Therapeutic targeting of E2F inhibits stemness of salivary gland mucoepidermoid carcinoma.

The E2F family of transcription factors plays essential roles in cell cycle regulation, DNA damage response, apoptosis, senescence, glucose metabolism, and angiogenesis. Although E2F pathway alterations were identified across multiple cancers, its role in salivary gland tumorigenesis remains elusive. Given the mechanistic role of E2F in cancer stemness, this pathway represents a promising therapeutic target for salivary malignancies. The purpose of this study was to evaluate the function of E2F1 and E2F4 in the stemness of salivary gland mucoepidermoid carcinoma (MEC), and to test whether pharmacologic inhibition of E2F ablates cancer stem cells (CSC) in MEC. Evaluation of a tissue microarray (TMA) of human MEC samples showed that E2F1 and E2F4 were overexpressed in MECs compared with control salivary glands, where their expression was restricted to ductal cells. CSCs showed higher expression of E2F1 and E2F4 compared to non-CSCs in 3 human MEC cell lines (UM-HMC-1,-3A,-3B). Therapeutic inhibition of E2F with HLM006474 induced expression of p53 and p21 while inhibiting expression of the stemness markers Bmi-1 and ALDH. Notably, the fraction of CSC (ALDHhighCD44high) was significantly reduced by HLM006474 in vitro, and in MEC tumor xenografts in vivo. Collectively, these data demonstrate that E2F inhibits stemness in mucoepidermoid carcinoma and suggest that patients with salivary gland malignancies might benefit from therapeutic inhibition of E2F.