Design, synthesis, and biological evaluation of a new palladium(II) complex: beta-lactoglobulin and K562 as targets

A water-soluble Pd(II) complex (2,2'-bipyridinglycinato Pd(II) nitrate) has been synthesized and characterized. The effect of synthesized complex on the carrier model protein structure and cell proliferation was investigated. Whey carrier protein beta-lactoglobulin-B (BLG-B) and chronic myelogenous leukemia cell line K562 were the targets. Fluorescence and CD instruments were used to assess effect of the complex on the protein structure at different temperatures. Growth inhibitory and apoptotic effect of the Pd(II) complex toward the cancer cells was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. This complex exhibited potent cytotoxic properties against chronic myelogenous leukemia cell line K562. The cells showed different sensitivity to complex. Cytotoxic studies shown that Pd(II) complex induced apoptosis of K562 cells in a concentration and time dependent manner. Then, it might be concluded that Pd(II) complex is a promising antiproliferative agent and should execute its biological effects by inducing apoptosis. Results of fluorescence studies revealed that Pd(II) complex can quench the intrinsic fluorescence emission of the protein at different temperatures. The far- and near-UV CD studies displayed that the Pd(II) complex induces changes in the secondary and tertiary structures of BLG-B at different temperatures. The biological significance of this work is evident since BLG serves as a carrier molecule for several antitumor compounds. Therefore, the interaction of the Pd(II) complex (with antitumor activity) can provide useful information to better design metal anticancer complexes with fewer side effects.

Binding Properties of a New Anti-tumor Component (2,2′-bipyridin octylglycinato Pd(II) nitrate) with Bovine β-lactoglobulin-A and -B

An new water soluble palladium (II) complex of formula [Pd(bpy)(Oct-Gly)]NO(3), (where bpy is 2,2'-bipyridine and Oct-Gly is octylglycine) have been synthesised. The Pd(II) complex has been characterized by elemental analysis and conductivity measurements as well as spectroscopic methods such as infrared, (1)H NMR, and ultraviolet-visible. The interaction between the new Pd(II)-complex (2,2'-bipyridin octylglycinato Pd(II) nitrate), an anti-tumor component, with beta-lactoglobulin-A and -B (BLG-A and -B) was studied by fluorescence spectroscopy and far and near-UV circular dichroism (CD) spectrophotometric techniques. A strong fluorescence quenching interaction of Pd(II) complex with BLG-A and -B was observed. The quenching constant was determined using the modified Stern-Volmer equation. The calculated binding constants of Pd(II) complex with BLG-A and -B were 0.51 and 0.28 (x 10(6) M(-1)) and the corresponding average number of binding sites were 2.8 and 1.5, respectively. Far-UV CD studies showed that the Pd(II) complex can significantly change the secondary structure of BLG-A and -B via an increase in the content of alpha-helix structure, which stabilizes the secondary structure of the proteins. Near-UV CD data clearly indicate the alteration in the tertiary structure of BLG-A and -B due to the interaction with Pd(II) complex. Pd(II) complex can change and stabilize both the secondary and tertiary structures of BLG-A more than BLG-B. These conformational changes may be considered to be a deleterious effect of the designed ligand on the protein structures. The difference in the interaction properties observed for BLG-A and -B with Pd(II) complex is due to the difference in the amino acid sequences between these two variants.

Spectroscopic and cytotoxic studies of the novel designed palladium(II) complexes: β-Lactoglobulin and K562 as the targets

Since palladium complexes have been reported to show fewer side effects relative to other heavy metal anticancer compounds, in this study a new class of four structurally related anticancer Pd(II) complexes including 2,2'-bipyridin-n-butyl dithiocarbamato Pd(II) nitrate (Com-1), 2,2'-bipyridin-n-hexyl dithiocarbamato Pd(II) nitrate (Com-2), 2,2'-bipyridin glycinato Pd(II) nitrate (Com-3) and 2,2'-bipyridin octylglycinato Pd(II) nitrate (Com-4) was designed. The effect of four synthesized ligands on the protein structure and cell proliferation were investigated. Whey carrier proteins beta-lactoglobulin-A and-B (BLG-A and-B) and chronic myelogenous leukemia cell line K562 were the targets. Fluorescence and CD instruments were used to assess effect of the ligands on the protein structure. Growth inhibitory effect of the Pd(II) complexes towards the cancer cells was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Results of fluorescence studies revealed that the complexes had no dithiocarbamate moiety (compounds 3 and 4) could quench the intrinsic fluorescence emission of the proteins at lower concentrations than those had such moiety (compounds 1 and 2). The far-UV-CD studies revealed that the regular secondary structure of BLG-A and -B did not show any noticeable alteration upon interaction with different of Pd(II)-complexes. The results of cell proliferation assay also displayed that Com-1 and Com-2 had more growth inhibitory activity against K562, than Com-3 and Com-4. Our results suggested that addition of dithiocarbamate moiety to structure of Pd(II) complexes probably has important role to improve the antiproliferative properties of the anticancer ligands and fewer effects on the carrier protein structure.

Comparative analysis of refolding of chemically denatured β-lactoglobulin types A and B using the dilution additive mode

The kinetic refolding of beta-lactoglobulin (BLG), types A and B, by beta-cyclodextrin, glucose and sorbitol has been investigated in aqueous solution using fluorescence, far UV-CD and UV-spectrophotometric techniques. A new Pd-complex has been used to denature the protein. CD and fluorescence studies indicated that when incubated with sugar, the denatured BLG is refolded into the native-like structure through the dilution additive mode resulting in a higher yield of active protein than without sugar. CD studies show that these sugars can induce a non-native alpha-helical structure in denatured BLG-A and -B, then aid in the refolding of the protein. Based on the present study, these sugars have a different effect on BLG-A than BLG-B because of their differences in protein thermal stability. BLG-A has a higher thermal stability than BLG-B due to differences in the amino acid sequences.

A microcalorimetry and spectroscopy study on the interaction of BSA with 2,2'-bipyridine octylglycinato palladium(II) nitrate

The interaction of bovine serum albumin (BSA) with a new palladium(II) complex [Pd(bpy)(Oct-Gly)]NO(3) (bpy, 2,2 -bipyridine; Oct-Gly, octyl-glycine) was studied by isothermal titration UV-visible spectrophotometry and microcalorimetry in 30 mmol/L Tris buffer, pH 7.0. There is a set of 18 binding sites for this complex on BSA at 300 and 310 K with positive cooperativity in the binding process. The Hill coefficients at 300 and 310 K are 2.2 and 2.4, respectively. The binding of this palladium complex on BSA is endothermic with mean association binding constant of 21.0 and 16.4 (mmol/L) (-1) at 300 and 310 K, respectively. The complex can denature the protein as surfactants. The stability of BSA in the interaction study with the complex is 84 and 58 kJ/mol at 300 and 310 K, respectively. Also, the enthalpy of BSA denaturation due to the interaction with the complex is 842 kJ/mol.