Eight 1,3,4-oxadiazole derivatives containing phenolic acid moieties (7a–h) and eight of their diacylhydrazine precursors (6a–h) were synthesized, characterized using spectroscopic methods and examined by scavenging of stable DPPH (2,2-diphenyl-1-picrylhydrazyl) radicals. The most potent phenolic 1,3,4-oxadiazoles showed better DPPH scavenging activity in comparison with their corresponding diacylhydrazine precursors as a result of participation of both aromatic rings and a 1,3,4-oxadiazole moiety in resonance stabilization of the formed phenoxyl radical. Four diacylhydrazines (6d, 6e, 6g, and 6h) and four 1,3,4-oxadiazoles (7d, 7e, 7g and 7h) with the best DPPH scavenging activity, were chosen for further evaluation of their antioxidant potential through various assays. The investigated compounds exerted pronounced ABTS radical scavenging capacity, moderate to good H₂O₂ scavenging properties and strong ferric ion reducing capacity. Further in vitro evaluation of the antioxidant properties of the most active compounds demonstrated their protective effects in normal lung fibroblasts MRC-5 against hydrogen peroxide induced oxidative stress. Diacylhydrazine 6h increased two times the activity of glutathione peroxidase in treated cells in comparison with a control sample and did not affect the superoxide dismutase activity.

Hybrid compounds that combine the 1,3,4-thiadiazole-containing catechol moiety with a chalcone motif were synthesized and examined for their antioxidant activity, cytotoxicity, and DNA-binding activity. A series of thirteen compounds showed strong antioxidant and cytotoxic effects on human acute promyelocytic leukemia HL-60 cells. Several compounds exerted good cytotoxic activities on cervical adenocarcinoma HeLa cells. The treatment of HeLa cells with IC₅₀ and double IC₅₀ concentrations of the compounds 5a, 5c, 5f, and 5m induced a statistically significant increase in the percentage of cells within a subG1 cell cycle phase. The examined compounds caused G2/M cell cycle arrest in HeLa cells. Each of these compounds triggered apoptosis in HeLa cells through activation of caspase-3, the main effector caspase, caspase-8, which is involved in the extrinsic apoptotic pathway, and caspase-9, which is involved in the intrinsic apoptotic pathway. All of the examined compounds decreased the expression levels of MMP2 in HeLa cells and levels of protumorigenic miR-133b. Compounds 5a and 5m lowered the expression level of oncogenic miR-21 in HeLa cells. In addition, compounds 5a, 5f, and 5m decreased the expression levels of oncogenic miR-155 while the treatment of HeLa cells with compounds 5a, 5c, and 5f increased expression of tumor-suppressive miR-206. Observed effects of these compounds on expression levels of four examined miRNAs suggest their prominent cancer-suppressive activity. An investigation by absorption and fluorescence spectroscopy showed more efficient calf thymus DNA binding activity of the compound 5m in comparison to other tested compounds. Results of a pUC19 plasmid cleavage study and comet assay showed DNA damaging activities of compounds 5a and 5c.

The speciation of Cu²⁺, Ni²⁺ and Zn²⁺ ions in the presence of the fluoroquinolones (FQs) moxifloxacin, ofloxacin, levofloxacin and ciprofloxacin, in human blood plasma was studied under physiological conditions by computer simulation. The speciation was calculated using an updated model of human blood plasma including over 6,000 species with the aid of the program Hyss2009. The identity and stability of metal-FQ complexes were determined by potentiometric (310 K, 0.15 mol/L NaCl), spectrophotometric, spectrofluorimetric, ESI-MS and ¹H-NMR measurements. In the case of Cu²⁺ ion the concentration of main low molecular weight (LMW) plasma complex (Cu(Cis)His) is very slightly influenced by all examined FQs. FQs show much higher influence on main plasma Ni²⁺ and Zn²⁺ complexes: (Ni(His)₂ and Zn(Cys)Cit, respectively. Levofloxacin exhibits the highest influence on the fraction of the main nickel complex, Ni(His)₂, even at a concentration level of 3 × 10⁻⁵ mol/L. The same effect is seen on the main zinc complex, Zn(Cys)Cit. Calculated plasma mobilizing indexes indicate that ciprofloxacin possesses the highest mobilizing power from plasma proteins, toward copper ion, while levofloxacin is the most influential on nickel and zinc ions. The results obtained indicate that the drugs studied are safe in relation to mobilization of essential metal ions under physiological conditions. The observed effects were explained in terms of competitive equilibrium reactions between the FQs and the main LMW complexes of the metal ions.