Histamine-succinyl-glycine (HSG) binding site (HSG binding site)

The Histamine-succinyl-glycine (HSG) binding site is a specialized molecular recognition domain located on the anti-HSG arm of bispecific antibodies, primarily utilized in pre-targeted radioimmunotherapy (PRIT) and diagnostic imaging. This site is typically derived from the 679 murine monoclonal antibody, which has been humanized for clinical use, and it possesses high affinity for the synthetic HSG hapten. In therapeutic applications, a bispecific antibody (such as TF2 or TF10) is administered first to localize at the tumor site by binding to tumor-associated antigens like CEA or MUC1. After the unbound antibody has cleared from the systemic circulation, a small HSG-conjugated peptide carrying a radioactive or cytotoxic payload is injected. This peptide is rapidly captured by the HSG binding site on the localized antibody, allowing for high-dose delivery to the tumor while minimizing systemic toxicity and radiation exposure to healthy tissues. This decoupling of the targeting agent from the effector payload represents a significant advancement in improving the therapeutic index of antibody-based treatments.

Other names

Anti-HSG arm679 antibody paratopeHSG recognition domainAnti-HSG Fab fragmentHSG-binding pocket

The HSG binding site functions as a capture mechanism in a multi-step pre-targeting strategy. A bispecific antibody is first administered to bind a tumor-associated antigen; once cleared from the blood, an HSG-conjugated payload is administered and specifically captured by this site at the tumor location.