An adenylated sulfoximine transition-state analogue 1, which inhibits human asparagine synthetase (hASNS) with nanomolar potency, has been reported to suppress the proliferation of an l-asparagine amidohydrolase (ASNase)-resistant MOLT-4 leukemia cell line (MOLT-4R) when l-asparagine is depleted in the medium. We now report the synthesis and biological activity of two new sulfoximine analogues of 1 that have been studied as part of systematic efforts to identify compounds with improved cell permeability and/or metabolic stability. One of these new analogues, an amino sulfoximine 5 having no net charge at cellular pH, is a better hASNS inhibitor (K(I)(∗)=8 nM) than 1 and suppresses proliferation of MOLT-4R cells at 10-fold lower concentration (IC(50)=0.1mM). More importantly, and in contrast to the lead compound 1, the presence of sulfoximine 5 at concentrations above 0.25 mM causes the death of MOLT-4R cells even when ASNase is absent in the culture medium. The amino sulfoximine 5 exhibits different dose-response behavior when incubated with an ASNase-sensitive MOLT-4 cell line (MOLT-4S), supporting the hypothesis that sulfoximine 5 exerts its effect by inhibiting hASNS in the cell. Our work provides further evidence for the idea that hASNS represents a chemotherapeutic target for the treatment of leukemia, and perhaps other cancers, including those of the prostate.
Nicotinamide adenine dinucleotide (NAD+) synthetase catalyzes
the last step in NAD+ biosynthesis. Depletion of NAD+ is
bactericidal for both active and dormant Mycobacterium
tuberculosis (Mtb). By inhibiting NAD+ synthetase (NadE)
from Mtb, we expect to eliminate NAD+ production which will result in
cell death in both growing and nonreplicating Mtb. NadE inhibitors have been
investigated against various pathogens, but few have been tested against Mtb.
Here, we report on the expansion of a series of urea-sulfonamides, previously
reported by Brouillette et al. Guided by docking studies,
substituents on a terminal phenyl ring were varied to understand the
structure-activity-relationships of substituents on this position. Compounds
were tested as inhibitors of both recombinant Mtb NadE and Mtb whole cells.
While the parent compound displayed very weak inhibition against Mtb NadE
(IC50 = 1000 μM), we observed up to a
10-fold enhancement in potency after optimization. Replacement of the
3,4-dichloro group on the phenyl ring of the parent compound with 4-nitro
yielded 4f, the most potent compound of the series with an
IC50 value of 90 μM against Mtb NadE. Our
modeling results show that these urea-sulfonamides potentially bind to the
intramolecular ammonia tunnel, which transports ammonia from the glutaminase
domain to the active site of the enzyme. This hypothesis is supported by data
showing that, even when treated with potent inhibitors, NadE catalysis is
restored when treated with exogenous ammonia. Most of these compounds also
inhibited Mtb cell growth with MIC values of 19-100
μg/mL. These results improve our understanding of the
SAR of the urea-sulfonamides, their mechanism of binding to the enzyme, and of
Mtb NadE as a potential antitubercular drug target.
Sensing and response to environmental cues, such as pH and chloride (Cl−), is critical in enabling Mycobacterium tuberculosis (Mtb) colonization of its host. Utilizing a fluorescent reporter Mtb strain in a chemical screen, we have identified compounds that dysregulate Mtb response to high Cl− levels, with a subset of the hits also inhibiting Mtb growth in host macrophages. Structure–activity relationship studies on the hit compound “C6,” or 2-(4-((2-(ethylthio)pyrimidin-5-yl)methyl)piperazin-1-yl)benzo[d]oxazole, demonstrated a correlation between compound perturbation of Mtb Cl− response and inhibition of bacterial growth in macrophages. C6 accumulated in both bacterial and host cells, and inhibited Mtb growth in cholesterol media, but not in rich media. Subsequent examination of the Cl− response of Mtb revealed an intriguing link with bacterial growth in cholesterol, with increased transcription of several Cl−-responsive genes in the simultaneous presence of cholesterol and high external Cl− concentration, versus transcript levels observed during exposure to high external Cl− concentration alone. Strikingly, oral administration of C6 was able to inhibit Mtb growth in vivo in a C3HeB/FeJ murine infection model. Our work illustrates how Mtb response to environmental cues can intersect with its metabolism and be exploited in antitubercular drug discovery.
Rifamycin antibiotics are a valuable class of antimicrobials for treating infections by mycobacteria and other persistent bacteria owing to their potent bactericidal activity against replicating and non-replicating pathogens. However, the clinical utility of rifamycins against Mycobacterium abscessus is seriously compromised by a novel resistance mechanism, namely, rifamycin inactivation by ADP-ribosylation. Using a structurebased approach, we rationally redesign rifamycins through strategic modification of the ansa-chain to block ADP-ribosylation while preserving on-target activity. Validated by a combination of biochemical, structural, and microbiological studies, the most potent analogs overcome ADP-ribosylation, restored their intrinsic low nanomolar activity and demonstrated significant in vivo antibacterial efficacy. Further optimization by tuning drug disposition properties afforded a preclinical candidate with remarkable potency and an outstanding pharmacokinetic profile.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.