Oral squamous cell carcinomas (OSCCs) are proposed to contain a subset of tumor cells whose stem cell-like molecular and functional properties are required to sustain tumor growth. In a hierarchical model, these cancer stem cells (CSCs) are the only cells with unlimited self-renewal capacity and thus may be targeted in isolation to achieve tumor control. However, there is increasing evidence that some non-CSCs have the phenotypic plasticity to return to the CSC pool and thus retain therapeutic relevance. Accurately defining non-CSCs that can support an oral CSC pool together with mechanisms that drive these cells toward a CSC state would establish novel paradigm for OSCC treatment. Our preliminary work has isolated OSCC cells residing in a "G0- like" cell state previously found to have high growth potential, innate drug resistance, and low levels of Akt. Despite lacking molecular markers of CSCs, these cells displayed high tumorigenicity in vivo. Our working hypothesis is that the functional properties of G0-like cells reflect their ability to transition t a CSC state. We have also identified a putative CSC population in OSCCs, based on high expression JARID1B, a histone demethylase known to maintain other malignant and normal stem cell phenotypes. JARID1Bhigh cells exhibit both functional and molecular stem cell traits and are further distinguished from the G0-like subset by hyper- activation of the PI3K-Akt signaling pathway. To explain these findings, our overall hypothesis is that reactivation of the PI3K-Akt pathway in G0-like cells supports their return to the CSC pool by driving their transition to a JARID1Bhigh state. To test this hypothesis, we will first test the roles of the JARID1Bhigh and G0- like subsets in OSCC growth using conventional CSC molecular and functional criteria (aim 1). We will specifically test whether JARID1Bhigh cells have independent CSC functions, while tumor formation by G0-like cells may depend upon the JARID1Bhigh fraction. Additional studies will elucidate how PI3K-Akt signals regulate transitions among CSCs, G0-like cells, and the broader non-CSC pool (aim 2). Here we will test whether modulation of the PI3K-Akt pathway affects the sizes of the G0-like and JARID1Bhigh pools and/or the ability of non-CSCs to transition toward a JARID1Bhigh CSC state. Together these studies would provide valuable insight into the hierarchical organization and plasticity of non-CSC and CSC subsets within OSCCs.
Oral squamous cell carcinomas (OSCCs), a major public health issue in the US, account for approximately 36,000 annual cases and 8000 deaths as well as severe treatment-related disabilities in many survivors. OSCCs putatively contain small subsets of cancer stem cells (CSCs) that are required to sustain tumor growth and contribute to drug resistance and tumor recurrence. The current proposal will use innovative and collaborative approaches to explore the cell types and mechanisms that maintain the CSC pool in OSCCs, providing a foundation for the development of novel, less toxic therapies to achieve durable CSC eradication and lasting tumor control in OSCC patients.
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