Yoon Sun Cho

Identification and validation of bioactive small molecule target through phenotypic screening

For effective bioactive small molecule discovery and development into new therapeutic drug, a systematic screening and target protein identification is required. Different from the conventional screening system, herein phenotypic screening in combination with multi-omics-based target identification and validation (MOTIV) is introduced. First, phenotypic screening provides visual effect of bioactive small molecules in the cell or organism level. It is important to know the effect on the cell or organism level since small molecules affect not only a single target but the entire cellular mechanism within a cell or organism. Secondly, MOTIV provides systemic approach to discover the target protein of bioactive small molecule. With the chemical genomics and proteomics approach of target identification methods, various target protein candidates are identified. Then network analysis and validations of these candidates result in identifying the biologically relevant target protein and cellular mechanism. Overall, the combination of phenotypic screening and MOTIV will provide an effective approach to discover new bioactive small molecules and their target protein and mechanism identification.

Convallatoxin, a Dual Inducer of Autophagy and Apoptosis, Inhibits Angiogenesis In Vitro and In Vivo

Autophagy and apoptosis are important processes that control cellular homeostasis and have been highlighted as promising targets for novel cancer therapies. Here, we identified convallatoxin (CNT), isolated from Antiaris toxicaria, as a dual inducer of autophagy and apoptosis. CNT exerts cytotoxic effects on a number of cancer and normal cell lines and induces apoptosis by increasing caspase-3 and poly ADP ribose polymerase (PARP) cleavage. Moreover, dose- and time-dependent autophagic activity was detected in CNT-treated cells, and mammalian target of rapamycin (mTOR)/p70S6K signal pathway inhibition was observed. Notably, CNT inhibits human umbilical vein endothelial cell (HUVEC) growth and exerts anti-angiogenic activity in vitro and in vivo. Collectively, these results demonstrate that the naturally occurring compound, CNT, is a novel anti-angiogenic compound via dual inducing of autophagy and apoptosis.

Autophagonizer, a novel synthetic small molecule, induces autophagic cell death.

Autophagy is an apoptosis-independent mechanism of cell death that protects the cell from environmental imbalances and infection by pathogens. We identified a novel small molecule, 2-(3-Benzyl-4-oxo-3,4,5,6,7,8-hexahydro-benzo[4,5]thieno[2,3-d]pyrimidin-2-ylsulfanylmethyl)-oxazole-4-carboxylic acid (2-pyrrolidin-1-yl-ethyl)-amide (referred as autophagonizer), using high-content cell-based screening and the autophagosome marker EGFP-LC3. Autophagonizer inhibited growth and induced cell death in the human tumor cell lines MCF7, HeLa, HCT116, A549, AGS, and HT1080 via a caspase-independent pathway. Conversion of cytosolic LC3-I to autophagosome-associated LC3-II was greatly enhanced by autophagonizer treatment. Transmission electron microscopy and acridine orange staining revealed increased autophagy in the cytoplasm of autophagonizer-treated cells. In conclusion, autophagonizer is a novel autophagy inducer with unique structure, which induces autophagic cell death in the human tumor cell lines.

Functional inhibition of UQCRB suppresses angiogenesis in zebrafish

As a subunit of mitochondrial complex III, UQCRB plays an important role in complex III stability, electron transport, and cellular oxygen sensing. Herein, we report UQCRB function regarding angiogenesis in vivo with the zebrafish (Danio rerio). UQCRB knockdown inhibited angiogenesis in zebrafish leading to the suppression of VEGF expression. Moreover, the UQCRB-targeting small molecule terpestacin also inhibited angiogenesis and VEGF levels in zebrafish, supporting the role of UQCRB in angiogenesis. Collectively, UQCRB loss of function by either genetic and pharmacological means inhibited angiogenesis, indicating that UQCRB plays a key role in this process and can be a prognostic marker of angiogenesis- and mitochondria-related diseases.

Control of autophagy with small molecules

Autophagy is the mass degradation system that removes long-lived proteins and malfunctioning organelles within the cell. Dysfunctional autophagic processes can cause various diseases such as cancer and neurodegenerative disorders, but the underlying mechanisms responsible for such events remain undefined. Small molecules that control autophagy could be powerful tools to reveal autophagy mechanisms, and to develop treatments for autophagy-related diseases including Alzheimer’s disease, Parkinson’s disease and various cancer types. This review discusses the small molecules that have been identified to control autophagy and how they can be used to understand signaling pathways important for autophagy in the context of chemical genomics.

Hydroxamic Acid Derivatives of Mycophenolic Acid Inhibit Histone Deacetylase at the Cellular Level

Mycophenolic acid (MPA, 1), an inhibitor of IMP-dehydrogenase (IMPDH) and a latent PPARγ agonist, is used as an effective immunosuppressant for clinical transplantation and recently entered clinical trials in advanced multiple myeloma patients. On the other hand, suberoylanilide hydroxamic acid (SAHA), a non-specific histone deacetylase (HDAC) inhibitor, has been approved for treating cutaneous T-cell lymphoma. MPA seemed to bear a cap, a linker, and a weak metal-binding site as a latent inhibitor of HDAC. Therefore, the hydroxamic acid derivatives of mycophenolic acid having an effective metal-binding site, mycophenolic hydroxamic acid (MPHA, 2), 7-O-acetyl mycophenolic acid (7-O-Ac MPHA, 3), and 7-O-lauroyl mycophenolic hydroxamic acid (7-O-L MPHA, 4) were designed and synthesized. All these compounds inhibited histone deacetylase with IC50 values of 1, 0.9 and 0.5 μM, and cell proliferation at concentrations of 2, 1.5 and 1 μM, respectively.

Antidepressant indatraline induces autophagy and inhibits restenosis via suppression of mTOR/S6 kinase signaling pathway

Indatraline is an antidepressive agent and a non-selective monoamine transporter inhibitor that blocks the reuptake of neurotransmitters (dopamine, serotonin, and norepinephrine). In this study, we report that indatraline induces autophagy via the suppression of mTOR/S6 kinase signaling. Autophagy induction was examined by a cell-based high content screening system using LysoTracker, which was followed by monodansylcadaverine staining and transmission electron microscope observation. Indatraline increased the number of EGFP-LC3 cells expressing autophagosomes in the cytoplasm. Conversion of LC3 was further validated by immunoblotting. Indatraline induced autophagy by affecting the AMPK/mTOR/S6K signaling axis and had no influence on the PI3K/AKT/ERK signaling. Moreover, indatraline induced autophagy in smooth muscle cells (SMCs); further, it exhibited therapeutic potential for restenosis by inhibiting SMC accumulation in a rat restenosis model. These results provide new insights into the role of monoamine transporters in autophagy regulation and identify indatraline as a novel agent for inducing autophagy.

The effect of indatraline on angiogenesis suppression through HIF-1α-mediated VEGF inhibition.

The present research reports a novel biological activity of indatraline, a compound clinically used as an antidepressant. We previously identified indatraline as an autophagy inducer. Autophagy is an intracellular catabolic pathway for degrading or recycling unnecessary organelles in response to cellular stress. Indatraline-mediated autophagy induction results from mTOR inhibition. The mTOR is a negative regulator of autophagy as well as a master regulator of angiogenesis. Angiogenesis defines the process by which new vessels are formed from pre-existing vascular tissues, providing nutrients to cancer cells, allowing rapid tumor progression. Accordingly, targeting angiogenesis to prevent cancer is an attractive therapeutic strategy. Here, we demonstrate that indatraline possibly acts to suppress tumor-mediated angiogenesis via downregulation of HIF-1α-mediated VEGF expression. The effects of indatraline on autophagy and angiogenesis could make it a potential drug candidate toward cancer treatment.

A histone demethylase inhibitor, methylstat, inhibits angiogenesis in vitro and in vivo

Histone methylation has been highlighted in the regulation of gene expression. To explore the role of histone methylation in angiogenesis, methylstat, a Jumonji C domain containing the histone demethylase inhibitor, was used as a chemical probe. Methylstat inhibited the cell cycle of human umbilical vascular endothelial cells (HUVECs) at lower concentrations than other cell lines tested. Furthermore, methylstat blocked in vitro and in vivo angiogenesis at a nontoxic dose. These results provide new insights into the role of histone demethylase in angiogenesis. Collectively, methylstat could be a promising chemical probe for addressing its role in angiogenesis.