MH3-B1 + rGel

**MH3-B1 + rGel** is a *recombinant immunotoxin* composed of the intermediate-affinity anti-HER2/neu single-chain variable fragment (scFv) antibody MH3-B1, genetically fused to recombinant gelonin (rGel), a ribosome-inactivating cytotoxic protein. This molecule targets HER2/neu-overexpressing tumor cells, binds to HER2/neu on the cell surface, is internalized, and releases rGel inside the cell, leading to inhibition of protein synthesis by inactivation of ribosomes and resulting in cell death[1][2][3]. MH3-B1/rGel shows improved tumor growth inhibition in HER2+ cancer models with lower off-target toxicity (notably hepatotoxicity) compared to higher-affinity immunotoxin constructs. Its cytotoxicity is potentiated by *photochemical internalization (PCI)*, which improves cytosolic drug delivery and overcomes resistance related to endocytic degradation, particularly in some ovarian cancer settings[2][3]. Main primary indications include HER2-positive cancers such as breast and ovarian cancer[1][2][3].