I 类组蛋白去乙酰化酶抑制剂恩替诺特抑制调节性 T 细胞，并增强肾和前列腺癌模型中的免疫疗法。

BACKGROUND: Immunosuppressive factors such as regulatory T cells (Tregs) limit the efficacy of immunotherapies. Histone deacetylase (HDAC) inhibitors have been reported to have antitumor activity in different malignancies and immunomodulatory effects. Herein, we report the Tregs-targeting and immune-promoting effect of a class I specific HDAC inhibitor, entinostat, in combination with either IL-2 in a murine renal cell carcinoma (RENCA) model or a survivin-based vaccine therapy (SurVaxM) in a castration resistant prostate cancer (CR Myc-CaP) model. METHODS AND RESULTS: RENCA or CR Myc-CaP tumors were implanted orthotopically or subcutaneously, respectively. Inoculated mice were randomized into four treatment groups: vehicle, entinostat, cytokine or vaccine, and combination. Tregs in the blood were assessed by FACS analysis. Real time quantitative PCR and Western blot analysis of isolated T cell subpopulations from spleen were performed to determine Foxp3 gene and protein expression. The suppressive function of Tregs was tested by T cell proliferation assay. Low dose (5 mg/kg) entinostat reduced Foxp3 levels in Tregs and this was associated with enhanced tumor growth inhibition in combination with either IL-2 or a SurVaxM vaccine. Entinostat down-regulated Foxp3 expression transcriptionally and blocked Tregs suppressive function without affecting T effector cells (Teffs). In vitro low dose entinostat (0.5 µM) induced STAT3 acetylation and a specific inhibitor of STAT3 partially rescued entinostat-induced down-regulation of Foxp3, suggesting that STAT3 signaling is involved in Foxp3 down-regulation by entinostat. CONCLUSIONS: These results demonstrate a novel immunomodulatory effect of class I HDAC inhibition and provide a rationale for the clinical testing of entinostat to enhance cancer immunotherapy.

背景：免疫抑制因子，如调节性 T 细胞（Tregs），限制了免疫疗法的疗效。组蛋白去乙酰化酶（HDAC）抑制剂已被报道在不同的恶性肿瘤中有抗肿瘤活性和免疫调节作用。在此，我们报告了 I 类特异性 HDAC 抑制剂恩替诺特在与 IL-2 联合应用于肾细胞癌（RENCA）模型或与 Survivin 为基础的疫苗治疗（SurVaxM）联合应用于去势抵抗性前列腺癌（CR Myc-CaP）模型中对 Tregs 的靶向作用和免疫促进作用。

方法和结果：将 RENCA 或 CR Myc-CaP 肿瘤分别原位或皮下植入。接种的小鼠随机分为四组：载体、恩替诺特、细胞因子或疫苗和联合组。通过 FACS 分析评估血液中的 Tregs。对来自脾脏的 T 细胞亚群进行实时定量 PCR 和 Western blot 分析，以确定 Foxp3 基因和蛋白表达。通过 T 细胞增殖测定来检测 Tregs 的抑制功能。低剂量（5mg/kg）恩替诺特降低了 Tregs 中的 Foxp3 水平，这与与 IL-2 或 SurVaxM 疫苗联合使用时增强肿瘤生长抑制有关。恩替诺特转录下调 Foxp3 表达并阻断 Tregs 的抑制功能，而不影响 T 效应细胞（Teffs）。体外低剂量恩替诺特（0.5µM）诱导 STAT3 乙酰化，STAT3 的特异性抑制剂部分挽救了恩替诺特诱导的 Foxp3 下调，这表明 STAT3 信号通路参与了恩替诺特诱导的 Foxp3 下调。

结论：这些结果证明了 I 类 HDAC 抑制的一种新的免疫调节作用，并为临床试验中使用恩替诺特增强癌症免疫治疗提供了依据。