Targeting IGF2BP1 Enhances Immune Checkpoint Therapy in High-grade Serous Ovarian Cancer [mouse]

High-grade serous ovarian cancer (HGSC) accounts for the vast majority (>70%) of ovarian cancer-associated deaths with minor therapeutic improvements. Among four proposed molecular subtypes of HGSC, the C5 subtype is distinguished by high proliferative potential and elevated immune evasion which is indicated by an unfavorable MHCI/PD-L1 ratio. However, the underlying key drivers of the C5 subtype remained elusive. Here we identify oncofetal RNA-binding proteins (RBPs) promoting the immune evasion of C5-HGSC. The IGF2 mRNA binding protein 1 (IGF2BP1) enhances expression of the E3 ligase MDM2, which induces degradation of IRF1 resulting in reduced MHCI presentation. Concomitantly, IGF2BP1 elevates PD-L1 synthesis by impairing its microRNA-directed silencing. This shifts the intra-tumoral MHCI/PD-L1 ratio, limits immune cell infiltration, and promotes evasion of tumor cells from cytotoxic T cells (CTLs) in human and syngeneic mouse models of ovarian cancer. The small molecule inhibitor BTYNB impairs IGF2BP1-directed regulation of MHCI/PD-L1 ratios, promotes CTL-directed killing as well as activation, and strongly synergizes with immune checkpoint inhibition (ICI) by Nivolumab in vitro and in vivo. Overall design: Intraperitoneal syngeneic mouse model using the IGF2BP1-directed small molecule inhibitor BTYNB (closed conformation) with or without PD-1 blocking antibodies. Ascites was analyzed by scRNA-seq.

高级别浆液性卵巢癌（High-grade serous ovarian cancer, HGSC）占卵巢癌相关死亡病例的70%以上，且治疗进展极为有限。在已报道的四种HGSC分子亚型中，C5亚型以高增殖潜能与显著免疫逃逸为核心特征，该特征可通过异常偏低的MHCI/PD-L1比值得以体现。然而，目前C5亚型的潜在关键调控驱动因子仍未明确。本研究鉴定出一类可促进C5型HGSC免疫逃逸的癌胚RNA结合蛋白（oncofetal RNA-binding proteins, RBPs）。胰岛素样生长因子2 mRNA结合蛋白1（IGF2 mRNA binding protein 1, IGF2BP1）可上调E3泛素连接酶MDM2的表达，后者通过介导IRF1降解，降低MHCI抗原呈递能力。与此同时，IGF2BP1通过抑制PD-L1的微小RNA（microRNA）介导的转录后沉默，提升PD-L1的合成水平。该机制可重塑肿瘤微环境内的MHCI/PD-L1比值，抑制免疫细胞浸润，并在人类及同基因小鼠卵巢癌模型中促进肿瘤细胞逃避细胞毒性T淋巴细胞（cytotoxic T cells, CTLs）的杀伤。小分子抑制剂BTYNB可阻断IGF2BP1对MHCI/PD-L1比值的调控作用，促进CTL的活化与杀伤功能，并在体内外实验中与纳武利尤单抗（Nivolumab）介导的免疫检查点抑制（immune checkpoint inhibition, ICI）产生显著协同效应。实验整体设计：采用靶向IGF2BP1的小分子抑制剂BTYNB（闭合构象）联合或不联合PD-1阻断抗体，构建腹腔内同基因小鼠模型；通过单细胞RNA测序（single-cell RNA-seq, scRNA-seq）对小鼠腹水样本进行分析。