PROJECT SUMMARYAdenoid cystic carcinoma (ACC) is the second most common malignancy of the salivary glands. Over 60% of theACC patients succumb to the disease within 15 years from diagnosis. The lack of reliable experimental modelsfor ACC has limited our progress in understanding the biology of the disease and the proliferation of preclinicalstudies to test new therapies. In this proposal we address this fundamental need by proposing the generation ofgenetically engineered mouse models that develop autochthonous ACCs. These mice will help determine the roleof molecular alterations frequently found in human ACCs and will generate an in vivo platform for molecularand preclinical studies that will help advance towards more effective therapies to treat ACC patients. MYB is byfar the most commonly altered gene in human ACCs as over 70% of the tumors overexpress MYB-NFIB fusionsor the full-length MYB. Our preliminary studies show that MYB overexpression in transgenic mice induces ACCswith long latency indicating that MYB promotes ACC development but also suggesting that additionalalterations are required for ACC development. Genetic alterations affecting MYB-unrelated genes are found atlower frequencies in human ACCs. Notably mutations in different genes that are predicted to result in activationof NOTCH signaling including activating mutations in NOTCH1 were found in 25%-35% of the human ACCsassociated with poor prognosis. Of those inactivating mutations in the SPEN gene were found in ~20% of theACCs. SPEN is a transcriptional repressor of NOTCH signaling and functions as a tumor suppressor throughNOTCH-dependent and NOTCH-independent mechanisms. Importantly these mutations co-exist with MYBalterations but their contribution to ACC development is presently unknown. In this proposal we will analyzethe cooperation of MYB with NOTCH activation or SPEN inactivation during ACC development in mouse modelsthat allow the activation of mutations in salivary glands. The inducible nature of the system used to activate thesealterations will allow us to determine whether they are required to maintain tumor growth and to identifymechanisms involved in tumor regression. Analysis of the transcriptomes of the tumors that develop in thesemice will allow us to identify MYB-regulated genes and pathways that contribute to ACC development some ofwhich may be required to maintain tumor growth and thus could be excellent targets to explore new therapiesfor ACC.