Histamine-Succinyl-Glycine (HSG) (HSG)

Histamine-Succinyl-Glycine (HSG) is a synthetic small-molecule hapten used as a critical docking moiety in pre-targeted radioimmunotherapy (PRIT) and diagnostic imaging (Sharkey et al., 2003). It does not possess endogenous biological functions in humans but is engineered to be recognized with extremely high affinity by specialized bispecific monoclonal antibodies (bsAbs), such as those utilizing the 679 antibody clone (Goldenberg et al., 2012). In a typical clinical workflow, a bsAb—designed with one arm targeting a tumor-associated antigen like Carcinoembryonic Antigen (CEA) and the other targeting HSG—is administered first to allow for tumor localization. Once the bsAb has cleared from the circulation, an HSG-conjugated peptide (e.g., IMP288) carrying a radiopharmaceutical or cytotoxic payload is administered (Schoffelen et al., 2013). This peptide rapidly binds to the localized bsAb at the tumor site, while unbound molecules are quickly excreted via the kidneys, significantly reducing systemic exposure and off-target toxicity (van Rij et al., 2014). This pre-targeting strategy decouples the slow targeting kinetics of antibodies from the rapid delivery of effector molecules, allowing for higher therapeutic doses to be delivered to tumors with a improved safety profile.

Other names

HSG haptenHistamine-succinyl-glycyl moietyHSG-peptide docking site

Pre-targeted delivery of therapeutic or diagnostic payloads through high-affinity binding between a bispecific antibody and an HSG-conjugated carrier molecule.