Pharmacological Exploration of the FK506-Binding Proteins 51 and 52 using PROTACs

fk506结合蛋白51 （FKBP51）及其对应物FKBP52是哺乳动物内分泌反应的关键调节因子，是应激相关疾病、代谢疾病、激素相关癌症和慢性疼痛的潜在治疗靶点。最近，我们开发了第一个针对FKBP51的fk506结合位点的选择性抑制剂，这大大增加了我们对FKBP51的了解。然而，FKBP52的选择性药理工具仍然缺乏。FKBP51和FKBP52都是多结构域蛋白，一个悬而未决的关键生化问题是，哪些结构域负责观察到的（分子）生物学效应（即fk506结合位点与蛋白质其他部分的支架功能）。这个化学生物项目的目标是基于最近开发的PROTAC技术合成FKBP配体，该技术允许在先进的模型系统中化学诱导FKBP51或FKBP52的细胞内降解。(i) FKBP51的主要目的是阐明FKBP51的哪些作用是由fk506结合位点介导的，哪些是由蛋白质的其他部分介导的。具体来说，我们的目标是证明FKBP51的降解，而不是抑制，阻断了FKBP51对糖皮质激素受体（GR）、NF-kB信号传导和激酶Akt的作用。（ii）对于FKBP52，主要目标是首次实现与FKBP51的药理学分化。具体来说，我们的目标是证明FKBP52的药理学操作允许减弱神经突生长，GR和AR信号和前列腺癌细胞进展。有了FKBP51和fkbp52选择性探针，我们将专门探索这两种蛋白之间的相互作用。（iii）为了提高PROTAC的效率，我们的目标是通过在低聚乙二醇主链中特定位点引入甲基侧链取代来稳定优选的连接剂构象。具体来说，我们将开发一种快速区域选择性和立体选择性合成乙烯/丙二醇共聚物的方法。该提案的结果将为探索人类fk506结合蛋白提供全新的工具，并将澄清FKBP51和FKBP52的重要未决问题。在PROTAC领域，预期的发现将是迄今为止最令人信服的证据，证明化学诱导的蛋白质降解可以打击其他难以处理的蛋白质功能。连接体优化策略将是提高功能性生物偶联物，特别是PROTACs有效性的一般方法。

The FK506-binding protein 51 (FKBP51) and its counterplayer FKBP52 are key regulators of endocrine responses in mammals and are potential therapeutic targets for stress-related disorder, metabolic diseases, hormone-related cancers, and chronic pain. Recently, we developed the first selective inhibitors directed to the FK506-binding site of FKBP51, which have substantially increased our understanding of FKBP51. However, selective pharmacological tools for FKBP52 are still lacking. FKBP51 and FKBP52 are both multi-domain proteins and a key pending biochemical question is, which domains are responsible for the observed (molecular)biological effects (i.e. FK506-binding site vs scaffolding functions of other parts of the proteins).The goal of this chemical-biological project is to synthesize FKBP ligands based on the recently developed PROTAC technology, which allow chemically induced intracellular degradation of FKBP51 or FKBP52 in advanced model systems.(i) The prime objective for FKBP51 is to clarify, which effects of FKBP51 are mediated by the FK506-binding site and which by other parts of the protein. Specifically, we aim to show that FKBP51 degradation, but not inhibition, blocks the effect of FKBP51 on the glucocorticoid receptor (GR), on NF-kB signalling and on the kinase Akt. (ii) For FKBP52, the prime objective is to allow for the first time to pharmacologically differentiate against FKBP51. Specifically, we aim to show that pharmacological manipulation of FKBP52 allows to attenuate neurite outgrowth, GR and AR signaling and prostate cancer cell progression. With FKBP51- and FKBP52-selective probes both in hand, we will specifically explore the interplay between these two proteins. (iii) For the enhancement of PROTAC efficiency, our objective is to stabilize preferred linker conformations by site-specific introduction of methyl side chain substitutions in the oligoethylene glycol backbone. Specifically, we will develop a method for the rapid regio- and stereo-selective synthesis of ethylene/propylene glycol co-oligomers. The results of this proposal will provide fundamentally novel tools to explore human FK506-binding proteins and will clarify important pending questions for FKBP51 and FKBP52. In the PROTAC field, the expected findings would be the so far most compelling evidence that chemically induced protein degradation allows to hit otherwise intractable protein functions. The linker optimization strategy will be a general approach to improve efficacy of functional bioconjugates and of PROTACs in particular.