In response to cellular stress, phosphatidylserine is exposed on the outer membrane leaflet of tumor blood vessels and cancer cells, motivating the development of phosphatidylserine-specific therapies. The generation of drug-conjugated phosphatidylserine-targeting agents represents an unexplored therapeutic approach, for which antitumor effects are critically dependent on efficient internalization and lysosomal delivery of the cytotoxic drug. In the current study, we have generated phosphatidylserine-targeting agents by fusing phosphatidylserine-binding domains to a human IgG1-derived Fc fragment. The tumor localization and pharmacokinetics of several phosphatidylserine-specific Fc fusions have been analyzed in mice and demonstrate that Fc-Syt1, a fusion containing the synaptotagmin 1 C2A domain, effectively targets tumor tissue. Conjugation of Fc-Syt1 to the cytotoxic drug monomethyl auristatin E results in a protein–drug conjugate (PDC) that is internalized into target cells and, due to the Ca2+ dependence of phosphatidylserine binding, dissociates from phosphatidylserine in early endosomes. The released PDC is efficiently delivered to lysosomes and has potent antitumor effects in mouse xenograft tumor models. Interestingly, although an engineered, tetravalent Fc-Syt1 fusion shows increased binding to target cells, this higher avidity variant demonstrates reduced persistence and therapeutic effects compared with bivalent Fc-Syt1. Collectively, these studies show that finely tuned, Ca2+-switched phosphatidylserine-targeting agents can be therapeutically efficacious. Mol Cancer Ther; 17(1); 169–82. ©2017 AACR.

中文翻译：

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用钙依赖性蛋白药物偶联物靶向磷脂酰丝氨酸治疗癌症

为应对细胞应激，磷脂酰丝氨酸暴露在肿瘤血管和癌细胞的外膜小叶上，促进了磷脂酰丝氨酸特异性疗法的发展。药物偶联的磷脂酰丝氨酸靶向剂的产生代表了一种尚未探索的治疗方法，其抗肿瘤作用严重依赖于细胞毒性药物的有效内化和溶酶体递送。在当前的研究中，我们通过将磷脂酰丝氨酸结合域与人 IgG1 衍生的 Fc 片段融合来生成磷脂酰丝氨酸靶向剂。已在小鼠中分析了几种磷脂酰丝氨酸特异性 Fc 融合物的肿瘤定位和药代动力学，并证明 Fc-Syt1（一种包含突触结合蛋白 1 C2A 结构域的融合物）有效靶向肿瘤组织。Fc-Syt1 与细胞毒性药物单甲基 auristatin E 的偶联产生蛋白质-药物偶联物 (PDC)，该偶联物被内化到靶细胞中，并且由于磷脂酰丝氨酸结合的 Ca2+ 依赖性，在早期内体中与磷脂酰丝氨酸分离。释放的 PDC 被有效地传递到溶酶体，并在小鼠异种移植肿瘤模型中具有有效的抗肿瘤作用。有趣的是，虽然经过改造的四价 Fc-Syt1 融合体显示出与靶细胞的结合增加，但与二价 Fc-Syt1 相比，这种更高亲和力的变体表现出降低的持久性和治疗效果。总的来说，这些研究表明，微调的、Ca2+ 转换的磷脂酰丝氨酸靶向剂在治疗上是有效的。摩尔癌症治疗; 17(1); 169-82。©2017 AACR。