Department of Pathology, Anatomy and Cell Biology and the Clinical and Translational Research Center of Excellence, Meharry Medical College, Nashville, TN, U.S.A.
Scripps Mercy Hospital, MER 35, San Diego, CA, U.S.A.
Anticancer Res. 2024 Oct;44(10):4165-4173. doi: 10.21873/anticanres.17247.
BACKGROUND/AIM: Recently, we demonstrated that cancer dormancy is initiated within the lymphovascular tumor embolus and consists of decreased proliferation and lower mammalian target of rapamycin (mTOR) activity. In the present study, we investigated other intersecting metabolism-signaling pathways that may ultimately determine whether the lymphovascular tumor embolus remains dormant or undergoes cell death.
The present study exploited a singular patient-derived xenograft (PDX) of inflammatory breast cancer (Mary-X) that spontaneously forms high density spheroids, the in vitro equivalent of emboli. The AMPK metabolic checkpoint pathway, the mTOR nutrient-responsive cell growth pathway, the P13K/Akt intracellular quiescence regulating pathway, and the calpain-mediated E-cadherin proteolytic pathway responsible for spontaneous spheroid-genesis were also investigated, to determine their relative contributions to dormancy.
The levels of phosphorylated AMPK proteins (AMPKα and β subunits) decreased gradually with the formation of MARY-X spheroids in vitro. Rapamycin down-regulated mTOR activity, yet dormancy persisted. LY294002, a PI3K/Akt inhibitor, completely abolished mTOR and induced spheroid disadherence and apoptosis. Compound C (AMPK inhibitor) up-regulated mTOR and induced spheroid disadherence and apoptosis. Increasing cellular metabolism led to cell death, even in enriched medium, whereas growing the spheroids in serum-free media (starvation) did not result in further mTOR inhibition, and dormancy was maintained.
An increase in our understanding of dormancy from the standpoint of internal signaling pathways might ultimately provide clues to the external stimuli (starvation, hypoxia or other not yet understood phenomena) that act through these pathways to maintain or disrupt dormancy.
背景/目的：最近，我们证明肿瘤休眠是在淋巴血管肿瘤栓子中启动的，其特征是增殖减少和哺乳动物雷帕霉素靶蛋白（mTOR）活性降低。在本研究中，我们研究了其他可能最终决定淋巴血管肿瘤栓子是否保持休眠或发生细胞死亡的交叉代谢信号通路。
本研究利用了一例炎症性乳腺癌（Mary-X）的独特患者来源的异种移植物（PDX），该肿瘤会自发形成高密度球体，这是栓子的体外等效物。还研究了 AMPK 代谢检查点通路、mTOR 营养响应细胞生长通路、PI3K/Akt 细胞内静止调节通路以及负责自发球体发生的钙蛋白酶介导的 E-钙黏蛋白蛋白水解通路，以确定它们对休眠的相对贡献。
在体外，随着 MARY-X 球体的形成，磷酸化 AMPK 蛋白（AMPKα和β亚基）的水平逐渐降低。雷帕霉素下调 mTOR 活性，但休眠仍然存在。PI3K/Akt 抑制剂 LY294002 完全抑制 mTOR 并诱导球体脱离和凋亡。AMPK 抑制剂 Compound C 上调 mTOR 并诱导球体脱离和凋亡。增加细胞代谢会导致细胞死亡，即使在富含培养基中也是如此，而在无血清培养基（饥饿）中培养球体不会导致进一步的 mTOR 抑制，并且保持休眠。
从内部信号通路的角度更深入地了解休眠可能最终提供线索，了解通过这些通路发挥作用的外部刺激（饥饿、缺氧或其他尚未了解的现象），以维持或破坏休眠。
