Zanidatamab is a recombinant, humanized bispecific monoclonal antibody developed to target human epidermal growth factor receptor 2 (HER2). It is also known by the development code ZW25 and is the active pharmaceutical ingredient of Ziihera. FDA identifies Zanidatamab as a bispecific IgG1 antibody, while the FDA substance record lists CAS 2169946-15-8 and UNII Z20OC92TDI.
Unlike conventional monoclonal antibodies that generally recognize a single epitope, Zanidatamab is biparatopic, meaning that it binds two non-overlapping regions of HER2. The antibody recognizes epitopes associated with extracellular domains 2 and 4 of HER2. This dual-binding mechanism is an important characteristic of Zanidatamab and contributes to its biological activity.
Zanidatamab is a complex biological drug substance rather than a conventional chemically synthesized small molecule. It is a humanized IgG1-class bispecific antibody produced using recombinant technology in Chinese hamster ovary (CHO) cells. FDA substance information identifies its protein type as a bispecific antibody and its sequence origin as humanized mouse.
Because Zanidatamab is a large recombinant protein, a conventional molecular formula and molecular weight expressed in the same manner as a small-molecule API are not the most appropriate primary identifiers. Protein molecular mass is evaluated using appropriate analytical techniques, while identity and structural integrity are established through multiple orthogonal characterization methods.
HER2 is a receptor tyrosine kinase that can be overexpressed in several cancers. Zanidatamab has been designed to recognize two different HER2 epitopes simultaneously.
Binding to HER2 can influence receptor signaling and promote immune-mediated mechanisms against HER2-expressing cells. EMA describes Zanidatamab as an antibody that recognizes and attaches to two different parts of the HER2 protein, allowing immune cells to contribute to removal of cancer cells.
Zanidatamab's pharmacological activity is based on its ability to bind HER2 through two distinct epitopes. This biparatopic binding can promote receptor clustering and internalization while also supporting immune effector mechanisms.
The antibody can engage immune mechanisms such as antibody-dependent cellular cytotoxicity and complement-related activity. The product's potency testing therefore requires biological and binding-based assays rather than relying solely on chemical HPLC assay.
The EMA assessment report confirms that Zanidatamab active-substance and finished-product testing includes potency assessments using binding and cell-based biological methods.
Zanidatamab is a biologic pharmaceutical active substance and requires a manufacturing and quality-control strategy appropriate for monoclonal antibody products.
Manufacturing begins with a qualified recombinant cell substrate followed by controlled cell-culture production, harvest, purification and formulation-related processing. Critical quality attributes are monitored throughout the manufacturing process to ensure consistency of the biological substance.
For a biological API such as Zanidatamab, quality is not established by a single assay. Identity, protein concentration, purity, molecular variants, charge variants, aggregation, biological potency, host-cell protein, residual DNA, microbial quality and endotoxin levels are among the important quality attributes considered in the control strategy. EMA confirms that these categories are included in the Zanidatamab active-substance specification.
Identity testing for Zanidatamab requires analytical methods capable of confirming the molecular identity of the recombinant antibody.
Protein identity can be evaluated through peptide mapping, chromatographic characterization, electrophoretic methods and other orthogonal analytical techniques. Bioidentity and target-binding assays can additionally confirm that the molecule retains its expected biological characteristics.
For monoclonal antibodies, identity testing is therefore fundamentally different from a conventional small-molecule API where an IR spectrum and HPLC retention time may be sufficient.
Purity and impurity testing are important elements of Zanidatamab API quality control. Product-related variants can arise from processes such as aggregation, fragmentation, oxidation, deamidation, glycation or other structural changes.
Process-related impurities may include host-cell proteins, residual host-cell DNA, process reagents and other manufacturing-related materials. EMA specifically reports controls for host-cell protein, residual DNA, endotoxin and bioburden in the Zanidatamab active substance.
Appropriate chromatographic, electrophoretic and immunochemical methods are used to characterize and monitor these attributes.
For Zanidatamab, protein content is controlled using an appropriate spectroscopic method rather than treating the API as a conventional HPLC small molecule.
Potency is particularly important because biological activity cannot be adequately represented by chemical purity alone. EMA reports that Zanidatamab potency is evaluated using binding and biological assays, including competition-binding ELISA and cell-based antiproliferation and ADCC bioassays.
This analytical strategy provides a more appropriate assessment of the functional quality of the biological API.
Zanidatamab is used as a HER2-directed oncology therapy. In the European Union, Ziihera is authorized as monotherapy for adults with unresectable locally advanced or metastatic HER2-positive biliary tract cancer that has previously been treated with at least one systemic therapy.
The regulatory status has subsequently expanded in the United States. On August 25, 2026, FDA approved zanidatamab-hrii in combination regimens for first-line treatment of adults with HER2-positive unresectable locally advanced or metastatic gastric, gastroesophageal junction or esophageal adenocarcinoma under the specified biomarker and treatment conditions.
This makes Zanidatamab a relevant modern HER2-targeted oncology biologic API for pharmaceutical research, development and manufacturing.
The marketed Ziihera product is supplied as a lyophilized powder for intravenous administration. The U.S. product information identifies Zanidatamab at 50 mg/mL after preparation and lists the active ingredient together with sucrose, succinate and polysorbate 20 as formulation components.
The drug product is supplied in a single-dose vial and requires preparation before intravenous administration. Its manufacturing and release testing includes appropriate biological, physicochemical and microbiological controls.
The EMA assessment report states that the Zanidatamab active-substance release specification includes appearance, pH, osmolality, identity, purity and product-related variants, protein content, potency, residual host-cell protein, residual DNA, bioburden and bacterial endotoxins.
These tests are aligned with the quality-control principles applicable to recombinant monoclonal antibodies and biological products.
For Zanidatamab, it would therefore be inappropriate to assign generic small-molecule limits such as 98–102% HPLC assay, residue on ignition, melting point or specific rotation without a validated product specification.
Zanidatamab is a protein-based biological substance and requires controlled storage and handling conditions established through stability studies. Protection from inappropriate temperature conditions, excessive agitation and other stresses that can affect protein structure is important.
The specific storage conditions for a commercial Zanidatamab drug substance should follow the validated manufacturer's specification and applicable regulatory documentation.
Zanidatamab represents an advanced class of HER2-targeted biological pharmaceutical ingredients. As a recombinant bispecific monoclonal antibody, its manufacture requires specialized biological production, purification, analytical characterization and quality-control capabilities.
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For Zanidatamab, appropriate documentation and quality attributes should be evaluated according to the applicable biological-product requirements, customer requirements and regulatory expectations.\
Zanidatamab is a recombinant humanized bispecific IgG1 monoclonal antibody targeting HER2. Its biparatopic mechanism enables binding to two non-overlapping HER2 regions, distinguishing it from conventional single-epitope HER2 antibodies.
The correct CAS Number for Zanidatamab is 2169946-15-8, with FDA UNII Z20OC92TDI.
Because it is a biological API, Zanidatamab requires specialized control of identity, purity, protein concentration, biological potency, product-related variants, host-cell protein, residual DNA, bioburden and endotoxins rather than conventional small-molecule quality parameters. EMA confirms these categories in its active-substance specification.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |