This paper reports synthesis of a bioreducible hyperbranched (HB) polymer by A₂+B₃ approach from commercially available dithiothreitol (DTT) (A₂) and an easily accessible trifunctional monomer (B₃) containing three reactive pyridyl-disulfide groups. Highly efficient thiol-activated disulfide exchange reaction leads to the formation of the HB polymer (M_w = 21000; Đ = 2.3) with bioreducible disulfide linkages in the backbone and two different functional groups, namely, hydroxyl and pyridyl-disulfide in the core and periphery, respectively, of the HB-polymer. Postpolymerization functionalization of the hydroxyl-groups with camptothecin (CPT), a topoisomerase inhibitor and known anticancer drug, followed by replacing the terminal pyridyl-disulfide groups with oligo-oxyethylene-thiol resulted in easy access to an amphiphilic HB polydisulfide-CPT conjugate (P1) with a very high drug loading content of ∼40%. P1 aggregated in water (above ∼10 μg/mL) producing drug-loaded nanoparticles (D_h ∼ 135 nm), which showed highly efficient glutathione (GSH)-triggered release of the active CPT. Mass spectrometry analysis of the GSH-treated P1 showed the presence of the active CPT drug as well as a cyclic monothiocarbonate product, which underpins the cascade-degradation mechanism involving GSH-triggered cleavage of the labile disulfide linkage, followed by intramolecular nucleophilic attack by the in situ generated thiol to the neighboring carbonate linkage, resulting in release of the active CPT drug. The P1 nanoparticle showed excellent cellular uptake as tested by confocal fluorescence microscopy in HeLa cells by predominantly endocytosis mechanism, resulting in highly efficient cell killing (IC₅₀ ∼ 0.6 μg/mL) as evident from the results of the MTT assay, as well as the apoptosis assay. Comparative studies with an analogous linear polymer-CPT conjugate showed much superior intracellular drug delivery potency of the hyperbranched polymer.

中文翻译：

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用于细胞内药物递送的生物可还原两亲性超支化聚合物-药物缀合物

本文报道了通过 A ₂ +B ₃方法从市售二硫苏糖醇 (DTT) (A ₂ ) 和含有三个反应性吡啶基二硫化物基团的易于获得的三官能单体 (B ₃ ) 合成生物可还原的超支化 (HB) 聚合物。高效的硫醇激活的二硫键交换反应导致形成HB聚合物（M _w = 21000；Đ = 2.3），其主链中具有可生物还原的二硫键和两个不同的官能团，即核心中的羟基和吡啶基二硫化物，以及分别是HB-聚合物的外围。用喜树碱（CPT）（一种拓扑异构酶抑制剂和已知的抗癌药物）对羟基进行聚合后官能化，然后用寡聚氧乙烯硫醇取代末端吡啶基二硫基，从而很容易获得两亲性 HB 聚二硫醚-CPT 缀合物（P1）具有非常高的载药量~40%。P1在水中聚集（高于 ∼10 μg/mL），产生载药纳米粒子（D _h ∼ 135 nm），这表明谷胱甘肽（GSH）触发活性 CPT 的高效释放。 GSH 处理的P1的质谱分析表明存在活性 CPT 药物以及环状单硫代碳酸酯产物，这支持了级联降解机制，涉及 GSH 触发的不稳定二硫键断裂，然后是 CPT 药物的分子内亲核攻击。原位生成硫醇到邻近的碳酸酯键上，导致活性 CPT 药物的释放。通过共聚焦荧光显微镜在 HeLa 细胞中通过主要的内吞作用机制测试， P1纳米粒子显示出优异的细胞摄取，导致高效的细胞杀伤（IC ₅₀ ∼ 0.6 μg/mL），这从 MTT 测定的结果以及细胞凋亡测定。与类似的线性聚合物-喜树碱缀合物的比较研究表明，超支化聚合物的细胞内药物递送能力要优越得多。