Polo-like kinase 1 (Plk1) is one of the key regulators of mitotic cell division. In addition to an N-terminal protein kinase catalytic domain, Plk1 possesses a phosphopeptide binding domain named polo box domain (PBD) at its C terminus. PBD is postulated to be essential for Plk1 localization and substrate targeting. Here, we developed a high-throughput screening system to identify inhibitors of PBD-dependent binding and screened a chemical library. We isolated a benzotropolone-containing natural compound derived from nutgalls (purpurogallin (PPG)) that inhibited PBD-dependent binding in vitro and in vivo. PPG not only delayed the onset of mitosis but also prolonged the progression of mitosis in HeLa cells. Although apparently normal bipolar spindles were formed even in the presence of PPG, the perturbation of chromosome alignment at metaphase plates activated the spindle assembly checkpoint pathway. These results demonstrate the predominant role of PBD-dependent binding on smooth chromosome congression at metaphase. In eukaryotes, Plk12 (or its orthologs) possesses a wide variety of essential functions during mitosis (1, 2). Although levels of Plk1 increase in late G 2 and rapidly decrease by proteolysis at the end of M phase, Plk1 localization changes dramatically when cells transit through the various mitotic stages. During late G 2 and prophase, Plk1 localizes primarily at the centrosomes, where Plk1 is involved in centrosome maturation, separation, and microtubule nucleation (3-5). At this stage, Plk1 also regulates mitotic entry through the phosphorylation and activation of Cdc25 (6, 7). In parallel, the phosphorylation of Wee1 by Plk1, which is primed by Cdk1, promotes the destruction of Wee1, the inhibitory kinase of mitotic entry (8, 9). By metaphase, a fraction of Plk1 relocalizes to the kinetochores, where it is involved in the regulation of the spindle assembly checkpoint pathway and proper chromosome segregation. Plk1 sensitizes the tension between sister chromatids and regulates the stability of kinetochore-microtubule interactions by phosphorylating kinetochore proteins such as BubR1 and proteins that harbor 3F3/2 epitopes (4, 10 -14). Although Plk1 localization at chromosome arms is required for loss of arm cohesion during M-phase (15, 16), localized Plk1 activity at the kinetochore is important for the proper accumulation of kinetochore proteins such as BubR1, Mad1, Mad2, Cdc20, and centromere/ kinetochore-associated protein-E (CENP-E) (4, 10 -12, 17, 18). During anaphase, Plk1 is concentrated in the spindle midzone, where it may facilitate microtubule sliding. After chromosomal segregation, Plk1 remains in the central spindle and midbody, where it is involved in formation of the cleavage furrow (19 -21).These various localizations of Plk1 are mediated by its noncatalytic C-terminal half, the polo box domain (PBD), which comprises two polo box motifs (22, 23). Recently, Yaffe and co-workers (24, 25) discovered that the PBD constitutes a phosphopeptide binding domain which binds with maximal affin...

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Current anti-hepatitis B virus (HBV) agents including interferons and nucleos(t)ide analogs efficiently suppress HBV infection. However, as it is difficult to eliminate HBV from chronically infected liver, alternative anti-HBV agents targeting a new molecule are urgently needed. In this study, we applied a chemical array to high throughput screening of small molecules that interacted with sodium taurocholate cotransporting polypeptide (NTCP), an entry receptor for HBV. From approximately 30,000 compounds, we identified 74 candidates for NTCP interactants, and five out of these were shown to inhibit HBV infection in cell culture. One of such compound, NPD8716, a coumarin derivative, interacted with NTCP and inhibited HBV infection without causing cytotoxicity. Consistent with its NTCP interaction capacity, this compound was shown to block viral attachment to host hepatocytes. NPD8716 also prevented the infection with hepatitis D virus, but not hepatitis C virus, in agreement with NPD8716 specifically inhibiting NTCP-mediated infection. Analysis of derivative compounds showed that the anti-HBV activity of compounds was apparently correlated with the affinity to NTCP and the capacity to impair NTCP-mediated bile acid uptake. These results are the first to show that the chemical array technology represents a powerful platform to identify novel viral entry inhibitors.

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that degrade many extracellular matrix components and that have been implicated in the pathogenesis of various human diseases including cancer metastasis. Here, we screened MMP-9 inhibitors using photo-cross-linked chemical arrays, which can detect small-molecule ligand-protein interactions on a chip in a high-throughput manner. The array slides were probed sequentially with His-MMP-9, anti-His antibody, and a Cy5-labeled secondary antibody and then scanned with a microarray scanner. We obtained 27 hits among 24,275 compounds from the NPDepo library; 2 of the identified compounds (isoxazole compound 1 and naphthofluorescein) inhibited MMP-9 enzyme activity in vitro. We further explored 17 analogs of 1 and found that compound 18 had the strongest inhibitory activity. Compound 18 also inhibited other MMPs, including MMP-2, MMP-12, and MMP-13 and significantly inhibited cell migration in human fibrosarcoma HT1080 cells. These results suggest that 18 is a broad-spectrum MMP inhibitor.

Background and Purpose: Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that degrade extracellular matrix components and that have been implicated in a wide range of pathological processes including tumor metastasis. Although many small-molecule MMP inhibitors have been developed, there are some problems related to specificity and side effects. In addition, recent studies have shown that several MMPs have nonproteolytic and tumor-suppressing functions depending upon the stage of cancer progression. Thus, much work remains for the elucidation of each MMP function and the development of new MMP inhibitors. Small-molecule microarrays represent a powerful new platform for facilitating target-based screens. Thousands of small molecules are arrayed on a slide glass and used to screen for protein-small molecule interactions in a high-throughput manner. We have developed unique photo-cross-linked chemical arrays, which enable the immobilization of a variety of small molecules on a solid support in a functional group-independent manner using a photoaffinity reaction. In this study, we screened MMP-9 inhibitors using the photo-cross-linked chemical arrays. Methods and Results: The array slides with compounds of the RIKEN NPDepo chemical library were probed sequentially with His-Myc-tagged human recombinant MMP-9, anti-His antibody, and a Cy5-labeled secondary antibody, and then scanned with a microarray scanner. The fluorescence signals from two slides treated with and without His-Myc-tagged MMP-9 were quantified. We obtained 27 hit compounds among 24,275 compounds; 2 of the identified compounds (isoxazole compound NPDK-1 and naphthofluorescein) inhibited MMP-9 enzyme activity in vitro. We further explored 17 analogs of NPDK-1 and found that NPDK-18 showed the strongest inhibitory activity against MMP-9, with an IC50 value of 3.8 μM. NPDK-18 inhibited the enzyme activities of MMP-2, MMP-12 and MMP-13, as well as MMP-9 and MMP-9/ΔHemopexin, with almost identical potency, but showed no inhibition against MMP-1 and MMP-7. The biological potency of NPDK-18 was confirmed in a wound-healing scratch assay, where NPDK-18 significantly inhibited cell migration of human fibrosarcoma HT1080 cells with no cell toxicity at 10 μM. Conclusion: These results suggest that NPDK-18 is a broad-spectrum MMP inhibitor. Our study has shown that the photo-cross-linked chemical arrays are useful for high-throughput drug screening. Citation Format: Makoto Kawatani, Yasumitsu Kondoh, Kaori Honda, Tomomi Sekine, Hiroyuki Osada. Chemical array screen identifies a novel MMP inhibitor NPDK-18 that suppresses tumor cell migration. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B131.