ABSTRACT Head and neck cancer is a complex malignancy with its major anatomical subsite, cancer of the oral cavity presenting mostly as oral squamous cell carcinoma (OSCC). This malignancy ranks among the most deadly and disfiguring cancers worldwide due to the lack of early detection and effective treatments. OSCC is characterized by heterogeneous cell states, including cancer stem cells (CSCs), and cells with p-EMT phenotypes which promote metastasis and therapy resistance. One of the key drivers of OSCC is the Wnt/β-catenin signaling pathway, where aberrant interaction of nuclear β-catenin with CREB-binding protein (CBP) leads to histone 3 lysine 27 acetylation (H3K27ac) and an open chromatin structure. The β-catenin/CBP complex has been also shown to recruit the histone methyltransferase MLL1, to further promote an open chromatin through trimethylation of histone 3 lysine 4 (H3K4me3). Growing evidence indicates that chronic Wnt/β-catenin signaling gives rise to highly plastic cell states by inducing epithelial cellular senescence, a state of cell cycle arrest that can contribute to tumorigenesis through an altered gene expression program known as the senescence associated secretory phenotype (SASP). To examine how Wnt/β-catenin mediated epigenetic activity drives OSCC evolution, I adapted a syngeneic mouse model of tobacco-associated OSCC using a mouse cell line 4MOSC1, derived from 4-nitroquinoline-1 oxide- (4NQO)-induced tongue tumors. When implanted into mouse tongues, 4MOSC1 cells generate tumors that recapitulate the human OSCC mutanome. My preliminary studies show that inhibition of β-catenin interaction with CBP using a reversible, competitive inhibitor, E7386, reduces isograft tumor growth by 70%, compared to the placebo cohort, providing evidence that the β-catenin/CBP signaling axis is a major contributor to OSCC in this mouse model. In vitro and in vivo experiments also show that E7386 treatment leads to decreased MLL1 protein abundance coincident with reduced levels of the open chromatin mark H3K4me3 at the transcription start sites of genes associated with cell plasticity. Because the median age of OSCC diagnosis is 66 years, I investigated the impact of age on 4MOSC1-derived OSCC isografts. Immunofluorescence analysis of tumor isografts from young (10 wks) and aging (64 wks) mice showed that the older mice had increased CBP and H3K4me3 fluorescence intensity concomitant with increased markers of cellular senescence. I hypothesize that the β-catenin/CBP/MLL1 epigenetic activity promotes OSCC evolution through cellular senescence and cell plasticity, which are exacerbated with age. I will investigate my hypotheses in two aims. Aim 1 will define the association between Wnt/β-catenin epigenetic activity, cellular senescence, and cell plasticity in OSCC in young and aged mice. Aim 2 will elucidate the functional significance of MLL1 in Wnt/β-catenin epigenetic activity, cell senescence and plasticity in OSCC and its dependence on age...