8 research outputs found
Aminopyrazinamides: Novel and Specific GyrB Inhibitors that Kill Replicating and Nonreplicating <i>Mycobacterium tuberculosis</i>
Aminopyrazinamides originated from a high throughput
screen targeting
the <i>Mycobacterium smegmatis</i> (Msm) GyrB ATPase. This
series displays chemical tractability, robust structure–activity
relationship, and potent antitubercular activity. The crystal structure
of Msm GyrB in complex with one of the aminopyrazinamides revealed
promising attributes of specificity against other broad spectrum pathogens
and selectivity against eukaryotic kinases due to novel interactions
at hydrophobic pocket, unlike other known GyrB inhibitors. The aminopyrazinamides
display excellent mycobacterial kill under <i>in vitro</i>, intracellular, and hypoxic conditions
2‑Phenylindole and Arylsulphonamide: Novel Scaffolds Bactericidal against <i>Mycobacterium tuberculosis</i>
A cellular activity-based screen
on <i>Mycobacterium tuberculosis</i> (Mtb) H37Rv using a
focused library from the AstraZeneca corporate
collection led to the identification of 2-phenylindoles and arylsulphonamides,
novel antimycobacterial scaffolds. Both the series were bactericidal <i>in vitro</i> and in an intracellular macrophage infection model,
active against drug sensitive and drug resistant Mtb clinical isolates,
and specific to mycobacteria. The scaffolds showed promising structure–activity
relationships; compounds with submicromolar cellular potency were
identified during the hit to lead exploration. Furthermore, compounds
from both scaffolds were tested for inhibition of known target enzymes
or pathways of antimycobacterial drugs including InhA, RNA polymerase,
DprE1, topoisomerases, protein synthesis, and oxidative-phosphorylation.
Compounds did not inhibit any of the targets suggesting the potential
of a possible novel mode of action(s). Hence, both scaffolds provide
the opportunity to be developed further as leads and tool compounds
to uncover novel mechanisms for tuberculosis drug discovery
Pyrazolopyrimidines Establish MurC as a Vulnerable Target in <i>Pseudomonas aeruginosa</i> and <i>Escherichia coli</i>
The bacterial peptidoglycan biosynthesis
pathway provides multiple
targets for antibacterials, as proven by the clinical success of β-lactam
and glycopeptide classes of antibiotics. The Mur ligases play an essential
role in the biosynthesis of the peptidoglycan building block, <i>N</i>-acetyl-muramic acid-pentapeptide. MurC, the first of four
Mur ligases, ligates l-alanine to UDP-<i>N</i>-acetylmuramic
acid, initiating the synthesis of pentapeptide precursor. Therefore,
inhibiting the MurC enzyme should result in bacterial cell death.
Herein, we report a novel class of pyrazolopyrimidines with subnanomolar
potency against both <i>Escherichia coli</i> and <i>Pseudomonas aeruginosa</i> MurC enzymes, which demonstrates
a concomitant bactericidal activity against efflux-deficient strains.
Radio-labeled precursor incorporation showed these compounds selectively
inhibited peptidoglycan biosynthesis, and genetic studies confirmed
the target of pyrazolopyrimidines to be MurC. In the presence of permeability
enhancers such as colistin, pyrazolopyrimidines exhibited low micromolar
MIC against the wild-type bacteria, thereby, indicating permeability
and efflux as major challenges for this chemical series. Our studies
provide biochemical and genetic evidence to support the essentiality
of MurC and serve to validate the attractiveness of target for antibacterial
discovery
Lead Optimization of 1,4-Azaindoles as Antimycobacterial Agents
In a previous
report, we described the discovery of 1,4-azaindoles, a chemical series
with excellent in vitro and in vivo antimycobacterial potency through
noncovalent inhibition of decaprenylphosphoryl-β-d-ribose-2′-epimerase
(DprE1). Nevertheless, high mouse metabolic turnover and phosphodiesterase
6 (PDE6) off-target activity limited its advancement. Herein, we report
lead optimization of this series, culminating in potent, metabolically
stable compounds that have a robust pharmacokinetic profile without
any PDE6 liability. Furthermore, we demonstrate efficacy for 1,4-azaindoles
in a rat chronic TB infection model. We believe that compounds from
the 1,4-azaindole series are suitable for in vivo combination and
safety studies
Thiazolopyridine Ureas as Novel Antitubercular Agents Acting through Inhibition of DNA Gyrase B
A pharmacophore-based search led
to the identification of thiazolopyridine
ureas as a novel scaffold with antitubercular activity acting through
inhibition of DNA Gyrase B (GyrB) ATPase. Evaluation of the binding
mode of thiazolopyridines in a Mycobacterium tuberculosis (Mtb) GyrB homology model prompted exploration of the side chains
at the thiazolopyridine ring C-5 position to access the ribose/solvent
pocket. Potent compounds with GyrB IC<sub>50</sub> ≤ 1 nM and
Mtb MIC ≤ 0.1 μM were obtained with certain combinations
of side chains at the C-5 position and heterocycles at the C-6 position
of the thiazolopyridine core. Substitutions at C-5 also enabled optimization
of the physicochemical properties. Representative compounds were cocrystallized
with Streptococcus pneumoniae (Spn)
ParE; these confirmed the binding modes predicted by the homology
model. The target link to GyrB was confirmed by genetic mapping of
the mutations conferring resistance to thiazolopyridine ureas. The
compounds are bactericidal in vitro and efficacious in vivo in an
acute murine model of tuberculosis
Azaindoles: Noncovalent DprE1 Inhibitors from Scaffold Morphing Efforts, Kill Mycobacterium tuberculosis and Are Efficacious <i>in Vivo</i>
We report 1,4-azaindoles as a new
inhibitor class that kills Mycobacterium tuberculosis <i>in vitro</i> and demonstrates efficacy in mouse tuberculosis
models. The series emerged from scaffold morphing efforts and was
demonstrated to noncovalently inhibit decaprenylphosphoryl-β-d-ribose2′-epimerase (DprE1). With “drug-like”
properties and no expectation of pre-existing resistance in the clinic,
this chemical class has the potential to be developed as a therapy
for drug-sensitive and drug-resistant tuberculosis
Novel N‑Linked Aminopiperidine-Based Gyrase Inhibitors with Improved hERG and in Vivo Efficacy against Mycobacterium tuberculosis
DNA
gyrase is a clinically validated target for developing drugs
against Mycobacterium tuberculosis (Mtb).
Despite the promise of fluoroquinolones (FQs) as anti-tuberculosis
drugs, the prevalence of pre-existing resistance to FQs is likely
to restrict their clinical value. We describe a novel class of N-linked
aminopiperidinyl alkyl quinolones and naphthyridones that kills Mtb
by inhibiting the DNA gyrase activity. The mechanism of inhibition
of DNA gyrase was distinct from the fluoroquinolones, as shown by
their ability to inhibit the growth of fluoroquinolone-resistant Mtb.
Biochemical studies demonstrated this class to exert its action via
single-strand cleavage rather than double-strand cleavage, as seen
with fluoroquinolones. The compounds are highly bactericidal against
extracellular as well as intracellular Mtb. Lead optimization resulted
in the identification of potent compounds with improved oral bioavailability
and reduced cardiac ion channel liability. Compounds from this series
are efficacious in various murine models of tuberculosis
4‑Aminoquinolone Piperidine Amides: Noncovalent Inhibitors of DprE1 with Long Residence Time and Potent Antimycobacterial Activity
4-Aminoquinolone piperidine amides
(AQs) were identified as a novel
scaffold starting from a whole cell screen, with potent cidality on Mycobacterium tuberculosis (Mtb). Evaluation of the
minimum inhibitory concentrations, followed by whole genome sequencing
of mutants raised against AQs, identified decaprenylphosphoryl-β-d-ribose 2′-epimerase (DprE1) as the primary target responsible
for the antitubercular activity. Mass spectrometry and enzyme kinetic
studies indicated that AQs are noncovalent, reversible inhibitors
of DprE1 with slow on rates and long residence times of ∼100
min on the enzyme. In general, AQs have excellent leadlike properties
and good in vitro secondary pharmacology profile. Although the scaffold
started off as a single active compound with moderate potency from
the whole cell screen, structure–activity relationship optimization
of the scaffold led to compounds with potent DprE1 inhibition (IC<sub>50</sub> < 10 nM) along with potent cellular activity (MIC = 60
nM) against Mtb