Exploring the interaction of a potent anti-cancer drug Selumetinib with bovine serum albumin: Spectral and computational attributes

The binding of drugs to plasma proteins determines its fate within the physiological system, hence profound understanding of its interaction within the bloodstream is important to understand its pharmacodynamics and pharmacokinetics and thereby its therapeutic potential. In this regard, our work delineates the mechanism of interaction of Selumetinib (SEL), a potent anti-cancer drug showing excellent effect against multiple solid tumors, with plasma protein bovine serum albumin (BSA), using methods such as absorption, steady-state fluorescence, time-resolved, fluorescence resonance energy transfer, Fourier transform infrared spectra (FTIR), circular dichroism (CD), synchronous and 3D-fluorescence, salt fluorescence, molecular docking and molecular dynamic simulations. The BSA fluorescence intensity was quenched with increasing concentration of SEL which indicates interactions of SEL with BSA. Stern-Volmer quenching analysis and lifetime studies indicate the involvement of dynamic quenching. However, some contributions from the static quenching mechanism could not be ruled out unambiguously. The association constant was found to be 5.34 × 105 M-1 and it has a single binding site. The Förster distance (r) indicated probable energy transmission between the BSA and SEL. The positive entropy changes and enthalpy change indicate that the main interacting forces are hydrophobic forces, also evidenced by the results of molecular modeling studies. Conformation change in protein framework was revealed from FTIR, synchronous and 3D fluorescence and CD studies. Competitive binding experiments as well as docking studies suggest that SEL attaches itself to site I (subdomain IIA) of BSA where warfarin binds. Molecular dynamic simulations indicate the stability of the SEL-BSA complex. The association energy between BSA and SEL is affected in the presence of different metals differently.

Molecular interactions and binding dynamics of Alpelisib with serum albumins: insights from multi-spectroscopic techniques and molecular docking

Alpelisib (ALP) is a potent anti-cancer drug showing promising activity against advanced breast cancers. Hence, profound understanding of its binding dynamics within the physiological system is vital. Herein, we have investigated interaction of ALP with human serum albumin (HSA) and bovine serum albumin (BSA) using spectroscopic techniques like absorption, fluorescence, time-resolved, synchronous and 3D-fluorescence, FRET, FT-IR, CD, and molecular docking studies. The intrinsic fluorescence of both BSA and HSA quenched significantly by ALP with an appreciable red shift in its emission maxima. Stern-Volmer analysis showed increase in Ksv with temperature indicating involvement of dynamic quenching process. This was further validated by no significant change in absorption spectrum of BSA and HSA (at 280 nm) upon ALP interaction, and by results of fluorescence time-resolved lifetime studies. ALP exhibited moderately strong binding affinity with BSA (of the order 106 M-1) and HSA (of the order 105 M-1), and the major forces accountable for stabilizing the interactions are hydrophobic forces. Competitive drug binding experiments and molecular docking suggested that ALP binds to site I in subdomain IIA of BSA and HSA. The Förster distance r was found to be less than 8 nm and 0.5 Ro < r < 1.5 Ro which suggests possible energy transfer between donors BSA/HSA and acceptor ALP. Synchronous and 3D-fluoresecnce, FT-IR and CD studies indicated that ALP induces conformational changes of BSA and HSA upon interaction.Communicated by Ramaswamy H. Sarma.

Insight into the Interaction of Malondialdehyde with Rabbit Meat Myofibrillar Protein: Fluorescence Quenching and Protein Oxidation

This research explored the effects of oxidative modification caused by different malondialdehyde (MDA) concentrations on rabbit meat myofibrillar protein (MP) structural characteristics and the interactions between MDA and MP. The fluorescence intensity of MDA-MP adducts, and surface hydrophobicity increased, whereas the intrinsic fluorescence intensity and free-amine content of MPs decreased as MDA concentration and incubation time increased. The carbonyl content was 2.06 nmol/mg for native MPs, while the carbonyl contents increased to 5.17, 5.57, 7.01, 11.37, 13.78, and 23.24 nmol/mg for MP treated with 0.25 to 8 mM MDA, respectively. When the MP was treated with 0.25 mM MDA, the sulfhydryl content and the α-helix content decreased to 43.78 nmol/mg and 38.46%, while when MDA concentration increased to 8 mM, the contents for sulfhydryl and α-helix decreased to 25.70 nmol/mg and 15.32%. Furthermore, the denaturation temperature and ΔH decreased with the increase in MDA concentration, and the peaks disappeared when the MDA concentration reached 8 mM. Those results indicate MDA modification resulted in structural destruction, thermal stability reduction, and protein aggregation. Besides, the first-order kinetics and Stern-Volmer equation fitting results imply that the quenching mechanism of MP by MDA may be mainly driven by dynamic quenching.

Inter-molecular Interaction Kinetics: Tale of Photon Anti-bunching and Bunching in Fluorescence Correlation Spectroscopy (FCS)

Molecular interactions are fundamental to any chemical or biological processes, and their rates define the operational sequence and control for any desirable product. Here, we deliberate on a recently developed novel fluorescence spectroscopic method, which combines fluorescence photon anti-bunching, photon bunching, time-correlated single-photon counting (TCSPC), and steady-state fluorescence spectroscopy, to study composite chemical reactions with single molecule sensitivity. The proposed method captures the full picture of the multifaceted quenching kinetics, which involves static quenching by ground state complexation and collisional quenching in the excited state under dynamic exchange of fluorophore in a heterogeneous media, and which cannot be seen by steady-state or lifetime measurements alone. Photon correlation in fluorescence correlation spectroscopy (FCS) provides access to interrogate interaction dynamics from picosecond to seconds, stitching all possible stages of dye-quencher interaction in a micellar media. This is not possible with the limited time window available to conventional ensemble techniques like TCSPC, flash photolysis, transient absorption, stop-flow, etc. The basic premises of such unified global analysis and sanctity of extracted parameters critically depends on the minimum but precise description of reaction scheme, for which careful inspection of ensemble spectroscopy data for photo-physical behaviour is very important. Though in this contribution we discussed and demonstrated the merits of photon antibunching and bunching spectroscopy for dye-quencher interaction in cationic cetyltrimethylammonium bromide (CTAB) micellar solution by photo-induced electron transfer mechanism and the influence of micellar charge and microenvironment on the interaction kinetics, but in principal similar arguments are equally applicable to any other interaction mechanisms which alter fluorescence photon correlations, like Förster resonance energy transfer (FRET), proton transfer, isomerisation, etc.

pH-responsive zwitterionic carbon dots for detection of rituximab antibody

Zwitterionic carbon dots (CDs) have received much attention as a result of good photostability, high biocompatibility, and high quantum yield. In this study, novel zwitterionic CDs were synthesized using a simple hydrothermal method of citric acid (CA) and l-histidine as carbon and nitrogen precursors, respectively. Prepared zwitterionic CDs have an average particle size of 4 nm diameter and showed green fluorescence with a peak at 530 nm when excited at 470 nm; quantum efficiency was 39.34% using rhodamine 6G as a baseline. The fluorescence intensity of zwitterionic CDs was quenched by rituximab in the range 0-400 μmol L^-1 , with a limit of detection of 27 μmol L^-1 . In addition, the synthesized zwitterionic CDs had low toxicity, good stability, and high selectivity and sensitivity sensing for rituximab, therefore zwitterionic CDs are a promising candidate for practical applications.

Binding properties of sodium glucose co-transporter-2 inhibitor empagliflozin to human serum albumin: spectroscopic methods and computer simulations

Empagliflozin is an oral sodium glucose co-transporter-2 inhibitor for type 2 diabetes mellitus. The interaction between empagliflozin and human serum albumin (HSA) was investigated experimentally and theoretically. Fluorescence quenching and time-resolved fluorescence spectroscopy indicated that the quenching mechanism of empagliflozin and HSA was dynamic and that the effective binding constant at body temperature was 3.495 × 10³ M^-1. Thermodynamic parameters showed that hydrophobic forces were the major binding force in the interaction between empagliflozin and HSA. Circular dichroism, Fourier transform infrared, and 3 D fluorescence spectroscopy revealed that empagliflozin showed a slight change in secondary structure without changing the basic carbon framework of HSA. Site marker displacement experiments revealed that empagliflozin bound to site I of HSA, which was supported by molecular docking. Molecular dynamic simulations indicated that empagliflozin could bind to HSA stably. This study provided insights into the binding mechanism between empagliflozin and HSA.Communicated by Ramaswamy H. Sarma.