Department of Periodontics and Oral Medicine, University of Michigan, Ann Arbor, MI, USA.
Department of Oral Pathology, University of São Paulo, São Paulo, SP, Brazil.
Cell Death Dis. 2021 Jan 21;12(1):108. doi: 10.1038/s41419-021-03391-7.
Advanced salivary gland mucoepidermoid carcinoma (MEC) is a relentless cancer that exhibits resistance to conventional chemotherapy. As such, treatment for patients with advanced MEC is tipically radical surgery and radiotherapy. Facial disfigurement and poor quality of life are frequent treatment challenges, and many patients succumb to loco-regional recurrence and/or metastasis. We know that cancer stem-like cells (CSC) drive MEC tumorigenesis. The current study tests the hypothesis that MEC CSC are sensitive to therapeutic inhibition of mTOR. Here, we report a correlation between the long-term clinical outcomes of 17 MEC patients and the intratumoral expression of p-mTOR (p = 0.00294) and p-S6K1 (p = 0.00357). In vitro, we observed that MEC CSC exhibit constitutive activation of the mTOR signaling pathway (i.e., mTOR, AKT, and S6K1), unveiling a potential strategy for targeted ablation of these cells. Using a panel of inhibitors of the mTOR pathway, i.e., rapamycin and temsirolimus (mTOR inhibitors), buparlisib and LY294002 (AKT inhibitors), and PF4708671 (S6K1 inhibitor), we observed consistently dose-dependent decrease in the fraction of CSC, as well as inhibition of secondary sphere formation and self-renewal in three human MEC cell lines (UM-HMC-1,-3A,-3B). Notably, therapeutic inhibition of mTOR with rapamycin or temsirolimus induced preferential apoptosis of CSC, when compared to bulk tumor cells. In contrast, conventional chemotherapeutic drugs (cisplatin, paclitaxel) induced preferential apoptosis of bulk tumor cells and accumulation of CSC. In vivo, therapeutic inhibition of mTOR with temsirolimus caused ablation of CSC and downregulation of Bmi-1 expression (major inducer of stem cell self-renewal) in MEC xenografts. Transplantation of MEC cells genetically silenced for mTOR into immunodeficient mice corroborated the results obtained with temsirolimus. Collectively, these data demonstrated that mTOR signaling is required for CSC survival, and unveiled the therapeutic potential of targeting the mTOR pathway for elimination of highly tumorigenic cancer stem-like cells in salivary gland mucoepidermoid carcinoma.
高级唾液腺癌黏液表皮样癌 (MEC) 是一种无情的癌症，对常规化疗具有耐药性。因此，晚期 MEC 患者的治疗通常是激进的手术和放疗。面部毁容和生活质量差是常见的治疗挑战，许多患者因局部区域复发和/或转移而死亡。我们知道癌症干细胞样细胞 (CSC) 驱动 MEC 肿瘤发生。本研究检验了 MEC CSC 对 mTOR 治疗抑制敏感的假设。在这里，我们报告了 17 名 MEC 患者的长期临床结果与肿瘤内 p-mTOR(p=0.00294)和 p-S6K1(p=0.00357)表达之间的相关性。在体外，我们观察到 MEC CSC 表现出 mTOR 信号通路的组成性激活（即 mTOR、AKT 和 S6K1），这揭示了靶向消融这些细胞的潜在策略。使用一组 mTOR 通路抑制剂，即雷帕霉素和替西罗莫司（mTOR 抑制剂）、buparlisib 和 LY294002（AKT 抑制剂）和 PF4708671（S6K1 抑制剂），我们观察到三种人 MEC 细胞系（UM-HMC-1、-3A、-3B）中 CSC 的比例一致地呈剂量依赖性下降，以及二级球体形成和自我更新的抑制。值得注意的是，与普通化疗药物（顺铂、紫杉醇）相比，用雷帕霉素或替西罗莫司治疗性抑制 mTOR 可诱导 CSC 的选择性凋亡。相比之下，普通化疗药物（顺铂、紫杉醇）诱导了大量肿瘤细胞的选择性凋亡和 CSC 的积累。在体内，替西罗莫司治疗性抑制 mTOR 导致 MEC 异种移植物中 CSC 的消融和 Bmi-1 表达的下调（干细胞自我更新的主要诱导因子）。将 mTOR 基因沉默的 MEC 细胞移植到免疫缺陷小鼠中，证实了替西罗莫司的结果。总的来说，这些数据表明 mTOR 信号通路对于 CSC 的存活是必需的，并揭示了靶向 mTOR 通路消除唾液腺癌黏液表皮样癌中高度致瘤性癌症干细胞样细胞的治疗潜力。
