A novel VHH nanobody against the active site (the CA domain) of tumor-associated, carbonic anhydrase isoform IX and its usefulness for cancer diagnosis

Expression of carbonic anhydrase IX (CAIX) significantly increases under hypoxic conditions in tumor cells. CAIX activity is executed by the catalytic domain (CA) located on the extracellular part of the enzyme. Neutralization of CAIX enzymatic activity reduces malignancy and survival of tumor cells. To inhibit the enzymatic activity, a VHH nanobody was developed against the CA domain of CAIX using phage display technology. Following immunization of a camel with the recombinant CAIX, VHH fragments were isolated by nested PCR on lymphocyte cDNA. Binding affinity of isolated nanobodies was tested by ELISA. A clone (K24) with the highest binding affinity was expressed in a soluble form. Affinity of K24 nanobody was determined to be approx. 2.3 × 10^?5. K24 nanobody recognized the expressed CAIX in the HeLa cell lines with high selectivity and specificity. These findings thus have usefulness for the diagnosis and treatment of cancers.