Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, and Graduate School of Biomedical Sciences, University of Texas, Houston, TX 77030, USA.
Clin Cancer Res. 2013 Feb 1;19(3):657-67. doi: 10.1158/1078-0432.CCR-11-1446. Epub 2012 Dec 18.
Vemurafenib, a selective inhibitor of BRAF(V600), has shown significant activity in BRAF(V600) melanoma but not in less than 10% of metastatic BRAF(V600) colorectal cancers (CRC), suggesting that studies of the unique hypermethylated phenotype and concurrent oncogenic activation of BRAF(mut) CRC may provide combinatorial strategies.
We conducted comparative proteomic analysis of BRAF(V600E) melanoma and CRC cell lines, followed by correlation of phosphoinositide 3-kinase (PI3K) pathway activation and sensitivity to the vemurafenib analogue PLX4720. Pharmacologic inhibitors and siRNA were used in combination with PLX4720 to inhibit PI3K and methyltransferase in cell lines and murine models.
Compared with melanoma, CRC lines show higher levels of PI3K/AKT pathway activation. CRC cell lines with mutations in PTEN or PIK3CA were less sensitive to growth inhibition by PLX4720 (P = 0.03), and knockdown of PTEN expression in sensitive CRC cells reduced growth inhibition by the drug. Combined treatment of PLX4720 with PI3K inhibitors caused synergistic growth inhibition in BRAF-mutant CRC cells with both primary and secondary resistance. In addition, methyltransferase inhibition was synergistic with PLX4720 and decreased AKT activation. In vivo, PLX4720 combined with either inhibitors of AKT or methyltransferase showed greater tumor growth inhibition than PLX4720 alone. Clones with acquired resistance to PLX4720 in vitro showed PI3K/AKT activation with EGF receptor (EGFR) or KRAS amplification.
We show that activation of the PI3K/AKT pathway is a mechanism of both innate and acquired resistance to BRAF inhibitors in BRAF(V600E) CRC and suggest combinatorial approaches to improve outcomes in this poor prognosis subset of patients.
Vemurafenib 是一种选择性 BRAF(V600)抑制剂，在 BRAF(V600)黑色素瘤中显示出显著的活性，但在不到 10%的转移性 BRAF(V600)结直肠癌（CRC）中无效，这表明对 BRAF(mut)CRC 独特的超甲基化表型和并发致癌激活的研究可能提供联合治疗策略。
我们对 BRAF(V600E)黑色素瘤和 CRC 细胞系进行了比较蛋白质组学分析，随后对磷酸肌醇 3-激酶（PI3K）通路的激活和对 vemurafenib 类似物 PLX4720 的敏感性进行了相关性分析。在细胞系和小鼠模型中，我们使用药理学抑制剂和 siRNA 联合 PLX4720 抑制 PI3K 和甲基转移酶。
与黑色素瘤相比，CRC 细胞系显示出更高水平的 PI3K/AKT 通路激活。PTEN 或 PIK3CA 突变的 CRC 细胞系对 PLX4720 的生长抑制作用不敏感（P = 0.03），而在敏感的 CRC 细胞中敲低 PTEN 表达会降低药物的生长抑制作用。PLX4720 与 PI3K 抑制剂联合治疗对原发性和继发性耐药的 BRAF 突变型 CRC 细胞具有协同的生长抑制作用。此外，甲基转移酶抑制与 PLX4720 联合使用可降低 AKT 激活，并具有协同作用。在体内，PLX4720 与 AKT 或甲基转移酶抑制剂联合使用比单独使用 PLX4720 可更有效地抑制肿瘤生长。体外对 PLX4720 获得耐药性的克隆显示出 PI3K/AKT 激活，同时伴有表皮生长因子受体（EGFR）或 KRAS 扩增。
我们表明，PI3K/AKT 通路的激活是 BRAF(V600E)CRC 中对 BRAF 抑制剂产生内在和获得性耐药的机制，并提出联合治疗方法来改善这一预后不良的患者亚群的治疗效果。
