Cells were incubated for 24 h at standard conditions Entinostat clinical trial and then cytotoxicity was estimated once more. Whereas, in the second approach cells were incubated with various concentrations of tested samples diluted in DMEM containing 1 % FBS for 24 h in standard conditions. After that time surviving fraction was determined by MTT assay. MTT assay Briefly, a solution of 3–(4,5–dimethylthiazo1–2–y1)–2,5–diphenyltetrazolium bromide (MTT, Sigma) was prepared at 5 mg/mL in PBS and was diluted

1:10 in DMEM without FBS. 200 μL of this solution was added to each well. After 4 h of incubation at 37 °C in a humidified incubator with 5 % CO2, the medium/MTT mixtures were removed, and the formazan crystals formed by the mitochondrial dehydrogenase activity of vital cells were dissolved in 100 μL of DMSO:CH3OH

dilution (1:1). The absorbance of soluble product was read with a microplate reader (Infinite 200 M PRO NanoQuant, Tecan, Switzerland) at 565 nm. mTOR inhibitor Data analysis Cell viability was GF120918 calculated using cells treated with DMEM containing 1 % FBS as control. Cell surviving fraction (%) was calculated using the formula: S/S0 (%) = [abs565nm of treated cells/abs565nm of untreated cells (control)] × 100. Each experiment was done in triplicate and was repeated at least twice. The inhibitory concentration (IC) values were calculated from a dose–response curve. IC50 values were determined from the fitting curve by calculating the concentration of agent that reduced the surviving fraction of treated cells by 50 %, compared to control cells. IC50 data are expressed as mean values ± standard deviation

(SD) and they are the average of two independent experiments, done in triplicate. Fluorescence microscopy Viable and dead cells were detected by staining with AO (5 mg/L) and PI (5 mg/L) for 20 min and examined using fluorescence- inverted microscope (Olympus IX51, Japan) with an excitation filter of 470/20 nm. Photographs of the cells after treatment with the tested compounds were taken under magnification 20.00×. Results and discussion The acid–base chemistry of methotrexate MTX molecule contains a 2,4-diaminopteridine ring and N,N-dimethyl-p-aminobenzoic acid residue linked with glutamic acid by a peptide bond (Fig. 1). It exists in Casein kinase 1 water solution in a fully protonated form as a H3L ligand. The acid–base properties of the moieties, which can be deprotonated with a rise of pH value, were determined using potentiometric measurements (Table 1). The first two obtained pK a values: 2.89 and 4.56 correspond to the deprotonation of carboxylic groups from glutamic acid, α-COOH and γ-COOH, respectively (Poe, 1973, 1977; Meloun et al., 2010). The highest value of pK a = 5.65 corresponds to the deprotonation process of the heterocyclic nitrogen (N1)H+ from the pteridine ring. The resulting pK a values are quite consistent with the literature data.

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