Gold(I) ion and the phosphine ligand are necessary for the anti-Toxoplasma gondii activity of auranofin

Auranofin, an FDA-approved drug for rheumatoid arthritis, has emerged as a promising antiparasitic medication in recent years. The gold(I) ion in auranofin is postulated to be responsible for its antiparasitic activity. Notably, aurothiomalate and aurothioglucose also contain gold(I), and, like auranofin, they were previously used to treat rheumatoid arthritis. Whether they have antiparasitic activity remains to be elucidated. Herein, we demonstrated that auranofin and similar derivatives, but not aurothiomalate and aurothioglucose, inhibited the growth of Toxoplasma gondii in vitro. We found that auranofin affected the T. gondii biological cycle (lytic cycle) by inhibiting T. gondii's invasion and triggering its egress from the host cell. However, auranofin could not prevent parasite replication once T. gondii resided within the host. Auranofin treatment induced apoptosis in T. gondii parasites, as demonstrated by its reduced size and elevated phosphatidylserine externalization (PS). Notably, the gold from auranofin enters the cytoplasm of T. gondii, as demonstrated by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).IMPORTANCEToxoplasmosis, caused by Toxoplasma gondii, is a devastating disease affecting the brain and the eyes, frequently affecting immunocompromised individuals. Approximately 60 million people in the United States are already infected with T. gondii, representing a population at-risk of developing toxoplasmosis. Recent advances in treating cancer, autoimmune diseases, and organ transplants have contributed to this at-risk population's exponential growth. Paradoxically, treatments for toxoplasmosis have remained the same for more than 60 years, relying on medications well-known for their bone marrow toxicity and allergic reactions. Discovering new therapies is a priority, and repurposing FDA-approved drugs is an alternative approach to speed up drug discovery. Herein, we report the effect of auranofin, an FDA-approved drug, on the biological cycle of T. gondii and how both the phosphine ligand and the gold molecule determine the anti-parasitic activity of auranofin and other gold compounds. Our studies would contribute to the pipeline of candidate anti-T. gondii agents.

PEST-domain-enriched tyrosine phosphatase and glucocorticoids as regulators of anaphylaxis in mice

BACKGROUND

PEST-domain-enriched tyrosine phosphatase (PEP) is a protein tyrosine phosphatase exclusively expressed in hematopoietic cells. It is a potent negative regulator of T-cell receptor signalling that acts on receptor-coupled protein tyrosine kinases. PEST-domain-enriched tyrosine phosphatase is also expressed in mast cell and is positively regulated by glucocorticoids, but its function is unknown. In this communication, the function of PEP is analysed in mast cells.

METHODS

Signal transduction cascades following IgE receptor cross-linking were compared in bone marrow-derived mast cells (BMMC) from PEP(-/-) and PEP(+/+) mice. Furthermore, antigen-induced passive systemic anaphylaxis (PSA) was analysed in PEP(+/+) and PEP(-/-) mice.

RESULTS

Bone marrow-derived mast cells from PEP(-/-) mice showed impaired PLCγ1 phosphorylation and Ca(2+) mobilization. Additionally, mice deficient in PEP showed impaired mast cell degranulation and were less susceptible to PSA. Treatment of wild-type BMMC or mice with an Au(I)-phosphine complex that selectively inhibits PEP activity produced defects in Ca(2+) signalling pathway and reduced anaphylaxis similar to that caused by the deletion of the PEP gene. Glucocorticoid that negatively regulates a wide range of mast cell action increased PEP expression and only partially inhibited anaphylaxis. However, glucocorticoid potently inhibited anaphylaxis when combined with the PEP inhibitor.

CONCLUSIONS

PEST-domain-enriched tyrosine phosphatase is an important positive regulator of anaphylaxis. Pharmacological inhibition of its activity together with glucocorticoid administration provide an effective rescue for PSA in mice.

Decomposition of alkyl-substituted urea molecules at a hydroxide-bridged dinickel center

The interactions between N-methylurea, N,N'-dimethylurea, N,N-dimethylurea, tetramethylurea, and thiourea and the hydroxide-bridged dinickel complex [Ni(2)(mu-OH)(mu-H2O)(bdptz)(H2O2](OTs)(3) were investigated. Structural characterization of [Ni(2)(mu-OH)(mu-H2O)(bdptz)(Me-urea)(CH3CN)](ClO4)(3) (1) and [Ni(2)(mu-OH)(mu-H2O)(bdptz)(thiourea)(CH3CN)](ClO4)(3) (2) provided insight into the interactions of the substrates with the dinickel center. In 1, the methylurea molecule coordinates to the dinickel complex through its carbonyl oxygen atom. Complex 2 has a similar geometry, with the thiourea molecule bound to a nickel ion through its sulfur atom. When the urea substrates are heated in the presence of the hydroxide-bridged dinickel complex, N-methylurea and N,N-dimethylurea react to form methylammonium cyanate and dimethylammonium cyanate, respectively. After long reaction times, thiourea reacts similarly, producing ammonium thiocyanate. The other substrates are unreactive. These results indicate that the dinickel complex promotes the elimination of alkylamines from urea substrates to form cyanate but cannot effect the direct hydrolysis of such substrates.

The reactivity of well defined diiron(III) peroxo complexes toward substrates: addition to electrophiles and hydrocarbon oxidation

The reactivity of previously reported peroxo adducts [Fe(mu-O2)(mu-L)(O2CPhCy)2(1-Bu-Im)2] (1), and [Fe(mu-O2)(mu-L)(O2CPhCy)2(py)2] (2), where L is a dinucleating ligand based on the m-xylylenediamine bis(Kemp's triacid imide), toward a variety of substrates is described. These studies were performed to probe the electronic properties of 1 and 2 and evaluate their potential as selective hydrocarbon oxidants. Compound 1 is nucleophilic at -77 degrees C, reacting with phenols and carboxylic acids to liberate hydrogen peroxide, whereas the less electron-rich pyridine analogue 2 is unreactive toward both reagents. By contrast, neither reacts at -77 degrees C with electrophilic reagents such as olefins or triphenylphosphine, or with weak hydrogen atom donors such as dimethylbenzylamine. When solutions of 1 are warmed to room temperature in solvents such as THF, toluene, and cyclopentane, mixtures of alcohol and ketone products derived from the solvent are formed. A detailed investigation of cyclopentane oxidation strongly points to a radical autoxidation pathway. These results are discussed in the context of the selective hydroxylation chemistry that occurs at the carboxylate-bridged diiron centers in soluble methane monooxygenase.