Development of betabodies: The next generation of phosphatidylserine targeting agents

• Published in: The Journal of biological chemistry 2024-09, Vol.300 (9), p.107681, Article 107681
• Main Authors: Phinney, Natalie Z., Huang, Xianming, Toombs, Jason E., Brekken, Rolf A.
• Format: Article
• Language: English
• Subjects: Animals; Antibodies, Monoclonal; Cell Line, Tumor; fusion protein; Humans; Mice; Neoplasms - drug therapy; Neoplasms - immunology; Neoplasms - metabolism; Neoplasms - pathology; phosphatidylserine; Phosphatidylserines - metabolism; PS-targeting; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Tumor Microenvironment; β2-glycoprotein 1
• ISSN: 0021-9258; 1083-351X; 1083-351X
• DOI: 10.1016/j.jbc.2024.107681

Externalized phosphatidylserine (PS) is a phospholipid and a selective marker of the tumor microenvironment (TME). It is exposed on the outer leaflet of the plasma membrane of tumor-associated endothelial cells, apoptotic tumor cells, and some viable tumor cells, where it functions in part to suppress immune responses by binding to PS receptors expressed on tumor-infiltrating myeloid cells. PS has been targeted with antibodies, such as bavituximab, that bind the phospholipid via a cofactor, β2-glycoprotein 1 (β2GP1); these antibodies showed excellent specificity for tumor vasculature and induce an immune stimulatory environment. We have advanced this concept by developing the next generation of PS targeting agent, a fusion protein (betabody) constructed by linking PS-binding domain V of β2GP1 to the Fc of an IgG2a. Betabodies bind to externalized PS with high affinity (∼1 nM), without the requirement of a co-factor and localize robustly to the TME. We demonstrate that betabodies are a direct PS-targeting agent that has the potential to be used as anti-tumor therapy, drug delivery vehicles, and tools for imaging the TME.