ALKBH5 Drives Immune Suppression Via Targeting AXIN2 to Promote Colorectal Cancer and Is a Target for Boosting Immunotherapy
Background & Aims: Immune checkpoint blockade therapy benefits only a small proportion of colorectal cancer (CRC) patients, highlighting the need to identify intrinsic CRC factors that influence the efficacy of such therapies. We discovered that AlkB homolog 5 (ALKBH5), an RNA N6-methyladenosine (m6A) demethylase, promotes immunosuppression and serves as a potential therapeutic target to enhance the effectiveness of immune checkpoint blockade in CRC.
Methods: The clinical relevance of ALKBH5 was assessed in human CRC samples (n = 205). To investigate the role of ALKBH5, we used allograft models, CD34+ humanized mice, and Alkbh5 knock-in mice. Immune changes were analyzed through flow cytometry, immunofluorescence, and functional assays. Methylated RNA immunoprecipitation sequencing and RNA sequencing were employed to identify ALKBH5 targets. Additionally, vesicle-like nanoparticles encapsulating ALKBH5-specific small interfering RNA (siRNA) were developed for in vivo targeting of ALKBH5.
Results: High expression of ALKBH5 was associated with poor prognosis in CRC. ALKBH5 promoted the accumulation of myeloid-derived suppressor cells (MDSCs) while reducing the presence of natural killer (NK) cells and cytotoxic CD8+ T cells, thereby facilitating colorectal tumorigenesis in allografts, CD34+ humanized mice, and intestine-specific Alkbh5 knock-in mice. Mechanistically, ALKBH5 was found to target AXIN2, a key Wnt pathway suppressor. ALKBH5 binds to AXIN2 mRNA, demethylates it, and induces its dissociation from the m6A reader protein IGF2BP1, leading to AXIN2 degradation. This process results in hyperactivation of the Wnt/β-catenin signaling pathway, which in turn upregulates Wnt/β-catenin targets, including Dickkopf-related protein 1 (DKK1). ALKBH5-induced DKK1 then recruits MDSCs, driving immune suppression in CRC. This effect was reversed by targeting DKK1, both in vitro and in vivo. Finally, treatment with vesicle-like nanoparticle-encapsulated ALKBH5-siRNA or anti-DKK1 enhanced the efficacy of anti-PD1 therapy, inhibiting CRC growth and boosting antitumor immunity.
Conclusions: Our study identifies an ALKBH5-N6-methyladenosine-AXIN2-Wnt-DKK1 axis that mediates immune suppression and promotes tumorigenesis in CRC. Targeting ALKBH5 offers a promising strategy to sensitize CRC to immune checkpoint blockade therapy, enhancing the effectiveness Cpd 20m of immunotherapy.