivation represents one of the most frequent molecular events in HNSCC. Here we studied a p53-reactivating small molecule, CP-31398, to prevent progression of premalignant oral squamous lesions to malignant HNSCC. We treated a panel of HNSCC cell lines with CP-31398 which resulted in a dose-dependent inhibition of cell proliferation as assessed by [3H]-Thymidine incorporation and cell cycle analysis, including induction of apoptotic cell death. These alterations were associated with an increased expression of the cell cycle inhibitor CDKN1A (p21WAF1) upon CP-31398 treatment. Interestingly, p53 function restoration by CP-31398 caused a marked decrease in activity of the PI3K/Akt/mTOR pathway, which is most frequently deregulated in HNSCC, and whose inhibition results in decreased tumorigenicity in multiple preclinical models systems. Indeed, CP-31398 treatment increased the expression of Sestrin 1/2 and REDD1; three well established p53-regulated genes that exert inhibitory activity over mTOR. Next, we evaluated the chemopreventive efficacy of CP-31398 in a 4-Nitroquinoline oxide (4NQO)-induced HNSCC mouse model that we have recently developed, which closely resembles development and progression of human HNSCC, including the induction of tp53 mutations as revealed by DNA sequencing. C57BL/6 mice were given 4NQO in the drinking water for a period of 14 weeks, during which all the animals developed an array of potential oral premalignant lesions. Upon 4NQO removal, mice were randomized into two groups receiving a control diet or a diet containing 250 ppm of CP-31398 for 8 weeks, in which the development and progression of tongue lesions were documented. At the conclusion of the study, 22 weeks, all mice were euthanized and subjected to full autopsies and histopathological evaluations. While 100% of the animals in the control group developed SCCs at the end of the study, there was a 70% reduction in the number of SCCs in the CP-31398- treated group. These findings suggest that the early, widespread alterations, of p53 during HNSCC progression can make this tumor type particularly vulnerable to intervention strategies, restoring p53 function by direct acting, p53 rescue agents. Hence, a large number of at risk patients exhibiting potential oral premalignant lesions harboring p53 mutations could benefit from the treatment with p53-reactivating small molecules such as CP-31398, which can also restrict the uncontrolled activation of the mTOR pathway. Overall, we present evidence of a novel chemopreventive intervention approach that exploits the emerging crosstalk between p53 and the mTOR pathways, including pharmacologic activation of mutant p53, individually and together with mTOR inhibitors, halting HNSCC progression.

Citation Format: Lynn A. Vitale-Cross, Daniel Martin, Chinthalapally V. Rao, Levy Kopelovich, J. Silvio Gutkind. CP-31398 prevents the progression of oral squamous cell carcinomas from carcinogen-induced premalignant lesions. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1260. doi:10.1158/1538-7445.AM2014-1260