Identification and Characterization of Neural-like Cancer Stem Cells in Salivary Adenoid Cystic Carcinoma

Abstract

Salivary adenoid cystic carcinoma (ACC) is prone to perineural invasion, late recurrence, and distal metastases, with 20-year survival of only 10%. Research defining new targets in ACC has lagged largely due to a dearth of in vitro models. In this thesis, a neurogenic gene signature intrinsic to ACC was characterized revealing genes involved in maintenance, differentiation, and function of non-cancerous neural crest stem cells, including TrkC and SOX10. Analyses of gene expression across tumor types revealed that melanoma, neuroblastoma, glioblastoma, and basal-like breast cancer expressed SOX10 and several SOX10 co-expressed genes, suggesting that tumors derived from cells originating in the neural crest may contain similar populations of stem-like cells. Examination of TrkC signaling revealed that TrkC supported cell migration, invasion, and ACC tumor growth, and that ACC cells produced the TrkC ligand. Optimization of newly-designed culturing techniques allowed for the first time establishment of ACC cell cultures from xenograft and primary ACC specimens. Gene expression analysis revealed that CD133 was co-expressed with SOX10, and remarkably, it marked a subpopulation of ACC cells that preferentially expressed NOTCH1 and SOX10, formed spheroids, and initiated tumors in nude mice. Depletion of NOTCH1 or pharmaceutical inhibition of Notch signaling depleted CD133+ cells, sensitized CD133+ cells to radiation, and suppressed spheroidogenesis and xenograft tumor formation. Optimization of culture techniques provides a framework for future experimentation, and identification of a stem-like subpopulation in ACC suggests that targeting signaling pathways critical for stem cell survival or behavior may provide a new avenue to ACC therapy.