Scott J. Hecker

Identification and Characterization of Inhibitors of Multidrug Resistance Efflux Pumps in Pseudomonas aeruginosa: Novel Agents for Combination Therapy

ABSTRACT Whole-cell assays were implemented to search for efflux pump inhibitors (EPIs) of the three multidrug resistance efflux pumps (MexAB-OprM, MexCD-OprJ, MexEF-OprN) that contribute to fluoroquinolone resistance in clinical isolates of Pseudomonas aeruginosa. Secondary assays were developed to identify lead compounds with exquisite activities as inhibitors. A broad-spectrum EPI which is active against all three known Mex efflux pumps from P. aeruginosa and their close Escherichia coli efflux pump homolog (AcrAB-TolC) was discovered. When this compound, MC-207,110, was used, the intrinsic resistance of P. aeruginosa to fluoroquinolones was decreased significantly (eightfold for levofloxacin). Acquired resistance due to the overexpression of efflux pumps was also decreased (32- to 64-fold reduction in the MIC of levofloxacin). Similarly, 32- to 64-fold reductions in MICs in the presence of MC-207,110 were observed for strains with overexpressed efflux pumps and various target mutations that confer resistance to levofloxacin (e.g., gyrA andparC). We also compared the frequencies of emergence of levofloxacin-resistant variants in the wild-type strain at four times the MIC of levofloxacin (1 μg/ml) when it was used either alone or in combination with EPI. In the case of levofloxacin alone, the frequency was ∼10−7 CFU/ml. In contrast, with an EPI, the frequency was below the level of detection (<10−11). In summary, we have demonstrated that inhibition of efflux pumps (i) decreased the level of intrinsic resistance significantly, (ii) reversed acquired resistance, and (iii) resulted in a decreased frequency of emergence of P. aeruginosa strains that are highly resistant to fluoroquinolones.

A Potent and Selective AMPK Activator That Inhibits de Novo Lipogenesis

AMP-activated protein kinase (AMPK) is a heterotrimeric kinase that regulates cellular energy metabolism by affecting energy-consuming pathways such as de novo lipid biosynthesis and glucose production as well as energy-producing pathways such as lipid oxidation and glucose uptake. Accordingly, compounds that activate AMPK represent potential drug candidates for the treatment of hyperlipidemia and type 2 diabetes. Screening of a proprietary library of AMP mimetics identified the phosphonic acid 2 that bears little structural resemblance to AMP but is capable of activating AMPK with high potency (EC50 = 6 nM vs AMP EC50 = 6 μM) and specificity. Phosphonate prodrugs of 2 inhibited de novo lipogenesis in cellular and animal models of hyperlipidemia.

Antibiotic resistance versus small molecules, the chemical evolution

Two discovery approaches directed to addressing the problem of increasing bacterial resistance are described. The first is a program to build activity against methicillin‐resistant Staphylococcus aureus (MRSA) into the cephalosporin class of antibacterials, by enhancing affinity for PBP2a, the penicilln‐binding protein responsible for this resistance. Through stepwise improvement in potency, human serum binding, solubility, and betalactamase stability, a stable of new compunds with excellent potential as anti‐MRSA agents was realized. From this set was chosen MC‐02, 479 (RWJ‐54428), which is now undergoing extensive preclinical evaluation. The second approach explores the uridyl peptide family of antibiotics, inhibitors of bacterial translocase (mraY), whose members include the pacidamycins, mureidomycins, and napsamycins. Access to a diverse set of analogs by total synthesis was catalyzed by the discovery that hydrogenation of the 4′‐exoenamidofuranosyl moiety causes no loss in biological activity. Depthful exploration of SAR required (1) establishment of the absolute stereochemistry of the central diaminobutyric acid (DABA) moiety and (2) determination of the stereochemistry of the 4′‐substituent on the deoxyfuranose unit. The former was accomplished by comparison of DABA derived from degradation of a natural product pacidamycin with a sample synthesized from L‐ threonine. The biological activity of one member of a synthesized library of possible stereoisomers of the natural product established the absolute stereochemistry of the remaining centers. A variety of analogs of the natural product were prepared utilizing the synthetic methods developed, and their biological activities provide important insights into the specificity and spectrum of the antibiotic class.

Synthesis and Biological Evaluation of a Series of Liver-Selective Phosphonic Acid Thyroid Hormone Receptor Agonists and Their Prodrugs

Phosphonic acid (PA) thyroid hormone receptor (TR) agonists were synthesized to exploit the poor distribution of PA-based drugs to extrahepatic tissues and thereby to improve the therapeutic index. Nine PAs showed excellent TR binding affinities (TRbeta(1), K(i) < 10 nM), and most of them demonstrated significant cholesterol lowering effects in a cholesterol-fed rat (CFR) model. Unlike the corresponding carboxylic acid analogue and T(3), PA 22c demonstrated liver-selective effects by inducing maximal mitochondrial glycerol-3-phosphate dehydrogenase activity in rat liver while having no effect in the heart. Because of the low oral bioavailability of PA 22c, a series of prodrugs was synthesized and screened for oral efficacy in the CFR assay. The liver-activated cyclic 1-(3-chlorophenyl)-1,3-propanyl prodrug (MB07811) showed potent lipid lowering activity in the CFR (ED(50) 0.4 mg/kg, po) and good oral bioavailability (40%, rat) and was selected for development for the treatment of hypercholesterolemia.

Synthetic dihydropacidamycin antibiotics: a modified spectrum of activity for the pacidamycin class.

Dihydropacidamycins having an antibacterial spectrum modified from that of the natural product pacidamycins and mureidomycins have been synthesized. Synthetic dihydropacidamycins with noteworthy antibacterial activity against wild-type and resistant Escherichia coli have been identified (MIC=4-8 microg/mL). Some dihydropacidamycins are shown to have activity against multi-resistant clinical strains of Mycobacterium tuberculosis. Compounds of this class are inhibitors of the cell wall biosynthetic enzyme, MraY.

New anti-MRSA cephalosporins with a basic aminopyridine at the C-7 position

Incorporation of a basic aminopyridine into the C-7 position of 3-(amine-substituted arylthio)-3-norcephalosporins, as in 3, afforded high potency against MRSA and acceptable solubility for intravenous administration.

Antiviral Efficacy upon Administration of a HepDirect Prodrug of 2′-C-Methylcytidine to Hepatitis C Virus-Infected Chimpanzees

ABSTRACT Hepatitis C virus (HCV) infects an estimated 170 million individuals worldwide, and the current standard of care, a combination of pegylated interferon alpha and ribavirin, is efficacious in achieving sustained viral response in ∼50% of treated patients. Novel therapies under investigation include the use of nucleoside analog inhibitors of the viral RNA-dependent RNA polymerase. NM283, a 3′-valyl ester prodrug of 2′-C-methylcytidine, has demonstrated antiviral efficacy in HCV-infected patients (N. Afdhal et al., J. Hepatol. 46[Suppl. 1]:S5, 2007; N. Afdhal et al., J. Hepatol. 44[Suppl. 2]:S19, 2006). One approach to increase the antiviral efficacy of 2′-C-methylcytidine is to increase the concentration of the active inhibitory species, the 5′-triphosphate, in infected hepatocytes. HepDirect prodrug technology can increase intracellular concentrations of a nucleoside triphosphate in hepatocytes by introducing the nucleoside monophosphate into the cell, bypassing the initial kinase step that is often rate limiting. Screening for 2′-C-methylcytidine triphosphate levels in rat liver after oral dosing identified 1-[3,5-difluorophenyl]-1,3-propandiol as an efficient prodrug modification. To determine antiviral efficacy in vivo, the prodrug was administered separately via oral and intravenous dosing to two HCV-infected chimpanzees. Circulating viral loads declined by ∼1.4 log10 IU/ml and by >3.6 log10 IU/ml after oral and intravenous dosing, respectively. The viral loads rebounded after the end of dosing to predose levels. The results indicate that a robust antiviral response can be achieved upon administration of the prodrug.

Relationships between structure, antibacterial activity, serum stability, pharmacokinetics and efficacy in 3-(heteroarylthio)cephems. Discovery of RWJ-333441 (MC-04,546).

SAR studies in a series of related 3-(heteroarylthio)cephems determined that a relatively high chemical reactivity of the beta-lactam ring, modulated by electronic effects of substituents at C-3 and C-7, is necessary to achieve high in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA). Such high reactivity results in lowered hydrolytic stability and concomitantly increases susceptibility to beta-lactam ring opening mediated by serum enzymes. Therefore, optimization of anti-MRSA activity versus stability toward serum-mediated degradation required a fine balance of substituent effects. Serum stability studies (measured as percentage of parent drug degraded after 60 min incubation) revealed up to 80-fold difference in degradation rate in a series of closely related (3-heteroarylthio)cephems. Of the compounds evaluated, RWJ-333441 (MC-04,546) possessed the best balance of serum stability (6% degradation after 60 min incubation) and in vitro activity versus MRSA (S. aureus COL MIC=1 microgram/mL). Accordingly, RWJ-333441 displayed excellent in vivo efficacy versus methicillin-susceptible Staphylococcus aureus (MSSA, ED(50)=0.39 mg/kg in mouse sepsis model with S. aureus Smith) and good pharmacokinetic properties in the rat (Cl(total)=0.39 L/h/kg).

Application of hygromycin a structure activity relationships to the antibiotic A201A.

Abstract Replacement of the disaccharide portion of A201A with an allyl ether, with concomitant 3-hydroxylation, affords an analog with biological activity comparable to that of the natural product. The response of biological activity to this modification closely parallels that observed with hygromycin A, which implies that these two natural products may share a common binding site.

Synthesis and vitro antibacterial activity of hygromycin a analogs modified at the C4′ aryl position

Abstract A variety of hygromycin A analogs are described which contain modifications of or replacements for the natural sugar. Antibacterial activities against Serpulina (Treponema) hyodysenteriae , an important animal health pathogen, are reported and indicate that small lipophilic C 4′ substituents serve as useful sugar surrogates in the hygromycin A class.