Milon Mondal

Structure‐Based Design of Inhibitors of the Aspartic Protease Endothiapepsin by Exploiting Dynamic Combinatorial Chemistry

Structure-based design (SBD) can be used for the design and/or optimization of new inhibitors for a biological target. Whereas de novo SBD is rarely used, most reports on SBD are dealing with the optimization of an initial hit. Dynamic combinatorial chemistry (DCC) has emerged as a powerful strategy to identify bioactive ligands given that it enables the target to direct the synthesis of its strongest binder. We have designed a library of potential inhibitors (acylhydrazones) generated from five aldehydes and five hydrazides and used DCC to identify the best binder(s). After addition of the aspartic protease endothiapepsin, we characterized the protein-bound library member(s) by saturation-transfer difference NMR spectroscopy. Cocrystallization experiments validated the predicted binding mode of the two most potent inhibitors, thus demonstrating that the combination of de novo SBD and DCC constitutes an efficient starting point for hit identification and optimization.

Fighting Malaria: Structure-Guided Discovery of Nonpeptidomimetic Plasmepsin Inhibitors

Plasmepsins (Plms) are aspartic proteases involved in the degradation of human hemoglobin by Plasmodium falciparum. Given that the parasite needs the resulting amino acid building blocks for its growth and development, plasmepsins are an important antimalarial drug target. Over the past decade, tremendous progress has been achieved in the development of inhibitors of plasmepsin using two strategies: structure-based drug design (SBDD) and structure-based virtual screening (SBVS). Herein, we review the inhibitors of Plms I-IV developed by SBDD or SBVS with a particular focus on obtaining selectivity versus the human Asp proteases cathepsins and renin and activity in cell-based assays. By use of SBDD, the flap pocket of Plm II has been discovered and constitutes a convenient handle to obtain selectivity. In SBVS, activity against Plms I-IV and selectivity versus cathepsins are not always taken into account. A combination of SBVS, SBDD, and molecular dynamics simulations opens up opportunities for future design cycles.

Fragment Linking and Optimization of Inhibitors of the Aspartic Protease Endothiapepsin : Fragment-Based Drug Design Facilitated by Dynamic Combinatorial Chemistry

Abstract Fragment‐based drug design (FBDD) affords active compounds for biological targets. While there are numerous reports on FBDD by fragment growing/optimization, fragment linking has rarely been reported. Dynamic combinatorial chemistry (DCC) has become a powerful hit‐identification strategy for biological targets. We report the synergistic combination of fragment linking and DCC to identify inhibitors of the aspartic protease endothiapepsin. Based on X‐ray crystal structures of endothiapepsin in complex with fragments, we designed a library of bis‐acylhydrazones and used DCC to identify potent inhibitors. The most potent inhibitor exhibits an IC50 value of 54 nm, which represents a 240‐fold improvement in potency compared to the parent hits. Subsequent X‐ray crystallography validated the predicted binding mode, thus demonstrating the efficiency of the combination of fragment linking and DCC as a hit‐identification strategy. This approach could be applied to a range of biological targets, and holds the potential to facilitate hit‐to‐lead optimization.

Fragment growing exploiting dynamic combinatorial chemistry of inhibitors of the aspartic protease endothiapepsin

Fragment-based drug design (FBDD) has emerged as an efficient hit-identification and/or -optimization strategy with a higher hit rate than high-throughput screening (HTS). Whereas fragment linking is more challenging, fragment growing has become the preferred fragment-optimization strategy, requiring synthesis of derivatives and validation of their binding mode at each step of the optimization cycle. Dynamic combinatorial chemistry (DCC) is a powerful and efficient strategy to identify ligands for biological targets. Here, we have demonstrated that the novel combination of fragment-growing and DCC is a highly powerful strategy to grow a fragment into a more potent, non-covalent inhibitor of the aspartic protease endothiapepsin. We have designed a library of acylhydrazones using fragment growing starting from a known fragment in complex with endothiapepsin. We have used DCC and a fluorescence-based enzymatic assay to identify the best hit(s) from the dynamic combinatorial libraries, displaying double-digit micromolar inhibition of endothiapepsin. In addition, each DCC experiment requires only very small amounts of protein compared with established methods of analysis and the protein needs to be in the assay mixture only for a short period of time, making this protocol ideal for precious and unstable proteins. These results constitute a proof of concept that the combination of fragment growing and DCC is a powerful and efficient strategy to convert a fragment into a hit.

Fragment-Based Drug Design Facilitated by Protein-Templated Click Chemistry: Fragment Linking and Optimization of Inhibitors of the Aspartic Protease Endothiapepsin.

Abstract There is an urgent need for the development of efficient methodologies that accelerate drug discovery. We demonstrate that the strategic combination of fragment linking/optimization and protein‐templated click chemistry is an efficient and powerful method that accelerates the hit‐identification process for the aspartic protease endothiapepsin. The best binder, which inhibits endothiapepsin with an IC50 value of 43 μm, represents the first example of triazole‐based inhibitors of endothiapepsin. Our strategy could find application on a whole range of drug targets.

Furoates and thenoates inhibit pyruvate dehydrogenase kinase 2 allosterically by binding to its pyruvate regulatory site

Abstract The last decade has witnessed the reawakening of cancer metabolism as a therapeutic target. In particular, inhibition of pyruvate dehydrogenase kinase (PDK) holds remarkable promise. Dichloroacetic acid (DCA), currently undergoing clinical trials, is a unique PDK inhibitor in which it binds to the allosteric pyruvate site of the enzyme. However, the safety of DCA as a drug is compromised by its neurotoxicity, whereas its usefulness as an investigative tool is limited by the high concentrations required to exert observable effects in cell culture. Herein, we report the identification – by making use of saturation-transfer difference NMR spectroscopy, enzymatic assays and computational methods – of furoate and thenoate derivatives as allosteric pyruvate-site-binding PDK2 inhibitors. This work substantiates the pyruvate regulatory pocket as a druggable target.

Structure-Based Optimization of Inhibitors of the Aspartic Protease Endothiapepsin.

Aspartic proteases are a class of enzymes that play a causative role in numerous diseases such as malaria (plasmepsins), Alzheimer’s disease (β-secretase), fungal infections (secreted aspartic proteases), and hypertension (renin). We have chosen endothiapepsin as a model enzyme of this class of enzymes, for the design, preparation and biochemical evaluation of a new series of inhibitors of endothiapepsin. Here, we have optimized a hit, identified by de novo structure-based drug design (SBDD) and DCC, by using structure-based design approaches focusing on the optimization of an amide–π interaction. Biochemical results are in agreement with SBDD. These results will provide useful insights for future structure-based optimization of inhibitors for the real drug targets as well as insights into molecular recognition.

Dynamic combinatorial chemistry

Dynamic combinatorial chemistry (DCC) has emerged as a powerful strategy to identify ligands for biological targets given that it enables the target to direct the synthesis and amplification of its strongest binder(s) from the library of interconverting compounds. Since the first report of DCC applied to the discovery of binders for a protein, this elegant tool has been employed on a range of protein targets at various stages of medicinal-chemistry projects. A series of suitable, reversible reactions that are biocompatible have been established and the portfolio of analytical techniques is growing. Despite progress, in most cases, the libraries employed remain of moderate size. We present here the most recent advances in the field of DCC applied to protein targets, paying particular attention to the experimental conditions and analytical methods chosen.