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1.  X-ray crystal structures of the Escherichia coli RNA polymerase in complex with Benzoxazinorifamycins 
Journal of medicinal chemistry  2013;56(11):4758-4763.
Rifampin, a semi-synthetic rifamycin, is the cornerstone of current tuberculosis treatment. Among many semi-synthetic rifamycins, benzoxazinorifamycins have great potential for TB treatment due to their superior affinity for wild-type and rifampin-resistant Mycobacterium tuberculosis RNA polymerases, and their reduced hepatic Cyp450 induction activity. In this study, we have determined the crystal structures of the Escherichia coli RNA polymerase complexes with two benzoxazinorifamycins. The ansa-naphthalene moieties of the benzoxazinorifamycins bind in a deep pocket of the β subunit, blocking the path of the RNA transcript. The C3′-tail of benzoxazinorifamycin fits a cavity between the β subunit and σ factor. We propose that, in addition to blocking RNA exit, the benzoxazinorifamycin C3′-tail changes the σ region3.2 loop position, which influences the template DNA at the active site thereby reducing the efficiency of transcription initiation. This study supports expansion of structure–activity relationships of benzoxazinorifamycins inhibition of RNA polymerase toward uncovering superior analogues with development potential.
doi:10.1021/jm4004889
PMCID: PMC3745299  PMID: 23679862
Escherichia coli RNA polymerase; Benzoxazinorifamycins; X-ray crystallography; Tuberculosis
2.  Optimization of Novel Nipecotic Bis(amide) Inhibitors of the Rho/MKL1/SRF Transcriptional Pathway as Potential Anti-metastasis Agents 
CCG-1423 (1) is a novel inhibitor of Rho/MKL1/SRF-mediated gene transcription that inhibits invasion of PC-3 prostate cancer cells in a Matrigel model of metastasis. We recently reported the design and synthesis of conformationally restricted analogs (e.g. 2) with improved selectivity for inhibiting invasion vs acute cytotoxicity. In this study we conducted a survey of aromatic substitution with the goal of improving physicochemical parameters (e.g. ClogP, MW) for future efficacy studies in vivo. Two new compounds were identified that attenuated cytotoxicity even further, and were 4-fold more potent than 2 at inhibiting PC-3 cell migration in a scratch wound assay. One of these (8a, CCG-203971, IC50 = 4.2 μM) was well tolerated in mice for 5 days at 100 mg/kg/day i.p., and was able to achieve plasma levels exceeding the migration IC50 for up to 3 hours.
doi:10.1016/j.bmcl.2013.04.080
PMCID: PMC3707396  PMID: 23707258
3.  Small Molecule Screening Identifies Regulators of the Transcription Factor ΔFosB 
ACS Chemical Neuroscience  2012;3(7):546-556.
ΔFosB protein accumulates in the striatum in response to chronic administration of drugs of abuse, L-DOPA, or stress, triggering long lasting neural and behavioral changes that underlie aspects of drug addiction, abnormal involuntary movements (dyskinesia), and depression. ΔFosB binds AP-1 DNA consensus sequences found in promoters of many genes and can both repress or activate gene transcription. In the striatum, ΔFosB is thought to dimerize with JunD to form a functional transcription factor, though strikingly JunD does not accumulate in parallel. One explanation is that ΔFosB can recruit different partners, including itself, depending on the neuron type in which it is induced and the chronic stimulus, generating protein complexes with different effects on gene transcription. To develop chemical probes to study ΔFosB, a high-throughput screen was carried out to identify small molecules that modulate ΔFosB function. Two compounds with low micromolar activity, termed C2 and C6, disrupt the binding of ΔFosB to DNA via different mechanisms, and in in vitro assays stimulate ΔFosB-mediated transcription. In cocaine-treated mice, C2 significantly elevates mRNA levels of the AMPA glutamate receptor GluR2 subunit with specificity, a known target gene of ΔFosB that plays a role in drug addiction and endogenous resilience mechanisms. C2 and C6 show different activities against ΔFosB homodimers compared to ΔFosB/JunD heterodimers, suggesting that these compounds can be used as probes to study the contribution of different ΔFosB-containing complexes on the regulation of gene transcription in biological systems and to assess the utility of ΔFosB as a therapeutic target.
doi:10.1021/cn3000235
PMCID: PMC3399579  PMID: 22860224
ΔFosB; high throughput screening; transcription factor; drug addiction; dyskinesia; depression
4.  MScreen: An Integrated Compound Management and High Throughput Screening (HTS) Data Storage and Analysis System 
Journal of biomolecular screening  2012;17(8):1080-1087.
High-throughput screening (HTS) has historically been used by the pharmaceutical industry to rapidly test hundreds of thousands of compounds to identify potential drug candidates. More recently, academic groups have used HTS to identify new chemical probes or small interfering RNA (siRNA) that can serve as experimental tools to examine the biology or physiology of novel proteins, processes, or interactions. HTS presents a significant challenge with the vast and complex nature of data generated. This report describes MScreen, a web-based, open-source cheminformatics application for chemical library and siRNA plate management, primary HTS and dose-response data handling, structure search, and administrative functions. Each project in MScreen can be secured with passwords or shared in an open information environment which enables collaborators to easily compare data from many screens, providing a useful means to identify compounds with desired selectivity. Unique features include compound, substance, mixture, and siRNA plate creation and formatting; automated dose-response fitting and quality control (QC); and user, target, and assay method administration. MScreen provides an effective means to facilitate HTS information handling and analysis in the academic setting so that users can efficiently view their screening data and evaluate results for follow-up.
doi:10.1177/1087057112450186
PMCID: PMC3600606  PMID: 22706349
chemoinformatics; data analysis software; open source; high-throughput screening
5.  Complementary Cell-Based High Throughput Screens Identify Novel Modulators of the Unfolded Protein Response 
Journal of Biomolecular Screening  2011;16(8):825-835.
Despite advances toward understanding the prevention and treatment of many cancers, patients who suffer from oral squamous cell carcinoma (OSCC) confront a survival rate that has remained unimproved for more than two decades indicating our ability to treat them pharmacologically has reached a plateau. In an ongoing effort to improve the clinical outlook for this disease, we previously reported that an essential component of the mechanism by which the proteasome inhibitor bortezomib (PS-341, Velcade) induced apoptosis in OSCC required the activation of a terminal unfolded protein response (UPR). Predicated on these studies, we hypothesized that high throughput screening (HTS) of large diverse chemical libraries might identify more potent or selective small molecule activators of the apoptotic arm of the UPR to control or kill OSCC. We have developed complementary cell-based assays using stably transfected CHO-K1 cell lines that individually assess the PERK/eIF2α/CHOP (apoptotic) or the IRE1/XBP1 (adaptive) UPR sub-pathways. A ~66K compound collection was screened at the University of Michigan Center for Chemical Genomics that included a unique library of pre-fractionated natural product extracts. The mycotoxin methoxycitrinin was isolated from a natural extract and found to selectively activate the CHOP-luciferase reporter at 80μM. A series of citrinin derivatives were isolated from these extracts, including a unique congener that has not been previously described. In an effort to identify more potent compounds we examined the ability of citrinin and the structurally related mycotoxins ochratoxin A and patulin to activate the UPR. Strikingly, we found that patulin at 2.5 – 10μM induced a terminal UPR in a panel of OSCC cells that was characterized by an increase in CHOP, GADD34 and ATF3 gene expression and XBP1 splicing. A luminescent caspase assay and the induction of several BH3-only genes indicated that patulin could induce apoptosis in OSCC cells. These data support the use of this complementary HTS strategy to identify novel modulators of UPR signaling and tumor cell death.
doi:10.1177/1087057111414893
PMCID: PMC3374590  PMID: 21844328
unfolded protein response; endoplasmic reticulum stress; cell-based assay; luciferase reporter; natural products
6.  Identification of Thieno[3,2-b]Pyrrole Derivatives as Novel Small Molecule Inhibitors of Neurotropic Alphaviruses 
The Journal of infectious diseases  2009;199(7):950-957.
Neurotropic alphaviruses such as western, eastern, and Venezuelan equine encephalitis viruses cause serious and potentially fatal central nervous system infections in humans and are high-priority potential bioterrorism agents. There are currently no widely available vaccines or licensed therapies for these virulent pathogens. To identify potential novel antiviral drugs, we developed a cell-based assay with a western equine encephalitis virus replicon that expresses a luciferase reporter gene and screened a small molecule diversity library of 51,028 compounds. We identified and validated a thieno[3,2-b]pyrrole compound with a half maximal inhibitory concentration of <10 µmol/L, a selectivity index >20, and potent activity against live virus in cultured neuronal cells. Furthermore, a structure-activity relationship analysis with 20 related compounds identified several with enhanced activity profiles, including 6 with submicromolar half maximal inhibitory concentrations. In conclusion, we have identified a novel class of promising inhibitors with potent activity against virulent neurotropic alphaviruses.
doi:10.1086/597275
PMCID: PMC2788236  PMID: 19239364
7.  Differences between high- and low-affinity complexes of enzymes and non-enzymes 
Journal of medicinal chemistry  2008;51(20):6432-6441.
Physical differences in small molecule binding between enzymes and non-enzymes were found through mining the protein-ligand database, Binding MOAD (Mother of All Databases). The data suggest that divergent approaches may be more productive for improving the affinity of ligands for the two classes of proteins. High-affinity ligands of enzymes are much larger than those with low affinity, indicating that the addition of complementary functional groups is likely to improve the affinity of an enzyme inhibitor. However, this process may not be as fruitful for ligands of non-enzymes. High- and low-affinity ligands of non-enzymes are nearly the same size, so modest modifications and isosteric replacement might be most productive. The inherent differences between enzymes and non-enzymes have significant ramifications for scoring functions and structure-based drug design. In particular, non-enzymes were found to have greater ligand efficiencies than enzymes. Ligand efficiencies are often used to indicate druggability of a target, and this finding supports the feasibility of non-enzymes as drug targets. The differences in ligand efficiencies do not appear to come from the ligands; instead, the pockets yield different amino acid compositions, despite very similar distributions of amino acids in the overall protein sequences.
doi:10.1021/jm8006504
PMCID: PMC2692211  PMID: 18826206

Results 1-7 (7)