| Adenoid cystic carcinoma (ACC) of the salivary gland is an indolent but highly lethal neuroinvasive tumor with a propensity for radiation resistance, recurrence, and metastasis. Molecular understanding of this rare tumor has been hampered by the absence of validated in vitro models and a limited number of xenografts. Therapeutic options for ACC are limited to surgery and radiation and are associated with an unacceptably low rate of cure. Cancer stem cells (CSC) are an attractive therapeutic target, and understanding their role in ACC may advance therapy. Our objectives were: 1) to establish and validate ACC cell cultures, 2) to determine if CSC exist in ACC, and if so, isolate and characterize these cells in ACC, and 3) to identify new therapeutic targets for ACC. To culture ACC and to isolate and initially characterize CSC from ACC, we modified a ROCK inhibitor-based cell culture technique, identified CD133 (PROM1) as a cell surface marker of CSCs, and used immunomagnetic cell sorting to separate and characterize RNA and protein expression in these cells. We found that CD133+ cells expressed NOTCH1 and SOX10, formed spheroids, and initiated tumors in nude mice more readily than CD133- cells. Depletion of NOTCH1 and SOX10 in cultured ACC induced death of CD133+ cells, indicating their essential roles in maintenance of stemness. An inhibitor of Notch activation, DAPT, selectively depleted CD133+ cells in vitro, sensitized CD133+ cells to radiation, and inhibited growth of ACC tumor in vivo. These results establish the presence of a previously uncharacterized population of CD133+ cells with neural stem properties in ACC whose survival is dependent on NOTCH1 and SOX10. Sensitivity of ACC cells to Notch inhibition offer new opportunities for targeted therapy in this orphan tumor. |
