5-membered cyclic hydroxamic acids as HDAC inhibitors

Conjugates of Iron-Transporting N-Hydroxylactams with Ciprofloxacin

Screening of a library of novel N-hydroxylactams amenable by the Castagnoli-Cushman reaction identified four lead compounds that facilitated ⁵⁵Fe transport into P. aeruginosa cells (one of these synthetic siderophores was found to be as efficient at promoting iron uptake as the natural siderophores pyoverdine, pyochelin or enterobactin). Conjugates of the four lead siderophores with ciprofloxacin were tested for antibacterial activity against P. aeruginosa POA1 (wild type) and the ∆pvdF∆pchA mutant strain. The antibacterial activity was found to be pronounced against the ∆pvdF∆pchA mutant strain grown in CAA medium but not for the POA1 strain. This may be indicative of these compounds being ‘Trojan horse’ antibiotics. Further scrutiny of the mechanism of the antibacterial action of the newly developed conjugates is warranted.

Hybrid inhibitors of DNA and HDACs remarkably enhance cytotoxicity in leukaemia cells

Chlorambucil is a nitrogen mustard-based DNA alkylating drug, which is widely used as a front-line treatment of chronic lymphocytic leukaemia (CLL). Despite its widespread application and success for the initial treatment of leukaemia, a majority of patients eventually develop acquired resistance to chlorambucil. In this regard, we have designed and synthesised a novel hybrid molecule, chloram-HDi that simultaneously impairs DNA and HDAC enzymes. Chloram-HDi efficiently inhibits the proliferation of HL-60 and U937 leukaemia cells with GI₅₀ values of 1.24 µM and 1.75 µM, whereas chlorambucil exhibits GI₅₀ values of 21.1 µM and 37.7 µM against HL-60 and U937 leukaemia cells, respectively. The mechanism behind its remarkably enhanced cytotoxicity is that chloram-HDi not only causes a significant DNA damage of leukaemia cells but also downregulates DNA repair protein, Rad52, resulting in the escalation of its DNA-damaging effect. Furthermore, chloram-HDi inhibits HDAC enzymes to induce the acetylation of α-tubulin and histone H3.

Green synthesized hydroxamic acid administered in high dose disrupts the antioxidant balance in the hepatic and splenic tissues of albino rats

Background

Hydroxamic acids are currently being used in diverse biological activities. We investigated the effect of hydroxamic acid, synthesized from Cyperus esculentus seeds, on the antioxidant status of the liver, spleen, and kidney of Wistar rats.

Methods

Twenty male rats were randomly divided into three treatment groups using hydroxamic acid at doses of 5, 15, and 50 mg/kg and a control group using distilled water. Rats were sacrificed 24 h after a seven-day repeated oral dosing. After that, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST), and the levels of glutathione (GSH) and malondialdehyde (MDA) were investigated in the organs.

Results

Our data showed that MDA levels remained unaltered in the liver, spleen, and kidney. However, it was found that hydroxamic acid at the dose of 50 mg/kg significantly increased SOD activity but depleted CAT, GPx activities and GSH levels in the liver when compared to the control groups. In splenic tissue, SOD activity and GSH levels were significantly diminished. Contrarily, in the kidney, treatment of rats with 50 mg/kg hydroxamic acid did not affect SOD activity, but GPx activity was increased while GST activity was decreased when compared to the controls.

Conclusion

Overall, hydroxamic acid may enhance antioxidant enzyme activities in the liver and kidney. However, caution is required at higher doses to forestall oxidative stress in the hepatic and splenic tissues.

Cyclic Hydroxamic Acid Analogues of Bacterial Siderophores as Iron-Complexing Agents prepared through the Castagnoli-Cushman Reaction of Unprotected Oximes

The first application of multicomponent chemistry (the Castagnoli-Cushman reaction) toward the convenient one-step preparation of cyclic hydroxamic acids is described. Cyclic hydroxamic acids are close analogues of bacterial siderophores (iron-binding compounds) and form stable complexes with Fe³⁺ ions as confirmed by spectrophotometric measurements. These compounds are potential components for the design of chelating agents for iron overload disease therapy, as well as siderophore-based carrier systems for antibiotic delivery across the bacterial cell wall.

Effect of donor atom identity on metal-binding pharmacophore coordination

The inhibition and binding of three metal-binding pharmacophores (MBPs), 2-hydroxycyclohepta-2,4,6-trien-1-one (tropolone), 2-mercaptopyridine-N-oxide (1,2-HOPTO), and 2-hydroxycyclohepta-2,4,6-triene-1-thione (thiotropolone) to human carbonic anhydrase II (hCAII) and a mutant protein hCAII L198G were investigated. These MBPs displayed bidentate coordination to the active site Zn(II) metal ion, but the MBPs respond to the mutation of L198G differently, as characterized by inhibition activity assays and X-ray crystallography. The L198G mutation increases the active site volume thereby decreasing the steric pressure exerted on MBPs upon binding, allowing changes in MBP coordination to be observed. When comparing the binding mode of tropolone to thiotropolone or 1,2-HOPTO (O,O versus O,S donor sets), structural modifications of the hCAII active site were shown to have a stronger effect on MBPs with an O,O versus O,S donor set. These findings were corroborated with density functional theory (DFT) calculations of model coordination complexes. These results suggest that the MBP binding geometry is a malleable interaction, particularly for certain ligands, and that the identity of the donor atoms influences the response of the ligand to changes in the protein active site environment. Understanding underlying interactions between a MBP and a metalloenzyme active site may aid in the design and development of potent metalloenzyme inhibitors.