PIK3CA missense mutations promote glioblastoma pathogenesis, but do not enhance targeted PI3K inhibition

BackgroundGlioblastoma (GBM) is the most common adult primary brain tumor. Multimodal treatment is empiric and prognosis remains poor. Recurrent PIK3CA missense mutations (PIK3CAmut) in GBM are restricted to three functional domains: adaptor binding (ABD), helical, and kinase. Defining how these mutations influence gliomagenesis and response to kinase inhibitors may aid in the clinical development of novel targeted therapies in biomarker-stratified patients.MethodsWe used normal human astrocytes immortalized via expression of hTERT, E6, and E7 (NHA). We selected two PIK3CAmut from each of 3 mutated domains and induced their expression in NHA with (NHARAS) and without mutant RAS using lentiviral vectors. We then examined the role of PIK3CAmut in gliomagenesis in vitro and in mice, as well as response to targeted PI3K (PI3Ki) and MEK (MEKi) inhibitors in vitro.ResultsPIK3CAmut, particularly helical and kinase domain mutations, potentiated proximal PI3K signaling and migration of NHA and NHARASin vitro. Only kinase domain mutations promoted NHA colony formation, but both helical and kinase domain mutations promoted NHARAS tumorigenesis in vivo. PIK3CAmut status had minimal effects on PI3Ki and MEKi efficacy. However, PI3Ki/MEKi synergism was pronounced in NHA and NHARAS harboring ABD or helical mutations.ConclusionPIK3CAmut promoted differential gliomagenesis based on the mutated domain. While PIK3CAmut did not influence sensitivity to single agent PI3Ki, they did alter PI3Ki/MEKi synergism. Taken together, our results demonstrate that a subset of PIK3CAmut promote tumorigenesis and suggest that patients with helical domain mutations may be most sensitive to dual PI3Ki/MEKi treatment.背景：胶质母细胞瘤（Glioblastoma, GBM）是成人最常见的原发性脑肿瘤。其多模态治疗仍为经验性方案，预后依旧不佳。胶质母细胞瘤中复发的PIK3CA错义突变（PIK3CAmut）仅局限于三个功能结构域：接头结合域（adaptor binding domain, ABD）、螺旋域与激酶域。阐明此类突变如何影响肿瘤发生及对激酶抑制剂的应答，或可助力针对生物标志物分层患者的新型靶向治疗临床开发。 方法：本研究使用通过表达hTERT、E6与E7永生化的正常人星形胶质细胞（NHA）。我们从3个突变结构域中各选取2种PIK3CAmut，借助慢病毒载体（lentiviral vectors）将其导入带有突变RAS（NHARAS）与不带突变RAS的NHA细胞中。随后分别在体外及小鼠模型中探究PIK3CAmut在胶质母细胞瘤发生中的作用，并检测其对靶向PI3K抑制剂（PI3Ki）与MEK抑制剂（MEKi）的体外应答情况。 结果：体外实验表明，PIK3CAmut，尤其是螺旋域与激酶域突变，可增强NHA及NHARAS细胞的近端PI3K信号通路活性与迁移能力。仅激酶域突变可促进NHA的集落形成，而螺旋域与激酶域突变均可在体内促进NHARAS的肿瘤发生。PIK3CAmut状态对PI3Ki与MEKi的单药疗效影响极小。然而，在携带ABD或螺旋域突变的NHA及NHARAS细胞中，PI3Ki与MEKi的协同作用尤为显著。 结论：PIK3CAmut可依据突变结构域的不同，对胶质母细胞瘤发生产生差异化影响。尽管PIK3CAmut不会改变细胞对单药PI3Ki的敏感性，但会改变PI3Ki与MEKi的协同效应。综上，本研究结果显示，部分PIK3CAmut可促进肿瘤发生，并提示携带螺旋域突变的患者或许对双药PI3Ki/MEKi联合治疗最为敏感。