p53 is a critical tumor-suppressor protein that guards the human genome against mutations by inducing cell-cycle arrest or apoptosis. Cancer cells subvert p53 by deletion, mutation, or overexpression of the negative regulators HDM2 and HDMX. For tumors that retain wild-type p53, its reactivation by pharmacologic targeting of HDM2 and/or HDMX represents a promising strategy, with a series of selective small-molecule HDM2 inhibitors and a dual HDM2/HDMX stapled-peptide inhibitor being evaluated in clinical trials. Because selective HDM2 targeting can cause hematologic toxicity, selective HDMX inhibitors could provide an alternative p53-reactivation strategy, but clinical candidates remain elusive. Here, we applied a mutation-scanning approach to uncover p53-based stapled peptides that are selective for HDMX. Crystal structures of stapled-peptide/HDMX complexes revealed a molecular mechanism for the observed specificity, which was validated by HDMX mutagenesis. Thus, we provide a blueprint for the development of HDMX-selective inhibitors to dissect and target the p53/HDMX interaction.

p53是一种重要的肿瘤抑制蛋白，通过诱导细胞周期停滞或凋亡来保护人类基因组免受突变。癌细胞通过阴性调节因子HDM2和HDMX的缺失，突变或过表达来破坏p53。对于保留野生型p53的肿瘤，其通过药理靶向HDM2和/或HDMX的活化代表了一种有前途的策略，在临床试验中评估了一系列选择性小分子HDM2抑制剂和双重HDM2 / HDMX短肽抑制剂。由于选择性靶向HDM2可以引起血液学毒性，因此选择性HDMX抑制剂可以提供另一种p53激活策略，但临床候选药物仍然难以捉摸。在这里，我们应用了突变扫描方法来发现对HDMX具有选择性的基于p53的固定肽。短肽/ HDMX复合物的晶体结构揭示了观察到的特异性的分子机制，这已通过HDMX诱变得到验证。因此，我们提供了开发HDMX选择性抑制剂以剖析和靶向p53 / HDMX相互作用的蓝图。