Small molecules with structural similarities to siderophores as novel antimicrobials against Mycobacterium tuberculosis and Yersinia pestis

Abstract

Drugs inhibiting the iron scarcity-induced, siderophore-mediated iron scavenging systems of Mycobacterium tuberculosis (Mtb) and Yersinia pestis (Yp) may provide new therapeutic lines of defense. Compounds with structural similarities to siderophores were synthesized and evaluated as antimicrobials against Yp and Mtb under iron limiting conditions, which mimic the iron scarcity these pathogens encounter and must adapt to in the host, and under standard iron rich conditions for comparison. New antimicrobials were identified, some of which warrant exploration as initial leads against potentially novel targets and small-molecule tools to assist in the elucidation of targets specific to iron-scarcity adapted Yp and Mtb. KeywordsSiderophore; Antimicrobial; drug target; Mycobacterium tuberculosis; Yersinia pestis; arylcarbothioamide-pyrazolines Mtb, the etiologic agent of tuberculosis, and Yp, the causative agent of plague and a potential agent of biowarfare and bioterrorism, are pathogens with serious impacts on global public health. MDR tuberculosis is an emerging pandemic and the surfacing of extensive drugresistant (XDR) tuberculosis poses a new global threat. 1,2 Plague is a re-emerging disease and the occurrence of MDR Yp strains and self-transferable Yp plasmids conferring antibiotic resistance raises concerns about future plague control. 3,4 These scenarios underscore the need for expanding the anti-tuberculosis and anti-plague drug repertoires. Anti-infective drugs against in vivo conditionally essential targets may offer novel therapeutic possibilities, help the fight against MDR/XDR strains and the prevention of their selection and dissemination, and increase biodefense preparedness. 5 *Corresponding authors: LENQ: Tel.: +1 212 746 4497, e-mail: leq2001@med.cornell.edu; JV: Tel.: +91-651-2275843, e-mail: venkatesanj@bitmesra.ac.in. † These authors contributed equally Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access, their production is induced under iron scarcity, and they are believed to be required for scavenging iron inside the host, where free iron is scarce (10 −25 -10 −15 M) and pathogens experience iron-limiting conditions. 6,7 The Mtb siderophore-deficient mutant is impaired for growth in macrophages and iron-limiting culture medium. 8 The Mtb mutant lacking the IrtAB ferri-siderophore uptake system is impaired for multiplication in macrophages, mouse lung, and iron-limiting medium. 9 Siderophore system-deficient Yp strains are avirulent in mice infected subcutaneously (a route imitating the fleabite transmission of Yp) and unable t...

Mutational and Phylogenetic Analyses of the Mycobacterial mbt Gene Cluster

“…M. smegmatis strain mc 2 155 (ATCC 700084) and its derivatives were routinely cultured under standard conditions in Middlebrook 7H9 broth (Difco) supplemented with 10% ADN (5% bovine serum albumin [BSA], 2% dextrose, 0.85% NaCl) and 0.05% Tween 80 (supplemented 7H9 broth) or on Middlebrook 7H11 agar (Difco) with ADN (supplemented 7H11 agar) (31). For analysis of MBT production, M. smegmatis cells were grown in iron-limiting GASTD medium (9,42). Escherichia coli DH5␣ (Invitrogen) cells were cultured under standard conditions in LuriaBertani medium (40).…”

“…MBT extraction and analysis were carried out according to previously reported methodologies (9). Briefly, exponential-phase cultures grown in GASTD (9,42) were diluted in fresh medium to an optical density at 595 nm (OD 595 ) of 0.6 and loaded into 24-well plates (1 ml/well). [ 14 C]salicylic acid (specific activity of 55 Ci/mol; American Radiolabeled Chemicals, Inc.) was added to the growth medium at 0.1 Ci/ml to produce 14 C-labeled MBT as reported previously (9).…”

“…This antibacterial inhibits a salicylic acid adenylation step of the MBT biosynthetic pathway (36), blocks siderophore production in M. tuberculosis, and restricts the growth of the pathogen with greater potency under iron-limiting conditions, where the siderophore system is crucial for the acquisition of essential iron (9). In addition, potent antimicrobial activity against M. tuberculosis has been reported for potential siderophore-mediated iron uptake inhibitors with structural features resembling the hydroxyphenyl-oxazoline-containing half of MBT (42).…”

Inactivation of tesA Reduces Cell Wall Lipid Production and Increases Drug Susceptibility in Mycobacteria

“…Antibiotic Susceptibility Assays-Dose-response experiments using standard 2/3-fold-microdilution assays in a 96-well plate platform were performed as reported (34). Cultures started at an A 595 of 0.005 were grown in 7H9 containing the antibiotic being tested and kanamycin (for plasmid maintenance).…”

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“…Penicillins containing a thiazole ring system (thiazolidine) 20 are also important naturally occurring products. Thiazoles and their derivatives are found to be associated with various biological activities such as antimicrobial 21,22 , antituberculosis 23 , and anti-HIV 24 activities. In the interest of the above suggestion, the present investigation was planned to synthesize a system that combines together two biolabile components that are 2-pyrazolines and thiazoles or oxazole, to give a compact structure like the title compounds.…”