Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong-Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong.
Institute of Digestive Disease and Department of Medicine and Therapeutics, State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong-Shenzhen Research Institute, The Chinese University of Hong Kong, Hong Kong; Department of Anesthesia and Intensive Care and Peter Hung Pain Research Institute, The Chinese University of Hong Kong, Hong Kong.
Gastroenterology. 2023 Aug;165(2):445-462. doi: 10.1053/j.gastro.2023.04.032. Epub 2023 May 9.
BACKGROUND & AIMS: Immune checkpoint blockade therapy benefits only a small subset of patients with colorectal cancer (CRC), and identification of CRC-intrinsic events modulating immune checkpoint blockade efficacy is an unmet need. We found that AlkB homolog 5 (ALKBH5), an RNA N-methyladenosine eraser, drives immunosuppression and is a molecular target to boost immune checkpoint blockade therapy in CRC.
Clinical significance of ALKBH5 was evaluated in human samples (n = 205). Function of ALKBH5 was investigated in allografts, CD34 humanized mice, and Alkbh5 knockin mice. Immunity change was determined by means of flow cytometry, immunofluorescence, and functional investigation. Methylated RNA immunoprecipitation sequencing and RNA sequencing were used to identify ALKBH5 targets. Vesicle-like nanoparticle-encapsulated ALKBH5-small interfering RNA was constructed for targeting ALKBH5 in vivo.
High ALKBH5 expression predicts poor prognosis in CRC. ALKBH5 induced myeloid-derived suppressor cell accumulation but reduced natural killer cells and cytotoxic CD8 T cells to induce colorectal tumorigenesis in allografts, CD34 humanized mice, and intestine-specific Alkbh5 knockin mice. Mechanistically, AXIN2, a Wnt suppressor, was identified as a target of ALKBH5. ALKBH5 binds and demethylates AXIN2 messenger RNA, which caused its dissociation from N-methyladenosine reader IGF2BP1 and degradation, resulting in hyperactivated Wnt/β-catenin. Subsequently, Wnt/β-catenin targets, including Dickkopf-related protein 1 (DKK1) were induced by ALKBH5. ALKBH5-induced DKK1 recruited myeloid-derived suppressor cells to drive immunosuppression in CRC, and this effect was abolished by anti-DKK1 in vitro and in vivo. Finally, vesicle-like nanoparticle-encapsulated ALKBH5-small interfering RNA, or anti-DKK1 potentiated anti-PD1 treatment in suppressing CRC growth by enhancing antitumor immunity.
This study identified an ALKBH5-N-methyladenosine-AXIN2-Wnt-DKK1 axis in CRC, which drives immune suppression to facilitate tumorigenesis. Targeting of ALKBH5 is a promising strategy for sensitizing CRC to immunotherapy.
免疫检查点阻断疗法仅使一小部分结直肠癌（CRC）患者受益，因此确定调节免疫检查点阻断疗效的 CRC 内在事件是未满足的需求。我们发现，RNA N6-甲基腺苷去甲基酶 AlkB 家族成员 5（ALKBH5）可驱动免疫抑制，是增强 CRC 免疫检查点阻断治疗的分子靶标。
在 205 个人类样本中评估了 ALKBH5 的临床意义。在同种异体移植物、CD34 人源化小鼠和 Alkbh5 基因敲入小鼠中研究了 ALKBH5 的功能。通过流式细胞术、免疫荧光和功能研究来确定免疫变化。采用甲基化 RNA 免疫沉淀测序和 RNA 测序来鉴定 ALKBH5 的靶标。构建了囊泡样纳米颗粒包裹的 ALKBH5 小干扰 RNA 用于体内靶向 ALKBH5。
高 ALKBH5 表达预示着 CRC 预后不良。ALKBH5 在同种异体移植物、CD34 人源化小鼠和肠道特异性 Alkbh5 基因敲入小鼠中诱导髓系来源的抑制细胞积聚，但减少自然杀伤细胞和细胞毒性 CD8 T 细胞，从而诱导结直肠肿瘤发生。在机制上，AXIN2（一种 Wnt 抑制剂）被确定为 ALKBH5 的靶标。ALKBH5 结合并去甲基化 AXIN2 信使 RNA，导致其与 N6-甲基腺苷阅读器 IGF2BP1 解离并降解，从而导致 Wnt/β-catenin 过度激活。随后，Wnt/β-catenin 靶标，包括 Dickkopf 相关蛋白 1（DKK1），被 ALKBH5 诱导。ALKBH5 诱导的 DKK1 募集髓系来源的抑制细胞，在 CRC 中驱动免疫抑制，这种作用在体外和体内被抗 DKK1 所消除。最后，囊泡样纳米颗粒包裹的 ALKBH5 小干扰 RNA 或抗 DKK1 通过增强抗肿瘤免疫来增强抗 PD1 治疗抑制 CRC 生长。
本研究在 CRC 中鉴定出一个 ALKBH5-N6-甲基腺苷-AXIN2-Wnt-DKK1 轴，它驱动免疫抑制以促进肿瘤发生。靶向 ALKBH5 是一种有前途的策略，可增强 CRC 对免疫治疗的敏感性。
