Junmin Quan

Novel Histone Demethylase LSD1 Inhibitors Selectively Target Cancer Cells with Pluripotent Stem Cell Properties

Histone modification determines epigenetic patterns of gene expression with methylation of histone H3 at lysine 4 (H3K4) often associated with active promoters. LSD1/KDM1 is a histone demethylase that suppresses gene expression by converting dimethylated H3K4 to mono- and unmethylated H3K4. LSD1 is essential for metazoan development, but its pathophysiologic functions in cancer remain mainly uncharacterized. In this study, we developed specific bioactive small inhibitors of LSD1 that enhance H3K4 methylation and derepress epigenetically suppressed genes in vivo. Strikingly, these compounds inhibited the proliferation of pluripotent cancer cells including teratocarcinoma, embryonic carcinoma, and seminoma or embryonic stem cells that express the stem cell markers Oct4 and Sox2 while displaying minimum growth-inhibitory effects on non-pluripotent cancer or normal somatic cells. RNA interference-mediated knockdown of LSD1 expression phenocopied these effects, confirming the specificity of small molecules and further establishing the high degree of sensitivity and selectivity of pluripotent cancer cells to LSD1 ablation. In support of these results, we found that LSD1 protein level is highly elevated in pluripotent cancer cells and in human testicular seminoma tissues that express Oct4. Using these novel chemical inhibitors as probes, our findings establish LSD1 and histone H3K4 methylation as essential cancer-selective epigenetic targets in cancer cells that have pluripotent stem cell properties.

L2DTL/CDT2 and PCNA Interact with p53 and Regulate p53 Polyubiquitination and Protein Stability through MDM2 and CUL4A/DDB1 Complexes

The CUL4-ROC1 E3 ligase complex regulates genome stability, replication, and cell cycle progression. A novel WD40 domain-containing protein, L2DTL, and PCNA were identified as proteins associated with CUL4/DDB1 complexes. Inactivation of CUL4A, L2DTL, PCNA, DDB1, or ROC1 induced p53 stabilization and growth arrest. L2DTL, PCNA, and DDB1/CUL4A complexes were found to physically interact with p53 tumor suppressor and its regulator MDM2/HDM2. The isolated CUL4A complexes display potent and robust polyubiquitination activity towards p53 and this activity is dependent on L2DTL, PCNA, DDB1, ROC1, and MDM2/HDM2. We also found that the interaction between p53 and CUL4 complex is regulated by DNA damage. Our data further showed that MDM2/HDM2 is rapidly proteolyzed in response to UV irradiation and this process is regulated by CUL4/DDB1 and PCNA. Our studies demonstrate that PCNA, L2DTL, and the DDB1-CUL4A complex play critical and differential roles in regulating the protein stability of p53 and MDM2/HDM2 in unstressed and stressed cells.

Structural basis for the inhibition of Polo-like kinase 1

Polo-like kinase 1 (PLK1) is a master regulator of mitosis and is considered a potential drug target for cancer therapy. PLK1 is characterized by an N-terminal kinase domain (KD) and a C-terminal Polo-box domain (PBD). The KD and PBD are mutually inhibited, but the molecular mechanisms of the autoinhibition remain unclear. Here we report the 2.3-Å crystal structure of the complex of the Danio rerio KD and PBD together with a PBD-binding motif of Drosophila melanogaster microtubule-associated protein 205 (Map205PBM). The structure reveals that the PBD binds and rigidifies the hinge region of the KD in a distinct conformation from that of the phosphopeptide-bound PBD. This structure provides a framework for understanding the autoinhibitory mechanisms of PLK1 and also sheds light on the activation mechanisms of PLK1 by phosphorylation or phosphopeptide binding.

Benzo[e]isoindole-1,3-diones as Potential Inhibitors of Glycogen Synthase Kinase-3 (GSK-3). Synthesis, Kinase Inhibitory Activity, Zebrafish Phenotype, and Modeling of Binding Mode

Benzo[e]isoindole-1,3-dione derivatives were synthesized, and the effects on GSK-3beta activity and zebrafish embryo growth were evaluated. A series of derivatives show obvious inhibitory activity against GSK-3beta. The most potent inhibitor, 7,8-dimethoxy-5-methylbenzo[e]isoindole-1,3-dione (8a), shows nanomolar IC(50) and obvious phenotype on zebrafish embryo growth associated with the inhibition of GSK-3beta at low micromolar concentration. The interaction mode between 8a and GSK-3beta was characterized by computational modeling.

A novel CyclinE/CyclinA-CDK Inhibitor targets p27Kip1 degradation, cell cycle progression and cell survival: Implications in cancer therapy

p27(Kip1) (p27) binds and inhibits the cyclin E- or cyclin A-associated cyclin-dependent kinases (CDKs)2 and other CDKs, and negatively regulates G1-G2 cell cycle progression. To develop specific CDK inhibitors, we have modeled the interaction between p27 and cyclin A-CDK2, and designed a novel compound that mimics p27 binding to cyclin A-CDK2. The chemically synthesized inhibitor exhibited high potency and selective inhibition towards cyclin E/cyclin A-CDK2 kinase in vitro but not other kinases. To facilitate permeability of the inhibitor, a cell penetrating peptide (CPP) was conjugated to the inhibitor to examine its effect in several cancer cell lines. The CPP-conjugated inhibitor significantly inhibited the proliferation of cancer cells. The treatment of the inhibitor resulted in the increased accumulation of p27 and p21(Cip1/Waf1) (p21) and hypo-phosphorylation of retinoblastoma protein (Rb). The degradation of p27, mediated through the phosphorylation of threonine-187 in p27, was also inhibited. Consequently, exposure of cells to the inhibitor caused cell cycle arrest and apoptosis. We conclude that specific cyclinE/cyclin A-CDK2 inhibitors can be developed based on the interaction between p27 and cyclin/CDK to block cell cycle progression to prevent tumor growth and survival.

One-pot syntheses of chromeno[3,4-c]pyrrole-3,4-diones via Ugi-4CR and intramolecular Michael addition.

One-pot and diastereoselective syntheses of diverse chromeno[3,4-c]pyrrole-3,4-diones from readily available starting materials were achieved via sequential Ugi-4CR and intramolecular Michael addition.

Formal synthesis of cortistatins.

A unified strategy toward the asymmetric facile construction of the [6.7.6.5]oxapentacyclic skeleton of cortistatins is reported, featuring intramolecular Diels-Alder (IMDA), oxidative dearomatization, and an oxy-Michael addition reaction.

Development of New Stereodiverse Diaminocyclitols as Inhibitors of Influenza Virus Neuraminidase

A concise and modular approach to synthesize a new type of cyclopentene-based diaminocyclitol library from D-serine and L-serine has been developed, and key steps in this synthesis are an aza-Claisen rearrangement, a ring-closing metathesis, and a Baylis-Hillman reaction. The developed chemistry may offer a unique way to investigate the neuraminidase (NA) mutation by systematically mapping the changes within its binding sites.

Identifying tumor cell growth inhibitors by combinatorial chemistry and zebrafish assays.

Cyclin-dependent kinases (CDKs) play important roles in regulating cell cycle progression, and altered cell cycles resulting from over-expression or abnormal activation of CDKs observed in many human cancers. As a result, CDKs have become extensive studied targets for developing chemical inhibitors for cancer therapies; however, protein kinases share a highly conserved ATP binding pocket at which most chemical inhibitors bind, therefore, a major challenge in developing kinase inhibitors is achieving target selectivity. To identify cell growth inhibitors with potential applications in cancer therapy, we used an integrated approach that combines one-pot chemical synthesis in a combinatorial manner to generate diversified small molecules with new chemical scaffolds coupled with growth inhibition assay using developing zebrafish embryos. We report the successful identification of a novel lead compound that displays selective inhibitory effects on CDK2 activity, cancer cell proliferation, and tumor progression in vivo. Our approaches should have general applications in developing cell proliferation inhibitors using an efficient combinatorial chemical genetic method and integrated biological assays. The novel cell growth inhibitor we identified should have potential as a cancer therapeutic agent.

Identification of Green Tea Catechins as Potent Inhibitors of the Polo‐Box Domain of Polo‐Like kinase 1

Polo‐like kinase 1 (PLK1) plays crucial functions in multiple stages of mitosis and is considered to be a potential drug target for cancer therapy. The functions of PLK1 are mediated by its N‐terminal kinase domain and C‐terminal polo‐box domain (PBD). Most inhibitors targeting the kinase domain of PLK1 have a selectivity issue because of a high degree of structural conservation within kinase domains of all protein kinases. Here, we combined virtual and experimental screenings to identify green tea catechins as potent inhibitors of the PLK1 PBD. Initially, (−)‐epigallocatechin, one of the main components of green tea polyphenols, was found to significantly block the binding of fluorescein‐labeled phosphopeptide to the PBD at a concentration of 10 μm. Next, additional catechins were evaluated for their dose‐dependent inhibition of the PBD and preliminary structure–activity relationships were derived. Cellular analysis further showed that catechins interfere with the proper subcellular localization of PLK1, lead to cell‐cycle arrest in the S and G2M phases, and induce growth inhibition of several human cancer cell types, such as breast adenocarcinoma (MCF7), lung adenocarcinoma (A549), and cervical adenocarcinoma (HeLa). Our data provides new insight into understanding the anticancer activities of green tea catechins.