将选择性AKT抑制剂capivasertib和SERD类药物fulvestrant相结合，在III期临床试验（CAPItello-291）中，治疗HR+乳腺癌患者，这些患者在使用芳香化酶抑制剂后，可有可无地使用CDK4/6抑制剂。然而，临床数据表明CDK4/6治疗可能会降低对随后单药内分泌治疗的反应。为了支持对CAPItello-291等试验的理解，并对这一新兴患者群体进行深入研究，我们探究了CDK4/6抑制剂对ER+乳腺肿瘤细胞功能和对fulvestrant和capivasertib的反应的影响。在RB+、RB-的T47D和MCF7 palbociclib耐药细胞中，ER通路ER和Greb-1的表达较原始细胞降低。在RB+细胞中，PI3K-AKT通路的激活也发生了改变，与母细胞相比，capivasertib在减少RB+细胞的pS6方面效果较差。母细胞与palbociclib耐药细胞之间的表达谱分析证实，capivasertib、fulvestrant和联合应用在耐药细胞中对基因表达调控产生了不同的影响，T47D细胞和MCF7细胞的反应也有所不同。fulvestrant对ER依赖基因的抑制作用降低。在耐药细胞中，联合应用较难减少细胞周期基因的表达，但是在原始细胞和耐药细胞中观察到S期细胞比例的一致性减少。尽管信号响应发生了改变，但是无论是RB+耐药细胞还是RB-耐药细胞均对联合治疗产生了反应，尽管相对疗效有所下降，并且在palbociclib耐药的PDX模型中具有体内有效性。总之，这些发现表明，同时抑制AKT和ER信号在代表palbociclib耐药模型中是有效的，尽管依赖通路发生了改变。© 2023. Springer Nature Limited.

Combining the selective AKT inhibitor, capivasertib, and SERD, fulvestrant improved PFS in a Phase III clinical trial (CAPItello-291), treating HR+ breast cancer patients following aromatase inhibitors, with or without CDK4/6 inhibitors. However, clinical data suggests CDK4/6 treatment may reduce response to subsequent monotherapy endocrine treatment. To support understanding of trials such as CAPItello-291 and gain insight into this emerging population of patients, we explored how CDK4/6 inhibitor treatment influences ER+ breast tumour cell function and response to fulvestrant and capivasertib after CDK4/6 inhibitor treatment. In RB+, RB- T47D and MCF7 palbociclib-resistant cells ER pathway ER and Greb-1 expression were reduced versus naïve cells. PI3K-AKT pathway activation was also modified in RB+ cells, with capivasertib less effective at reducing pS6 in RB+ cells compared to parental cells. Expression profiling of parental versus palbociclib-resistant cells confirmed capivasertib, fulvestrant and the combination differentially impacted gene expression modulation in resistant cells, with different responses seen in T47D and MCF7 cells. Fulvestrant inhibition of ER-dependent genes was reduced. In resistant cells, the combination was less effective at reducing cell cycle genes, but a consistent reduction in cell fraction in S-phase was observed in naïve and resistant cells. Despite modified signalling responses, both RB+ and RB- resistant cells responded to combination treatment despite some reduction in relative efficacy and was effective in vivo in palbociclib-resistant PDX models. Collectively these findings demonstrate that simultaneous inhibition of AKT and ER signalling can be effective in models representing palbociclib resistance despite changes in pathway dependency.© 2023. Springer Nature Limited.