Mechanistic and conformational studies on the interaction of a platinum(II) complex containing an antiepileptic drug, levetiracetam, with bovine serum albumin by optical spectroscopic techniques in aqueous solution

Interaction of food colorant indigo carmine with human and bovine serum albumins: A multispectroscopic, calorimetric, and theoretical investigation

In this work we have studied the interaction of the food dye Indigo-Carmine (IndC) with the most studied model transport proteins i.e. human and bovine serum albumin (HSA & BSA). A multispectroscopic approach was used to analyze the details of the binding process. The intrinsic fluorescence of both the albumins was significantly quenched by IndC and the quenching was both static and dynamic in nature with the former being dominant. The HSA-lndC and BSA-IndC distance after complexation was determined by Förster resonance energy transfer (FRET) method which suggested efficient energy transfer from the albumins to IndC. Thermodynamics of serum protein-IndC complexation was estimated by isothermal titration calorimetry (ITC) which revealed that the binding was enthalpy driven. Circular dichroism (CD) and FTIR spectroscopy revealed that the binding of IndC induced secondary structural changes in both the serum proteins. Synchronous and 3D fluorescence spectroscopy revealed that the binding interaction caused microenvironmental changes of protein fluorophores. Molecular docking analysis suggested that hydrogen bonding and hydrophobic interactions are the major forces involved in the complexation process.

Exploring the Interaction Between the Newly Designed Antitumor Zn(II) Complex and CT-DNA/BSA: Spectroscopic Methods, DFT Computational Analysis, and Docking Simulation

A new zinc(II) complex formulated as [Zn(pipr-ac)2], where pipr-ac stands for piperidineacetate, was synthesized and structurally identified with the help of experimental and DFT methods. Frontier molecular orbital (FMO) analysis demonstrated that the new complex has higher biological activity compared to the free ligand. Molecular electrostatic potential (MEP) showed the nitrogen atoms and oxygen of carbonyl groups are the active sites of Zn(II) compound. Also, natural bond orbital (NBO) analysis confirmed the charge transfer from the ligating atoms to the metal ion and formation of four coordinated Zn(II) complex. MTT assay illustrated a noticeable cytotoxic activity of the new zinc(II) complex compared to cisplatin on K562 cell line. The CT-DNA and serum albumin (SA) binding of the Zn(II) complex were explored individually. In this regard, UV-Vis spectroscopy and florescence titration revealed the occurrences of fluorescence quenching of CT-DNA/SA by metal compound via static mechanism and creation of hydrogen bonds and van der Waals interactions between them. The binding was further confirmed by viscosity measurement and gel electrophoresis assay for CT-DNA and circular dichroism spectroscopy for SA. Moreover, molecular docking simulation demonstrated that the new compound binds mainly through hydrogen bonds to the groove of DNA and hydrogen bonds and van der Waals interactions to site I of SA.

Copper(II) Affects the Biochemical Behavior of Proinsulin C-peptide by Forming Ternary Complexes with Serum Albumin

Peptide hormones are essential signaling molecules with therapeutic importance. Identifying regulatory factors that drive their activity gives important insight into their mode of action and clinical development. In this work, we demonstrate the combined impact of Cu(II) and the serum protein albumin on the activity of C-peptide, a 31-mer peptide derived from the same prohormone as insulin. C-peptide exhibits beneficial effects, particularly in diabetic patients, but its clinical use has been hampered by a lack of mechanistic understanding. We show that Cu(II) mediates the formation of ternary complexes between albumin and C-peptide and that the resulting species depend on the order of addition. These ternary complexes notably alter peptide activity, showing differences from the peptide or Cu(II)/peptide complexes alone in redox protection as well as in cellular internalization of the peptide. In standard clinical immunoassays for measuring C-peptide levels, the complexes inflate the quantitation of the peptide, suggesting that such adducts may affect biomarker quantitation. Altogether, our work points to the potential relevance of Cu(II)-linked C-peptide/albumin complexes in the peptide's mechanism of action and application as a biomarker.

Preclinical Therapeutic Assessment of a New Chemotherapeutics [Dichloro(4,4’-Bis(2,2,3,3-Tetrafluoropropoxy) Methyl)-2,2’-Bipryridine) Platinum] in an Orthotopic Patient-Derived Xenograft Model of Triple-Negative Breast Cancers

Cisplatin is one of the most common therapeutics used in treatments of several types of cancers. To enhance cisplatin lipophilicity and reduce resistance and side effects, a polyfluorinated bipyridine-modified cisplatin analogue, dichloro[4,4’-bis(2,2,3,3-tetrafluoropropoxy)methyl)-2,2’-bipryridine] platinum (TFBPC), was synthesized and therapeutic assessments were performed. TFBPC displayed superior effects in inhibiting the proliferation of several cisplatin-resistant human cancer cell lines, including MDA-MB-231 breast cancers, COLO205 colon cancers and SK-OV-3 ovarian cancers. TFBPC bound to DNA and formed DNA crosslinks that resulted in DNA degradation, triggering the cell death program through the PARP/Bax/Bcl-2 apoptosis and LC3-related autophagy pathway. Moreover, TFBPC significantly inhibited tumor growth in both animal models which include a cell line-derived xenograft model (CDX) of cisplatin-resistant MDA-MB-231, and a patient-derived xenograft (PDX) model of triple-negative breast cancers (TNBCs). Furthermore, the biopsy specimen from TFBPC-treated xenografts revealed decreased expressions of P53, Ki-67 and PD-L1 coupled with higher expression of cleaved caspase 3, suggesting TFBPC treatment was effective and resulted in good prognostic indications. No significant pathological changes were observed in hematological and biochemistry tests in blood and histological examinations from the specimen of major organs. Therefore, TFBPC is a potential candidate for treatments of patients suffering from TNBCs as well as other cisplatin-resistant cancers.

Binding Studies of AICAR and Human Serum Albumin by Spectroscopic, Theoretical, and Computational Methodologies

The interactions of small molecule drugs with plasma serum albumin are important because of the influence of such interactions on the pharmacokinetics of these therapeutic agents. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) is one such drug candidate that has recently gained attention for its promising clinical applications as an anti-cancer agent. This study sheds light upon key aspects of AICAR’s pharmacokinetics, which are not well understood. We performed in-depth experimental and computational binding analyses of AICAR with human serum albumin (HSA) under simulated biochemical conditions, using ligand-dependent fluorescence sensitivity of HSA. This allowed us to characterize the strength and modes of binding, mechanism of fluorescence quenching, validation of FRET, and intermolecular interactions for the AICAR–HSA complexes. We determined that AICAR and HSA form two stable low-energy complexes, leading to conformational changes and quenching of protein fluorescence. Stern–Volmer analysis of the fluorescence data also revealed a collision-independent static mechanism for fluorescence quenching upon formation of the AICAR–HSA complex. Ligand-competitive displacement experiments, using known site-specific ligands for HSA’s binding sites (I, II, and III) suggest that AICAR is capable of binding to both HSA site I (warfarin binding site, subdomain IIA) and site II (flufenamic acid binding site, subdomain IIIA). Computational molecular docking experiments corroborated these site-competitive experiments, revealing key hydrogen bonding interactions involved in stabilization of both AICAR–HSA complexes, reaffirming that AICAR binds to both site I and site II.

Kinetic and Thermodynamic Investigation of Human Serum Albumin Interaction with Anticancer Glycine Derivative of Platinum Complex by Using Spectroscopic Methods and Molecular Docking

In this paper, a new anticancer Pt (II) complex, cis-[Pt (NH₃)₂(tertpentylgly)]NO₃, was synthesized with glycine-derivative ligand and characterized. Cytotoxicity of this water-soluble Pt complex was studied against human cancer breast cell line of MCF-7. The interaction of human serum albumin (HSA) with Pt complex was studied by using UV-Vis, fluorescence spectroscopy methods, and molecular docking at 27 and 37 °C in the physiological situation (I = 10 mM, pH = 7.4). The negative [Formula: see text] and positive [Formula: see text] indicated that electrostatic force may be a major mode in the binding between Pt complex and HSA. Binding constant values were obtained through UV-Vis and fluorescence spectroscopy that reveal strong interaction. The negative Gibbs free energy that was obtained by using the UV-Vis method offers spontaneous interaction. Fluorescence quenching the intensity of HSA by adding Pt complex confirms the static mode of interaction is effective for this binding process. Hill coefficients, n_H, Hill constant, k_H, complex aggregation number around HSA, <J>, number of binding sites, g, HSA melting temperature, T_m, and Stern-Volmer constant, k_SV, were also obtained. The kinetics of the interaction was studied, which showed a second-order kinetic. The results of molecular docking demonstrate the position of binding of Pt complex on HSA is the site I in the subdomain IIA.

Single-protein-based theranostic nanosystem within sub-10 nm scale for tumor imaging and therapy

A single-protein-based theranostic nanosystem within sub-10 nm scale was developed for tumor imaging and therapy.