E3 ligase Ligand 18 is a small molecule ligand that specifically binds to E3 ubiquitin ligase, and E3 ligase Ligand 18 can be chemically linked to a protein-targeting ligand through a molecular linker to construct proteolysis-targeting chimeras (PROTACs), which subsequently induce ubiquitination-mediated degradation of disease-related proteins such as oncogenic factors, thereby supporting the study of targeted protein degradation in cancer biology.