Abstract：
Fragile X mental retardation protein (FMRP), an RNA binding protein (RBP), is aberrantly hyper-expressed in human tumors and plays an essential role in tumor invasion, metastasis and immune evasion. However, there is no small-molecule inhibitor for FMRP so far. In this study, we developed the first FMRP-targeting degrader based on PROteolysis TArgeting Chimera (PROTAC) technology and constructed a heterobifunctional PROTAC through linking a FMRP-targeting G-quadruplex RNA (sc1) to a von Hippel-Lindau (VHL)-targeting ligand peptide (named as sc1-VHLL). Sc1-VHLL specifically degraded endogenous FMRP via ubiquitination pathway in both mouse and human cancer cells. The FMRP degradation significantly changed the secretion pattern of cancer cells, resulting in higher expression of pro-inflammatory cytokine and smaller amounts of immunomodulatory contents. Furthermore, sc1-VHLL, when encapsulated into ionizable liposome nanoparticles (LNP) efficiently targeted tumor site and degraded FMRP in cancer cells. In CT26 tumor-bearing mouse model, FMRP degradation within tumors substantially promoted the infiltration of lymphocytes and CD8 T cells and reduced the proportion of Treg cells, reshaping the proinflammatory tumor microenvironment and accordingly transforming cold tumor into hot tumor. When combined with immune checkpoint blockade (ICB) therapy, sc1-VHLL based treatment remarkably inhibited the tumor growth.
摘要：
脆性X智力低下蛋白(FMRP),RNA结合蛋白（RBP），在人类肿瘤中异常高表达，在肿瘤侵袭中起重要作用，转移和免疫逃避。然而,目前尚无FMRP的小分子抑制剂。在这项研究中,我们开发了第一个FMRP靶向降解剂,该降解剂基于PROteasolsisTArgeting嵌合体(PROTAC)技术,并通过将FMRP靶向G-四链体RNA(sc1)连接到vonHippel-Lindau(VHL)靶向配体肽(命名为sc1-VHLL),构建了异双功能PROTAC。Sc1-VHLL在小鼠和人类癌细胞中通过泛素化途径特异性降解内源性FMRP。FMRP降解显著改变了癌细胞的分泌模式,导致促炎细胞因子的较高表达和较少量的免疫调节内容物。此外，sc1-VHLL,当包封到可电离的脂质体纳米颗粒（LNP）中时，可以有效地靶向肿瘤部位并降解癌细胞中的FMRP。在CT26荷瘤小鼠模型中，FMRP在肿瘤内的降解显著促进了淋巴细胞和CD8T细胞的浸润，降低了Treg细胞的比例，重塑促炎肿瘤微环境，从而将冷肿瘤转化为热肿瘤。当联合免疫检查点阻断（ICB）治疗时，基于sc1-VHLL的治疗显著抑制肿瘤生长。
