SAR Exploration of Tight-Binding Inhibitors of Influenza Virus PA Endonuclease.

Significant efforts have been reported on the development of influenza antivirals including inhibitors of the RNA-dependent RNA polymerase PA N-terminal (PAN) endonuclease. Based on recently identified, highly active metal-binding pharmacophores (MBPs) for PAN endonuclease inhibition, a fragment-based drug development campaign was pursued. Guided by coordination chemistry and structure-based drug design, MBP scaffolds were elaborated to improve activity and selectivity. Structure-activity relationships were established and used to generate inhibitors of influenza endonuclease with tight-binding affinities. The activity of these inhibitors was analyzed using a fluorescence-quenching-based nuclease activity assay, and binding was validated using differential scanning fluorometry. Lead compounds were found to be highly selective for PAN endonuclease against several related dinuclear and mononuclear metalloenzymes. Combining principles of bioinorganic and medicinal chemistry in this study has resulted in some of the most active in vitro influenza PAN endonuclease inhibitors with high ligand efficiencies.

Targeting Metalloenzymes for Therapeutic Intervention.

Metalloenzymes are central to a wide range of essential biological activities, including nucleic acid modification, protein degradation, and many others. The role of metalloenzymes in these processes also makes them central for the progression of many diseases and, as such, makes metalloenzymes attractive targets for therapeutic intervention. Increasing awareness of the role metalloenzymes play in disease and their importance as a class of targets has amplified interest in the development of new strategies to develop inhibitors and ultimately useful drugs. In this Review, we provide a broad overview of several drug discovery efforts focused on metalloenzymes and attempt to map out the current landscape of high-value metalloenzyme targets.

Structure-Activity Relationships in Metal-Binding Pharmacophores for Influenza Endonuclease.

Metalloenzymes represent an important target space for drug discovery. A limitation to the early development of metalloenzyme inhibitors has been the lack of established structure-activity relationships (SARs) for molecules that bind the metal ion cofactor(s) of a metalloenzyme. Herein, we employed a bioinorganic perspective to develop an SAR for inhibition of the metalloenzyme influenza RNA polymerase PAN endonuclease. The identified trends highlight the importance of the electronics of the metal-binding pharmacophore (MBP), in addition to MBP sterics, for achieving improved inhibition and selectivity. By optimization of the MBPs for PAN endonuclease, a class of highly active and selective fragments was developed that displays IC50 values <50 nM. This SAR led to structurally distinct molecules that also displayed IC50 values of ∼10 nM, illustrating the utility of a metal-centric development campaign in generating highly active and selective metalloenzyme inhibitors.

Isosteres of hydroxypyridinethione as drug-like pharmacophores for metalloenzyme inhibition.

Hydroxypyridinethiones (HOPTOs) are strong ligands for metal ions and potentially useful pharmacophores for inhibiting metalloenzymes relevant to human disease. However, HOPTOs have been sparingly used in drug discovery efforts due, in part, to concerns that this scaffold will act as a promiscuous, non-selective metalloenzyme inhibitor, as well as possess poor pharmacokinetics (PK), which may undermine drug candidates containing this functional group. To advance HOPTOs as a useful pharmacophore for metalloenzyme inhibitors, a library of 22 HOPTO isostere compounds has been synthesized and investigated. This library demonstrates that it is possible to maintain the core metal-binding pharmacophore (MBP) while generating diversity in structure, electronics, and PK properties. This HOPTO library has been screened against a set of four different metalloenzymes, demonstrating that while the same metal-binding donor atoms are maintained, there is a wide range of activity between metalloenzyme targets. Overall, this work shows that HOPTO isosteres are useful MBPs and valuable scaffolds for metalloenzyme inhibitors.

High-throughput screening of solid-state catalysts for nerve agent degradation.

A high-throughput screening (HTS) method was devised to increase the rate of discovery and evaluation of nerve agent degradation catalysts. Using this HTS method, >90 solid state materials, predominantly metal-organic frameworks (MOFs), were analyzed for their ability to hydrolyze the nerve agent simulant methyl paraoxon at two pH values (8.0 and 10.0).

Dipicolinic Acid Derivatives as Inhibitors of New Delhi Metallo-ß-lactamase-1.

The efficacy of ß-lactam antibiotics is threatened by the emergence and global spread of metallo-ß-lactamase (MBL) mediated resistance, specifically New Delhi metallo-ß-lactamase-1 (NDM-1). By utilization of fragment-based drug discovery (FBDD), a new class of inhibitors for NDM-1 and two related ß-lactamases, IMP-1 and VIM-2, was identified. On the basis of 2,6-dipicolinic acid (DPA), several libraries were synthesized for structure-activity relationship (SAR) analysis. Inhibitor 36 (IC50 = 80 nM) was identified to be highly selective for MBLs when compared to other Zn(II) metalloenzymes. While DPA displayed a propensity to chelate metal ions from NDM-1, 36 formed a stable NDM-1:Zn(II):inhibitor ternary complex, as demonstrated by 1H NMR, electron paramagnetic resonance (EPR) spectroscopy, equilibrium dialysis, intrinsic tryptophan fluorescence emission, and UV-vis spectroscopy. When coadministered with 36 (at concentrations nontoxic to mammalian cells), the minimum inhibitory concentrations (MICs) of imipenem against clinical isolates of Eschericia coli and Klebsiella pneumoniae harboring NDM-1 were reduced to susceptible levels.

Fragment-Based Identification of Influenza Endonuclease Inhibitors.

The influenza virus is responsible for millions of cases of severe illness annually. Yearly variance in the effectiveness of vaccination, coupled with emerging drug resistance, necessitates the development of new drugs to treat influenza infections. One attractive target is the RNA-dependent RNA polymerase PA subunit. Herein we report the development of inhibitors of influenza PA endonuclease derived from lead compounds identified from a metal-binding pharmacophore (MBP) library screen. Pyromeconic acid and derivatives thereof were found to be potent inhibitors of endonuclease. Guided by modeling and previously reported structural data, several sublibraries of molecules were elaborated from the MBP hits. Structure-activity relationships were established, and more potent molecules were designed and synthesized using fragment growth and fragment merging strategies. This approach ultimately resulted in the development of a lead compound with an IC50 value of 14 nM, which displayed an EC50 value of 2.1 µM against H1N1 influenza virus in MDCK cells.