Abstract 4837: Role of Notch signaling in human mucoepidermoid carcinoma and combined targeting of Notch and EGFR signaling as an anti-cancer strategy

Abstract

Abstract Mucoepidermoid carcinoma (MEC) is the most common salivary gland malignancy and currently no targeted therapy is available for MEC patients. MEC is characterized by a unique chromosomal translocation t(11;19)(q14-21;p12-13) that generates the CRTC1-MAML2 fusion. Our understanding of CRTC1-MAML2-mediated tumorigenesis and maintenance remains limited. MEC is considered a disease of stem/progenitor cells; however, the regulation of human MEC stem/progenitor cells has not yet been characterized. In this study, we focused on Notch signaling, a pathway important in regulating normal and cancerous stem cells, and investigated its regulatory role in human MEC cancer stem/progenitor cells as well as its potential therapeutic potential. First, we determined the status of Notch signaling activation in MEC cells. Western blotting showed the presence of cleaved active NOTCH1 and the expression of Notch downstream target gene HES1 in human CRTC1-MAML2 fusion-positive MEC cells, indicative of active Notch signaling in MEC. Second, we utilized two approaches of blocking endogenous Notch signaling in human MEC cells in vitro and in vivo, i.e. dnMAML1, a pan-Notch inhibitor that blocks the formation of the Notch transcriptional activation complex, and dibenzazepine (DBZ), a γ-secretase inhibitor that interferes with Notch receptor processing. We observed that Notch signaling inhibition had no effect on the proliferation of bulk MEC cells, but significantly reduced oncosphere forming capacity and ALDH-positive population in human MEC in vitro, suggesting that Notch signaling contributes to the maintenance of MEC stem/progenitor cells. Further, Notch signaling inhibition significantly reduced the growth of human MEC xenografts, indicating an essential role of Notch signaling in MEC growth in vivo. Finally, since we previously showed that the CRTC1-MAML2-induced autocrine AREG-EGFR signaling was required for the growth and survival of human MEC cells, we reasoned that simultaneous targeting of Notch and EGFR signaling will eliminate cancer stem and non-stem cell populations, likely improving therapeutic efficacy. Indeed, concurrent inhibition of Notch and EGFR signaling via respective DBZ and Erlotinib synergistically blocked the colony and oncosphere formation capacity of human MEC cells in vitro and in vivo. Collectively, our data demonstrate that Notch signaling is a critical regulator for maintaining MEC cancer-initiating cells and that the combination strategy targeting Notch and EGFR signaling is a potentially effective approach for MEC treatment. Citation Format: Wei Ni, Zirong Chen, Xin Zhou, Rongqiang Yang, Frederic Kaye, Lizi Wu. Role of Notch signaling in human mucoepidermoid carcinoma and combined targeting of Notch and EGFR signaling as an anti-cancer strategy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4837.