The signal transducer and activator of transcription 3 (STAT3) protein is constitutively activated in several cancers. STAT3 activity can be blocked by inhibiting its Src Homology 2 (SH2) domain, but phosphotyrosine and its isosteres have poor bioavailability. In this work, we develop peptide-based inhibitors of STAT3-SH2 by combining chemical strategies that have proven effective for targeting other SH2 domains. These strategies include a STAT3-specific selectivity sequence, non-hydrolyzable phosphotyrosine isosteres, and a high-efficiency cell-penetrating peptide. Peptides that combined these three strategies had substantial biological stability and cytosolic delivery, as measured using highly quantitative cell-based assays. However, these peptides did not inhibit STAT3 activity in cells. By comparing in vitro binding affinity, cell penetration, and proteolytic stability, this work explores the delicate balance of factors that contribute to biological activity for peptidic inhibitors of STAT3.

信号转导子和转录激活子 3 (STAT3) 蛋白在多种癌症中被组成型激活。 STAT3的活性可以通过抑制其Src同源2（SH2）结构域来阻断，但磷酸酪氨酸及其电子等排体的生物利用度较差。在这项工作中，我们通过结合已被证明可有效靶向其他 SH2 结构域的化学策略来开发基于肽的 STAT3-SH2 抑制剂。这些策略包括 STAT3 特异性选择性序列、不可水解的磷酸酪氨酸电子等排体和高效细胞穿透肽。使用高度定量的基于细胞的测定法测量，结合这三种策略的肽具有显着的生物稳定性和胞质递送。然而，这些肽并不抑制细胞中的 STAT3 活性。通过比较体外结合亲和力、细胞渗透性和蛋白水解稳定性，这项工作探索了有助于 STAT3 肽抑制剂生物活性的因素的微妙平衡。