Characterization of the interaction between a platinum(II) complex and human serum albumin: spectroscopic analysis and molecular docking

Tracking the binding site of anticancer drug fluxoridin with Fe-related proteins to achieve intelligent drug delivery

In cancer cells that need a lot of iron for growth and metastasis, halo-transferrin (TF-containing iron) enters the cell with the help of the transferrin receptor 1 (TFR1) protein. If the anticancer drug can bind to the iron site by interacting with apo-transferrin (iron-free FT), it can enter the cancer cell by the same mechanism. Two iron-related proteins, Bovine liver catalase (BLC) and apo-Transferrin (TF), that are important in cancer patients were selected and their interaction with the anti-cancer drug Floxuridine (FUDR) was investigated. Here, the protective role of FUDR was evaluated by several variables such as drug concentration, interaction time, and temperature-induced degradation of enzyme function. The results showed that the protective effect of the FUDR is greater in high concentrations (in 5 × 10-5 M:1.78 % and 2.59 % after 24 and 48 h). The interaction of the FUDR with both proteins can reduce the intensity of the fluorescence emission by a static mechanism. The binding strength of the FUDR with both proteins was almost similar and with the order of 104 M-1 (Kb = 3.90 ± 0.41 × 104 M-1 for BLC-FUDR and 5.01 ± 0.36 × 104 M-1 for TF-FUDR at 310 K). The thermodynamic calculations (in agreement with the docking results) indicated that FUDR-protein complex formation was exothermic and the main binding forces in the binding process were van der Waals interactions and hydrogen bonds. Both fluorophores tryptophan (Trp) and tyrosine (Tyr) of both proteins had significant roles in fluorescence quenching and the interaction process, the polarity of their microenvironment changed. CD results showed that the secondary structure changes of TF are slightly more than BLC. Molecular docking showed that the binding of the FUDR to TF is very close to the Fe-specific site and is placed in the cavity among the wrapping domain, N-Terminal arm, and β-barrel in BLC.

A binuclear Cu(I)-phosphine complex as a specific HSA site I binder: synthesis, X-ray structure determination, and a comprehensive HSA interaction analysis

In this research, we present a method for synthesis and a detailed description of geometry characterization of a novel binuclear Cu(I) phosphine complex, along with analysis of its interaction with HSA using spectroscopic and simulation methods. The Cu atoms are coordinated in a tetrahedral geometry, which results in coordination by two nitrogen atoms from the N,N'-(ethane-1,2-diyl)bis(1-(pyridin-2-yl)methanimine ligand (L), a chloride, and a PPh3. The complex binding constant to HSA in a biochemical environment was determined to be ∼106, which is indicative of a strong interaction. The fluorescence of HSA is significantly quenched by binding to the complex via a static mechanism, whereas the microenvironment of the tryptophan residue remains unchanged. A spontaneous binding process was indicated by a negative value for ΔG. Thermodynamic signatures reflect the dominance of hydrophobic forces during the interaction. The site marker competitive experiment combined with docking simulation analysis revealed the closeness position of the complex binding site to warfarin location in specific ligand site I of HSA. The information generated in the present study would be valuable to understand the interaction mechanistic and pharmacological behavior of Cu(I) complexes.Communicated by Ramaswamy H. Sarma.

Probing the biomolecular (DNA/BSA) interaction by new Pd(II) complex via in-depth experimental and computational perspectives: synthesis, characterization, cytotoxicity, and DFT approach

Scientists should not forget that the rate of death as a result of cancer is far more than that of other diseases like influenza or coronavirus (COVID-19), so the research in this field is of cardinal significance. Therefore, a new and hydrophilic palladium(II) complex of the general formula [Pd(bpy)(proli-dtc)]NO₃, in which bpy and proli-dtc are 2,2'-bipyridine and pyrroline dithiocarbamate ligands, respectively, was synthesized and characterized utilizing spectral and analytical procedures. Density functional theory (DFT) calculation was also performed with B3LYP method in the gas phase. The DFT and spectral analysis specified that the Pd(II) atom is found in a square-planar geometry. HOMO/LUMO analysis, quantum chemical parameters and MEP surface of the complex were investigated to acquire an intuition about the nature of the compound. Partition coefficient and water solubility determination showed that both lipophilicity and hydrophilicity of the compound are more than cisplatin. The 50% inhibition concentration (IC₅₀) value was evaluated against K562 cancer cells, the obtained result has revealed a promising cytotoxic effect. DNA and BSA binding of the complex were explored through multi-spectroscopic (UV–Vis, fluorescence, FRET, and CD) and non-spectroscopic (gel electrophoresis, viscosity and docking simulation) techniques. The obtained findings demonstrated that the complex strongly interacts with CT-DNA by hydrophobic interactions and possesses medium interaction with BSA via hydrogen bond and van der Waals forces, thus BSA could efficiently carry out complex transportation. Furthermore, the results of docking simulation agree well with the experimental findings. In conclusion, the new Pd(II) complex has cytotoxic activity and could interact with DNA and BSA effectively.

Synthesis, characterization, cytotoxicity and DNA/BSA binding of two amino acid palladium(II) complexes derived from alanine and valine

Two novel palladium(II)-amino acid complexes, [Pd(Ala)₂]·H₂O (PA) and [Pd(Val)₂].H₂O (PV) (Ala = alanine; Val = valine) were synthesized and characterized through FTIR, UV/Vis, ¹H-NMR spectroscopies, CHN analysis, X-ray crystallography and molar conductivity measurement. Furthermore, cytotoxicity of Pd(II) complexes against human leukemia cancer cell line, MOLT4 showed promising cancer cell death (CC₅₀ = 0.71 ± 0.046 µM for PA; CC₅₀ = 0.85 ± 0.063 µM for PV) that were less than cisplatin (1.59 ± 0.25 µM). Moreover, the interaction of both the complexes with DNA and BSA was studied using UV-Vis absorption and emission spectroscopic techniques that demonstrated the bindings occurred via van der Waals forces and hydrogen bond. Furthermore, the fluorescence titration showed that static quenching mechanism plays predominate role in binding process. All results showed that both complexes have more binding tendency to DNA in compared to BSA that can be a significant achievement for further medical purposes as a potential antitumor candidate. Finally, molecular docking simulation was performed for PA and PV complexes with DNA and BSA and demonstrated both complexes bind to the groove of DNA mainly by hydrogen bond and interact with site I of BSA via hydrogen bond as well.

Two new monofunctional platinum(II) dithiocarbamate complexes: phenanthriplatin-type axial protection, equatorial-axial conformational isomerism, and anticancer and DNA binding studies

The syntheses of two platinum(ii) dithiocarbamate complexes (1 and 2) that show quinoplatin- and phenanthriplatin-type axial protection of the Pt-plane are described. The Pt-plane of complex 2 is axially more protected than that of complex 1. Furthermore, both complexes adopt two different stereochemical conformations in the solid state (based on single-crystal X-ray structures) owing to the structurally flexible piperazine backbone; i.e., C-e,e-Anti (1) and C-e,a-Syn (2), where "C" stands for the chair configuration, "e" and "a" stand for the equatorial and axial positions and "Anti" (opposite side) and "Syn" (same side) represent the relative orientations in space of the terminal substituents on the piperazine ring. In complex 2, the C-e,a-Syn conformation may provide additional steric hindrance to the Pt-plane. Despite the lower lipophilicity of 2 as compared to that of 1, the in vitro anticancer action against selected cancer cell lines is better for the former revealing the superior role of the axial protection over lipophilicity in modulating anticancer activity. The activity against the cancer promoting protein NF-κB signifies that the mode of cancer cell death may be the result of hindering the activity of NF-κB in the initiation of apoptosis. The apoptotic mode of cell death has been established earlier in a study using Annexin V-FITC. Finally, DNA binding studies revealed that the complex-DNA adduct formation is spontaneous and the mode of interaction is non-intercalative (electrostatic/covalent).

Interaction between DNA, Albumin and Apo-Transferrin and Iridium(III) Complexes with Phosphines Derived from Fluoroquinolones as a Potent Anticancer Drug

A group of cytotoxic half-sandwich iridium(III) complexes with aminomethyl(diphenyl)phosphine derived from fluoroquinolone antibiotics exhibit the ability to (i) accumulate in the nucleus, (ii) induce apoptosis, (iii) activate caspase-3/7 activity, (iv) induce the changes in cell cycle leading to G2/M phase arrest, and (v) radicals generation. Herein, to elucidate the cytotoxic effects, we investigated the interaction of these complexes with DNA and serum proteins by gel electrophoresis, fluorescence spectroscopy, circular dichroism, and molecular docking studies. DNA binding experiments established that the complexes interact with DNA by moderate intercalation and predominance of minor groove binding without the capability to cause a double-strand cleavage. The molecular docking study confirmed two binding modes: minor groove binding and threading intercalation with the fluoroquinolone part of the molecule involved in pi stacking interactions and the Ir(III)-containing region positioned within the major or minor groove. Fluorescence spectroscopic data (HSA and apo-Tf titration), together with molecular docking, provided evidence that Ir(III) complexes can bind to the proteins in order to be transferred. All the compounds considered herein were found to bind to the tryptophan residues of HSA within site I (subdomain II A). Furthermore, Ir(III) complexes were found to dock within the apo-Tf binding site, including nearby tyrosine residues.

Anionic versus neutral Pt(II) complexes: The relevance of the charge for human serum albumin binding

The focus of this work is pointing out the different behavior of two structurally related Pt^(II) complexes, the anionic cyclometalated NBu₄[(Bzq)Pt(Thio)], 1 and the neutral [(Phen)Pt(Thio)], 2, (Bzq = benzo[h]quinoline, Phen = 1,10-phenantroline, Thio = 1,2-benzenedithiolate), on the interaction with human serum albumin (HSA), a key drug-delivery protein in the bloodstream. Being very limited the number of anionic Pt^(II) complexes reported to date, this is a pioneering example of report on a protein-ligand interaction involving a negatively charged platinum compound. The study was carried out by using fluorescence spectroscopy, differential scanning calorimetry and molecular docking simulations. The results revealed a strong binding affinity between the anionic compound and the protein, whereas a weak/moderate binding interaction was highlighted for the neutral one. Comparative studies with site specific ligands (warfarin and ibuprofen), allowed us to identify the protein binding sites of the two compounds. The work aims to shed light on the relevance of the charge in designing new drugs with a favorable binding affinity for HSA, which strongly contributes to influence their pharmacological and toxicological profile.

Nonionic but water soluble, [Glycine-Pd-Alanine] and [Glycine-Pd-Valine] complexes. Their synthesis, characterization, antitumor activities and rich DNA/HSA interaction studies

Two novel, neutral and water soluble Pd(II) complexes of formula [Pd(Gly)(Ala)] (1) and [Pd(Gly)(Val)] (2) (Gly, Ala, and Val are anionic forms of glycine, alanine, and valine amino acids, respectively) have been synthesized and characterized by FT-IR, UV-Vis, ¹H-NMR, elemental analysis, and molar conductivity measurement. The data revealed that each amino acid binds to Pd(II) through the nitrogen of -NH₂ and the oxygen of -COO^- groups and acts as a bidentate chelate. These complexes have been assayed against leukemia cells (K₅₆₂) using MTT method. The results indicated that both of the complexes display more cytotoxicity than the well-known anticancer drug, cisplatin. The interaction of the compounds with calf thymus DNA (CT-DNA) and human serum albumin (HSA) were assayed by a series of experimental techniques including electronic absorption, fluorescence, viscometry, gel electrophoresis, and FT-IR. The results indicated that the two complexes have interesting binding propensities toward CT-DNA as well as HSA and the binding affinity of (1) is more than (2). The fluorescence data indicated that both complexes strongly quench the fluorescence of ethidium bromide-DNA system as well as the intrinsic fluorescence of HSA via static quenching procedures. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) calculated from the fluorescence studies showed that hydrogen bonds and van der Waals interactions play a major role in the binding of the complexes to DNA and HSA. We suggest that both of the Pd(II) complexes exhibit the groove binding mode with CT-DNA and interact with the main binding pocket of HSA. Communicated by Ramaswamy H. Sarma.

In vitro interaction of cefotaxime with calf thymus DNA: Insights from spectroscopic, calorimetric and molecular modelling studies

Cefotaxime is third generation antibiotic with known therapeutic efficacy against bacterial infections including cerebral abscesses and bacterial meningitis. The β-lactam group of drugs are considered safest antibiotics. Many antibiotics directly interact with DNA and alter their expression profile. Thus, it is necessary to understand the binding mode and its relevance to drug activity and toxicity. There is considerably a remarkable focus on deciphering the binding mechanism of these therapeutic agents as DNA is one of the major target for wide range of drugs. Cefotaxime has been extensively studied for its pharmacological properties while its binding mode to DNA has not been explicated so far. In this study, we have unveiled the binding mechanism of cefotaxime to DNA by using various biophysical, thermodynamic and in silico techniques. UV-vis spectroscopy confirmed the formation cefotaxime-DNA complex along with a brief idea about the extent of interaction. Fluorescence spectroscopy yielded the values of various binding constants and explained mode of fluorescence quenching to be static. CD spectroscopy, thermal denaturation, KI quenching and viscosity measurement explained that cefotaxime is groove binder. Measuring the effect of ions on cefotaxime-DNA complex ensured that it does not bind to DNA electrostatically. Dye displacement experiments finally confirmed that cefotaxime binds to the minor groove of DNA. ITC gave the thermodynamic profile of this binding in which negative value of Gibb's free energy change revealed that the process is spontaneous. Molecular modelling finally strengthened our experimental results that cefotaxime was located in curved contour of minor groove of DNA. The findings support on safety of drug and may have a little interference on normal biological functions.

Palladium(II) complexes of biorelevant ligands. Synthesis, structures, cytotoxicity and rich DNA/HSA interaction studies

In this work, a pair of new palladium(II) complexes, [Pd(Gly)(Phe)] and [Pd(Gly)(Tyr)], (where Gly is glycine, Phe is phenylalanine, and Tyr is tyrosine) were synthesized and characterized by UV-Vis, FT-IR, elemental analysis, ¹H-NMR, and conductivity measurements. The detailed ¹H NMR and infrared spectral studies of these Pd(II) complexes ascertain the mode of binding of amino acids to palladium through nitrogen of -NH₂ and oxygen of -COO^- groups as bidentate chelates. The Pd(II) complexes have been tested for in vitro cytotoxicity activities against cancer cell line of K₅₆₂. Interactions of these Pd(II) complexes with CT-DNA and human serum albumin were identified through absorption/emission titrations and gel electrophoresis which indicated significant binding proficiency. The binding distance (r) between these synthesized complexes and HSA based on Forster's theory of non-radiation energy transfer were calculated. Alterations of HSA secondary structure induced by complexes were confirmed by FT-IR measurements. The results of emission quenching at three temperatures have revealed that the quenching mechanism of these Pd(II) complexes with CT-DNA and HSA were the static and dynamic quenching mechanism, respectively. Binding constants (K_b), binding site number (n), and the corresponding thermodynamic parameters were calculated and revealed that the hydrogen binding and hydrophobic forces played a major role when Pd(II) complexes interacted with DNA and HSA, respectively. We bid that [Pd(Gly)(Phe)] and [Pd(Gly)(Tyr)] complexes exhibit the groove binding with CT-DNA and interact with the main binding pocket of HSA. The complexes follow the binding affinity order of [Pd(Gly)(Tyr)] > [Pd(Gly)(Phe)] with CT-DNA- and HSA-binding.

Binding forces between a novel Schiff base palladium(II) complex and two carrier proteins: human serum albumi and β-lactoglobulin

Ligand binding studies on carrier proteins are crucial in determining the pharmacological properties of drug candidates. Here, a new palladium(II) complex was synthesized and characterized. The in vitro binding studies of this complex with two carrier proteins, human serum albumin (HSA), and β-lactoglobulin (βLG) were investigated by employing biophysical techniques as well as computational modeling. The experimental results showed that the Pd(II) complex interacted with two carrier proteins with moderate binding affinity (K_b ≈ .5 × 10⁴ M^-1 for HSA and .2 × 10³ M^-1 for βLG). Binding of Pd(II) complex to HSA and βLG caused strong fluorescence quenching of both proteins through static quenching mechanism. In two studied systems hydrogen bonds and van der Waals forces were the major stabilizing forces in the drug-protein complex formation. UV-Visible and FT-IR measurements indicated that the binding of above complex to HSA and βLG may induce conformational and micro-environmental changes of two proteins. Protein-ligand docking analysis confirmed that the Pd(II) complex binds to residues located in the subdomain IIA of HSA and site A of βLG. All these experimental and computational results suggest that βLG and HSA might act as carrier protein for Pd(II) complex to deliver it to the target molecules.

Synthesis, characterization, protein interaction and antibacterial activity of a lanthanum(iii) complex [La(Trp)3(OH2)2] (Trp = tryptophan) as a new precursor for synthesis of La2O2CO3 nanoparticles

In the present study, a lanthanum(iii) complex containing tryptophan amino acid was synthesized and characterized.

Assessment of the interaction procedure between Pt(IV) prodrug [Pt(5,5'-dmbpy)Cl4 and human serum albumin: Combination of spectroscopic and molecular modeling technique

In this study, a cytotoxic Pt(IV) complex [Pt(5,5'-dmbpy)Cl₄ (5,5'-dmbpy is 5,5'-dimethyl-2,2'-bipyridine) was selected to investigate its affinity to human serum albumin (HSA) by spectroscopy and molecular docking methods. This complex has a bidentate nitrogen donor ligand with four chloride anions attached to a Pt(IV) metal in a distorted octahedral environment. The fluorescence data showed this complex quench the intrinsic fluorescence of HSA through a static quenching mechanism. The binding constant (K_b) and the number of binding sites (n) were obtained based on the results of fluorescence measurements. UV-vis, circular dichroism spectroscopy, and three-dimensional fluorescence spectroscopy proved that the Pt(IV) complex could slightly change the secondary structure of protein. Thermodynamic parameters show that the Pt(IV) complex binds to HSA through electrostatic and Vander Waals interactions with one binding site. The molecular docking results confirmed the spectroscopic results and showed that Pt(IV) complex is embedded into subdomain IIA of protein. The aim of this study is to describe the performance of effective anti-cancer drugs when faced with proteins such as HSA.

α-Mangostin Extraction from the Native Mangosteen (Garcinia mangostana L.) and the Binding Mechanisms of α-Mangostin to HSA or TRF

In order to obtain the biological active compound, α-mangostin, from the traditional native mangosteen (Garcinia mangostana L.), an extraction method for industrial application was explored. A high yield of α-mangostin (5.2%) was obtained by extraction from dried mangosteen pericarps with subsequent purification on macroporous resin HPD-400. The chemical structure of α-mangostin was verified mass spectrometry (MS), nuclear magnetic resonance (¹H NMR and ¹³C NMR), infrared spectroscopy (IR) and UV-Vis spectroscopy. The purity of the obtained α-mangostin was 95.6% as determined by HPLC analysis. The binding of native α-mangostin to human serum albumin (HSA) or transferrin (TRF) was explored by combining spectral experiments with molecular modeling. The results showed that α-mangostin binds to HSA or TRF as static complexes but the binding affinities were different in different systems. The binding constants and thermodynamic parameters were measured by fluorescence spectroscopy and absorbance spectra. The association constant of HSA or TRF binding to α-mangostin is 6.4832×10⁵ L/mol and 1.4652×10⁵ L/mol at 298 K and 7.8619×10⁵ L/mol and 1.1582×10⁵ L/mol at 310 K, respectively. The binding distance, the energy transfer efficiency between α-mangostin and HSA or TRF were also obtained by virtue of the Förster theory of non-radiation energy transfer. The effect of α-mangostin on the HSA or TRF conformation was analyzed by synchronous spectrometry and fluorescence polarization studies. Molecular docking results reveal that the main interaction between α-mangostin and HSA is hydrophobic interactions, while the main interaction between α-mangostin and TRF is hydrogen bonding and Van der Waals forces. These results are consistent with spectral results.

Synthesis, characterization, in vitro cytotoxicity, in silico ADMET analysis and interaction studies of 5-dithiocarbamato-1,3,4-thiadiazole-2-thiol and its zinc(ii) complex with human serum albumin: combined spectroscopy and molecular docking investigations

The binding site of new complex Zn(ii) of 5-dithiocarbamato-1,3,4-thiadiazole-2-thiol and HAS.