Carbonic anhydrase 9 (CA9/CAIX) is an enzyme that in humans is encoded by the CA9gene.
Carbonic anhydrases (CAs) are a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide. They participate in a variety of biological processes, including respiration, calcification, acid-base balance, bone resorption, and the formation of aqueous humor, cerebrospinal fluid, saliva, and gastric acid. They show extensive diversity in tissue distribution and in their subcellular localization. CAIX is a transmembrane protein and is a tumor-associated carbonic anhydrase isoenzyme. It is over-expressed in VHL mutated clear-cell renal cell carcinoma (ccRCC) and hypoxic solid tumors, but is low-expressed in normal kidney and most other normal tissues. It may be involved in cell proliferation and transformation. This gene is mapped to 9p13-p12.
CAIX has been licensed by the Dendreon Corporation. It is under development as a target for Autologous Cellular Immunotherapy. Product candidates targeted at CA9 are in preclinical development for the treatment of kidney, colon, and cervical cancer.
CAIX is considered to be one of the best cellular biomarkers of hypoxia. Furthermore, recent studies examining the association between CAIX levels and various clinicopathological outcomes suggest that CAIX expression may also be a valuable prognostic indicator for overall survival. Antibodies against CAIX serve as excellent biomarkers of hypoxic regions in many solid tumors.
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