Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Department of Genomic Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Clin Cancer Res. 2024 Nov 15;30(22):5166-5179. doi: 10.1158/1078-0432.CCR-24-1166.
BRAFV600E-mutated colorectal cancer exhibits a strong correlation with DNA hypermethylation, suggesting that this subgroup of tumors presents unique epigenomic phenotypes. Nonetheless, 5-azacitidine, which inhibits DNA methyltransferase activity, is not efficacious in BRAFV600E colorectal cancer in vivo.
We randomized and treated mice implanted with patient-derived tumor xenografts harboring BRAFV600E mutation with control, 5-azacitidine, vemurafenib (BRAF inhibitor), or the combination. Comprehensive epigenomic profiling was conducted on control and 5-azacitidine-treated tumor samples, including DNA methylation, histone modifications, chromatin accessibility, and gene expression. Combinations of epigenetic agents were explored in preclinical BRAFV600E colorectal cancer models.
A profound reduction of DNA methylation levels upon 5-azacitidine treatment was confirmed, however, transcriptional repression was not relieved. This study unbiasedly explored the adaptive engagement of other epigenomic modifications upon 5-azacitidine treatment. A loss of histone acetylation and a gain of histone methylations, including H3K27 and H3K4 trimethylation, were observed around these hypomethylated regions, suggesting the involvement of polycomb repressive complex (PRC) activity around the genome with loss of DNA methylation, therefore maintaining the repression of key tumor-suppressor genes. Combined inhibition of PRC activity through EZH2 inhibition with 5-azacitidine treatment additively improved efficacies in BRAFV600E colorectal cancer cells.
In conclusion, DNA hypomethylation by 5-azacitidine exhibits a close association with H3K27me3 and PRC activity in BRAFV600E colorectal cancer, and simultaneous blockade of DNA methyltransferase and EZH2 holds promise as a potential therapeutic strategy for patients with BRAFV600E-mutated colorectal cancer.
BRAFV600E 突变的结直肠癌与 DNA 超甲基化强烈相关，这表明该亚组肿瘤具有独特的表观基因组表型。然而，体内 BRAFV600E 结直肠癌中，抑制 DNA 甲基转移酶活性的 5-氮杂胞苷并无疗效。
我们对携带 BRAFV600E 突变的患者源性肿瘤异种移植小鼠进行随机分组和治疗，分别给予对照组、5-氮杂胞苷、vemurafenib（BRAF 抑制剂）或联合治疗。对对照组和 5-氮杂胞苷处理的肿瘤样本进行全面的表观基因组分析，包括 DNA 甲基化、组蛋白修饰、染色质可及性和基因表达。在 BRAFV600E 结直肠癌的临床前模型中探索了联合使用表观遗传药物的方案。
5-氮杂胞苷处理后，DNA 甲基化水平显著降低，但转录抑制并未得到缓解。本研究在无偏见的情况下，探索了 5-氮杂胞苷处理后其他表观遗传修饰的适应性参与。在这些低甲基化区域周围观察到组蛋白乙酰化丢失和组蛋白甲基化（包括 H3K27 和 H3K4 三甲基化）增加，表明基因组中多梳抑制复合物（PRC）活性的参与以及 DNA 甲基化的丢失，从而维持关键肿瘤抑制基因的抑制。EZH2 抑制与 5-氮杂胞苷联合抑制 PRC 活性可显著提高 BRAFV600E 结直肠癌细胞的疗效。
总之，5-氮杂胞苷的 DNA 低甲基化与 BRAFV600E 结直肠癌中的 H3K27me3 和 PRC 活性密切相关，同时抑制 DNA 甲基转移酶和 EZH2 有望成为 BRAFV600E 突变结直肠癌患者的一种潜在治疗策略。
