Investigation of the Binding Behavior between the S-heterocyclic Aromatic Palladium(II) Complex and Human Serum Albumin: Spectroscopic Approach

New anticancer Pd and Pt complexes of tertamyl dithiocarbamate and DACH ligands against HT29 and Panc1 cell lines

To investigate the reduction of side effects of commercial antitumor drugs such as cisplatin, two new platinum and palladium complexes with a formula of [M(DACH)(tertamyl.dtc)]NO₃ were synthesized (DACH is 1R, 2R-diaminocyclohexane, tertamyl-dtc is tertpentyl dithiocarbamate, and M is palladium or platin ionic metals) and characterized by spectroscopic methods. The in vitro cytotoxicity of these compounds against HT29 and Panc1 cell lines showed that the IC₅₀ values against Panc1 cell line of [Pt(DACH)(tertamyl.dtc)]NO₃ and [Pd(DACH)(tertamyl.dtc)]NO₃ were 263.1 and 198.7 µM, and also against HT29 cell line were 241.9 and 258.2 µM, respectively. They were similar to the value obtained for oxaliplatin and lower than cisplatin value. Thermal stability and circular dichroism results demonstrated that both metal complexes could bind to DNA via electrostatic bonds. Due to electrostatic interaction, the configuration of B-DNA to C-DNA changed, though the possibility of groove interaction may be strengthened. Furthermore, molecular docking simulation showed higher negative docking energy for [Pd(DACH)(tertamyl.dtc)]NO₃ complex with a higher tendency for DNA interaction. In vitro cytotoxicity of two new Pt and Pd compounds have been studied against two cell lines (HT29 and Panc 1), which are almost equal to the value obtained for oxaliplatin and they are lower than cisplatin value. Thermal stability studies and CD results demonstrated that both complexes bind to DNA via electrostatic bonds. Further, molecular docking showed higher negative docking energy for [Pd(DACH)(tertamyl.dtc)]NO3 complex with a higher tendency for interaction.Communicated by Ramaswamy H. Sarma.

Biological effect and molecular docking of anticancer palladium and platinum complexes with morpholine dithiocarbamate on human serum albumin as a blood carrier protein

The aim of this study was to examine the interaction of [Pd(2,2'-bipyridine) (morpholinedithiocarbamate)]NO₃ and [Pt (2,2'-bipyridine)(morpholinedithiocarbamate)]NO₃ with human serum albumin under physiological conditions by using fluorescence, absorption, and circular dichroism spectroscopic techniques. Spectroscopic analysis of the emission quenching at different temperatures demonstrated that the quenching mechanism was static quenching. From the circular dichroism results, thermal stability study, it was found that the interaction of the complexes with human serum albumin caused a conformational change of the protein reversibly. These 2 anticancer Pd and Pt complexes were activated against chronic myelogenous leukemia cell line K562, so that 50% cytotoxic concentration values of 16 and 26 μM for Pd and Pt complexes, respectively, were observed, which were much lower than that of cisplatin (154 μM). Biological activities of both Pd and Pt complexes were also assayed against selective microorganisms by the disc diffusion method. These results showed that the Pd(II) complex is antifungal agent but Pt(II) complex has antibacterial activity. Also, the interaction of both metal derivative complexes was studied by molecular docking. Complementary molecular docking results may be useful to determine the binding mechanism of human serum albumin in pharmaceutical and biophysical studies providing new insight in the novel pharmacology.

Comparative study of an osazone based ligand and its palladium(II) complex with human serum albumin: A spectroscopic, thermodynamic and molecular docking approach

An osazone based ligand, hexane-3,4-dione-bis(2'-phenylhydrazone) (LH₂), was synthesized by 1:2M Schiff base condensation of 3,4-hexanedione and phenylhydrazine in dehydrated methanol. Its palladium(II) complex (1) has also been synthesized. LH₂ and 1 have thoroughly been characterized by several spectroscopic and analytical means. DFT optimized structure of 1 shows that it is a monomeric Pd(II) complex having 'N₂Cl₂' coordination chromophore. Our BVS analysis also satisfactorily reproduces the oxidation number of the palladium center. 1 shows irreversible Pd(II)/Pd(I) reduction in its CV in methanol. 1 is three-fold more emissive than LH₂. This enhanced emission has also been supported by time correlated single photon counting (TCSPC) measurements at room temperature. Human serum albumin (HSA) binding aspects of both LH₂ and 1 have been investigated through various biophysical techniques. The binding constants as determined from Benesi-Hilderbrand plot using the absorbance spectral analyses were found respectively to be 1.18×10⁵ and 4.38×10⁴M^-1 for LH₂ and 1. The experimental findings confirm that both are good HSA binders. The thermodynamic parameters (∆G°, ∆H° and ∆S°) have also been evaluated by isothermal titration calorimetric (ITC) experiments. These parameters indicate that the binding processes are spontaneous both for LH₂ and 1. Molecular docking analyses reveal that both LH₂ and 1 reside in domain-I of HSA.