Signal transducer and activator of transcription 3 (Stat3) transmits signals from growth factors and interleukin-6 family cytokines by binding to their receptors via its Src homology 2 (SH2) domain. This results in phosphorylation of Tyr705, dimerization, translocation to the nucleus, and regulation of transcription of downstream genes. Stat3 is constitutively activated in several human cancers and is a target for anti-cancer drug design. We have shown previously phosphorylation of Tyr705 in intact cancer cells can be inhibited with prodrugs of phosphopeptide mimics targeting the SH2 domain. In a series of prodrugs consisting of bis-pivaloyloxymethyl esters of 4′-phosphonodifluoromethyl cinnamoyl-Haic-Gln-NHBn, appending methyl group to the β-position of the cinnamate increased potency ca. twofold, which paralleled the increase in affinity of the corresponding phosphopeptide models. However, dramatic increases in potency were observed when the C-terminal C(O)NHBn of Gln-NHBn was replaced with a simple methyl group. In this communication we continue to explore the effects of structural modifications of prodrugs on their ability to inhibit Tyr705 phosphorylation. A set of 4-substituted prolines incorporated into β-methyl-4-phosphocinnamoyl-leucinyl-Xaa-4-aminopentamide model peptides exhibited affinities of 88–317 nM by fluorescence polarization (Pro IC₅₀ = 156 nM). In corresponding prodrugs, Pro inhibited constitutive Stat3 phosphorylation at 10 μM in MDA-MB-468 breast tumor cells. However, 4,4-difluoroproline and 4,4-dimethylproline resulted in complete inhibition at 0.5 μM. These results suggest that the prodrug with native proline undergoes metabolism that those with substituted prolines do not. In conclusion, changes in structure with minimal impact on intrinsic affinity can nevertheless have profound effects on the cellular potency of prodrug inhibitors of Stat3.

中文翻译：

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靶向信号转导器和转录激活剂 3 (Stat3) 的 Src 同源 2 (SH2) 域的拟磷酸肽前药的构效研究。

信号转导和转录激活因子 3 (Stat3) 通过其 Src 同源 2 (SH2) 结构域与其受体结合，从而传输来自生长因子和白细胞介素 6 家族细胞因子的信号。这导致 Tyr705 磷酸化、二聚化、易位到细胞核和下游基因转录的调节。Stat3 在几种人类癌症中被组成型激活，并且是抗癌药物设计的目标。我们之前已经表明，靶向 SH2 结构域的磷酸肽模拟物前药可以抑制完整癌细胞中 Tyr705 的磷酸化。在由 4'-膦酰二氟甲基肉桂酰-Haic-Gln-NHBn 的双-新戊酰氧基甲酯组成的一系列前药中，将甲基附加到肉桂酸酯的 β 位可增加效力约。双重，这与相应磷酸肽模型的亲和力增加平行。然而，当 Gln-NHBn 的 C 末端 C(O)NHBn 被简单的甲基取代时，观察到效力的显着增加。在本文中，我们继续探索前药结构修饰对其抑制 Tyr705 磷酸化能力的影响。通过荧光偏振（Pro IC 在本文中，我们继续探索前药结构修饰对其抑制 Tyr705 磷酸化能力的影响。通过荧光偏振（Pro IC 在本文中，我们继续探索前药结构修饰对其抑制 Tyr705 磷酸化能力的影响。通过荧光偏振（Pro IC₅₀  = 156 nM）。在相应的前药中，Pro 抑制 MDA-MB-468 乳腺肿瘤细胞中 10 μM 的组成型 Stat3 磷酸化。然而，4,4-二氟脯氨酸和 4,4-二甲基脯氨酸在 0.5 μM 时导致完全抑制。这些结果表明具有天然脯氨酸的前药经历了具有取代脯氨酸的前药没有的代谢。总之，对内在亲和力影响最小的结构变化仍然可以对 Stat3 前药抑制剂的细胞效力产生深远的影响。