Centro de Investigaciones Básicas y Aplicadas, Universidad Nacional del Noroeste de la Provincia de Buenos Aires, Junín, Buenos Aires, Argentina.
Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires (CITNOBA) - UNNOBA-UNSAdA-CONICET, Pergamino, Buenos Aires, Argentina.
Tumour Biol. 2022;44(1):85-105. doi: 10.3233/TUB-211500.
Prolactinomas are the most frequent pituitary tumor subtype. Despite most of them respond to medical treatment, a proportion are resistant and become a challenge in clinical management. Wnt/β-Catenin pathway has been implicated in several cancers including pituitary tumors and other sellar region malignancies. Interestingly, Wnt/β-Catenin inhibition augments the cytotoxicity of the chemotherapeutic agent Temozolomide (TMZ) in different cancers. TMZ is now being implemented as rescue therapy for aggressive pituitary adenoma treatment. However, the molecular mechanisms associated with TMZ action in pituitary tumors remain unclear.
Our aims in the present study were to evaluate differential β-Catenin expression in human resistant prolactinomas and Wnt/β-Catenin signaling activation and involvement in Prolactin (PRL) secreting experimental models treated with TMZ.
We first evaluated by immunohistochemistry β-Catenin localization in human resistant prolactinomas in which we demonstrated reduced membrane β-Catenin in prolactinoma cells compared to normal pituitaries, independently of the Ki-67 proliferation indexes. In turn, in vivo 15 mg/kg of orally administered TMZ markedly reduced PRL production and increased prolactinoma cell apoptosis in mice bearing xenografted prolactinomas. Intratumoral β-Catenin strongly correlated with Prl and Cyclin D1, and importantly, TMZ downregulated both β-Catenin and Cyclin D1, supporting their significance in prolactinoma growth and as candidates of therapeutic targets. When tested in vitro, TMZ directly reduced MMQ cell viability, increased apoptosis and produced G2/M cell cycle arrest. Remarkably, β-Catenin activation and VEGF secretion were inhibited by TMZ in vitro.
We concluded that dopamine resistant prolactinomas undergo a β-Catenin relocalization in relation to normal pituitaries and that TMZ restrains experimental prolactinoma tumorigenicity by reducing PRL production and β-Catenin activation. Together, our findings contribute to the understanding of Wnt/β-Catenin implication in prolactinoma maintenance and TMZ therapy, opening the opportunity of new treatment strategies for aggressive and resistant pituitary tumors.
催乳素瘤是最常见的垂体肿瘤亚型。尽管大多数催乳素瘤对药物治疗有反应，但仍有一部分是耐药的，这给临床治疗带来了挑战。Wnt/β-连环蛋白途径已被牵涉到包括垂体肿瘤和其他鞍区恶性肿瘤在内的几种癌症中。有趣的是，Wnt/β-连环蛋白抑制增强了替莫唑胺（TMZ）在不同癌症中的细胞毒性。TMZ 现在被用作侵袭性垂体腺瘤治疗的挽救疗法。然而，与 TMZ 在垂体肿瘤中的作用相关的分子机制仍不清楚。
本研究旨在评估人类耐药性催乳素瘤中β-连环蛋白的差异表达，以及 Wnt/β-连环蛋白信号通路的激活及其在 TMZ 治疗的催乳素（PRL）分泌实验模型中的作用。
我们首先通过免疫组织化学评估了人类耐药性催乳素瘤中β-连环蛋白的定位，结果表明与正常垂体相比，催乳素瘤细胞中的膜结合β-连环蛋白减少，这与 Ki-67 增殖指数无关。相反，在体内，口服 15mg/kg 的 TMZ 可显著降低荷有异种移植催乳素瘤的小鼠的 PRL 产生，并增加催乳素瘤细胞凋亡。肿瘤内β-连环蛋白与 Prl 和 Cyclin D1 强烈相关，重要的是，TMZ 下调了β-连环蛋白和 Cyclin D1，支持它们在催乳素瘤生长中的重要性及其作为治疗靶点的候选物。在体外进行测试时，TMZ 直接降低 MMQ 细胞活力，增加细胞凋亡，并导致 G2/M 细胞周期阻滞。值得注意的是，TMZ 在体外抑制了β-连环蛋白的激活和 VEGF 的分泌。
我们得出的结论是，多巴胺耐药性催乳素瘤与正常垂体相比，β-连环蛋白发生了重新定位，TMZ 通过减少 PRL 的产生和β-连环蛋白的激活来抑制实验性催乳素瘤的肿瘤发生。总之，我们的研究结果有助于了解 Wnt/β-连环蛋白在催乳素瘤维持和 TMZ 治疗中的作用，为侵袭性和耐药性垂体肿瘤的新治疗策略开辟了机会。
