Zhuorong Li

Jadomycin B, an Aurora-B kinase inhibitor discovered through virtual screening

Aurora kinases have emerged as promising targets for cancer therapy because of their critical role in mitosis. These kinases are well-conserved in all eukaryotes, and IPL1 gene encodes the single Aurora kinase in budding yeast. In a virtual screening attempt, 22 compounds were identified from nearly 15,000 microbial natural products as potential small-molecular inhibitors of human Aurora-B kinase. One compound, Jadomycin B, inhibits the growth of ipl1-321 temperature-sensitive mutant more dramatically than wild-type yeast cells, raising the possibility that this compound is an Aurora kinase inhibitor. Further in vitro biochemical assay using purified recombinant human Aurora-B kinase shows that Jadomycin B inhibits Aurora-B activity in a dose-dependent manner. Our results also indicate that Jadomycin B competes with ATP for the kinase domain, which is consistent with our docking prediction. Like other Aurora kinase inhibitors, Jadomycin B blocks the phosphorylation of histone H3 on Ser10 in vivo. We also present evidence suggesting that Jadomycin B induces apoptosis in tumor cells without obvious effects on cell cycle. All the results indicate that Jadomycin B is a new Aurora-B kinase inhibitor worthy of further investigation. [Mol Cancer Ther 2008;7(7):2386–93]

DH166, a beta-carboline derivative, inhibits the kinase activity of PLK1

A better way to treat complex diseases such as cancer is to aim for several targets at once. Beta-carboline derivatives have been shown to have anticancer activity, but these compounds may target several enzymes required for cell division. Polo-like kinases (PLKs) are well conserved serine/threonine kinases and PLK1 plays multiple roles in cell proliferation. Thus, PLK1 is one of the attractive mitotic targets for anticancer drugs. We found that DH166, a beta-carboline derivative, inhibits the growth of cdc5-2 temperature-sensitive mutant more profoundly than wild-type yeast cells. Because Cdc5 is the human PLK1 homologue in budding yeast, this observation indicates that DH166 might be a PLK1 inhibitor. Indeed, DH166 inhibits the kinase activity of purified PLK1 at low micromolar concentration in an ATP-competitive manner, which is consistent with the docking result based on the crystal structure of PLK1. In addition, DH166 blocks cancer cell proliferation, causes a mitotic arrest, increases cyclin B1 accumulation, induces aberrant mitotic spindles and apoptosis, presumably due to the down-regulation of PLK1. Although beta-carboline derivatives have been demonstrated to show antitumor activities through multiple mechanisms, our data indicate for the first time that their cytotoxicity to tumor cells might be attributable to the inhibition of PLK1 as well.

Synthesis and anticancer activity of novel 3,4-diarylthiazol-2(3H)-ones (imines)

A series of 3,4-diarylthiazol-2(3H)-ones and three 3,4-diarylthiazol-2(3H)-imines were synthesized and evaluated for their cytotoxicity in a panel of human cancer cell lines. Compounds 21 and 22 showed potential anticancer activity against human CEM cells with IC50 values of 0.12 and 0.24microM, respectively.

Identification of Upregulators of BMP2 Expression via High-Throughput Screening of a Synthetic and Natural Compound Library

Bone morphogenetic protein II (BMP2), a member of the transforming growth factor—β (TGF-β) superfamily, is highly expressed in osteoblasts and is a crucial regulator of osteogenic differentiation. Many observations clearly indicate the high potency of BMP2 as an inducer of osteogenesis, and it may be a novel therapeutic target for diseases associated with bone loss, especially in menopausal and postmenopausal women. To discover new agents that enhance the expression of the mouse BMP2, the authors developed a high-throughput assay to screen a synthetic and natural compound library. The cell-based high-throughput screen was conducted in 96-well plates using the clonal murine calvarial MC3T3-E1 cells. These cells were stably transfected with mouse BMP2 promoter-luciferase and calibrated with the known antiosteoporosis compound genistein. Among 3192 compounds screened, 3 agents (daidzein, formononetin, and 2-Acetyldibenzothiophene) were picked up by the high-throughput screening assay, and those compounds were identified as upregulators of BMP2 expression by real-time quantitative reverse transcription—polymerase chain reaction and flow cytometry. Thus, it is demonstrated that this screening model is useful for identifying lead compounds to treat osteoporosis and maintain bone metabolism balance.

A discovery of novel Mycobacterium tuberculosis pantothenate synthetase inhibitors based on the molecular mechanism of actinomycin D inhibition

Mycobacterium tuberculosis pantothenate synthetase is a potential anti-tuberculosis target, and a high-throughput screening system was previously developed to identify its inhibitors. Using a similar system, we screened a small library of compounds and identified actinomycin D (ActD) as a weak inhibitor of pantothenate synthetase. A new method was established to discover more effective inhibitors by determining the molecular mechanism of ActD inhibition followed by structure-based virtual screening. The molecular interaction of inhibition was determined by circular dichroism and tryptophan fluorescence quenching. The structure-based search and virtual screening were performed using the Molecular Operating Environment (MOE) program and SYBYL 7.5, respectively. Two inhibitors were identified with an IC(50) for pantothenate synthetase that was at least ten times better than that of ActD.

Identification of Hydroxyxanthones as Na/K-ATPase Ligands

We have screened a chemical library and identified several novel structures of Na/K-ATPase inhibitors. One group of these inhibitors belongs to polyphenolic xanthone derivatives. Functional characterization reveals the following properties of this group of inhibitors. First, like ouabain, they are potent inhibitors of the purified Na/K-ATPase. Second, their effects on the Na/K-ATPase depend on the number and position of phenolic groups. Methylation of these phenolic groups reduces the inhibitory effect. Third, further characterization of the most potent xanthone derivative, MB7 (3,4,5,6-tetrahydroxyxanthone), reveals that it does not change either Na+ or ATP affinity of the enzyme. Finally, unlike that of ouabain, the inhibitory effect of MB7 on Na/K-ATPase is not antagonized by K+. Moreover, MB7 does not activate the receptor Na/K-ATPase/Src complex and fails to stimulate protein kinase cascades in cultured cells. Thus, we have identified a group of novel Na/K-ATPase ligands that can inhibit the pumping function without stimulating the signaling function of Na/K-ATPase.

Synthesis and biological evaluation of heat-shock protein 90 inhibitors: geldanamycin derivatives with broad antiviral activities.

Background: Previous studies have suggested that geldanamycin (GA) inhibits the replication of several viruses in vitro. Here, we aimed to synthesize and evaluate the antiviral activity of 17-amino-17-demethoxygeldanamycin derivatives. Methods: A series of 17-substituted and 17-,19-disubstituted GA derivatives were screened for antiviral activities against eight different viral strains, including herpesvirus, hepatitis virus, retrovirus and picornavirus. Results: Most of the tested compounds showed inhibitory activity against the viruses and showed reduced cytotoxicity in vitro as compared with the parent compound GA. In vivo efficacy evaluation results showed that compound 6 noticeably inhibited duckling hepatitis B virus DNA replication in duckling serum after oral administration. Viral rebound did not occur after termination of the treatment. The modified GA derivatives also showed median lethal dose values that were higher than that of the parent GA in mice intraperitoneally treated with the study compounds. Conclusions: Targeting heat-shock protein 90 could be a new antiviral approach that is not prone to the development of drug resistance. The 17-amino-17-demethoxygeldanamycin derivatives could be novel agents with potential antiviral activity.

Synthesis and Antiviral Activity of N-Phenylbenzamide Derivatives, a Novel Class of Enterovirus 71 Inhibitors

A series of novel N-phenylbenzamide derivatives were synthesized and their anti-EV 71 activities were assayed in vitro. Among the compounds tested, 3-amino-N-(4-bromophenyl)-4-methoxybenzamide (1e) was active against the EV 71 strains tested at low micromolar concentrations, with IC50 values ranging from 5.7 ± 0.8–12 ± 1.2 μM, and its cytotoxicity to Vero cells (TC50 = 620 ± 0.0 μM) was far lower than that of pirodavir (TC50 = 31 ± 2.2 μM). Based on these results, compound 1e is a promising lead compound for the development of anti-EV 71 drugs.

A novel class of geldanamycin derivatives as HCV replication inhibitors targeting on Hsp90: synthesis, structure–activity relationships and anti-HCV activity in GS4.3 replicon cells

A novel class of geldanamycin (GA) derivatives as hepatitis C virus (HCV) replication inhibitors has been synthesized and their anti-HCV activities were evaluated in GS4.3 HCV replicon cells. Most of the synthesized compounds demonstrated potential activities against HCV in vitro. Substitution with an aliphatic cyclic group (2b) and polar phosphate group (2f) at the 17 position of GA resulted in more potent inhibitory activity. The configurations of the tetrahydrofurfurylamino (THFM) substituents obviously affected their antiviral activities. The 2b with a 2′-(R)-THFM group at the 17 position showed much potent activity and higher selectivity than its 2′-(S) and 2′-(R, S) epimers. In the tested GA derivatives, 2b and 2f show the most potential leading compounds for development of novel anti-HCV agents.

Synthesis and evaluation of 1-(benzo[b]thiophen-2-yl)ethanone analogues as novel anti-osteoporosis agents acting on BMP-2 promotor

A novel series of 1-(benzo[b]thiophen-2-yl)ethanone analogues were prepared and evaluated for enhancing BMP-2 expression. Compounds 1-5, 7, 8, 12, 13 and 16, with upregulation rate values of 35.6%, 27.9%, 39.8%, 32.0%, 37.1%, 30.2%, 28.0%, 33.5%, 22.8% and 27.3% in vitro, respectively, at a concentration of 4muM, exhibited potent effect for enhancing BMP-2 expression. We also found that compounds 1 and 12 produced a dose-dependent increase on bone histology and histomorphometry, and effectively reduced bone defects induced by ovariectomy in an ovariectomized rat model (OVX).