Mammalian target of rapamycin-dependent acinar cell neoplasia after inactivation of Apc and Pten in the mouse salivary gland: Implications for human acinic cell carcinoma

Cross-talk between the canonical Wnt and mammalian target of rapamycin (mTOR) signaling pathways occurs at multiple levels in the cell and likely contributes to the oncogenic effects of these pathways in human cancer. To gain more insight into the interplay between Wnt and mTOR signaling in salivary gland tumorigenesis, we developed a mouse model in which both pathways are constitutively activated by the conditional inactivation of the Apc and Pten tumor suppressor genes. Loss of either Apc or Pten alone did not cause tumor development. However, deletion of both genes resulted in the formation of salivary gland tumors with 100% penetrance and short latency that showed a remarkable morphologic similarity to human acinic cell carcinoma. Treatment of tumor-bearing mice using the mTOR inhibitor rapamycin led to complete regression of tumors, indicating that tumor growth was dependent on continued mTOR signaling. Importantly, we found that human salivary gland acinic cell carcinomas also express markers of activated mTOR signaling. Together, these results suggest that aberrant activation of mTOR signaling plays a pivotal role in acinar cell neoplasia of the salivary gland. Because rapamycin analogues are approved for treating other types of human malignancies, our findings suggest that rapamycin therapy should be evaluated for treating patients with salivary gland acinic cell carcinoma.