BRAFV600E mutations occur in ∼10% of colorectal cancer cases, are associated with poor survival, and have limited responses to BRAF/MEK inhibition with or without EGFR inhibition. There is an unmet need to understand the biology of poor prognostic BRAFMT colorectal cancer. We have used differential gene expression and pathway analyses of untreated stage II and stage III BRAFMT (discovery set: n = 31; validation set: n = 26) colorectal cancer, and an siRNA screen to characterize the biology underpinning the BRAFMT subgroup with poorest outcome. These analyses identified the unfolded protein response (UPR) as a novel and druggable pathway associated with the BRAFMT colorectal cancer subgroup with poorest outcome. We also found that oncogenic BRAF drives endoplasmic reticulum (ER) stress and UPR pathway activation through MEK/ERK. Furthermore, inhibition of GRP78, the master regulator of the UPR, using siRNA or small molecule inhibition, resulted in acute ER stress and apoptosis, in particular in BRAFMT colorectal cancer cells. In addition, dual targeting of protein degradation using combined Carfilzomib (proteasome inhibitor) and ACY-1215 (HDAC6-selective inhibitor) treatment resulted in marked accumulation of protein aggregates, acute ER stress, apoptosis, and therapeutic efficacy in BRAFMT in vitro and xenograft models. Mechanistically, we found that the apoptosis following combined Carfilzomib/ACY-1215 treatment is mediated through increased CHOP expression. Taken together, our findings indicate that oncogenic BRAF induces chronic ER stress and that inducers of acute ER stress could be a novel treatment strategy for poor prognostic BRAFMT colorectal cancer. Mol Cancer Ther; 17(6); 1280–90. ©2018 AACR.

中文翻译：

---

未折叠蛋白反应：预后不良的 BRAF 突变结直肠癌的新治疗靶点

BRAFV600E 突变发生在约 10% 的结直肠癌病例中，与较差的存活率相关，并且对有或没有 EGFR 抑制的 BRAF/MEK 抑制反应有限。了解预后不良的 BRAFMT 结直肠癌的生物学有一个未满足的需求。我们使用了未治疗的 II 期和 III 期 BRAFMT（发现集：n = 31；验证集：n = 26）结直肠癌的差异基因表达和通路分析，以及 siRNA 筛选来表征支持最差结果的 BRAFMT 亚组的生物学特征. 这些分析将未折叠蛋白反应 (UPR) 鉴定为一种与结果最差的 BRAFMT 结直肠癌亚组相关的新型药物通路。我们还发现致癌 BRAF 通过 MEK/ERK 驱动内质网 (ER) 应激和 UPR 通路激活。此外，使用 siRNA 或小分子抑制来抑制 UPR 的主要调节因子 GRP78，导致急性内质网应激和细胞凋亡，特别是在 BRAFMT 结肠直肠癌细胞中。此外，使用联合 Carfilzomib（蛋白酶体抑制剂）和 ACY-1215（HDAC6 选择性抑制剂）治疗的蛋白质降解双重靶向导致 BRAFMT 体外和异种移植模型中蛋白质聚集体、急性内质网应激、细胞凋亡和治疗效果的显着积累. 从机制上讲，我们发现联合 Carfilzomib/ACY-1215 治疗后的细胞凋亡是通过增加 CHOP 表达介导的。总之，我们的研究结果表明致癌 BRAF 诱导慢性 ER 应激，而急性 ER 应激的诱导剂可能是预后不良的 BRAFMT 结直肠癌的新治疗策略。摩尔癌症治疗; 17(6); 1280-90。©2018 AACR。