The University of Queensland Diamantina Institute, Princess Alexandra Hospital, Ipswich Road, Brisbane, Queensland 4102, Australia.
Breast Cancer Res. 2011 Apr 1;13(2):R36. doi: 10.1186/bcr2858.
Estrogen receptor-negative (ER-) breast cancer is a heterogeneous disease with limited therapeutic options. The molecular apocrine subtype constitutes 50% of ER-tumors and is characterized by overexpression of steroid response genes including androgen receptor (AR). We have recently identified a positive feedback loop between the AR and extracellular signal-regulated kinase (ERK) signaling pathways in the molecular apocrine subtype. In this feedback loop, AR regulates ERK phosphorylation through the mediation of ErbB2 and, in turn, ERK-CREB1 signaling regulates the transcription of AR in molecular apocrine cells. In this study, we investigated the therapeutic implications of the AR-ERK feedback loop in molecular apocrine breast cancer.
We examined a synergy between the AR inhibitor flutamide and the MEK inhibitor CI-1040 in the molecular apocrine cell lines MDA-MB-453, HCC-1954 and HCC-202 using MTT cell viability and annexin V apoptosis assays. Synergy was measured using the combination index (CI) method. Furthermore, we examined in vivo synergy between flutamide and the MEK inhibitor PD0325901 in a xenograft model of the molecular apocrine subtype. The effects of in vivo therapies on tumor growth, cell proliferation and angiogenesis were assessed.
We demonstrate synergistic CI values for combination therapy with flutamide and CI-1040 across three molecular apocrine cell lines at four dose combinations using both cell viability and apoptosis assays. Furthermore, we show in vivo that combination therapy with flutamide and MEK inhibitor PD0325901 has a significantly higher therapeutic efficacy in reducing tumor growth, cellular proliferation and angiogenesis than monotherapy with these agents. Moreover, our data suggested that flutamide and CI-1040 have synergy in trastuzumab resistance models of the molecular apocrine subtype. Notably, the therapeutic effect of combination therapy in trastuzumab-resistant cells was associated with the abrogation of an increased level of ERK phosphorylation that was developed in the process of trastuzumab resistance.
In this study, we demonstrate in vitro and in vivo synergies between AR and MEK inhibitors in molecular apocrine breast cancer. Furthermore, we show that combination therapy with these inhibitors can overcome trastuzumab resistance in molecular apocrine cells. Therefore, a combination therapy strategy with AR and MEK inhibitors may provide an attractive therapeutic option for the ER-/AR+ subtype of breast cancer.
雌激素受体阴性（ER-）乳腺癌是一种具有有限治疗选择的异质性疾病。分子大汗腺癌亚型构成了 ER 肿瘤的 50%，其特征是包括雄激素受体（AR）在内的类固醇反应基因的过度表达。我们最近在分子大汗腺癌亚型中发现了 AR 和细胞外信号调节激酶（ERK）信号通路之间的正反馈环。在这个反馈环中，AR 通过 ErbB2 的介导调节 ERK 磷酸化，反过来，ERK-CREB1 信号通路调节分子大汗腺细胞中 AR 的转录。在这项研究中，我们研究了 AR-ERK 反馈环在分子大汗腺癌中的治疗意义。
我们使用 MTT 细胞活力和 Annexin V 凋亡检测法，在 MDA-MB-453、HCC-1954 和 HCC-202 这三个分子大汗腺细胞系中检查了 AR 抑制剂氟他胺和 MEK 抑制剂 CI-1040 的协同作用。使用组合指数（CI）方法测量协同作用。此外，我们在分子大汗腺癌亚型的异种移植模型中检查了氟他胺和 MEK 抑制剂 PD0325901 的体内协同作用。评估了体内治疗对肿瘤生长、细胞增殖和血管生成的影响。
我们证明了在三种分子大汗腺细胞系的四种剂量组合中，氟他胺和 CI-1040 的组合治疗具有协同的 CI 值，使用细胞活力和凋亡检测两种方法都可以得到。此外，我们在体内证明了氟他胺和 MEK 抑制剂 PD0325901 的联合治疗在降低肿瘤生长、细胞增殖和血管生成方面比这些药物的单药治疗具有更高的治疗效果。此外，我们的数据表明，氟他胺和 CI-1040 在分子大汗腺癌的曲妥珠单抗耐药模型中有协同作用。值得注意的是，联合治疗在曲妥珠单抗耐药细胞中的治疗效果与曲妥珠单抗耐药过程中产生的 ERK 磷酸化水平的增加有关。
在这项研究中，我们在分子大汗腺癌的体外和体内证明了 AR 和 MEK 抑制剂之间的协同作用。此外，我们表明，这些抑制剂的联合治疗可以克服分子大汗腺细胞中的曲妥珠单抗耐药性。因此，AR 和 MEK 抑制剂的联合治疗策略可能为 ER-/AR+ 乳腺癌亚型提供一种有吸引力的治疗选择。
