Endocrine therapies targeting estrogen signaling have significantly improved breast cancer (BC) patient survival, although 40% of ERα-positive BCs do not respond to those therapies. Aside from genomic signaling, estrogen triggers non-genomic pathways by forming a complex containing methylERα/Src/PI3K, a hallmark of aggressiveness and resistance to tamoxifen. We aimed to confirm the prognostic value of this complex and investigated whether its targeting could improve tumor response in vivo. The interaction of ERα/Src and ERα/PI3K was studied by proximity ligation assay (PLA) in a cohort of 440 BC patients. We then treated patient-derived BC xenografts (PDXs) with fulvestrant or the PI3K inhibitor alpelisib (BYL719) alone or in combination. We analyzed their anti-proliferative effects on 6 ERα+ and 3 ERα− PDX models. Genomic and non-genomic estrogen signaling were assessed by measuring ERα/PI3K interaction by PLA and the expression of estrogen target genes by RT-QPCR, respectively. We confirmed that ERα/Src and ERα/PI3K interactions were associated with a trend to poorer survival, the latter displaying the most significant effects. In ERα+ tumors, the combination of BYL719 and fulvestrant was more effective than fulvestrant alone in 3 models, irrespective of PI3K, PTEN status, or ERα/PI3K targeting. Remarkably, resistance to fulvestrant was associated with non-genomic ERα signaling, since genomic degradation of ERα was unaltered in these tumors, whereas the treatment did not diminish the level of ERα/PI3K interaction. Interestingly, in 2 ERα− models, fulvestrant alone impacted tumor growth, and this was associated with a decrease in ERα/PI3K interaction. Our results demonstrate that ERα/PI3K may constitute a new prognostic marker, as well as a new target in BC. Indeed, resistance to fulvestrant in ERα+ tumors was associated with a lack of impairment of ERα/PI3K interaction in the cytoplasm. In addition, an efficient targeting of ERα/PI3K in ERα− tumors could constitute a promising therapeutic option.

中文翻译：

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PI3K 抑制剂 alpelisib (BYL719) 和氟维司群联合治疗的乳腺癌 PDX 模型中雌激素受体的基因组和非基因组信号分析

针对雌激素信号的内分泌疗法显着提高了乳腺癌 (BC) 患者的生存率，尽管 40% 的 ERα 阳性 BC 对这些疗法没有反应。除了基因组信号外，雌激素通过形成包含甲基 ERα/Src/PI3K 的复合物触发非基因组通路，这是对他莫昔芬的攻击性和抗性的标志。我们旨在确认该复合物的预后价值，并研究其靶向是否可以改善体内肿瘤反应。ERα/Src 和 ERα/PI3K 的相互作用通过邻近结扎试验 (PLA) 在 440 名 BC 患者队列中进行研究。然后，我们单独或联合使用氟维司群或 PI3K 抑制剂 alpelisib (BYL719) 治疗源自患者的 BC 异种移植物 (PDX)。我们分析了它们对 6 个 ERα+ 和 3 个 ERα− PDX 模型的抗增殖作用。基因组和非基因组雌激素信号分别通过测量 PLA 的 ERα/PI3K 相互作用和 RT-QPCR 的雌激素靶基因表达来评估。我们证实 ERα/Src 和 ERα/PI3K 相互作用与生存率下降的趋势相关，后者显示出最显着的影响。在 ERα+ 肿瘤中，无论 PI3K、PTEN 状态或 ERα/PI3K 靶向如何，BYL719 和氟维司群的组合在 3 个模型中都比单独使用氟维司群更有效。值得注意的是，对氟维司群的抗性与非基因组 ERα 信号传导有关，因为在这些肿瘤中 ERα 的基因组降解没有改变，而治疗并没有降低 ERα/PI3K 相互作用的水平。有趣的是，在 2 个 ERα− 模型中，氟维司群单独影响肿瘤生长，这与 ERα/PI3K 相互作用的减少有关。我们的结果表明 ERα/PI3K 可能构成一个新的预后标志物，以及一个新的 BC 靶点。事实上，在 ERα+ 肿瘤中对氟维司群的抗性与细胞质中 ERα/PI3K 相互作用没有受损有关。此外，在 ERα- 肿瘤中有效靶向 ERα/PI3K 可能构成一种有希望的治疗选择。