The terminal sialic acid of stage-specific embryonic antigen-4 has a crucial role in binding to a cancer-targeting antibody

Abstract

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.

Targeting glycosphingolipids for cancer immunotherapy

“…Antibodies against several GSLs, designated as stage‐specific embryonic antigens (SSEAs), have been widely used to characterize the GSL profiles of embryonic stem cells (ESCs). Since these antibodies often display cross‐reactivities [4], GSL profiles in human ESCs and differentiated derivatives are more accurately delineated by systematic survey using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI TOF MS) and tandem mass spectrometry analyses. We previously reported that during differentiation of ESC to embryoid body, the core structures of GSLs switched from globo‐ and lacto‐ to ganglio‐series [5].…”

Sialic acids in gynecological cancer development and progression: Impact on diagnosis and treatment

“…The glycolipid stage‐specific embryonic antigen‐4 (SSEA‐4) is stabilized by its terminal sialic acid and is present in the OC cell lines and breast cancer cell lines. Soliman et al found that mouse‐human chimeric antibody ch28/11 recognizes this sialic acid of SSEA‐4, representing a promising therapeutic avenue for targeting OC 41 …”

“…Soliman et al found that mouse‐human chimeric antibody ch28/11 recognizes this sialic acid of SSEA‐4, representing a promising therapeutic avenue for targeting OC. 41 …”

Stage-specific Embryogenic Antigen-4 Expression in Castration-resistant Prostate Cancer and its Correlation With the Androgen Receptor

“…In recent years, SSEA-4 has been suggested to be a novel therapeutic target in a variety of malignancies (42)(43)(44). For example, a mAb directed against SSEA-4 (MC-813-70) has been suggested as a potential therapeutic agent for triplenegative breast cancer cells expressing SSEA-4 (43).…”