Spectroscopic and molecular modeling studies on the interaction of tyrosine kinase inhibitors with human serum albumin / Md. Zahirul Kabir

Targeted therapies, involving new class drug molecules have shown inhibitory activities against signaling pathways that are responsible for triggering various carcinomas. Tyrosine kinases form an important class of enzymes of these signaling pathways and can be a useful target to develop effective therapeutic agents as tyrosine kinase inhibitors to treat various cancers. Some of the FDA-approved drug molecules, known as tyrosine kinase inhibitors are vandetanib (VDB), lapatinib (LAP), gefitinib (GEF) and sunitinib (SU), which are currently being used for the treatment of medullary thyroid, breast, lung and renal cancers, respectively. Interaction mechanisms of VDB, LAP, GEF and SU binding to human serum albumin (HSA), the major transport protein in the human blood circulation were explored using various spectroscopic techniques such as fluorescence, absorption and circular dichroism (CD) along with in silico studies. Quenching of the protein fluorescence upon addition of these ligands was characterized as the static quenching, which confirmed the complex formation between the ligand and the protein. Such complex formation was also affirmed by absorption spectral results. Moderate binding affinity for these interactions was evident from the binding constant (Ka) values, obtained at 298 K, which had fallen in the range of 104– 105 M–1 except VDB–HSA interaction, which showed relatively weaker binding affinity. Thermodynamic data for the binding equilibria predicted involvement of hydrophobic and van der Waals interactions along with hydrogen bonds in stabilizing drug–HSA complexes, which was also supported by molecular docking results. The far- UV and the near-UV CD spectra showed changes in the secondary and the tertiary structures, respectively, of HSA upon ligand binding. Three-dimensional fluorescence spectral results also indicated ligand-induced microenvironmental perturbations around protein fluorophores. Binding of these ligands to HSA offered significant protection to the protein against thermal denaturation. Competitive site-marker displacement results as well as molecular docking analyses revealed preferred binding location of these drug molecules primarily at site I for VDB and SU while at site III for LAP and GEF, located in subdomains IIA and IB, respectively, of HSA. The influence of a few common ions on the binding reaction between the ligand and HSA was also noticed

Differences in levels of E. coli contamination of point of use drinking water in Bangladesh

This study aimed to quantify the inequalities and identify the associated factors of the UN sustainable development goal (SDG) targets in relation to safe drinking water. The concentration of the gut bacterium Escherichia coli in drinking water at the point of use (POU) and other information were extracted from the latest wave of the nationally representative Bangladesh Multiple Indicator Cluster Survey (MICS 2019). Bivariate and multivariable multinomial logistic regression models were used to identify potential predictors of contamination, whereas, classification trees were used to determine specific combinations of background characteristics with significantly higher rates of contamination. A higher risk of contamination from drinking water was observed for households categorized as middle or low wealth who collected water from sources with higher concentrations of E. coli. Treatment of drinking water significantly reduced the risk of higher levels of contamination, whereas owning a pet was significantly associated with recontamination. Regional differences in the concentrations of E. coli present in drinking water were also observed. Interventions in relation to water sources should emphasize reducing the level of E. coli contamination. Our results may help in developing effective policies for reducing diarrheal diseases by reducing water contamination risks

Interactive association between RhoA transcriptional signaling inhibitor, CCG1423 and human serum albumin: Biophysical and in silico studies

Multiple spectroscopic techniques, such as fluorescence, absorption, and circular dichroism along with in silico studies were used to characterize the binding of a potent inhibitor molecule, CCG1423 to the major transport protein, human serum albumin (HSA). Fluorescence and absorption spectroscopic results confirmed CCG1423–HSA complex formation. A strong binding affinity stabilized the CCG1423–HSA complex, as evident from the values of the binding constant (Ka = 1.35 × 106–5.43 × 105 M−1). The KSV values for CCG1423–HSA system were inversely correlated with temperature, suggesting the involvement of static quenching mechanism. Thermodynamic data anticipated that CCG1423–HSA complexation was mainly driven by hydrophobic and van der Waals forces as well as hydrogen bonds. In silico analysis also supported these results. Three-dimensional fluorescence and circular dichroism spectral analysis suggested microenvironmental perturbations around protein fluorophores and structural (secondary and tertiary) changes in the protein upon CCG1423 binding. CCG1423 binding to HSA also showed some protection against thermal denaturation. Site-specific marker-induced displacement results revealed CCG1423 binding to Sudlow’s site I of HSA, which was also confirmed by the computational results. A few common ions were also found to interfere with the CCG1423–HSA interaction

Molecular Recognition between Anticancer Drug, Regorafenib and Human Serum Albumin: Interaction Revisited

The wet-lab techniques (fluorimetry and spectrophotometry), along with computational techniques (molecular docking and molecular dynamics (MD) simulation), were applied to re-examine the association of an anticancer drug, regorafenib (REG) with human serum albumin (HSA). The REG-induced protein fluorescence quenching was characterized as static quenching based on a decrement in the KSV (Stern-Volmer constant) with increasing temperature and hyperchromic effect in the absorption spectra. The REG–HSA complex (Ka = 0.63 – 1.17 × 105 M–1) was stabilized by hydrophobic and van der Waals interactions in combination with hydrogen bonds, as revealed by thermodynamic data (ΔrS° = +17.17 J mol–1 K–1 and ΔrH° = –23.00 kJ mol–1), and further supported by molecular docking assessment. Microenvironmental fluctuations around HSA fluorophores and better protein stability against thermal stress were evident due to REG-HSA complexation. Accessibility of both Sudlow\u27s Sites I and II but priority for Site I of the protein for REG was inferred by the competitive ligand displacement and molecular docking assessments. MD simulation results supported the stability of the complex

Probing the interaction of 2,4-dichlorophenoxyacetic acid with human serum albumin as studied by experimental and computational approaches

To characterize the binding of a widely used herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) to the major transporter in human circulation, human serum albumin (HSA), multi-spectroscopic approaches such as fluorescence, absorption and circular dichroism along with computational methods were employed. Analysis of the fluorescence and absorption spectroscopic data confirmed the 2,4-D–HSA complex formation. A static quenching mechanism was evident from the inverse temperature dependence of the KSV values. The complex was stabilized by a weak binding affinity (Ka = 5.08 × 103 M−1 at 298 K). Quantitative analysis of thermodynamic data revealed participation of hydrophobic and van der Waals interactions as well as hydrogen bonds in the binding process. Circular dichroism and three-dimensional fluorescence spectral results showed structural (secondary and tertiary) changes in HSA as well as microenvironmental perturbation around protein fluorophores (Trp and Tyr residues) upon 2,4-D binding. Addition of 2,4-D to HSA was found to improve protein's thermal stability. Competitive displacement results as well as computational analyses suggested preferred location of the 2,4-D binding site as Sudlow's site I (subdomain IIA) in HSA

Molecular interaction study of an anticancer drug, ponatinib with human serum albumin using spectroscopic and molecular docking methods

Binding of a potent anticancer agent, ponatinib (PTB) to human serum albumin (HSA), main ligand transporter in blood plasma was analyzed with several spectral techniques such as fluorescence, absorption and circular dichroism along with molecular docking studies. Decrease in the K SV value with increasing temperature pointed towards PTB-induced quenching as the static quenching, thus affirming complexation between PTB and HSA. An intermediate binding affinity was found to stabilize the PTB-HSA complex, as suggested by the K a value. Thermodynamic analysis of the binding phenomenon revealed participation of hydrophobic and van der Waals interactions along with hydrogen bonds, which was also supported by molecular docking analysis. Changes in both secondary and tertiary structures as well as in the microenvironment around Trp and Tyr residues of HSA were anticipated upon PTB binding to the protein, as manifested from circular dichroism and three-dimensional fluorescence spectra, respectively. Binding of PTB to HSA led to protein's thermal stabilization. Competitive ligand displacement experiments using different site markers such as warfarin, indomethacin and ketoprofen disclosed the binding site of PTB as Sudlow's site I in HSA, which was further confirmed by molecular docking analysis. © 2019 Elsevier B.V

Spectroscopic studies on the interaction of green synthesized-gold nanoparticles with human serum albumin

The interaction of gold nanoparticles, synthesized using Curcuma mangga extract (CM-AuNPs) with human serum albumin (HSA) was investigated with the help of fluorescence, UV absorption and circular dichroism (CD) spectroscopy. In view of the positive correlation of Stern-Volmer constant with temperature, quenching of protein fluorescence observed upon addition of CM-AuNPs seems to occur through collisional mechanism. The quenching mechanism was further substantiated by UV absorption spectral results, where no significant change in the absorption spectrum of HSA was observed upon addition of CM-AuNPs. Analysis of the fluorescence quenching titration data revealed moderate binding affinity (Ka = 0.97 × 104 M−1 at 298 K) between CM-AuNP and HSA. The complexation between CM-AuNP and HSA was predicted to be stabilized by hydrophobic forces, as reflected from the thermodynamic data (ΔH = +35.5 kJ mol−1 and ΔS = +195.62 J mol−1 K−1). Three-dimensional fluorescence spectral analysis demonstrated perturbation of microenvironment around Trp and Tyr residues in HSA upon CM-AuNPs addition. While interaction between CM-AuNP and HSA produced significant tertiary structural change in the protein, secondary structures remained unaltered, as elucidated by near-UV and far-UV CD spectral analyses, respectively. ANS displacement experiments suggested Sudlow's Site II, located in subdomain IIIA, as the preferred binding site of CM-AuNP on HSA

Exploring the interaction mechanism of a dicarboxamide fungicide, iprodione with bovine serum albumin

Abstract: Binding of iprodione (IPR), a dicarboxamide fungicide, to the carrier protein in bovine circulation, bovine serum albumin (BSA) was characterized with the help of fluorescence, absorption, circular dichroism and Fourier transform infrared (FTIR) spectral measurements in combination with computational analysis. The increase in the KSV (Stern–Volmer constant) value with temperature and absorption spectral results characterized the IPR-induced quenching of BSA fluorescence as dynamic quenching. On the other hand, higher value (> 1011 M−1 s−1) of the bimolecular quenching rate constant (kq) suggested complex formation between IPR and BSA. In view of it, increase in KSV value with temperature can be considered as an indication of the involvement of endothermic apolar (hydrophobic) interactions in stabilizing the IPR–BSA complex, as these forces are maximized at higher temperature. A weak binding affinity was anticipated from the values of the binding constant (Ka = 0.83–2.69 × 103 M−1) for IPR–BSA association. Thermodynamic analysis of the binding data further supported contribution of hydrophobic interactions in the IPR–BSA association process. This result was validated by the computational docking analysis. Spectral results from three-dimensional fluorescence and circular dichroism demonstrated microenvironmental changes around BSA fluorophores and protein’s structural (secondary and tertiary) alterations, respectively, upon IPR binding to the protein. Slight variation in the secondary structures of BSA in the presence of IPR was also verified from FTIR spectral results. IPR was found to bind to both site I (subdomain IIA) and site II (subdomain IIIA) of BSA, showing more preference toward site II, as identified by the competitive drug displacement results and supported by the computational analysis. Graphic abstract: [Figure not available: see fulltext.]. © 2019, Institute of Chemistry, Slovak Academy of Sciences

Interactive association between RhoA transcriptional signaling inhibitor, CCG1423 and human serum albumin: Biophysical and <i>in silico</i> studies

<p>Multiple spectroscopic techniques, such as fluorescence, absorption, and circular dichroism along with <i>in silico</i> studies were used to characterize the binding of a potent inhibitor molecule, CCG1423 to the major transport protein, human serum albumin (HSA). Fluorescence and absorption spectroscopic results confirmed CCG1423–HSA complex formation. A strong binding affinity stabilized the CCG1423–HSA complex, as evident from the values of the binding constant (<i>K</i>_<i>a</i> = 1.35 × 10⁶–5.43 × 10⁵ M⁻¹). The <i>K</i>_<i>SV</i> values for CCG1423–HSA system were inversely correlated with temperature, suggesting the involvement of static quenching mechanism. Thermodynamic data anticipated that CCG1423–HSA complexation was mainly driven by hydrophobic and van der Waals forces as well as hydrogen bonds. <i>In silico</i> analysis also supported these results. Three-dimensional fluorescence and circular dichroism spectral analysis suggested microenvironmental perturbations around protein fluorophores and structural (secondary and tertiary) changes in the protein upon CCG1423 binding. CCG1423 binding to HSA also showed some protection against thermal denaturation. Site-specific marker-induced displacement results revealed CCG1423 binding to Sudlow’s site I of HSA, which was also confirmed by the computational results. A few common ions were also found to interfere with the CCG1423–HSA interaction.</p