EGFR inhibitors have shown poor efficacy in head and neck squamous cell carcinoma (HNSCC) with demonstrated involvement of the insulin-like growth factor-1 receptor (IGF1R) in resistance to EGFR inhibition. IGF1R activates the PI3K–Akt pathway, which phosphorylates proline-rich Akt substrate of 40 kDa (PRAS40) to cease mTOR inhibition resulting in increased mTOR signaling. Proliferation assays separated six HNSCC cell lines into two groups: sensitive to EGFR inhibition or resistant; all sensitive cell lines demonstrated reduced sensitivity to EGFR inhibition upon IGF1R activation. Reverse phase protein microarray analysis and immunoblot identified a correlation between increased PRAS40 phosphorylation and IGFR-mediated resistance to EGFR inhibition. In sensitive cell lines, PRAS40 phosphorylation decreased 44%–80% with EGFR inhibition and was restored to 98%–196% of control by IGF1R activation, while phosphorylation was unaffected in resistant cell lines. Possible involvement of mTOR in this resistance mechanism was demonstrated through a similar pattern of p70S6K phosphorylation. However, addition of temsirolimus, an mTORC1 inhibitor, was insufficient to overcome IGF1R-mediated resistance and suggested an alternative mechanism. Forkhead box O3a (FOXO3a), which has been reported to complex with PRAS40 in the cytoplasm, demonstrated a 6-fold increase in nuclear to cytoplasmic ratio upon EGFR inhibition that was eliminated with concurrent IGF1R activation. Transcription of FOXO3a-regulated TRAIL and PTEN-induced putative kinase-1 (PINK1) was increased with EGFR inhibition in sensitive cell lines; this effect was diminished with IGF1R stimulation. Implications: These data suggest PRAS40 may play an important role in IGF1R-based therapeutic resistance to EGFR inhibition, and this likely occurs via inhibition of FOXO3a-mediated proapoptotic gene transcription.

中文翻译：

---

PRAS40 磷酸化与胰岛素样生长因子 1 受体诱导的头颈癌细胞对表皮生长因子受体抑制的抗性相关

EGFR 抑制剂在头颈部鳞状细胞癌 (HNSCC) 中的疗效不佳，证明胰岛素样生长因子 1 受体 (IGF1R) 参与了 EGFR 抑制的耐药性。IGF1R 激活 PI3K–Akt 通路，该通路磷酸化 40 kDa 的富含脯氨酸的 Akt 底物 (PRAS40) 以停止 mTOR 抑制，从而导致 mTOR 信号传导增加。增殖试验将 6 个 HNSCC 细胞系分为两组：对 EGFR 抑制敏感或耐药；所有敏感细胞系都表现出在 IGF1R 激活后对 EGFR 抑制的敏感性降低。反相蛋白微阵列分析和免疫印迹确定了 PRAS40 磷酸化增加与 IGFR 介导的 EGFR 抑制抗性之间的相关性。在敏感细胞系中，PRAS40 磷酸化随 EGFR 抑制降低 44%–80%，并通过 IGF1R 激活恢复至对照的 98%–196%，而磷酸化在耐药细胞系中未受影响。通过类似的 p70S6K 磷酸化模式证明了 mTOR 可能参与这种抗性机制。然而，添加 mTORC1 抑制剂替西罗莫司不足以克服 IGF1R 介导的耐药性，并提出了另一种机制。Forkhead box O3a (FOXO3a) 据报道在细胞质中与 PRAS40 复合，表明在 EGFR 抑制后核质比增加 6 倍，同时 IGF1R 激活消除。在敏感细胞系中，FOXO3a 调节的 TRAIL 和 PTEN 诱导的推定激酶 1 (PINK1) 的转录随 EGFR 抑制而增加；这种效应随着 IGF1R 刺激而减弱。意义：这些数据表明 PRAS40 可能在基于 IGF1R 的治疗对 EGFR 抑制的抗性中发挥重要作用，这可能是通过抑制 FOXO3a 介导的促凋亡基因转录而发生的。