The adsorption of Cu(II) ions onto the chitosan derived Schiff bases obtained from the condensation of chitosan with salicyaldehyde (polymer I), 2,4-dihydroxybenzaldehyde (polymer II) and with 4-(diethylamino) salicyaldehyde (polymer III) in aqueous solutions was investigated. Batch adsorption experiments were carried out as a function of contact time, pH, and polymer mass. The amount of metal-ion uptake of the polymers was determined by using atomic absorption spectrometry (AAS) and the highest Cu(II) ions uptake was achieved at pH 7.0 and by using sodium perchlorate as an ionic strength adjuster for polymers I, II, and III. The isothermal behavior and the kinetics of adsorption of Cu(II) ions on these polymers with respect to the initial mass of the polymer and temperature were also investigated; adsorption isothermal equilibrium data could be clearly explained by the Langmuir equation. The experimental data of the adsorption equilibrium from Cu(II) solution correlates well with the Langmuir isotherm equation.

Chemoresistance is the major cause of cancer recurrence, relapse and eventual death. Doxorubicin resistance is one such challenge in breast cancer. The use of quercetin, an antioxidant, in combination with doxorubicin has been investigated for offering protection to normal cells from the toxic side effects of doxorubicin in addition to modulation of its resistance. The present study aimed to investigate the effects of quercetin in prevention of a doxorubicin‑chemoresistant phenotype in both doxorubicin‑sensitive and ‑resistant human MCF‑7 breast cancer cell lines. A doxorubicin‑resistant MCF‑7 cell line was established. The development of resistant cells was closely monitored for changes in morphological features. Sensitivity to doxorubicin and the doxorubicin/quercetin combination was assessed using the tetrazolium assay. To determine the mechanism by which quercetin sensitizes the doxorubicin MCF‑7‑resistant cell line to doxorubicin, gene expression alterations in breast cancer‑related genes were examined using the reverse transcription‑quantitative PCR (RT‑qPCR) array technology. Resistant MCF cells were successfully developed and the inhibitory concentration (IC₅₀) value of doxorubicin increased from 0.133 to 4 µM (wild‑type to resistant). The effects of the quercetin/doxorubicin combination exhibited different effects on wild‑type vs. resistant cells. The IC50 of doxorubicin was reduced in wild cells, whereas resistant cells showed an increase in cell viability at lower concentrations and a potentiation of the effects of doxorubicin only at higher concentrations. Annexin V/propidium iodide staining demonstrated that quercetin drives cells into late apoptosis and necrosis, but in resistant cells, necrosis predominates. RT‑qPCR results revealed that quercetin led to a reversal in doxorubicin effects via up‑ and downregulation of important genes such as SNAI2, PLAU and CSF1 genes. Downregulation of cell migration genes, SNAI2 (‑31.23‑fold) and plasminogen activator, urokinase (PLAU; ‑30.62‑fold), and the apoptotic pathway gene, colony stimulating factor 1 (CSF1; ‑17.25‑fold) were the most important querticin‑associated events. Other gene alterations were also observed involving cell cycle arrest and DNA repair pathways. The results of the present study indicated that quercetin could lead to a reversal of doxorubicin resistance in breast cancer cells via downregulation of the expression of important genes, such as SNAI2, PLAU and CSF1. Such findings may represent a potential strategy for reversing breast cancer cell‑related chemoresistance.