MDM2 Antagonist Idasanutlin Reduces HDAC1/2 Abundance and Corepressor Partners but Not HDAC3

Histone deacetylases 1–3 (HDAC1, HDAC2, and HDAC3) and their associated corepressor complexes play important roles in regulating chromatin structure and gene transcription. HDAC enzymes are also validated drug targets for oncology and offer promise toward new drugs for neurodegenerative diseases and cardiovascular diseases. We synthesized four novel heterobifunctional molecules designed to recruit the mouse double minute 2 homologue (MDM2) E3 ligase to degrade HDAC1–3 utilizing the MDM2 inhibitor idasanutlin, known as proteolysis targeting chimeras (PROTACs). Idasanutlin inhibits the MDM2-P53 protein–protein interaction and is in clinical trials. Although two MDM2-recruiting heterobifunctional molecules reduced HDAC1 and HDAC2 abundance with complete selectivity over HDAC3 and reduced HDAC1/2 corepressor components LSD1 and SIN3A, we were surprised to observe that idasanutlin alone was also capable of this effect. This finding suggests an association between the MDM2 E3 ligase and HDAC1/2 corepressor complexes, which could be important for designing future dual/bifunctional HDAC- and MDM2-targeting therapeutics, such as PROTACs.