Project Summary Synthetic inhibitors of protein-protein interactions (PPIs) are emerging as a promising approach for discovery of new therapeutics. However, despite recent progress, PPIs remain challenging targets and the in vivo potential of small molecule PPI inhibitors remains insufficiently characterized. We will develop rationally designed small molecule inhibitors of an interaction that is critical for HPV-associated head and neck squamous cell carcinoma (HNSCC). Strong preliminary results, including in vivo animal data, support our strategy. HNSCC is the sixth most common cancer with an annual incidence of approximately 600,000 cases worldwide. Recent evidence supports the recognition that HPV infection is a major risk factor for HNSCC, in particular oropharyngeal SCC. High-risk HPV16 is by far the most frequent, ~90%, HPV type detected in HNSCC. Epidemiological data indicate that the prevalence of HPV-positive HNSCC has rapidly increased by about 3-fold in the past three decades in the United States and Europe. Based on these alarming numbers, it has been suggested that an epidemic of HPV-positive HNSCC will emerge in the near future. Therefore, there is a clinical need to identify alternative therapeutic strategies to manage HPV-positive HNSCC patients. In HPV16-associated HNSCC, the tumor suppressors, p53 and Rb, are expressed as wild type but inactivated by the HPV16E6 and E7 proteins. Simultaneous reactivation of p53 and Rb offers an appealing strategy for developing anti-cancer leads for HPV16-associated HNSCC. p53 and Rb function are modulated through post-translational acetylation by the transcriptional co-activator p300. HPV16E6 and HPV16E7 bind the CH1 and CH3 protein-protein interaction domains of p300. Since p300 is known to be a limited resource, we hypothesized that HPV16E6 and HPV16E7 hijack p300 activity in HPV16-positive HNSCC. We will leverage our preliminary results and advance prototype HPV16E6-p300 small molecule modulators as rationally designed molecularly targeted therapeutics for HPV16-positive HNSCC. The project will have broad impact on discovery of PPI inhibitors because little is known about the in vivo potential and selectivity of small molecule PPI modulators. We have assembled a multi-disciplinary team of experts in head and neck cancer biology and signal transduction (Pan) and chemistry (Arora) to successfully complete this proposal.