近日,来自国家应急防控药物工程技术研究中心与华北理工大学研究团队合作在国际权威药物化学期刊《Journal of Medicinal Chemistry》上发表了一篇题为“Discovery of Highly Potent and Selective IKZF2 Degraders for Cancer Immunotherapy”的研究论文(DOI: 10.1021/acs.jmedchem.6c00500)。该研究突破现有IKZF2降解剂的异吲哚啉酮骨架局限,基于全新酞嗪酮骨架,成功开发出一类高效、高选择性IKZF2分子胶降解剂,其中化合物25表现出优于临床药物DKY709的降解活性与安全性,单药及联合PD-1抑制剂均展现优秀的抗肿瘤效果,为攻克肿瘤免疫逃逸、提升免疫治疗疗效提供了具有转化价值的新分子。
01 研究背景:免疫治疗的关键难题
肿瘤免疫治疗已成为癌症治疗的核心手段,但调节性T细胞(Treg)在肿瘤微环境中大量浸润,会强力抑制效应T细胞功能,导致免疫检查点抑制剂(如PD-1抗体)疗效不佳,甚至出现原发/继发耐药 [1]。IKZF2(Helios)属于Ikaros锌指转录因子家族,特异性高表达于胸腺来源Treg,是维持Treg稳定性与免疫抑制功能的核心“开关分子”。特异性降解IKZF2可削弱Treg免疫抑制功能,促进IL-2、IFN-γ等促炎因子释放,诱导肿瘤局部Treg向效应T细胞转化,且仅作用于肿瘤局部Treg,不影响外周免疫稳态 [2, 3]。因此,选择性降解IKZF2被公认为是增强抗肿瘤免疫、克服ICB 耐药的前沿策略。然而,现有IKZF2降解剂存在明显短板:如骨架单一,均为异吲哚啉酮结构 [4];脱靶降解IKZF1/3、SALL4(致畸风险)、GSPT1等;最大降解率(Dmax)偏低;存在心脏毒性(hERG抑制)潜在安全性问题等[5]。因此,研发新型骨架、高选择性、低毒性、口服有效的IKZF2降解剂,成为肿瘤免疫治疗领域的迫切需求。
02 研究内容:从全新骨架到最优分子
研究团队依托自主研发的酞嗪酮母核[6, 7],跳出传统异吲哚啉酮结构局限,通过多轮结构修饰、构效关系(SAR)分析与活性筛选,完成了从苗头化合物到候选分子的全链条优化,最终获得最优候选分子化合物25。
① 分子设计:突破传统骨架,实现高选择性降解
研究团队跳出传统异吲哚啉酮骨架,以自主发现的酞嗪酮(phthalazinone)为核心母核,从泛IKZF降解剂MGD-11为起点,开展系统结构优化:
l调整芳香环取代基类型,提升IKZF2结合偏好性。
l将取代位点由3’-位移至4’-位,显著增强对IKZF2的选择性;
l延长侧链并引入氰基、苯基哌嗪等基团,强化π-π堆积、疏水作用与氢键;
l最终通过连接位点微调+氰基取代,获得最优分子化合物25。
② 纳摩尔级降解活性,高选择性性
定量蛋白组,免疫印迹WB及HiBit实验结果表明,与临床对照化合物DKY709(Jurkat细胞中DC50 = 9.56 nM,Dmax = 80.5%)相比,经过多轮优化最终获得化合物25对IKZF2对降解效力更强(Jurkat细胞中DC50 = 1.59 nM,Dmax = 92.2%),且完全不降解IKZF1/IKZF3(DC50 > 10 μM)和 SALL4(无致畸风险),且化合物25对hERG抑制IC50 = 26.3 μM,优于DKY709(7.57 μM),安全性更高。此外,化合物25对GSPT1、CK1α、ZFP91等CRBN新底物均无降解活性。
Compound 25 exhibited rapid, highly selective and potent degradation effect on IKZF2. (A) Proteomics analysis of Jurkat cells treated with compound 25 (Cpd 25, 100 nM) or DMSO for 4 h. The volcano plot visualizes significant downregulation of IKZF2 in compound 25-treated cells relative to vehicle (FDR < 1%, n = 3 biological replicates per group). The x-axis denotes log2(fold change) of protein abundance (treated vs. DMSO), and the y-axis represents statistical significance (-log10P value). Significance thresholds are indicated by horizontal (p < 0.01) and vertical (|log2(fold change)| > 1) lines. (B) Heatmap depicting abundance changes of neosubstrates following compound 25 (100 nM) or DKY709 (100 nM) treatment for 4 h, as determined by whole-proteome quantification. (C) Comparative DC50 and Dmax values of compound 25, DKY709 or pomalidomide across multiple neosubstrates-HiBiT degradation assay in 293T cells treated for 48 h. Data are presented as mean ± SEM (n = 3). (D) Time-dependent luminescence signals of IKZF1/2/3-HiBit reporters. Engineered HEK293T cells treated with compound 25 (100 nM) for increasing durations. Error bars denote standard deviations from three independent experiments. Statistical significance: ns: significance; **p < 0.01 (Student’s t-test). (E) Jurkat cells were treated with escalating compound 25, DKY709 (100 nM) and pomalidomide (Pom, 1k nM) or vehicle control (DMSO) for 48 h, respectively. Data are representative of three independent experiments; mean ± SD (n = 3). (F) Western blot validation of multiple neosubstrates protein expression. Jurkat cells were treated with compound 25 (escalating doses), DKY709, Pomalidomide or vehicle (DMSO) for 24 h.
③ 作用机制依赖CRBN-泛素–蛋白酶体通路
该研究通过一系列严谨的机制实验证实:
lCRBN依赖性:CRBN敲除细胞中,IKZF2降解完全消失;
l蛋白酶体依赖性:蛋白酶体抑制剂MG132、Neddylation抑制剂 MLN4924可完全阻断降解;
l关键结合位点:依赖IKZF2蛋白His141/Gly146关键残基形成三元复合物,突变后降解完全丧失;
l分子胶模式:化合物25作为“分子胶水”,稳定CRBN-IKZF2三元复合物,促进IKZF2泛素化并被蛋白酶体降解。
Compound 25 exhibited IKZF2 degradation activity via a Cullin-CRBN dependent pathway. (A) Levels of HiBit-tagged IKZF2 were measured after 24 hours of incubation with increasing concentrations of compound 25 in control vector-transduced (CRBNVector) and CRBN knockout (CRBN−/−) HEK293T cells. Data are mean ± SD (n = 3 per group) from a representative experiment. The experiment was repeated independently in triplicate. (B) Western blot analysis of IKZF2 degradation in CRBN−/− Jurkat cells, and wild-type cells preincubated with MLN4924 (1 μM) or MG132 (1 μM) for 1 h prior to compound 25 (100 nM) treatment for 24 h. (C) Western blot analysis of IKZF2 in Jurkat cells overexpressing IKZF2Vector, IKZF2H141Q and IKZF2G146N mutant treated with compound 25 (100 nM). (D) IKZF2 HiBit-tagged protein levels IKZF2Vector, IKZF2H141Q and IKZF2G146N mutant to CRBN in HEK293T cells treated with increasing doses of compound 25. Data are mean ± SD (n = 3 per group) from a representative experiment.
⑤ 体外功能:重编程免疫细胞,激活抗肿瘤免疫
RNA-seq、细胞因子、Treg功能实验显示:
l显著激活TCR 通路、NF-κB通路、TNF信号通路;
l剂量依赖性提升IL-2分泌(IKZF2降解的经典药效标志);
l在人原代Treg中高效降解 IKZF2(DC50 = 6.19 nM),削弱免疫抑制功能;
l显著提升耗竭 CD4⁺/CD8⁺ T细胞的IFN-γ产生能力;
l下调AML细胞中MYC、HOXA9,抑制肿瘤干细胞特性。
In vitro effects of compound 25 treatment on T cells and Treg cells. (A.) Heatmap of differentially expressed genes from RNA-seq result of Jurkat cells treated with DMSO (vehicle control) or compound 25 at 100 nM for 24 h. Heatmap shows 277 up- and 130 downregulated genes in compound 25 -treated cells compared with DMSO control, with |log2fold change| >1 with adjusted p-value < 0.05. (B) KEGG pathway analysis of differentially expressed genes in the transcriptome of Jurkat cells treated with compound 25 (100 nM) for 24h (The 14 significantly activated pathways are shown). (C) Western blot analysis of HOXA9 and MYC expression in MV-4-11 cells at 24 h following compound 25 treatment. (D) Secreted IL-2 levels in CD3/CD28‑activated Jurkat cells (bead‑to‑cell ratio, 1:4) following 24 h treatment with increasing doses of compound 25. Data are expressed as mean ± SD (n = 3 biological replicates per condition). ns: not significant; **p < 0.01 (one-way ANOVA). (E) Levels of IKZF2 in the presence of compound 25 or DKY709 in primary human Tregs after 6 h in vitro treatment. Data presented as mean ± SD, with n = 3 biological replicates for each concentration. (F, G) Frequencies of IFNγ+ CD4+ T cells (F) CD8+ T cells (G) Intracellular concentrations in the specified subset of dysfunctional Teff cells generated in vitro via repeated TCR stimulation, following treatment with compound 25. Data were pooled from eight independent experiments using distinct donors. Data presented as mean ± SD, with n = 8 biological replicates for each concentration. ns: significance; **p < 0.01 (one-way ANOVA).
⑥ 体内研究:口服成药性、抗肿瘤效果优异
l药代动力学(PK)
口服吸收良好,绝对生物利用度14.49%;Cmax = 460.6 ng/mL,AUC暴露充足;快速分布至脾脏、胸腺等免疫器官。
l药效动力学(PD)
单次口服10/30 mg/kg,3小时即实现显著IKZF2 降解;6-12小时维持高效降解,作用持久。
PK/PD evaluation of compound 25 in humanized CRBNI391V C57BL/6 mice. (A, B) PK profiles and corresponding parameters in mouse for compound 25 obtained after i.v. and p.o. administration (mean ± SD, n = 5) using C57BL/6 mice. (C, D) IKZF2 degradation induced by compound 25 in spleen and thymus tissues in mice. Data are shown as mean ± SD (n = 4), ns: significance; **p < 0.01 (one-way ANOVA).
l抗肿瘤药效(B16F10黑色素瘤模型)
单药治疗:30 mg/kg每日口服,TGI = 77.30%;联合抗PD-1单抗协同效应显著,TGI = 93.66%,部分小鼠实现肿瘤完全消退;安全性良好,无体重下降,心、肝、脾、肺、肾等器官无病理损伤,HE染色未见明显炎症与毒性。
Compound 25 significantly suppressed tumor growth and showed synergistic anti-cancer efficacy with anti-PD-1 therapies. (A) Treatment schedule for the B16F10 cell xenograft tumor model in immune-competent CRBNI391V C57BL/6 mice, treated with compound 25 monotherapy or compound 25 in combination with PD-1 blockade. (B-E) B16F tumor volume changes (B), tumor growth inhibition (TGI) rates (C), individual tumor growth kinetics in each treatment group (D), and body weight changes of mice in each group (E) are presented (n = 8 biological replicates). Data are shown as mean ± SD; **p < 0.01 (one-way ANOVA).
03 研究总结:IKZF2降解,免疫治疗新范式
本研究首次将酞嗪酮骨架应用于高选择性IKZF2降解剂,突破现有专利与结构限制,为同类分子设计提供全新范式。化合物25可作为单药用于“冷肿瘤”与免疫抑制型肿瘤,可与PD-1/PD-L1抑制剂联合使用,逆转耐药、大幅提升响应率,为Treg调控、肿瘤免疫微环境重塑理论依据。综上,本研究建立了一套从新骨架设计→高选择性分子胶→免疫激活→体内抗肿瘤的全链条发现体系,为推动分子胶技术在肿瘤免疫治疗中的应用奠定了坚实基础。
原文链接:https://pubs.acs.org/doi/10.1021/acs.jmedchem.6c00500
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