Daniel W. Carney

Restriction of the Conformational Dynamics of the Cyclic Acyldepsipeptide Antibiotics Improves Their Antibacterial Activity

The cyclic acyldepsipeptide (ADEP) antibiotics are a new class of antibacterial agents that kill bacteria via a mechanism that is distinct from all clinically used drugs. These molecules bind and dysregulate the activity of the ClpP peptidase. The potential of these antibiotics as antibacterial drugs has been enhanced by the elimination of pharmacological liabilities through medicinal chemistry efforts. Here, we demonstrate that the ADEP conformation observed in the ADEP-ClpP crystal structure is fortified by transannular hydrogen bonding and can be further stabilized by judicious replacement of constituent amino acids within the peptidolactone core structure with more conformationally constrained counterparts. Evidence supporting constraint of the molecule into the bioactive conformer was obtained by measurements of deuterium-exchange kinetics of hydrogens that were proposed to be engaged in transannular hydrogen bonds. We show that the rigidified ADEP analogs bind and activate ClpP at lower concentrations in vitro. Remarkably, these compounds have up to 1200-fold enhanced antibacterial activity when compared to those with the peptidolactone core structure common to two ADEP natural products. This study compellingly demonstrates how rational modulation of conformational dynamics may be used to improve the bioactivities of natural products.

A Retrograde Trafficking Inhibitor of Ricin and Shiga-Like Toxins Inhibits Infection of Cells by Human and Monkey Polyomaviruses

ABSTRACT Polyomaviruses are ubiquitous pathogens that cause severe disease in immunocompromised individuals. JC polyomavirus (JCPyV) is the causative agent of the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML), whereas BK polyomavirus (BKPyV) causes polyomavirus-induced nephropathy and hemorrhagic cystitis. Vaccines or antiviral therapies targeting these viruses do not exist, and treatments focus on reducing the underlying causes of immunosuppression. We demonstrate that retro-2cycl, an inhibitor of ricin and Shiga-like toxins (SLTs), inhibits infection by JCPyV, BKPyV, and simian virus 40. Retro-2cycl inhibits retrograde transport of polyomaviruses to the endoplasmic reticulum, a step necessary for productive infection. Retro-2cycl likely inhibits polyomaviruses in a way similar to its ricin and SLT inhibition, suggesting an overlap in the cellular host factors used by bacterial toxins and polyomaviruses. This work establishes retro-2cycl as a potential antiviral therapy that broadly inhibits polyomaviruses and possibly other pathogens that use retrograde trafficking. IMPORTANCE The human polyomaviruses JC polyomavirus (JCPyV) and BK polyomavirus (BKPyV) cause rare but severe diseases in individuals with reduced immune function. During immunosuppression, JCPyV disseminates from the kidney to the central nervous system and destroys oligodendrocytes, resulting in the fatal disease progressive multifocal leukoencephalopathy. Kidney transplant recipients are at increased risk of BKPyV-induced nephropathy, which results in kidney necrosis and loss of the transplanted organ. There are currently no effective therapies for JCPyV and BKPyV. We show that a small molecule named retro-2cycl protects cells from infection with JCPyV and BKPyV by inhibiting intracellular viral transport. Retro-2cycl treatment reduces viral spreading in already established infections and may therefore be able to control infection in affected patients. Further optimization of retro-2cycl may result in the development of an effective antiviral therapy directed toward pathogens that use retrograde trafficking to infect their hosts. The human polyomaviruses JC polyomavirus (JCPyV) and BK polyomavirus (BKPyV) cause rare but severe diseases in individuals with reduced immune function. During immunosuppression, JCPyV disseminates from the kidney to the central nervous system and destroys oligodendrocytes, resulting in the fatal disease progressive multifocal leukoencephalopathy. Kidney transplant recipients are at increased risk of BKPyV-induced nephropathy, which results in kidney necrosis and loss of the transplanted organ. There are currently no effective therapies for JCPyV and BKPyV. We show that a small molecule named retro-2cycl protects cells from infection with JCPyV and BKPyV by inhibiting intracellular viral transport. Retro-2cycl treatment reduces viral spreading in already established infections and may therefore be able to control infection in affected patients. Further optimization of retro-2cycl may result in the development of an effective antiviral therapy directed toward pathogens that use retrograde trafficking to infect their hosts.

Crystal structure of Mycobacterium tuberculosis ClpP1P2 suggests a model for peptidase activation by AAA+ partner binding and substrate delivery

Significance Caseinolytic peptidase P (ClpP) normally collaborates with ATPases associated with diverse activities (AAA+) partner proteins, such as ClpX and ClpC, to carry out energy-dependent degradation of proteins within cells. The ClpP enzyme from Mycobacterium tuberculosis is required for survival of this human pathogen, is a validated drug target, and is unusual in consisting of discrete ClpP1 and ClpP2 rings. We solved the crystal structure of ClpP1P2 bound to peptides that mimic binding of protein substrates and small molecules that mimic binding of a AAA+ partner and cause unregulated rogue proteolysis. These studies explain why two different ClpP rings are required for peptidase activity and provide a foundation for the rational development of drugs that target ClpP1P2 and kill M. tuberculosis. Caseinolytic peptidase P (ClpP), a double-ring peptidase with 14 subunits, collaborates with ATPases associated with diverse activities (AAA+) partners to execute ATP-dependent protein degradation. Although many ClpP enzymes self-assemble into catalytically active homo-tetradecamers able to cleave small peptides, the Mycobacterium tuberculosis enzyme consists of discrete ClpP1 and ClpP2 heptamers that require a AAA+ partner and protein–substrate delivery or a peptide agonist to stabilize assembly of the active tetradecamer. Here, we show that cyclic acyldepsipeptides (ADEPs) and agonist peptides synergistically activate ClpP1P2 by mimicking AAA+ partners and substrates, respectively, and determine the structure of the activated complex. Our studies establish the basis of heteromeric ClpP1P2 assembly and function, reveal tight coupling between the conformations of each ring, show that ADEPs bind only to one ring but appear to open the axial pores of both rings, provide a foundation for rational drug development, and suggest strategies for studying the roles of individual ClpP1 and ClpP2 rings in Clp-family proteolysis.

Investigation of the configurational stabilities of chiral isocyanoacetates in multicomponent reactions.

Isocyanoacetates are uniquely reactive compounds characterized by an ambivalent isocyano functional group and an enolizable α-carbon. It is widely believed that chiral α-substituted isocyanoacetates are configurationally unstable in some synthetically useful isocyanide-based multicomponent reactions. Herein, we demonstrate that chiral isocyanoacetates can be used with minimal to negligible epimerization in a variety of canonical Ugi four-component condensations as well as Joullié-Ugi three-component condensations, reactions that are particularly useful for constructing complex peptide structures in a single synthetic operation.

Structural optimization of a retrograde trafficking inhibitor that protects cells from infections by human polyoma- and papillomaviruses.

Human polyoma- and papillomaviruses are non-enveloped DNA viruses that cause severe pathologies and mortalities. Under circumstances of immunosuppression, JC polyomavirus causes a fatal demyelinating disease called progressive multifocal leukoencephalopathy (PML) and the BK polyomavirus is the etiological agent of polyomavirus-induced nephropathy and hemorrhagic cystitis. Human papillomavirus type 16, another non-enveloped DNA virus, is associated with the development of cancers in tissues like the uterine cervix and oropharynx. Currently, there are no approved drugs or vaccines to treat or prevent polyomavirus infections. We recently discovered that the small molecule Retro-2(cycl), an inhibitor of host retrograde trafficking, blocked infection by several human and monkey polyomaviruses. Here, we report diversity-oriented syntheses of Retro-2(cycl) and evaluation of the resulting analogs using an assay of human cell infections by JC polyomavirus. We defined structure-activity relationships and also discovered analogs with significantly improved potency as suppressors of human polyoma- and papillomavirus infection in vitro. Our findings represent an advance in the development of drug candidates that can broadly protect humans from non-enveloped DNA viruses and toxins that exploit retrograde trafficking as a means for cell entry.

A Conformationally Constrained Cyclic Acyldepsipeptide Is Highly Effective in Mice Infected with Methicillin-Susceptible and -Resistant Staphylococcus aureus

Background Cyclic acyldepsipeptides (ADEPs) are a novel class of antibacterial agents, some of which (e.g., ADEP 4) are highly active against Gram-positive bacteria. The focus of these in vivo studies is ADEP B315, a rationally designed compound that has the most potent in vitro activity of any ADEP analog reported to date. Methods In vivo efficacy experiments were performed using lethal intraperitoneal mice infection models with a methicillin-sensitive S. aureus (MSSA) and a methicillin-resistant (MRSA) strain. The infected mice were treated with ADEP B315, a des-methyl analog of ADEP 4, vancomycin, or the vehicle used for the ADEPs and their survival was assessed daily. A subset of MSSA-infected mice was sacrificed soon after inoculation and the bacterial burden was measured in their livers and spleens. The toxicity of ADEP B315 was assessed in viability assays using human whole blood cultures. Results In the MSSA experiments, all mice treated with the vehicle succumbed to the infection within 24 hours. All tested compounds were effective in prolonging survival of infected mice (p<0.001). Mice treated with ADEP B315 had a 39% survival rate by 10 days compared to 7% survival in mice treated with a des-methyl ADEP 4 analog (p = 0.017). Survival of the infected mice treated with ADEP B315 was comparable to those treated with vanocmycin (p = 0.12) at the same dose. Further, bacterial burden in the liver and spleen was significantly lower in mice treated with ADEP B315 compared to controls. In the MRSA experiments, ADEP B315 was able to significantly prolong survival compared to mice treated with either the vehicle (p = 0.001) or vancomycin (p = 0.007). ADEP B315 exhibited no significant toxicity in human whole blood cultures at concentrations up to 25 μg/ml. Conclusions ADEP B315 is safe and can cure mice that have lethal infections of methicillin-sensitive and -resistant strains of S. aureus.

Fragment-Based Strategy for Investigating and Suppressing the Efflux of Bioactive Small Molecules.

Membrane protein-mediated drug efflux is a phenomenon that compromises our ability to treat both infectious diseases and cancer. Accordingly, there is much interest in the development of strategies for suppression of the mechanisms by which therapeutic agents are effluxed. Here, using resistance to the cyclic acyldepsipeptide (ADEP) antibacterial agents as a model, we demonstrate a new counter-efflux strategy wherein a fragment of an actively exported bioactive compound competitively interferes with its efflux and potentiates its activity. A fragment comprising the N-heptenoyldifluorophenylalanine side chain of the pharmacologically optimized ADEPs potentiates the antibacterial activity of the ADEPs against actinobacteria to a greater extent than reserpine, a well-known efflux inhibitor. Beyond their validation of a new approach to studying molecular recognition by drug efflux pumps, our findings have important implications for killing Mycobacterium tuberculosis with ADEPs and reclaiming the efficacies of therapeutic agents whose activity has been compromised by efflux pumps.