Cancer remains a leading cause of morbidity and mortality worldwide, requiring ongoing development of targeted therapeutics such as monoclonal antibodies. Carbohydrates on embryonic cells are often highly expressed in cancer and are therefore attractive targets for antibodies. Stage-specific embryonic antigen-4 (SSEA-4) is one such glycolipid target expressed in many cancers, including breast and ovarian carcinomas. Here, we defined the structural basis for recognition of SSEA-4 by a novel monospecific chimeric antibody (ch28/11). Five X-ray structures of ch28/11 Fab complexes with the SSEA-4 glycan headgroup, determined at 1.5-2.7 Å resolutions, displayed highly similar three-dimensional structures indicating a stable binding mode. The structures also revealed that by adopting a horseshoe-shaped conformation in a deep groove, the glycan headgroup likely sits flat against the membrane to allow the antibody to interact with SSEA-4 on cancer cells. Moreover, we found that the terminal sialic acid of SSEA-4 plays a dominant role in dictating the exquisite specificity of the ch28/11 antibody. This observation was further supported by molecular dynamics simulations of the ch28/11-glycan complex, which show that SSEA-4 is stabilized by its terminal sialic acid, unlike SSEA-3, which lacks this sialic acid modification. These high-resolution views of how a glycolipid interacts with an antibody may help to advance a new class of cancer-targeting immunotherapy.

中文翻译：

---

阶段特异性胚胎抗原-4的末端唾液酸在与靶向癌症的抗体结合中具有至关重要的作用。

癌症仍然是全世界发病率和死亡率的主要原因，需要不断开发靶向治疗药物，例如单克隆抗体。胚胎细胞上的碳水化合物通常在癌症中高表达，因此是抗体的诱人靶标。阶段特异性胚胎抗原4（SSEA-4）是一种在许多癌症（包括乳腺癌和卵巢癌）中表达的糖脂靶标。在这里，我们定义了新型单特异性嵌合抗体（ch28 / 11）识别SSEA-4的结构基础。ch28 / 11 Fab配合物具有SSEA-4聚糖头基的五个X射线结构（分辨率为1.5-2.7Å）显示出高度相似的三维结构，表明稳定的结合模式。这些结构还表明，通过在深槽中采用马蹄形的构形，聚糖头基可能会平放在膜上，以使抗体与癌细胞上的SSEA-4相互作用。此外，我们发现SSEA-4的末端唾液酸在决定ch28 / 11抗体的特异性方面起着主导作用。ch28 / 11-聚糖复合物的分子动力学模拟进一步支持了这一观察结果，该模拟表明SSEA-4被其末端唾液酸所稳定，这与缺少该唾液酸修饰的SSEA-3不同。这些关于糖脂如何与抗体相互作用的高分辨率视图可能有助于推进新型的靶向癌症的免疫治疗。我们发现SSEA-4的末端唾液酸在决定ch28 / 11抗体的特异性方面起着主导作用。ch28 / 11-聚糖复合物的分子动力学模拟进一步支持了这一观察结果，该模拟表明SSEA-4被其末端唾液酸所稳定，这与缺少该唾液酸修饰的SSEA-3不同。这些关于糖脂如何与抗体相互作用的高分辨率视图可能有助于推进新型的靶向癌症的免疫治疗。我们发现SSEA-4的末端唾液酸在决定ch28 / 11抗体的特异性方面起着主导作用。ch28 / 11-聚糖复合物的分子动力学模拟进一步支持了这一观察结果，该模拟表明SSEA-4被其末端唾液酸所稳定，这与缺少该唾液酸修饰的SSEA-3不同。这些关于糖脂如何与抗体相互作用的高分辨率视图可能有助于推进新型的靶向癌症的免疫疗法。