Project Summary Incidence of HPV+ OPC has been increasing for several decades and this upward trend is expected to continue until at least 2060. Current first-line modalities to manage HPV+ OPC patients are effective but not without limitations. A key event in HPV-driven tumorigenesis is the inactivation of the p53 tumor suppressor program. HPV oncogene, E6, inactivates p53 through two distinct pathways: HPVE6 promotes the assembly of the HPVE6-E6AP-p53 trimeric protein complex resulting in ubiquitination and degradation of p53, and HPVE6 directly binds to p300 to block p300-directed acetylation and activation of p53. We hypothesized that disrupting the HPVE6-p300 interaction will liberate sufficient p300 to restore p53 and p300 functionality simultaneously in HPV+ OPC. Our team initiated a drug discovery platform to target the HPVE6-p300 interaction. Our work showed that in HPV+ OPC models: (a) HPVE6 binds to the CH1 domain of p300, (b) our lead molecule, OHM1, a CH1/p300 ligand, disrupts HPVE6-p300 interaction and reactivates p53 and p300, (c) OHM1 is active in vitro and in vivo, and (d) concurrent OHM1+cisplatin combination treatment yields durable complete anti-tumor responses in vivo. Our results are very compelling and, supports further research and development of dual p53 and p300 reactivation as a therapeutic strategy for HPV+ OPC. In this project, we propose to extensively determine the mechanisms of action of p53 and p300 reactivation in response to OHM1 in HPV+ OPC. The specific aims are: (1) determine if OHM1 modulates the p53 post-translational modification code to control p53 functionality and levels, and promote anti-cancer activity in HPV+ OPC, (2) to determine if OHM1 reshapes the tumor-microenvironment and boost immunotherapy response in HPV+ OPC.