Authors' Affiliations: Divisions of Clinical Studies, Cancer Therapeutics, and Molecular Pathology, The Institute of Cancer Research, Sutton, Surrey; Histopathology Department, The Royal Marsden Hospital NHS Foundation Trust, London, United Kingdom; and Department of Neuropathology, University of Bonn, Bonn, Germany.
Clin Cancer Res. 2013 Nov 1;19(21):5940-51. doi: 10.1158/1078-0432.CCR-13-0850. Epub 2013 Aug 5.
To provide rationale for using phosphoinositide 3-kinase (PI3K) and/or mitogen-activated protein kinase (MAPK) pathway inhibitors to treat rhabdomyosarcomas, a major cause of pediatric and adolescent cancer deaths.
The prevalence of PI3K/MAPK pathway activation in rhabdomyosarcoma clinical samples was assessed using immunohistochemistry. Compensatory signaling and cross-talk between PI3K/MAPK pathways was determined in rhabdomyosarcoma cell lines following p110α short hairpin RNA-mediated depletion. Pharmacologic inhibition of reprogrammed signaling in stable p110α knockdown lines was used to determine the target-inhibition profile inducing maximal growth inhibition. The in vitro and in vivo efficacy of inhibitors of TORC1/2 (AZD8055), MEK (AZD6244), and P13K/mTOR (NVP-BEZ235) was evaluated alone and in pairwise combinations.
PI3K pathway activation was seen in 82.5% rhabdomyosarcomas with coactivated MAPK in 36% and 46% of alveolar and embryonal subtypes, respectively. p110α knockdown in cell lines over the short and long term was associated with compensatory expression of other p110 isoforms, activation of the MAPK pathway, and cross-talk to reactivate the PI3K pathway. Combinations of PI3K pathway and MAP-ERK kinase (MEK) inhibitors synergistically inhibited cell growth in vitro. Treatment of RD cells with AZD8055 plus AZD6244 blocked reciprocal pathway activation, as evidenced by reduced AKT/ERK/S6 phosphorylation. In vivo, the synergistic effect on growth and changes in pharmacodynamic biomarkers was recapitulated using the AZD8055/AZD6244 combination but not NVP-BEZ235/AZD6244. Pharmacokinetic analysis provided evidence of drug-drug interaction with both combinations.
Dual PI3K/MAPK pathway activation and compensatory signaling in both rhabdomyosarcoma subtypes predict a lack of clinical efficacy for single agents targeting either pathway, supporting a therapeutic strategy combining a TORC1/2 with a MEK inhibitor.
为使用磷酸肌醇 3-激酶（PI3K）和/或丝裂原活化蛋白激酶（MAPK）通路抑制剂治疗横纹肌肉瘤提供依据，这是导致儿科和青少年癌症死亡的主要原因。
使用免疫组织化学评估横纹肌肉瘤临床样本中 PI3K/MAPK 通路的激活情况。在横纹肌肉瘤细胞系中，用 p110α 短发夹 RNA 介导的耗竭法确定 PI3K/MAPK 通路的代偿性信号和串扰。在稳定的 p110α 敲低系中，使用药物抑制重编程信号来确定诱导最大生长抑制的靶抑制谱。单独评估和组合评估 TORC1/2（AZD8055）、MEK（AZD6244）和 PI3K/mTOR（NVP-BEZ235）抑制剂的体外和体内疗效。
82.5%的横纹肌肉瘤存在 PI3K 通路激活，其中肺泡和胚胎亚型分别有 36%和 46%存在 MAPK 共激活。细胞系中 p110α 的短期和长期敲低与其他 p110 同工型的代偿性表达、MAPK 通路的激活以及重新激活 PI3K 通路的串扰有关。PI3K 通路和 MAP-ERK 激酶（MEK）抑制剂的组合协同抑制体外细胞生长。用 AZD8055 和 AZD6244 处理 RD 细胞阻断了相互通路的激活，这表现在 AKT/ERK/S6 磷酸化减少。在体内，用 AZD8055/AZD6244 组合而非 NVP-BEZ235/AZD6244 组合重现了对生长的协同作用和药效学生物标志物的变化。药代动力学分析提供了两种组合均存在药物相互作用的证据。
两种横纹肌肉瘤亚型中均存在 PI3K/MAPK 通路的双重激活和代偿性信号，预示着针对任一通路的单一药物治疗均缺乏临床疗效，支持联合使用 TORC1/2 和 MEK 抑制剂的治疗策略。
