Structure-Based Optimization of Covalent, Small-Molecule Stabilizers of the 14-3-3σ/ERα Protein-Protein Interaction from Nonselective Fragments

The stabilization of protein-protein interactions (PPIs) has emerged as a promising strategy in chemical biology and drug discovery. The identification of suitable starting points for stabilizing native PPIs and their subsequent elaboration into selective and potent molecular glues lacks structure-guided optimization strategies. We have previously identified a disulfide fragment that stabilized the hub protein 14-3-3σ bound to several of its clients, including ERα and C-RAF. Here, we show the structure-based optimization of the nonselective fragment toward selective and highly potent small-molecule stabilizers of the 14-3-3σ/ERα complex. The more elaborated molecular glues, for example, show no stabilization of 14-3-3σ/C-RAF up to 150 μM compound. Orthogonal biophysical assays, including mass spectrometry and fluorescence anisotropy, were used to establish structure-activity relationships. The binding modes of 37 compounds were elucidated with X-ray crystallography, which further assisted the concomitant structure-guided optimization. By targeting specific amino acids in the 14-3-3σ/ERα interface and locking the conformation with a spirocycle, the optimized covalent stabilizer 181 achieved potency, cooperativity, and selectivity similar to the natural product Fusicoccin-A. This case study showcases the value of addressing the structure, kinetics, and cooperativity for molecular glue development. </p

From Tethered to Freestanding Stabilizers of 14-3-3 Protein-Protein Interactions through Fragment Linking

Small-molecule stabilization of protein-protein interactions (PPIs) is a promising strategy in chemical biology and drug discovery. However, the systematic discovery of PPI stabilizers remains a largely unmet challenge. Herein we report a fragment-linking approach targeting the interface of 14-3-3 and a peptide derived from the estrogen receptor alpha (ERα) protein. Two classes of fragments—a covalent and a noncovalent fragment—were co-crystallized and subsequently linked, resulting in a noncovalent hybrid molecule in which the original fragment interactions were largely conserved. Supported by 20 crystal structures, this initial hybrid molecule was further optimized, resulting in selective, 25-fold stabilization of the 14-3-3/ERα interaction. The high-resolution structures of both the single fragments, their co-crystal structures and those of the linked fragments document a feasible strategy to develop orthosteric PPI stabilizers by linking to an initial tethered fragment.</p

2.3 Å resolution cryo-EM structure of human p97 and mechanism of allosteric inhibition

p97 is a hexameric AAA ATPase that is an attractive target for cancer drug development. Here, we report cryo-EM structures for ADP-bound, full-length, hexameric wild-type p97 in the presence and absence of an allosteric inhibitor at resolutions of 2.3 Å and 2.4 Å, respectively. We also report cryo-EM structures at ~ 3.3 Å, 3.2 Å and 3.3 Å resolutions respectively, for three distinct, co-existing functional states of p97 with occupancies of 0, 1 or 2 molecules of ATPγS per protomer. A large corkscrew-like change in molecular architecture coupled with upward displacement of the N-domain is observed only when ATPγS is bound to both D1 and D2 domains. These cryo-EM structures establish the sequence of nucleotide-driven structural changes in p97 at atomic resolution. They also enable elucidation of the binding mode of an allosteric small molecule inhibitor to p97 and illustrate how inhibitor binding at the interface between D1 and D2 domains prevents propagation of the conformational changes necessary for p97 function

Allosteric Indole Amide Inhibitors of p97: Identification of a Novel Probe of the Ubiquitin Pathway

A high-throughput screen to discover inhibitors of p97 ATPase activity identified an indole amide that bound to an allosteric site of the protein. Medicinal chemistry optimization led to improvements in potency and solubility. Indole amide 3 represents a novel uncompetitive inhibitor with excellent physical and pharmaceutical properties that can be used as a starting point for drug discovery efforts

Total synthesis of the structure of the putative landomycin aglycone, revision of the structure and studies directed toward the synthesis of the proposed structure of the landomycin aglycone.

As an extension of our program towards the total synthesis of carbohydrate natural products, we became interested in landomycin A almost ten years ago. Landomycin A is the largest anti-tumor antibiotic of the angucycline family and has been shown to interact with DNA and inhibit cell cycle progression from the G0 to S phase as well as to possess activity against 60 cancerous cell lines. Our interest in this molecule stems both from the complex nature of the hexasaccharide chain, which features six 2,6-di-deoxysugars, as well as the delicate tetracyclic aglycone. Our synthesis of the hexasaccharide was completed in 1999, at which time, work on the aglycone began. The synthesis of the reported structure of the landomycin aglycone featured a late stage, intramolecular Michael addition to a quinone to generate the desired tetracycle. The substrate for this reaction was generated by a Dotz benzannulation reaction of a Fischer carbene derived from hydroquinone and a functionalized, mono-substituted alkyne. Upon completion of the synthesis, spectral data from the synthetic material failed to match that reported for the natural aglycone. After investigating any possible issues of conformational isomerism being responsible for the spectral disparity, we concluded the structure of the natural product had been mis-assigned. Based on examination and comparison of the spectral data for the synthetic and natural material, as well as a derivative of each, an alternate structure was proposed. The alternate structure differs from the reported structure only by the regiochemistry of a single alcohol. Four approaches towards the synthesis of the alternate structure have been investigated. Dotz benzannulation was again used to provide advanced intermediates to attempt an intramolecular Michael addition, however in this case the Michael closure was not successful. Another approach involved late-stage epoxidation followed by reductive oxirane opening. This scheme proved untenable due to side oxidations undergone by the electron rich aromatic substrate in lieu of epoxidation. Radical mediated closure was attempted, but failed owing to the demanding steric environment around the radical precursor. A final approach entailed an intramolecular Heck reaction to close the tetracyclic aglycone. This route failed to provide the desired product of simple ring closure, producing instead a structurally interesting pentacyclic ketone.Ph.D.Organic chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123921/2/3106135.pd

Structure-Activity Relationships for Inhibition of Cysteine Protease Activity and Development of Plasmodium falciparum by Peptidyl Vinyl Sulfones

The Plasmodium falciparum cysteine proteases falcipain-2 and falcipain-3 appear to be required for hemoglobin hydrolysis by intraerythrocytic malaria parasites. Previous studies showed that peptidyl vinyl sulfone inhibitors of falcipain-2 blocked the development of P. falciparum in culture and exerted antimalarial effects in vivo. We now report the structure-activity relationships for inhibition of falcipain-2, falcipain-3, and parasite development by 39 new vinyl sulfone, vinyl sulfonate ester, and vinyl sulfonamide cysteine protease inhibitors. Levels of inhibition of falcipain-2 and falcipain-3 were generally similar, and many potent compounds were identified. Optimal antimalarial compounds, which inhibited P. falciparum development at low nanomolar concentrations, were phenyl vinyl sulfones, vinyl sulfonate esters, and vinyl sulfonamides with P(2) leucine moieties. Our results identify independent structural correlates of falcipain inhibition and antiparasitic activity and suggest that peptidyl vinyl sulfones have promise as antimalarial agents

TPT sulfonate, a single, oral dose schistosomicidal prodrug: In vivo efficacy, disposition and metabolic profiling.

Treatment of schistosomiasis relies precariously on just one drug, praziquantel (PZQ). In the search for alternatives, 15 S-[2-(alkylamino)alkane] thiosulfuric acids were obtained from a previous research program and profiled in mice for efficacy against both mature (&gt;42-day-old) and juvenile (21-day-old) Schistosoma mansoni using a screening dose of 100 mg/kg PO QDx4. One compound, S-[2-(tert-butylamino)-1-phenylethane] thiosulfuric acid (TPT sulfonate), was the most effective by decreasing female and male worm burdens by ≥ 90% and ≥46% (mature), and ≥89% and ≥79% (juvenile), respectively. In contrast, PZQ decreased mature female and male worm burdens by 95% and 94%, respectively, but was ineffective against juvenile stages. Against 7-day-old lung-stage worms, TPT sulfonate was only effective at twice the dose decreasing female and male burdens by 95 and 80%, respectively. Single oral doses at 400 and/or 600 mg/kg across various developmental time-points (1-, 7-, 15-, 21- and/or 42 day-old) were consistent with the QD x4 data; efficacy was strongest once the parasites had completed lung migration, and female and male burdens were decreased by at least 90% and 80%, respectively. In vitro, TPT sulfonate is inactive against the parasite suggesting a pro-drug mechanism of action. In mice, TPT sulfonate is fully absorbed and subject to rapid, non-CYP-mediated, first-pass metabolism that is initiated by desulfation and yields a series of metabolites. The initially-formed free thiol-containing metabolite, termed TP thiol, was chemically synthesized; it dose-dependently decreased S. mansoni and Schistosoma haematobium motility in vitro. Also, when administered as a single 50 mg/kg IP dose, TP thiol decreased 33-day-old S. mansoni female and male burdens by 35% and 44%, with less severe organomegaly. Overall, TPT sulfonate's efficacy profile is competitive with that of PZQ. Also, the characterization of a parasiticidal metabolite facilitates an understanding and improvement of the chemistry, and identification of the mechanism of action and/or target