Targeting the HSP60/10 chaperonin systems of Trypanosoma brucei as a strategy for treating African sleeping sickness

Sulfur (SⅥ)-containing heterocyclic hybrids as antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA) and its SAR

The discovery of new small molecule-based inhibitors is an attractive field in medicinal chemistry. Structurally diversified heterocyclic derivatives have been investigated to combat multi-drug resistant bacterial infections and they offers several mechanism of action. Methicillin-resistant Staphylococcus aureus (MRSA) is becoming more and more deadly to humans because of its simple method of transmission, quick development of antibiotic resistance, and ability to cause hard-to-treat skin and filmy diseases. The sulfur (SVI) particularly sulfonyl and sulfonamide based heterocyclic moieties, have found to be good anti-MRSA agents. The development of new nontoxic, economical and highly active sulfur (SVI) containing derivatives has become hot research topics in drug discovery research. Presently, more than 150 FDA approved Sulfur (SVI)-based drugs are available in the market, and they are widely used to treat various types of diseases with different therapeutic potential. The present collective data provides the latest advancements in Sulfur (SVI)-hybrid compounds as antibacterial agents against MRSA. It also examines the outcomes of in-vitro and in-vivo investigations, exploring potential mechanisms of action and offering alternative perspectives on the structure-activity relationship (SAR). Sulfur (SVI)-hybrids exhibits synergistic effects with existing drugs to provide antibacterial action against MRSA.

Bis-aryl-α,β-unsaturated ketone (ABK) chaperonin inhibitors exhibit selective cytotoxicity to colorectal cancer cells that correlates with levels of aberrant HSP60 in the cytosol

While many studies have established the importance of protein homeostasis in tumor progression, little effort has been made to examine the therapeutic potential of targeting the HSP60 chaperonin system. In healthy cells, HSP60 is localized to the mitochondrial matrix; however, emerging evidence indicates HSP60 can be over-expressed and mis-localized to the cytosol of cancer cells, which is hypothesized to promote tumor cell survival and proliferation. This opens a potential avenue to selectively target the aberrant HSP60 in the cytosol as a chemotherapeutic strategy. In the present work, we examined a series of bis-aryl-α,β-unsaturated ketone (ABK) HSP60 inhibitors for their ability to selectively target cancerous vs non-cancerous colon and intestine cells. We found that lead analogs inhibited migration and clonogenicity of cancer cells, with cytotoxicity correlating with the level of aberrant HSP60 in the cytosol.

Structural Basis of Parasitic HSP90 ATPase Inhibition by Small Molecules

Protozoan parasites are responsible for several harmful and widespread human diseases that cause high morbidity and mortality. Currently available treatments have serious limitations due to poor efficiency, strong adverse effects, and high cost. Hence, the identification of new targets and the development of specific drug therapies against parasitic diseases are urgent needs. Heat shock protein 90 (HSP90) is an ATP-dependent molecular chaperone that plays a key role in parasite survival during the various differentiation stages, spread over the vector insect and the human host, which they undergo during their life cycle. The N-terminal domain (NTD) of HSP90, containing the main determinants for ATPase activity, represents the most druggable domain for inhibitor targeting. The molecules investigated on parasite HSP90 are mainly developed from known inhibitors of the human counterpart, and they have strong limitations due to selectivity issues, accounting for the high conservation of the ATP-binding site between the parasite and human proteins. The current review highlights the recent structural progress made to support the rational design of new molecules able to effectively block the chaperone activity of parasite HSP90.

Effects of Suramin on Polycystic Kidney Disease in a Mouse Model of Polycystin-1 Deficiency

The aberrant activation of the purinergic signaling pathway has been shown to promote cyst growth and fluid secretion in autosomal dominant polycystic kidney disease (ADPKD). Suramin is an anti-parasitic drug that has strong anti-purinergic properties. Whether suramin could have a therapeutic effect on ADPKD has not been fully investigated. We examined the effect of suramin on cyst progression in a Pkd1 microRNAs transgenic mouse model that presented stable Pkd1 knockdown and moderate disease progression. The Pkd1-deficient mice were treated with suramin (60 mg/kg) by intraperitoneal injection twice a week from postnatal days 35 to 90. Kidney-to-body weight ratios, cyst indices, and blood urea nitrogen (BUN) levels were measured. Cell proliferation and macrophage infiltration were determined by immunohistochemistry. The suramin-treated group had significantly lower renal cyst densities, cell proliferation, and macrophage infiltration compared with saline-treated controls. Suramin significantly inhibited ERK phosphorylation and the expression of Il1b, Il6, Nlrp3, Tgfb, Fn1, P2rx7, and P2ry2 mRNAs in the kidneys. However, BUN levels remained high despite the reduction in cyst growth. Furthermore, plasma cystatin C and neutrophil gelatinase-associated lipocalin (NGAL) levels were significantly higher in the suramin-treated group compared with the control group. Periodic acid-Schiff staining revealed degenerative changes and epithelial cell vacuolation in the non-cystic renal tubules, which indicated phospholipidosis following suramin treatment. These results suggest that suramin may reduce renal cyst growth and inflammation, but the associated tubular cell injuries could limit its therapeutic potential. Other purinergic receptor antagonists with less nephrotoxicity may deserve further investigation for the treatment of ADPKD.

In-depth analysis of amino acid and nucleotide sequences of Hsp60: how conserved is this protein?

Chaperonin Hsp60, as a protein found in all organisms, is of great interest in medicine, since it is present in many tissues and can be used both as a drug and as an object of targeted therapy. Hence, Hsp60 deserves a fundamental comparative analysis to assess its evolutionary characteristics. It was found that the percent identity of Hsp60 amino acid sequences both within and between phyla was not high enough to identify Hsp60s as highly conserved proteins. However, their ATP binding sites are largely conserved. The amino acid composition of Hsp60s remained relatively constant. At the same time, the analysis of the nucleotide sequences showed that GC content in the Hsp60 genes was comparable to or greater than the genomic values, which may indicate a high resistance to mutations due to tight control of the nucleotide composition by DNA repair systems. Natural selection plays a dominant role in the evolution of Hsp60 genes. The degree of mutational pressure affecting the Hsp60 genes is quite low, and its direction does not depend on taxonomy. Interestingly, for the Hsp60 genes from Chordata, Arthropoda, and Proteobacteria the exact direction of mutational pressure could not be determined. However, upon further division into classes, it was found that the direction of the mutational pressure for Hsp60 genes from Fish differs from that for other chordates. The direction of the mutational pressure affects the synonymous codon usage bias. The number of high and low represented codons increases with increasing GC content, which can improve codon usage. Special server has been created for bioinformatics analysis of Hsp60: http://oka.protres.ru:4202/.

Heat shock proteins with an emphasis on HSP 60

Heat shock phenomenon is a process by which cells express a set of proteins called heat shock proteins (HSPs) against heat stress. HSPs include several families depending upon the molecular weight of the respective protein. Among the different HSPs, The HSP60 is one of the main components representing the framework of chaperone system. HSP60 plays a myriad number of roles like chaperoning, thermotolerance, apoptosis, cancer, immunology and embryonic development. In this review we discussed briefly the general knowledge and focussed on HSP60 in terms of structure, regulation and function in various physiological and pathological conditions.

Exploiting the HSP60/10 chaperonin system as a chemotherapeutic target for colorectal cancer

Over the past few decades, an increasing variety of molecular chaperones have been investigated for their role in tumorigenesis and as potential chemotherapeutic targets; however, the 60 kDa Heat Shock Protein (HSP60), along with its HSP10 co-chaperone, have received little attention in this regard. In the present study, we investigated two series of our previously developed inhibitors of the bacterial homolog of HSP60/10, called GroEL/ES, for their selective cytotoxicity to cancerous over non-cancerous colorectal cells. We further developed a third "hybrid" series of analogs to identify new candidates with superior properties than the two parent scaffolds. Using a series of well-established HSP60/10 biochemical screens and cell-viability assays, we identified 24 inhibitors (14%) that exhibited > 3-fold selectivity for targeting colorectal cancer over non-cancerous cells. Notably, cell viability EC₅₀ results correlated with the relative expression of HSP60 in the mitochondria, suggesting a potential for this HSP60-targeting chemotherapeutic strategy as emerging evidence indicates that HSP60 is up-regulated in colorectal cancer tumors. Further examination of five lead candidates indicated their ability to inhibit the clonogenicity and migration of colorectal cancer cells. These promising results are the most thorough analysis and first reported instance of HSP60/10 inhibitors being able to selectively target colorectal cancer cells and highlight the potential of the HSP60/10 chaperonin system as a viable chemotherapeutic target.

Potential therapeutic targets shared between leishmaniasis and cancer

The association of leishmaniasis and malignancies in human and animal models has been highlighted in recent years. The misdiagnosis of coexistence of leishmaniasis and cancer and the use of common drugs in the treatment of such diseases prompt us to further survey the molecular biology of Leishmania parasites and cancer cells. The information regarding common expressed proteins, as possible therapeutic targets, in Leishmania parasites and cancer cells is scarce. Therefore, the current study reviews proteins, and investigates the regulation and functions of several key proteins in Leishmania parasites and cancer cells. The up- and down-regulations of such proteins were mostly related to survival, development, pathogenicity, metabolic pathways and vital signalling in Leishmania parasites and cancer cells. The presence of common expressed proteins in Leishmania parasites and cancer cells reveals valuable information regarding the possible shared mechanisms of pathogenicity and opportunities for therapeutic targeting in leishmaniasis and cancers in the future.

Functional Differences between E. coli and ESKAPE Pathogen GroES/GroEL

As the GroES/GroEL chaperonin system is the only bacterial chaperone that is essential under all conditions, we have been interested in the development of GroES/GroEL inhibitors as potential antibiotics. Using Escherichia coli GroES/GroEL as a surrogate, we have discovered several classes of GroES/GroEL inhibitors that show potent antibacterial activity against both Gram-positive and Gram-negative bacteria. However, it remains unknown if E. coli GroES/GroEL is functionally identical to other GroES/GroEL chaperonins and hence if our inhibitors will function against other chaperonins. Herein we report our initial efforts to characterize the GroES/GroEL chaperonins from clinically significant ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). We used complementation experiments in GroES/GroEL-deficient and -null E. coli strains to report on exogenous ESKAPE chaperone function. In GroES/GroEL-deficient (but not knocked-out) E. coli, we found that only a subset of the ESKAPE GroES/GroEL chaperone systems could complement to produce a viable organism. Surprisingly, GroES/GroEL chaperone systems from two of the ESKAPE pathogens were found to complement in E. coli, but only in the strict absence of either E. coli GroEL (P. aeruginosa) or both E. coli GroES and GroEL (E. faecium). In addition, GroES/GroEL from S. aureus was unable to complement E. coli GroES/GroEL under all conditions. The resulting viable strains, in which E. coli groESL was replaced with ESKAPE groESL, demonstrated similar growth kinetics to wild-type E. coli, but displayed an elongated phenotype (potentially indicating compromised GroEL function) at some temperatures. These results suggest functional differences between GroES/GroEL chaperonins despite high conservation of amino acid identity.IMPORTANCE The GroES/GroEL chaperonin from E. coli has long served as the model system for other chaperonins. This assumption seemed valid because of the high conservation between the chaperonins. It was, therefore, shocking to discover ESKAPE pathogen GroES/GroEL formed mixed-complex chaperonins in the presence of E. coli GroES/GroEL, leading to loss of organism viability in some cases. Complete replacement of E. coli groESL with ESKAPE groESL restored organism viability, but produced an elongated phenotype, suggesting differences in chaperonin function, including client specificity and/or refolding cycle rates. These data offer important mechanistic insight into these remarkable machines, and the new strains developed allow for the synthesis of homogeneous chaperonins for biochemical studies and to further our efforts to develop chaperonin-targeted antibiotics.

Analogs of nitrofuran antibiotics are potent GroEL/ES inhibitor pro-drugs

In two previous studies, we identified compound 1 as a moderate GroEL/ES inhibitor with weak to moderate antibacterial activity against Gram-positive and Gram-negative bacteria including Bacillus subtilis, methicillin-resistant Staphylococcus aureus, Klebsiella pneumonia, Acinetobacter baumannii, and SM101 Escherichia coli (which has a compromised lipopolysaccharide biosynthetic pathway making bacteria more permeable to drugs). Extending from those studies, we developed two series of analogs with key substructures resembling those of known antibacterials, nitroxoline (hydroxyquinoline moiety) and nifuroxazide/nitrofurantoin (bis-cyclic-N-acylhydrazone scaffolds). Through biochemical and cell-based assays, we identified potent GroEL/ES inhibitors that selectively blocked E. faecium, S. aureus, and E. coli proliferation with low cytotoxicity to human colon and intestine cells in vitro. Initially, only the hydroxyquinoline-bearing analogs were found to be potent inhibitors in our GroEL/ES-mediated substrate refolding assays; however, subsequent testing in the presence of an E. coli nitroreductase (NfsB) in situ indicated that metabolites of the nitrofuran-bearing analogs were potent GroEL/ES inhibitor pro-drugs. Consequently, this study has identified a new target of nitrofuran-containing drugs, and is the first reported instance of such a unique class of GroEL/ES chaperonin inhibitors. The intriguing results presented herein provide impetus for expanded studies to validate inhibitor mechanisms and optimize this antibacterial class using the respective GroEL/ES chaperonin systems and nitroreductases from E. coli and the ESKAPE bacteria.

TCP1γ Subunit Is Indispensable for Growth and Infectivity of Leishmania donovani

T-complex protein-1 (TCP1) is a ubiquitous group II chaperonin and is known to fold various proteins, such as actin and tubulin. In Leishmania donovani, the γ subunit of TCP1 (LdTCP1γ) has been cloned and characterized. It forms a high-molecular-weight homo-oligomeric complex that performs ATP-dependent protein folding. In the present study, we evaluated the essentiality of the LdTCP1γ gene. Gene replacement studies indicated that LdTCP1γ is essential for parasite survival. The LdTCP1γ single-allele-replacement mutants exhibited slowed growth and decreased infectivity in mouse macrophages compared to the growth and infectivity of the wild-type parasites. Modulation of LdTCP1γ expression in promastigotes also modulated cell cycle progression. Suramin, an antitrypanosomal drug, not only inhibited the luciferase refolding activity of the recombinant LdTCP1γ (rLdTCP1γ) homo-oligomeric complex but also exhibited potential antileishmanial efficacy both in vitro and in vivo The interaction of suramin and LdTCP1γ was further validated by isothermal titration calorimetry. The study suggests LdTCP1γ as a potential drug target and also provides a framework for the development of a new class of drugs.

Multitargeting Compounds: A Promising Strategy to Overcome Multi-Drug Resistant Tuberculosis

Tuberculosis is still an urgent global health problem, mainly due to the spread of multi-drug resistant M. tuberculosis strains, which lead to the need of new more efficient drugs. A strategy to overcome the problem of the resistance insurgence could be the polypharmacology approach, to develop single molecules that act on different targets. Polypharmacology could have features that make it an approach more effective than the classical polypharmacy, in which different drugs with high affinity for one target are taken together. Firstly, for a compound that has multiple targets, the probability of development of resistance should be considerably reduced. Moreover, such compounds should have higher efficacy, and could show synergic effects. Lastly, the use of a single molecule should be conceivably associated with a lower risk of side effects, and problems of drug–drug interaction. Indeed, the multitargeting approach for the development of novel antitubercular drugs have gained great interest in recent years. This review article aims to provide an overview of the most recent and promising multitargeting antitubercular drug candidates.

100 Years of Suramin

Suramin is 100 years old and is still being used to treat the first stage of acute human sleeping sickness, caused by Trypanosoma brucei rhodesiense Suramin is a multifunctional molecule with a wide array of potential applications, from parasitic and viral diseases to cancer, snakebite, and autism. Suramin is also an enigmatic molecule: What are its targets? How does it get into cells in the first place? Here, we provide an overview of the many different candidate targets of suramin and discuss its modes of action and routes of cellular uptake. We reason that, once the polypharmacology of suramin is understood at the molecular level, new, more specific, and less toxic molecules can be identified for the numerous potential applications of suramin.

Sulfated Non-Saccharide Glycosaminoglycan Mimetics as Novel Drug Discovery Platform for Various Pathologies

Glycosaminoglycans (GAGs) are very complex, natural anionic polysaccharides. They are polymers of repeating disaccharide units of uronic acid and hexosamine residues. Owing to their template-free, spatiotemporally-controlled, and enzyme-mediated biosyntheses, GAGs possess enormous polydispersity, heterogeneity, and structural diversity which often translate into multiple biological roles. It is well documented that GAGs contribute to physiological and pathological processes by binding to proteins including serine proteases, serpins, chemokines, growth factors, and microbial proteins. Despite advances in the GAG field, the GAG-protein interface remains largely unexploited by drug discovery programs. Thus, Non-Saccharide Glycosaminoglycan Mimetics (NSGMs) have been rationally developed as a novel class of sulfated molecules that modulate GAG-protein interface to promote various biological outcomes of substantial benefit to human health. In this review, we describe the chemical, biochemical, and pharmacological aspects of recently reported NSGMs and highlight their therapeutic potentials as structurally and mechanistically novel anti-coagulants, anti-cancer agents, anti-emphysema agents, and anti-viral agents. We also describe the challenges that complicate their advancement and describe ongoing efforts to overcome these challenges with the aim of advancing the novel platform of NSGMs to clinical use.

Serological Testing for Mycobacterial Heat Shock Protein Hsp65 Antibody in Health and Diseases

Mycobacterial heat shock protein 65 gene (Hsp65) has been widely used for classification of Mycobacterial species, and detection of Mycobacterial genes by molecular methods and has proven useful in identification of Mycobacterial infection in various clinical conditions. Circulating antibody against Mycobacterial hsp65 has been found in many clinical diseases including autoimmune diseases (Crohn's disease, lupus erythematosus, multiple sclerosis, diabetes, etc.), atherosclerosis and cancers. The prevalence of anti-Hsp65 antibody in the normal healthy population is unknown. We determined the blood levels of antibody against Mycobacterial hsp65 in the normal population represented by 288 blood donors of the American Red Cross and tested the blood of 109 patients with Crohn's disease and 28 patients with Sjogren's syndrome for comparison. The seroprevalence of anti-Hsp65 IgG in the normal population of Red Cross donors was 2.8% (8 of 288 positive). The Hsp65 antibody levels were significantly elevated in patients with Crohn's disease and Sjogren's syndrome. The prevalence of Hsp65 antibody in Crohn's disease patients was 67.9% (74 of 109 patients), and 85.7% for Sjogren's patients (24 of 28 patients). Our data indicate that anti-Hsp65 antibody is rare in the normal population, but frequent in chronic diseases. The presence of circulating Hsp65 antibody reflects an abnormal immune (adaptive) response to Mycobacterial exposure in patients with chronic diseases, thus differentiating the patients with chronic diseases from those clinical mimics.

Small Molecule Inhibitors Targeting the Heat Shock Protein System of Human Obligate Protozoan Parasites

Obligate protozoan parasites of the kinetoplastids and apicomplexa infect human cells to complete their life cycles. Some of the members of these groups of parasites develop in at least two systems, the human host and the insect vector. Survival under the varied physiological conditions associated with the human host and in the arthropod vectors requires the parasites to modulate their metabolic complement in order to meet the prevailing conditions. One of the key features of these parasites essential for their survival and host infectivity is timely expression of various proteins. Even more importantly is the need to keep their proteome functional by maintaining its functional capabilities in the wake of physiological changes and host immune responses. For this reason, molecular chaperones (also called heat shock proteins)-whose role is to facilitate proteostasis-play an important role in the survival of these parasites. Heat shock protein 90 (Hsp90) and Hsp70 are prominent molecular chaperones that are generally induced in response to physiological stress. Both Hsp90 and Hsp70 members are functionally regulated by nucleotides. In addition, Hsp70 and Hsp90 cooperate to facilitate folding of some key proteins implicated in cellular development. In addition, Hsp90 and Hsp70 individually interact with other accessory proteins (co-chaperones) that regulate their functions. The dependency of these proteins on nucleotide for their chaperone function presents an Achille's heel, as inhibitors that mimic ATP are amongst potential therapeutic agents targeting their function in obligate intracellular human parasites. Most of the promising small molecule inhibitors of parasitic heat shock proteins are either antibiotics or anticancer agents, whose repurposing against parasitic infections holds prospects. Both cancer cells and obligate human parasites depend upon a robust protein quality control system to ensure their survival, and hence, both employ a competent heat shock machinery to this end. Furthermore, some inhibitors that target chaperone and co-chaperone networks also offer promising prospects as antiparasitic agents. The current review highlights the progress made so far in design and application of small molecule inhibitors against obligate intracellular human parasites of the kinetoplastida and apicomplexan kingdoms.

Dual-targeting GroEL/ES chaperonin and protein tyrosine phosphatase B (PtpB) inhibitors: A polypharmacology strategy for treating Mycobacterium tuberculosis infections

Current treatments for Mycobacterium tuberculosis infections require long and complicated regimens that can lead to patient non-compliance, increasing incidences of antibiotic-resistant strains, and lack of efficacy against latent stages of disease. Thus, new therapeutics are needed to improve tuberculosis standard of care. One strategy is to target protein homeostasis pathways by inhibiting molecular chaperones such as GroEL/ES (HSP60/10) chaperonin systems. M. tuberculosis has two GroEL homologs: GroEL1 is not essential but is important for cytokine-dependent granuloma formation, while GroEL2 is essential for survival and likely functions as the canonical housekeeping chaperonin for folding proteins. Another strategy is to target the protein tyrosine phosphatase B (PtpB) virulence factor that M. tuberculosis secretes into host cells to help evade immune responses. In the present study, we have identified a series of GroEL/ES inhibitors that inhibit M. tuberculosis growth in liquid culture and biochemical function of PtpB in vitro. With further optimization, such dual-targeting GroEL/ES and PtpB inhibitors could be effective against all stages of tuberculosis - actively replicating bacteria, bacteria evading host cell immune responses, and granuloma formation in latent disease - which would be a significant advance to augment current therapeutics that primarily target actively replicating bacteria.

HSP60/10 chaperonin systems are inhibited by a variety of approved drugs, natural products, and known bioactive molecules

All living organisms contain a unique class of molecular chaperones called 60 kDa heat shock proteins (HSP60 - also known as GroEL in bacteria). While some organisms contain more than one HSP60 or GroEL isoform, at least one isoform has always proven to be essential. Because of this, we have been investigating targeting HSP60 and GroEL chaperonin systems as an antibiotic strategy. Our initial studies focused on applying this antibiotic strategy for treating African sleeping sickness (caused by Trypanosoma brucei parasites) and drug-resistant bacterial infections (in particular Methicillin-resistant Staphylococcus aureus - MRSA). Intriguingly, during our studies we found that three known antibiotics - suramin, closantel, and rafoxanide - were potent inhibitors of bacterial GroEL and human HSP60 chaperonin systems. These findings prompted us to explore what other approved drugs, natural products, and known bioactive molecules might also inhibit HSP60 and GroEL chaperonin systems. Initial high-throughput screening of 3680 approved drugs, natural products, and known bioactives identified 161 hit inhibitors of the Escherichia coli GroEL chaperonin system (4.3% hit rate). From a purchased subset of 60 hits, 29 compounds (48%) re-confirmed as selective GroEL inhibitors in our assays, all of which were nearly equipotent against human HSP60. These findings illuminate the notion that targeting chaperonin systems might be a more common occurrence than we previously appreciated. Future studies are needed to determine if the in vivo modes of action of these approved drugs, natural products, and known bioactive molecules are related to GroEL and HSP60 inhibition.

Hydroxybiphenylamide GroEL/ES Inhibitors Are Potent Antibacterials against Planktonic and Biofilm Forms of Staphylococcus aureus

We recently reported the identification of a GroEL/ES inhibitor (1, N-(4-(benzo[ d]thiazol-2-ylthio)-3-chlorophenyl)-3,5-dibromo-2-hydroxybenzamide) that exhibited in vitro antibacterial effects against Staphylococcus aureus comparable to vancomycin, an antibiotic of last resort. To follow up, we have synthesized 43 compound 1 analogs to determine the most effective functional groups of the scaffold for inhibiting GroEL/ES and killing bacteria. Our results identified that the benzothiazole and hydroxyl groups are important for inhibiting GroEL/ES-mediated folding functions, with the hydroxyl essential for antibacterial effects. Several analogs exhibited >50-fold selectivity indices between antibacterial efficacy and cytotoxicity to human liver and kidney cells in cell culture. We found that MRSA was not able to easily generate acute resistance to lead inhibitors in a gain-of-resistance assay and that lead inhibitors were able to permeate through established S. aureus biofilms and maintain their bactericidal effects.

Sulfonamido-2-arylbenzoxazole GroEL/ES Inhibitors as Potent Antibacterials against Methicillin-Resistant Staphylococcus aureus (MRSA)

Extending from a study we recently published examining the antitrypanosomal effects of a series of GroEL/ES inhibitors based on a pseudosymmetrical bis-sulfonamido-2-phenylbenzoxazole scaffold, here, we report the antibiotic effects of asymmetric analogs of this scaffold against a panel of bacteria known as the ESKAPE pathogens ( Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). While GroEL/ES inhibitors were largely ineffective against K. pneumoniae, A. baumannii, P. aeruginosa, and E. cloacae (Gram-negative bacteria), many analogs were potent inhibitors of E. faecium and S. aureus proliferation (Gram-positive bacteria, EC₅₀ values of the most potent analogs were in the 1-2 μM range). Furthermore, even though some compounds inhibit human HSP60/10 biochemical functions in vitro (IC₅₀ values in the 1-10 μM range), many of these exhibited moderate to low cytotoxicity to human liver and kidney cells (CC₅₀ values > 20 μM).

Toward Developing Chemical Modulators of Hsp60 as Potential Therapeutics

The 60 kDa heat shock protein (Hsp60) is classically known as a mitochondrial chaperonin protein working together with co-chaperonin 10 kDa heat shock protein (Hsp10). This chaperonin complex is essential for folding proteins newly imported into mitochondria. However, Hsp60, and/or Hsp10 have also been shown to reside in other subcellular compartments including extracellular space, cytosol, and nucleus. The proteins in these extra-mitochondrial compartments may possess a wide range of functions dependent or independent of its chaperoning activity. But the mechanistic details remain unknown. Mutations in Hsp60 gene have been shown to be associated with neurodegenerative disorders. Abnormality in expression level and/or subcellular localization have also been detected from different diseased tissues including inflammatory diseases and various cancers. Therefore, there is a strong interest in developing small molecule modulators of Hsp60. Most of the reported inhibitors were discovered through various chemoproteomics strategies. In this review, we will describe the recent progress in this area with reported inhibitors from both natural products and synthetic compounds. The former includes mizoribine, epolactaene, myrtucommulone, stephacidin B, and avrainvillamide while the latter includes o-carboranylphenoxyacetanilides and gold (III) porphyrins. The potencies of the known inhibitors range from low micromolar to millimolar concentrations. The potential applications of these inhibitors include anti-cancer, anti-inflammatory diseases, and anti-autoimmune diseases.