NSC 687852 (b-AP15)

IC50: N/A

NSC 687852 is a 19S regulatory particle inhibitor.

The 19S particles bind polyubiquitin-linked polypeptides and present them to the 20S degradative units. USP14 and UCHL5 are cysteine enzymes that become activated after being associated with the proteasome.

In vitro: NSC 687852 blocked deubiquitylating activity of USP14 and UCHL5 selectively without inhibiting proteasome activity. NSC 687852 decreased viability in multiple myeloma (MM) cell lines and patient MM cells, inhibited MM cell proliferation even in the presence of bone marrow stroma cells, and overcomed bortezomib resistance. Anti-MM activity of NSC 687852 was associated with growth arrest through downregulating CDC2, CDC25C, and cyclin B1, as well as induction of caspase-dependent apoptosis and activation of unfolded protein response [1].

In vivo: In vivo studies using distinct human MM xenograft models showed that NSC 687852 was well tolerated, inhibited tumor growth, and prolonged mouse survival. Combination of NSC 687852 with suberoylanilide hydroxamic acid, lenalidomide, or dexamethasone was found to induce synergistic anti-MM activity [1].

Clinical trial: N/A

Reference:
[1] Ze Tian,Padraig D'Arcy,Xin Wang,Arghya Ray,Yu-Tzu Tai,Yiguo Hu,Ruben D Carrasco,Paul Richardson,Stig Linder,Dharminder Chauhan,Kenneth C Anderson.  A novel small molecule inhibitor of deubiquitylating enzyme USP14 and UCHL5 induces apoptosis in multiple myeloma and overcomes bortezomib resistance. Blood. 2014 Jan 30; 123(5): 706–716.

Inhibition of proteasome deubiquitinating activity as a new cancer therapy.[Pubmed:22057347]

Nat Med. 2011 Nov 6;17(12):1636-40.

Ubiquitin-tagged substrates are degraded by the 26S proteasome, which is a multisubunit complex comprising a proteolytic 20S core particle capped by 19S regulatory particles. The approval of bortezomib for the treatment of multiple myeloma validated the 20S core particle as an anticancer drug target. Here we describe the small molecule b-AP15 as a previously unidentified class of proteasome inhibitor that abrogates the deubiquitinating activity of the 19S regulatory particle. b-AP15 inhibited the activity of two 19S regulatory-particle-associated deubiquitinases, ubiquitin C-terminal hydrolase 5 (UCHL5) and ubiquitin-specific peptidase 14 (USP14), resulting in accumulation of polyubiquitin. b-AP15 induced tumor cell apoptosis that was insensitive to TP53 status and overexpression of the apoptosis inhibitor BCL2. We show that treatment with b-AP15 inhibited tumor progression in four different in vivo solid tumor models and inhibited organ infiltration in an acute myeloid leukemia model. Our results show that the deubiquitinating activity of the 19S regulatory particle is a new anticancer drug target.

Induction of the lysosomal apoptosis pathway by inhibitors of the ubiquitin-proteasome system.[Pubmed:19089926]

Int J Cancer. 2009 Mar 15;124(6):1463-9.

The lysosomal apoptosis pathway is a potentially interesting therapeutic target. Since apoptosis involving the lysosomal pathway has been described to involve cathepsins, we screened a drug library for agents that induce cathepsin-dependent apoptosis. Using pharmacological inhibitors and siRNA, we identified 2 structurally related agents (NSC687852 and NSC638646) that induced cathepsin D-dependent caspase-cleavage activity in human breast cancer cells. Both agents were found to induce the mitochondrial apoptosis pathway. NSC687852 and NSC638646 were found to inhibit the activity of ubiquitin isopeptidases and to induce the accumulation of high-molecular-mass ubiquitins in cells. We show that 3 other inhibitors of the proteasome degradation pathway induce lysosomal membrane permeabilization (LMP) and that cathepsin-D siRNA inhibits apoptosis induced by these agents. We conclude that a screen for cathepsin-dependent apoptosis-inducing agents resulted in the identification of ubiquitin isopeptidase inhibitors and that proteasome inhibitors with different mechanisms of action induce LMP and cathepsin D-dependent apoptosis.