Department of Cancer Biology, Beckman Research Institute of City of Hope, Duarte, CA, 91010, USA.
Department of Medical Oncology, City of Hope Medical Center, Duarte, CA, 91010, USA.
Breast Cancer Res Treat. 2019 Apr;174(3):615-625. doi: 10.1007/s10549-018-05104-9. Epub 2019 Jan 3.
Palbociclib is an approved cyclin-dependent kinase (CDK) 4/6 inhibitor for treatment of patients with ER-positive and HER2-negative breast cancers. While Retinoblastoma protein (pRb), a major substrate of CDK4/6, is a potential target in triple negative breast cancer (TNBC), the usefulness of CDK4/6 inhibitors in this cancer has not been established. This preclinical study investigated the combination effects of palbociclib and the dual mammalian target of rapamycin (mTOR) kinase inhibitor MLN0128 in estrogen receptor (ER)-negative breast cancer in vitro and in vivo.
The combined effects of two drugs on three TNBC cell lines (MB231, MB468, and CAL148) and an ER-negative and HER2-positive cell line (MB453) were investigated by MTT assay and colony formation analysis. Cell cycle measurements were examined as well as changes in expression of molecules related to G1/S transition and the mTOR pathway. Importantly, a pRb-expressing TNBC patient-derived xenograft (PDX) model was used to assess the effects of the combination in vivo.
A combination of palbociclib and MLN0128 synergistically inhibited the proliferation of pRb-expressing cell lines and induced G1 cell cycle arrest. Western blot analysis revealed that CDK4/6-pRb and mTOR pathways were inhibited by these treatments. In pRb-expressing TNBC PDX, the combination treatment drastically suppressed tumor growth compared to either the control or single drug treatments. In addition, the combination treatment significantly reduced the number of Ki67-positive cells.
We revealed that palbociclib and MLN0128 had synergistic anti-cancer activity in both pRb + ER-negative cell lines and a TNBC PDX model. Our results indicate that such combination therapy is worthy of further investigation in a clinical setting.
帕博西尼（Palbociclib）是一种已被批准的细胞周期蛋白依赖性激酶（CDK）4/6 抑制剂，用于治疗雌激素受体（ER）阳性和人表皮生长因子受体 2（HER2）阴性的乳腺癌患者。虽然视网膜母细胞瘤蛋白（pRb）是 CDK4/6 的主要底物，是三阴性乳腺癌（TNBC）的潜在靶点，但 CDK4/6 抑制剂在这种癌症中的作用尚未得到证实。本临床前研究旨在探讨帕博西尼与双重哺乳动物雷帕霉素靶蛋白（mTOR）激酶抑制剂 MLN0128 在体外和体内对 ER 阴性乳腺癌的联合作用。
通过 MTT 检测和集落形成分析，研究了两种药物对三种 TNBC 细胞系（MB231、MB468 和 CAL148）和一种 ER 阴性和 HER2 阳性细胞系（MB453）的联合作用。还检测了细胞周期测量以及与 G1/S 转换和 mTOR 通路相关的分子表达的变化。重要的是，使用表达 pRb 的 TNBC 患者来源异种移植（PDX）模型评估了体内联合治疗的效果。
帕博西尼和 MLN0128 的联合抑制了表达 pRb 的细胞系的增殖，并诱导了 G1 细胞周期停滞。Western blot 分析显示，这些治疗抑制了 CDK4/6-pRb 和 mTOR 通路。在表达 pRb 的 TNBC PDX 中，与对照组或单一药物治疗相比，联合治疗明显抑制了肿瘤生长。此外，联合治疗还显著减少了 Ki67 阳性细胞的数量。
我们发现，帕博西尼和 MLN0128 在表达 pRb 的 ER 阴性细胞系和 TNBC PDX 模型中具有协同抗癌活性。我们的研究结果表明，这种联合治疗值得在临床环境中进一步研究。
