Team 8 "Cell survival and tumor escape in breast cancer," UMR 892 INSERM/6299 CNRS/Université de Nantes, Institut de Recherche Thérapeutique de l'Université de Nantes, 8, quai Moncousu, BP 70721, 44007 Nantes Cedex 1, France.
Breast Cancer Res. 2012 Jun 15;14(3):R96. doi: 10.1186/bcr3214.
Inappropriate Notch signaling, downstream of γ-secretase activity, is understood to have tumor-promoting function and to be associated with poor outcome in cancer, of the breast in particular. The molecular basis of antitumoral effects of its inhibitors, however, remains poorly characterized. Moreover, the effects of their combination with the pro-apoptotic pharmacologic inhibitor of Bcl-2/Bcl-xL, ABT-737, have never been evaluated. In this study, we thus specifically addressed the biologic consequences of targeting γ-secretase and Bcl-2/Bcl-xL, alone or simultaneously, in breast cancer cell lines as well as in a novel human breast cancer ex vivo assay.
By using in vitro 2D or 3D cultures of breast cancer cells plus a novel preclinical short-term ex vivo assay that correctly maintains human mammary tissue integrity and preserves tumor microenvironment, we tested the effects of the pharmacologic γ-secretase inhibitor GSIXII used as a single agent or in combination with ABT-737.
We show herein that the γ-secretase inhibitor, GSIXII, efficiently induces apoptosis in breast cancer cell lines by a process that relies on the induction of Noxa, a pro-apoptotic Bcl2-homology 3 domain (BH3)-only protein of the Bcl-2 family that functions as an inhibitor of antiapoptotic Mcl1. GSIXII also targets mammary cancer stem-like cells because it dramatically prevents in vitro mammosphere formation. Moreover, combining GSIXII treatment with ABT-737, a BH3-mimetic inhibitor of additional antiapoptotic proteins, such as Bcl-2 and Bcl-xL, leads to both a synergistic apoptotic response in breast cancer cells and to an inhibitory effect on mammosphere formation. These effects are also found when a Notch transcriptional inhibitor, SAHM1, is used. Finally, we evaluated individual human tumor responses to γ-secretase inhibition alone or in combination with ABT-737 in ex vivo assays. Analysis of a series of 30 consecutive tumors indicated that a majority of tumors are sensitive to apoptosis induction by GSIXII and that association of GSIXII with ABT-737 leads to an enhanced induction of apoptosis in tumor cells.
We thus provide evidence that γ-secretase, and downstream Notch signaling, are relevant targets in breast cancer. GSIXII, used as single agent or in combination with clinically relevant BH3-mimetics, is a promising innovative proapoptotic strategy to treat mammary tumors.
γ-分泌酶活性下游的 Notch 信号传导被认为具有促进肿瘤的功能，并与癌症，特别是乳腺癌的不良预后相关。然而，其抑制剂的抗肿瘤作用的分子基础仍知之甚少。此外，它们与促凋亡的 Bcl-2/Bcl-xL 药理学抑制剂 ABT-737 联合使用的效果从未被评估过。在这项研究中，我们特别针对乳腺癌细胞系中单独或同时靶向 γ-分泌酶和 Bcl-2/Bcl-xL 的生物学后果进行了研究，同时还在新的人类乳腺癌体外检测中进行了研究。
通过使用体外 2D 或 3D 培养的乳腺癌细胞加上一种新型的临床前短期体外检测，该检测正确地保持了人乳腺组织的完整性并保留了肿瘤微环境，我们测试了作为单一药物或与 ABT-737 联合使用的药理学 γ-分泌酶抑制剂 GSIXII 的作用。
我们在此证明，γ-分泌酶抑制剂 GSIXII 通过一种依赖于 Noxa 诱导的过程有效地诱导乳腺癌细胞凋亡，Noxa 是 Bcl-2 同源性 3 结构域（BH3）仅蛋白家族的一种促凋亡蛋白，可作为抗凋亡 Mcl1 的抑制剂。GSIXII 还靶向乳腺癌症干细胞，因为它可显著防止体外乳腺球体的形成。此外，将 GSIXII 与 ABT-737 联合治疗，ABT-737 是一种 BH3 模拟物抑制剂，可以抑制其他抗凋亡蛋白，如 Bcl-2 和 Bcl-xL，可导致乳腺癌细胞的协同凋亡反应，并抑制乳腺球体的形成。当使用 Notch 转录抑制剂 SAHM1 时也会发现这些效果。最后，我们在体外检测中评估了单独使用 γ-分泌酶抑制剂或与 ABT-737 联合使用对个人类肿瘤的反应。对 30 例连续肿瘤的分析表明，大多数肿瘤对 GSIXII 诱导的凋亡敏感，并且 GSIXII 与 ABT-737 联合使用可增强肿瘤细胞的凋亡诱导。
因此，我们提供了证据表明 γ-分泌酶和下游 Notch 信号传导是乳腺癌的相关靶点。GSIXII 作为单一药物或与临床相关的 BH3 模拟物联合使用，是一种有前途的创新促凋亡策略，可用于治疗乳腺肿瘤。
