HDAC9 and cancer: However, this specificity limitsthe PROTAC approach, with HA able to degrade other HDAC isoforms.Considering the key role played by HDAC3 in cancer, the Liao researchgroup investigated the possibility to achieve its selective degradationby developing an HDAC3-PROTAC (Figure ). Specifically, theyconjugated compound 3, endowedwith a certain HDAC3 selectivity, with the ligand for the Von Hippel–Lindau(VHL) E3 ubiquitin ligase at its terminal solvent-exposed phenyl ring,thus giving compound 24a (XZ9002).