Induction of selective degradation of target proteins by small molecules (protein knockdown) would be useful for biological research and treatment of various diseases. To achieve protein knockdown, we utilized the ubiquitin ligase activity of cellular inhibitor of apoptosis protein 1 (cIAP1), which is activated by methyl bestatin (MeBS, 2). We speculated that formation of an artificial (nonphysiological) complex of cIAP1 and a target protein would be induced by a hybrid molecule consisting of MeBS (2) linked to a ligand of the target protein, and this would lead to cIAP1-mediated ubiquitination and subsequent proteasomal degradation of the target protein. To verify this hypothesis, we focused on cellular retinoic acid-binding proteins (CRABP-I and -II) and designed hybrid molecules (compounds 4) consisting of MeBS (2) coupled via spacers of various lengths to all-trans retinoic acid (ATRA, 3), a ligand of CRABPs. Compounds 4 induced selective loss of CRABP-I and -II proteins in cells. We confirmed that 4b induced formation of a complex of cIAP1 and CRABP-II in vitro and induced proteasomal degradation of CRABP-II in cells. When neuroblastoma IMR-32 cells were treated with 4b, the level of CRABP-II was reduced and cell migration was inhibited, suggesting potential value of CRABP-II-targeting therapy for controlling tumor metastasis. Our results indicate that 4b possesses sufficient activity, permeability, and stability in cells to be employed in cellular assays. Hybrid molecules such as 4 should be useful not only as chemical tools for studying the biological/physiological functions of CRABPs but also as candidate therapeutic agents targeting CRABPs.

Selective inhibitors of Jumonji domain-containing protein (JMJD) histone demethylases are candidate anticancer agents as well as potential tools for elucidating the biological functions of JMJDs. On the basis of the crystal structure of JMJD2A and a homology model of JMJD2C, we designed and prepared a series of hydroxamate analogues bearing a tertiary amine. Enzyme assays using JMJD2C, JMJD2A, and prolyl hydroxylases revealed that hydroxamate analogue 8 is a potent and selective JMJD2 inhibitor, showing 500-fold greater JMJD2C-inhibitory activity and more than 9100-fold greater JMJD2C-selectivity compared with the lead compound N-oxalylglycine 2. Compounds 17 and 18, prodrugs of compound 8, each showed synergistic growth inhibition of cancer cells in combination with an inhibitor of lysine-specific demethylase 1 (LSD1). These findings suggest that combination treatment with JMJD2 inhibitors and LSD1 inhibitors may represent a novel strategy for anticancer chemotherapy.

Chronic stress-induced aberrant gene expression in the brain and subsequent dysfunctional neuronal plasticity have been implicated in the etiology and pathophysiology of mood disorders. In this study, we examined whether altered expression of small, regulatory, noncoding microRNAs (miRNAs) contributes to the depression-like behaviors and aberrant neuronal plasticity associated with chronic stress. Mice exposed to chronic ultra-mild stress (CUMS) exhibited increased depression-like behaviors and reduced hippocampal expression of the brain-enriched miRNA-124 (miR-124). Aberrant behaviors and dysregulated miR-124 expression were blocked by chronic treatment with an antidepressant drug. The depression-like behaviors are likely not conferred directly by miR-124 downregulation because neither viral-mediated hippocampal overexpression nor intrahippocampal infusion of an miR-124 inhibitor affected depression-like behaviors in nonstressed mice. However, viral-mediated miR-124 overexpression in hippocampal neurons conferred behavioral resilience to CUMS, whereas inhibition of miR-124 led to greater behavioral susceptibility to a milder stress paradigm. Moreover, we identified histone deacetylase 4 (HDAC4), HDAC5, and glycogen synthase kinase 3␤ (GSK3␤) as targets for miR-124 and found that intrahippocampal infusion of a selective HDAC4/5 inhibitor or GSK3 inhibitor had antidepressant-like actions on behavior. We propose that miR-124-mediated posttranscriptional controls of HDAC4/5 and GSK3␤ expressions in the hippocampus have pivotal roles in susceptibility/resilience to chronic stress.

Selective inhibitors of human sirtuin 2 (SIRT2), a deacetylase, are candidate therapeutic agents for neurodegenerative diseases such as Parkinson's disease and Huntington's disease as well as potential tools for elucidating the biological functions of SIRT2. On the basis of homology models of SIRT1 and SIRT2, we designed and prepared a series of 2-anilinobenzamide analogues. Enzyme assays using recombinant SIRT1 and SIRT2 revealed that 3'-phenethyloxy-2-anilinobenzamide analogues such as 33a and 33i are potent and selective SIRT2 inhibitors, showing more than 3.5-fold greater SIRT2-inhibitory activity and more than 35-fold greater SIRT2-selectivity compared with AGK2 (3), a previously reported SIRT2-selective inhibitor. Compound 33a also induced a dose-dependent selective increase of α-tubulin acetylation in human colon cancer HCT116 cells, indicating selective inhibition of SIRT2 in the cells. These 3'-phenethyloxy-2-anilinobenzamide derivatives represent an entry into a new class of SIRT2-selective inhibitors.

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Edited by Noboru MizushimaKeywords: Cellular inhibitor of apoptosis protein 1 Cellular retinoic acid binding protein-II Protein knockdown Ubiquitin Proteasome a b s t r a c t Manipulation of protein stability with small molecules is a challenge in the field of drug discovery. Here we show that cellular retinoic acid binding protein-II (CRABP-II) can be specifically degraded by a novel compound, SNIPER-4, consisting of (À)-N-[(2S,3R)-3-amino-2-hydroxy-4-phenylbutyryl]-L-leucine methyl ester and all-trans retinoic acid that are ligands for cellular inhibitor of apoptosis protein 1 (cIAP1) and CRABP-II, respectively. Mechanistic analysis revealed that SNIPER-4 induces cIAP1-mediated ubiquitylation of CRABP-II, resulting in the proteasomal degradation. The protein knockdown strategy employing the structure of SNIPER-4 could be applicable to other target proteins.

To find HDAC8-selective inhibitors, we designed a library of HDAC inhibitor candidates, each containing a zinc-binding group that coordinates with the active-site zinc ion, linked via a triazole moiety to a capping structure that interacts with residues on the rim of the active site. These compounds were synthesized by using click chemistry. Screening identified HDAC8-selective inhibitors including C149 (IC(50) = 0.070 μM), which was more potent than PCI-34058 (6) (IC(50) = 0.31 μM), a known HDAC8 inhibitor. Molecular modeling suggested that the phenylthiomethyl group of C149 binds to a unique hydrophobic pocket of HDAC8, and the orientation of the phenylthiomethyl and hydroxamate moieties (fixed by the triazole moiety) is important for the potency and selectivity. The inhibitors caused selective acetylation of cohesin in cells and exerted growth-inhibitory effects on T-cell lymphoma and neuroblastoma cells (GI(50) = 3-80 μM). These findings suggest that HDAC8-selective inhibitors have potential as anticancer agents.