CSN5i-3 is a novel, potent, highly selective, and orally bioavailable small molecule inhibitor that targets the CSN5/Jab1 (COPS5) protein—a key protein hydrolytic subunit of the COP9 signaling complex. CSN5i-3 exhibits extremely high inhibitory activity against this target, with an IC50 value of 5.8nM[1, 2]. The core function of CSN5 is to cleave the NEDD8 modification from the Cullin-RING E3 ubiquitin ligase. CSN5i-3 can potently inhibit this de-Neddase activity of CSN5, thereby interfering with the normal function of the CRL ubiquitin ligase[3].
In vitro, treatment of human breast cancer BT474 and SKBR3 cells with CSN5i-3 (2µM) for 24h significantly induced apoptosis and G1 phase cell cycle arrest, and increased the levels of the apoptosis marker cleaved PARP and the cell cycle-related protein p27[4]. Treatment of human umbilical vein endothelial cells (HUVECs) with CSN5i-3 (1, 4µM) for 5h induced a significant weakening of endothelial barrier function, induced the expression of RhoGTPase RhoB in endothelial cells, and formed actin stress fibers[5].
In vivo, subcutaneous injection of CSN5i-3 (10mg/kg) into MDA-MB-231 cell xenograft mice for 18 days inhibited tumor growth in mice, and combined treatment with Talazoparib significantly enhanced the antitumor efficacy[6].
References:
[1] Schlierf A, Altmann E, Quancard J, et al. Targeted inhibition of the COP9 signalosome for treatment of cancer[J]. Nature communications, 2016, 7(1): 13166.
[2] Yin L, Xue Y, Shang Q, et al. Pharmaceutical inhibition of neddylation as promising treatments for various cancers[J]. Current Topics in Medicinal Chemistry, 2019, 19(12): 1059-1069.
[3] Wu J T, Chan Y R, Chien C T. Protection of cullin–RING E3 ligases by CSN–UBP12[J]. Trends in cell biology, 2006, 16(7): 362-369.
[4] Xiao H, Claret F X, Shen Q. The novel Jab1 inhibitor CSN5i-3 suppresses cell proliferation and induces apoptosis in human breast cancer cells[J]. Neoplasma, 2019, 66(3).
[5] Majolée J, Pronk M C A, Jim K K, et al. CSN5 inhibition triggers inflammatory signaling and Rho/ROCK-dependent loss of endothelial integrity[J]. Scientific reports, 2019, 9(1): 8131.
[6] Peng X, Wang Y, Yu Z, et al. Jab1 regulates HRR mRNA stability to modulate PARP inhibitor sensitivity in triple-negative breast cancer[J]. Molecular Cancer, 2025, 24(1): 217.