68Ga-4B043

68Ga-4B043 is a gallium-68 labeled monocyclic peptide radioligand targeting Carbonic Anhydrase IX (CAIX). Developed by PepLib using their peptide discovery and optimization platform, 4B043 is a 19-amino acid peptide with a single disulfide bond that binds to human CAIX with sub-nanomolar affinity (KD ≈ 86 pM). CAIX is a hypoxia-inducible transmembrane enzyme highly overexpressed in clear cell renal cell carcinoma (ccRCC) and several other solid tumors, making it an ideal target for radiotheranostic applications. Preclinical studies in mouse models demonstrated high tumor uptake and favorable biodistribution. The agent has advanced into human investigator-initiated trials (IIT) for the imaging of ccRCC patients, where it has demonstrated high uptake in renal tumor lesions and a significantly higher tumor-to-kidney ratio compared to preclinical models.