Anti-histamine-succinyl-glycine Fab paratope (Anti-HSG Fab)

The anti-histamine-succinyl-glycine (HSG) Fab paratope is an engineered molecular recognition site used primarily in pre-targeted radioimmunotherapy (PRIT) and immuno-PET imaging (Goldenberg et al., 2012, J Clin Oncol). It is derived from high-affinity antibodies, most notably the murine 679 clone, which has been humanized for clinical use. This paratope is incorporated as one arm of a bispecific monoclonal antibody (bsAb), while the other arm targets a tumor-associated antigen such as carcinoembryonic antigen (CEA) or MUC1 (Sharkey et al., 2003, Cancer Res). The biological function of the anti-HSG paratope is to serve as a highly specific, non-endogenous docking station at the tumor site. In a clinical setting, the bsAb is administered first and allowed to accumulate on tumor cells; subsequently, a small HSG-conjugated peptide carrying a diagnostic or therapeutic radionuclide (e.g., IMP-288) is injected (Schoffelen et al., 2013, J Nucl Med). The anti-HSG paratope captures the peptide with high affinity, ensuring that radiation is concentrated at the tumor while the small, unbound peptide is rapidly cleared through the kidneys, thereby minimizing systemic toxicity and improving the therapeutic window for cancer treatment.

Other names

Anti-HSG679 antibody paratopeHSG-binding siteAnti-histamine-succinyl-glycine

The anti-HSG Fab paratope serves as a high-affinity docking site in a pre-targeting strategy. It captures radiolabeled HSG-conjugated peptides at the tumor site after a bispecific antibody has localized to a tumor-associated antigen, thereby decoupling the targeting and effector phases.