HDAC inhibitors are efficacious for treating lymphoma, but display limited efficacy in treating solid tumors. Here, we investigated the relationship between HDAC inhibitor resistance and the tumor immune environment in colorectal cancer. Our data indicated that among the investigated immune factors, B7x expression was enhanced in HDAC inhibitor-resistant colorectal cancer models in vitro and in vivo. In addition, gene manipulation results demonstrated that xenograft mice with tumors derived from a B7x-overexpressing CT-26 colorectal cancer cell line were resistant to HDAC inhibitor treatment. Notably, we found that there is a negative relationship between HDAC and B7x expression in both colorectal cancer cell lines and patients’ tumors. Furthermore, our data indicated that elevated expression of B7x was related to a poor prognosis in colorectal tumor patients. Interestingly, treatment with a specific inhibitor or siRNA of HDAC3, but not HDAC2, 6, and 8, resulted in obvious upregulation of B7x expression in colorectal cancer cells. In addition, our data showed that a cell line with high HDAC3 expression and low B7x expression had decreased enrichment of acetylated histone H3 in the promoter region of the gene encoding B7x. This pattern was reversed by addition of HDAC3 inhibitors. Mechanistically, we found that HDAC3 regulated B7x transcription by promoting the binding of the transcription activator C/EBP-α with the B7x promoter region. Importantly, our data indicated that an antibody neutralizing B7x augmented the response to HDAC inhibitor in the colorectal cancer xenograft model and the lung metastasis model by increasing the ratios of both CD4-positive and CD8-positive T cells. In summary, we demonstrated a role of B7x in HDAC inhibitor resistance and identified the mechanism that dysregulates B7x in colorectal cancer. Our work provides a novel strategy to overcome HDAC inhibitor resistance.

HDAC 抑制剂可有效治疗淋巴瘤，但在治疗实体瘤方面效果有限。在这里，我们研究了结直肠癌中 HDAC 抑制剂耐药性与肿瘤免疫环境之间的关系。我们的数据表明，在研究的免疫因子中，B7x 在体外和体内 HDAC 抑制剂耐药的结直肠癌模型中表达增强。此外，基因操作结果表明，具有源自 B7x 过表达 CT-26 结肠直肠癌细胞系的肿瘤的异种移植小鼠对 HDAC 抑制剂治疗具有抗性。值得注意的是，我们发现结直肠癌细胞系和患者肿瘤中 HDAC 和 B7x 表达之间存在负相关。此外，我们的数据表明，B7x 表达升高与结直肠肿瘤患者的预后不良有关。有趣的是，用 HDAC3 的特异性抑制剂或 siRNA 处理，而不是 HDAC2、6 和 8，导致结直肠癌细胞中 B7x 表达的明显上调。此外，我们的数据显示，具有高 HDAC3 表达和低 B7x 表达的细胞系在编码 B7x 的基因的启动子区域中降低了乙酰化组蛋白 H3 的富集。通过添加 HDAC3 抑制剂逆转了这种模式。从机制上讲，我们发现 HDAC3 通过促进转录激活因子 C/EBP-α 与 B7x 启动子区域的结合来调节 B7x 转录。重要的，我们的数据表明，中和 B7x 的抗体通过增加 CD4 阳性和 CD8 阳性 T 细胞的比率，增强了结直肠癌异种移植模型和肺转移模型中对 HDAC 抑制剂的反应。总之，我们证明了 B7x 在 HDAC 抑制剂耐药性中的作用，并确定了 B7x 在结直肠癌中失调的机制。我们的工作提供了一种克服 HDAC 抑制剂耐药性的新策略。