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.

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 optimizing the MBPs for PAN endonuclease, a class of highly active and selective fragments were developed that display 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.

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.

The principle of isosteres or bioisosteres in medicinal chemistry is a central and essential concept in modern drug discovery. For example, carboxylic acids are often replaced by bioisosteres to mitigate issues related to lipophilicity or acidity while retaining acidic characteristics in addition to hydrogen bond donor/acceptor abilities. Separately, the development of metal-binding pharmacophores (MBPs) for binding to the active site metal ion in metalloenzymes of therapeutic interest is an emerging area in the realm of fragment-based drug discovery (FBDD). The direct application of the bioisostere concept to MBPs has not been well-described or systematically investigated. Herein, the picolinic acid MBP is used as a case study for the development of MBP isosteres (so-called MBIs). Many of these isosteres are novel compounds, and data on their physicochemical properties, metal binding capacity, and metalloenzyme inhibition characteristics are presented. The results show that MBIs of picolinic acid generally retain metal coordinating properties and exhibit predictable metalloenzyme inhibitory activity while possessing a broad range of physicochemical properties (e.g., p K, log P). These findings demonstrate the use of bioisosteres results in an untapped source of metal binding functional groups suitable for metalloenzyme FBDD. These MBIs provide a previously unexplored route for modulating the physicochemical properties of metalloenzyme inhibitors and improving their drug-likeness.

Polymer–MOF hybrid materials (polyMOFs) are shown to adhere to the principle of isoreticular expansion, generating polyMOFs with large surface areas and enhanced stability.