Article pubs.acs.org/jmc
Discovery of Novel Pyridone-Conjugated Monosulfactams as Potent and Broad-Spectrum Antibiotics for Multidrug-Resistant GramNegative Infections Liang Tan,†,‡ Yunliang Tao,§ Ting Wang,∥ Feng Zou,∥ Shuhua Zhang,∥ Qunhuan Kou,†,‡ Ao Niu,⊥ Qian Chen,†,‡ Wenjing Chu,†,‡ Xiaoyan Chen,†,‡ Haidong Wang,*,§ and Yushe Yang*,†,‡ †
State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China ‡ University of Chinese Academy of Sciences, Beijing 100049, China § College of Biological, Chemical Sciences and Engineering, Jiaxing University, Jiaxing, Zhejiang Province 314001, China ∥ Department of Microbiology, Sichuan Primed Bio-Tech Group Co., Ltd., Chengdu, Sichuan Province 610041, China ⊥ Department of Pharmacology, School of Pharmacy, China Pharmaceutical University, Nanjing, Jiangsu Province 210009, China S Supporting Information *
ABSTRACT: Conjugating a siderophore to an antibiotic is a promising strategy to overcome the permeability-mediated resistance of Gram-negative pathogens. On the basis of the structure of BAL30072, novel pyridone-conjugated monosulfactams incorporating diverse substituents into the methylene linker between the 1,3-dihydroxypyridin-4(1H)-one and the aminothiazole oxime were designed and synthesized. Structure−activity relationship studies revealed that a variety of substituents were tolerated, with isopropyl (compound 12c) and methylthiomethyl (compound 16a) showing the best efficacy against multidrug-resistant (MDR) Gram-negative pathogens. In addition, compound 12c exhibits a good free fraction rate in an in vitro human plasma protein binding test, along with a low clearance and favorable plasma exposure in vivo. In a murine systemic infection model with MDR Klebsiella pneumoniae, compound 12c shows an ED50 of 10.20 mg/kg. Taken together, the results indicate that compound 12c is a promising drug candidate for the treatment of serious infections caused by MDR Gram-negative pathogens.
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INTRODUCTION Infections caused by multidrug-resistant (MDR) bacteria, particularly by Gram-negative pathogens, represent a serious and growing threat to human health. The “ESKAPE” pathogens, such as Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa, are emerging as threatening pathogens.1,2 In particular, the carbapenem-resistant Enterobacteriaceae (CRE, mostly contributed by K. pneumoniae) represent the most worrisome antibiotic resistance crisis, which typically exhibit extremely drug-resistant (XDR) phenotypes, and CRE infections are associated with high mortality rates.2 Despite the dramatic increase prevalence of highly resistant Gram-negative pathogens, there are few treatment options for related infections, besides polymyxins, an old antibiotic class with serious nephrotoxicity issues.2,3 Furthermore, the number of new Gram-negative antibiotic candidates under development is limited and these candidates are not capable of providing coverage against all of the four serious pathogens described above.4,5 Therefore, there is an urgent need for new and broadspectrum Gram-negative antibiotics. © 2017 American Chemical Society
The reduction of outer membrane permeability represents a major mechanism of resistance of Gram-negative pathogens,6−8 and one strategy to circumvent the penetration issue is to exploit the iron uptake pathway of Gram-negative pathogens by conjugating a siderophore to an antibiotic.9 Siderophores are small iron-chelating molecules secreted by bacteria to acquire iron from the environment.10,11 In response to icon deficiency, siderophores are excreted and sequester iron(III), and the resulting complexes are recognized by specific outer membrane receptors and translocated into the microbial cell. Plenty of studies have been reported in the past in understanding the iron binding and recognition processes mentioned above.12−18 This siderophore-mediated iron uptake mechanism is very efficient, microbially selective, and essential for bacteria, making it an important target to circumvent the permeability-mediated resistance of Gram-negative pathogens through a “Trojan Horse” approach.9,19 β-Lactam antibiotics target the penicillinReceived: August 19, 2016 Published: March 13, 2017 2669
DOI: 10.1021/acs.jmedchem.6b01261 J. Med. Chem. 2017, 60, 2669−2684
Journal of Medicinal Chemistry
Article
Figure 1. Compound 1 and pyridone-conjugated monocyclic β-lactams 2−5.
Figure 2. Design of new compounds based on compound 6.
Figure 2),33 a monosulfactam discovered by Basilea Pharmaceutica, has ever been investigated in phase I clinical studies.34 It exhibits potent activity against MDR P. aeruginosa and A. baumannii, including carbapenem-resistant strains.35 In a rat soft tissue infection model, compound 6 was active against most of tested A. baumannii strains.36 However, it was reported to be ineffective against some Enterobacteriaceae, especially for K. pneumoniae,35,37 which would limit its application in the treatment of associated infections. Discovered from products of saprophytic bacteria in 1979, monobactam is a new class of β-lactams characterized by a 2oxoazetidine-1-sulfonic acid moiety.38,39 Initially, extensive structural modifications around the C-3 amide side chain and C-4 positions of the azetidinone ring led to the discovery of aztreonam.40 Subsequently, other acidic and electronegative groups such as phosphonate and O-sulfate groups were investigated for their activating potential at the N-1 position.41−43 As shown in Figure 2, compound 7 (tigemonam) is a monosulfactam activated by an O-sulfate group, and it exhibits high level of oral absorption in laboratory animals.44 Compound 6 was derived from 7 through conjugating 1,3-dihydroxypyridin4(1H)-one to the aminothiazole oxime side chain.33 To date, there has been limited structure−activity relationships (SAR) generated on 6.33,45 The clinical potential of 6, along with its drawbacks, which have been discussed above, encourages further optimization of its structure, which we anticipate would provide opportunities to discover better drug candidates. In this article, we report our recent efforts on this topic, which include the
binding proteins (PBPs), which are located in the periplasm, thus only the outer membrane has to be crossed by β-lactam antibiotics for these compounds to be effective antibacterial agents. Therefore, siderophore-conjugated β-lactam antibiotics comply with the “Trojan Horse” strategy perfectly.9 Natural siderophores most often contain three bidentate ligands for stoichiometric binding of iron(III).11 To reduce this inherent complexity, a large number of simplified conjugates, which incorporate a single bidentate ligand such as a catechol or a hydroxypyridone, have been studied since the 1980s.20−22 One precedent example is compound 1 (S-649266, Figure 1),23 a catechol-conjugated cephalosporin, which has progressed into phase II/III clinical trials.24,25 Among all β-lactam antibiotics, the monocyclic β-lactam subclass is supposedly a preferred drug moiety to conjugate to a siderophore because of their potent antimicrobial activity against Gram-negative bacteria, as well as their resistance to βlactamases, including the metallo-β-lactamases.26 Structures of representative pyridone-conjugated monocyclic β-lactams are shown in Figure 1. Compounds such as 2 (U-78608),27 3 (MC1),28 and 429 are potent monocarbams against P. aeruginosa and resistant to β-lactamases.30 However, the therapeutic potential of these compounds might be limited by their poor hydrolytic stability and high plasma protein binding (PPB).28 Monobactam 5 (MB-1) demonstrates excellent in vitro activity against P. aeruginosa along with an improved PPB profile; however, it was reported to be ineffective in vivo.31,32 None of these compounds have progressed into clinical trials. Compound 6 (BAL30072, 2670
DOI: 10.1021/acs.jmedchem.6b01261 J. Med. Chem. 2017, 60, 2669−2684
Journal of Medicinal Chemistry
Article
Table 1. Antibacterial Activity of Monosulfactams 8−11
MIC (μg/mL)a
a
compd
Eco
Kpn
Aba
Pae
8 9 10 11 6 aztronam meropenem ceftizoxime sodium
4−32 0.25−4 1−8 1−>64 0.25−1 0.5−32 0.125−8 0.5−2
32−>64 4−>64 16−64 8−64 0.25−>64 >64 32−>64 32−>64
16−64 4−64 16−64 8−64 0.5−>64 ≥64 64 32−>64
≥64 64 16−64 64 1−4 4−64 32−64 >64
Eco, E. coli, 5 strains; Kpn, MDR K. pneumoniae, 5 strains; Aba, MDR A. baumannii, 5 strains; Pae, MDR P. aeruginosa, 5 strains.
Table 2. Antibacterial Activity and Physiochemical Properties of Monosulfactams 12−16
MIC (μg/mL)a compd
Eco
Kpn
Aba
Pae
human PPB ( f u)b
stabilityc (degradation) (%)
12a 12b 12c 12d 12e 13a 13b 13c 14a 14b 14c 15a 15b 15c 16a 16b 16c 6
0.06−0.25 0.25−2
