MS479 is a BRD4 PROTAC degrader that binds with high affinity to BRD4-BD2 and GLP (BRD4-BD2: Kd = 200 nM; GLP: Kd = 306 nM). It effectively reduces the protein levels of BRD4 short isoforms. By directly binding to its substrate GLP, MS479 recruits the E3 ligase SPOP as a bridging protein. Additionally, MS479 can be utilized to inhibit the proliferation of colorectal cancer cells.

MS479 (Compound 9) exhibits optimal degradation of BRD4 (S) in the HT29 cell line at concentrations between 0.5-5 μM over 24 hours, with degradation rates exceeding 50% at 5 μM. However, its effect on BRD4 (L) protein levels is relatively weaker, achieving around 50% degradation at 10 μM (DC 50 = 13.2 μM) over the same period. MS479 regulates BRD4 protein levels in HT29 cells via post-translational mechanisms within the range of 1-10 μM. A concentration of 5 μM over 24 hours suggests BRD4 (S) degradation relies on the participation of BRD4, GLP, SPOP, and UPS in HT29 cells. Additionally, MS479 demonstrates significant, concentration-dependent antiproliferative effects in HT29 cells (GI 50 = 4.5 μM) over 72 hours, while showing no cytotoxicity in normal cells.