Arsenic Trioxide Rescues Structural p53 Mutations through a Cryptic Allosteric Site

TP53 is the most frequently mutated gene in cancer, yet these mutations remain therapeutically non-actionable. Major challenges in drugging p53 mutations include heterogeneous mechanisms of inactivation and the absence of broadly-applicable allosteric sites. Here we report the identification of small molecules including arsenic trioxide (ATO), an established agent in treating acute promyelocytic leukemia, as cysteine-reactive compounds that rescue structural p53 mutations. Crystal structures of arsenic-bound p53 mutants reveal a cryptic allosteric site involving three arsenic coordinating cysteines within the DNA-binding domain, distal to the zinc-binding site. Arsenic binding stabilizes the DNA-binding loop-sheet-helix motif alongside the overall β-sandwich fold, endowing p53 mutants with thermostability and transcriptional activity. In cellular and mouse xenograft models, ATO reactivates mutant p53 for tumor suppression. Investigation of the most frequent twenty-five p53 mutations informs patient stratification for clinical exploration. Our results provide mechanistic basis for repurposing ATO to target p53 mutations for widely-applicable yet personalized cancer therapies.

TP53是癌症中突变频率最高的基因，但其相关突变至今仍缺乏临床可行的靶向治疗方案。以p53突变体为药物靶点所面临的主要挑战包括其失活机制具有异质性，且缺乏普适性的变构结合位点（allosteric site）。本研究鉴定出一系列半胱氨酸反应性小分子，其中包括已获批用于治疗急性早幼粒细胞白血病（acute promyelocytic leukemia）的三氧化二砷（arsenic trioxide, ATO），这类小分子可挽救结构性p53突变的功能。结合砷的p53突变体晶体结构揭示了一处隐蔽的变构结合位点：该位点位于DNA结合结构域（DNA-binding domain）内，包含三个可与砷配位的半胱氨酸残基，且距离锌结合位点（zinc-binding site）较远。砷结合可稳定p53的DNA结合环-片-螺旋基序（loop-sheet-helix motif）与整体β三明治折叠结构（β-sandwich fold），赋予突变型p53热稳定性与转录活性。在细胞与小鼠异种移植模型（cellular and mouse xenograft models）中，ATO可重新激活突变型p53，从而发挥肿瘤抑制效果。针对25种最常见的p53突变的研究，可为临床探索中的患者分层（patient stratification）提供参考依据。本研究结果为将ATO重定位为靶向p53突变的治疗药物提供了机制基础，有望开发出兼具普适性与个性化的癌症治疗策略。