Imtiyaz Yousuf

Enantiomeric fluoro-substituted benzothiazole Schiff base-valine Cu(II)/Zn(II) complexes as chemotherapeutic agents: DNA binding profile, cleavage activity, MTT assay and cell imaging studies

To evaluate the biological preference of chiral drugs toward DNA target, new metal-based chemotherapeutic agents of Cu(II) and Zn(II), l-/d-fluorobenzothiazole Schiff base-valine complexes 1 &2 (a and b), respectively were synthesized and thoroughly characterized. Preliminary in vitro DNA binding studies of ligand L and complexes 1 &2 (a and b) were carried out in Tris-HCl buffer at pH 7.2 to demonstrate the chiral preference of l-enantiomeric complexes over the d-analogues. The extent of DNA binding propensity was ascertained quantitatively by Kb, K and Ksv values which revealed greater binding propensity by l-enantiomeric Cu(II) complex 1a and its potency to act as a chemotherapeutic agent. The cleavage studies with pBR322 plasmid DNA revealed higher nuclease activity of 1a as compared to 2avia hydrolytic cleavage mechanism. The complexes 1 &2 (a and b) were also screened for antimicrobial activity which demonstrated significantly good activity for l-enantiomeric complexes. Furthermore, cytotoxicity of the complexes 1a and 1b was evaluated by the MTT assay on human HeLa cancer cell line which implicated that more than 50% cells were viable at 15μM. These results were further validated by cell imaging studies which demonstrated the nuclear blebbing.

Synthesis and spectroscopic characterization of diorganotin(IV) complexes of N′-(4-hydroxypent-3-en-2-ylidene)isonicotinohydrazide: chemotherapeutic potential validation by in vitro interaction studies with DNA/HSA, DFT, molecular docking and cytotoxic activity

Diorganotin(IV) complexes 1–3 (R = Me, 1; Bu, 2; Ph, 3) derived from the ligand N′-(4-hydroxypent-3-en-2-ylidene)isonicotinohydrazide were synthesized and thoroughly characterized by elemental analysis and spectroscopic techniques (UV-vis, IR, 1H, 13C and 119Sn NMR and ESI-MS). The molecular structure of diphenyltin(IV) complex 3 was further established by single crystal X-ray crystallography which showed that the complex crystallized in the monoclinic space group C21/c. To ascertain the pharmacokinetic and chemotherapeutic aspects of the synthesized diorganotin(IV) complexes 1–3, in vitro interaction studies were carried out with CT DNA/HSA by employing various biophysical methods viz., UV-vis, fluorescence, FT IR (in case of HSA only) and circular dichroism. Notably, all of the complexes exhibited a high propensity for DNA binding via electrostatic modes; the binding affinity was found to be in the order 2 > 3 > 1 and also revealed static quenching of the HSA fluorophore. The experimental findings were validated by density functional theory (DFT) calculations which determined the quantum mechanical (QM) reactivity descriptors viz., single point energy (H), hardness (η), electronic chemical potential (μ), electrophilicity (ω); on that basis the binding trend of the complexes with CT DNA and HSA could be predicted. Further, molecular docking studies were performed to visualize the preferential binding sites of diorganotin(IV) complexes with DNA and HSA. In vitro cytotoxicity of di-n-butyltin(IV) complex 2 was carried out in a panel of human cancer cell lines viz., U373MG (CNS), PC3 (prostrate), Hop62 (lung), HL60 (leukemia), HCT15 (colon), SK-OV-3 (ovarian), HeLa (cervix) and MCF7 (breast) which revealed significantly good activity with GI50 values of <10 μg mL−1 for most of the cell lines tested.

Crystal structure determination, spectroscopic characterization and biological profile of a tailored ionic molecular entity, Sn(IV) iminodiacetic acid–piperazinediium conjugate: in vitro DNA/RNA binding studies, Topo I inhibition activity, cytotoxic and systemic toxicity studies

A novel ionic tin(IV) iminodiacetic acid–piperazinediium conjugate (1) was designed and synthesized as a potential antitumor chemotherapeutic molecular entity and was thoroughly characterized by elemental analysis, FT-IR, 1H, 13C and 119Sn NMR, ESI MS and single crystal X-ray crystallography. Complex 1 resulted from the proton transfer reaction between iminodiacetic acid (H2IDA) and piperazine (pipz), and its subsequent complexation with tin(IV) chloride salt. 1 crystallized in orthorhombic space group Ima2 and comprises of an anionic metallic unit, a piperazinediium cation and a chloride ion. In continuity of our previous strategy in search of robust metal-based antitumor drug entities exhibiting reduced systemic toxicity, we have carried out in vitro interaction studies of 1 with ct-DNA, tRNA and Topo I targets, to validate its chemotherapeutic potential. Complex 1 exhibited more avid binding propensity with RNA which was reflected by its higher Kb and K values with RNA as compared to DNA. Topoisomerase inhibition activity of 1 was performed by gel electrophoresis which revealed significant inhibitory effect on the catalytic activity of the enzyme at 30 μM concentration. Molecular docking studies of the complex were carried out with DNA (PDB ID: 1BNA), RNA (PDB ID: 6TNA) and Topo I (PDB ID: ISC7) targets to ascertain the specific binding mode thereby substantiated the spectroscopic results. Cytotoxic studies were carried out on a panel of eight human cancer cell lines; U373MG, PC3, Hop62, HL60, HCT15, SK-OV-3, HeLa and MCF-7 by SRB assay which revealed significant regression specifically for HCT15, HOP62, MCF-7 and SK-OV-3 human cancer cell lines (GI50 value < 10) as compared to the standard drug Adriamycin. Systemic toxicity of 1 was carried out by the estimation of oxidative stress biomarkers such as lipid peroxides (expressed as malondialdehyde; MDA) and reduced glutathione (GSH) levels in kidney and liver homogenates and the study was supported by the histopathologic examination of kidney and liver of female Wistar rats.

In vitro DNA binding profile of enantiomeric dinuclear Cu(II)/Ni(II) complexes derived from l–/d–histidine–terepthaldehyde reduced Schiff base as potential chemotherapeutic agents

New chiral reduced Schiff base ligands, L1 and L2 derived from l-/d-histidine and terepthaldehyde, and their Cu(II) and Ni(II) dinuclear complexes 1 &2 (a and b) were synthesized and thoroughly characterized by various spectroscopic techniques. Comparative binding profile of both l-/d-enantiomeric Cu(II) and Ni(II) complexes with ct-DNA was studied by employing optical and spectroscopic techniques to evaluate their enantiopreferential selectivity towards molecular target DNA and thereby explore their relative chemotherapeutic potential. Quantitative assessment of DNA binding propensity was ascertained by calculating Kb, K and Ksv values of 1 &2 (a and b) which demonstrated higher binding affinity of l-enantiomeric Cu(II) complex, 1a and followed the order as 1a>1b>2a>2b. Scanning electron microscopy (SEM) was used to analyze the morphological changes of the DNA condensate in presence of complexes 1 (a and b). The SEM micrographs condensates revealed morphological transitions and formation of different structural features implicating the condensation process between the complexes and biomolecule occurred to form compact massive structures. The gel electrophoretic assay of complex 1a was carried out with pBR322 plasmid DNA which revealed an efficient cleaving ability of the complex via oxidative pathway with the involvement of singlet oxygen (1O2) and the superoxide anion (O2•-) radicals as the ROS responsible the cleavage reactions. Molecular docking studies of 1 (a and b) with DNA revealed selective recognition of G-C residues of the narrow minor groove of the DNA duplex and complex 1a demonstrated binding affinity towards DNA ascertained from its higher binding energy values. Furthermore, the cytotoxic assessment of 1a was examined on a panel of cancer cell lines of different histological origin employing SRB assay which revealed remarkably good cytotoxic activity towards HL60, HeLa and MCF7 cancer cell lines.

Single X-ray crystal structure, DFT studies and topoisomerase I inhibition activity of a tailored ionic Ag(I) nalidixic acid–piperazinium drug entity specific for pancreatic cancer cells

Novel ionic Ag(I)−piperazinium nalidixic acid conjugate 1 was synthesized as a potential antitumor agent and was thoroughly characterized by elemental analysis, FT-IR, 1H and 13C NMR and single X-ray crystal diffraction studies. Complex 1 crystallized in the triclinic space group P1 and comprises a dipiperazinium–Ag(I) cationic unit, two nalidixate (naI−) anionic moieties and a nitrate ion. The Ag(I) ion adopted a linear configuration upon coordination with two nitrogen atoms of piperazinium cations (pipzH+) arranged in a trans fashion. The density functional theory (DFT) studies of 1 revealed the HOMO and LUMO to be localized on the metal center viz., the dx2−y2 orbital and partially localized on the C27, C28, C29, C30, C31, C32, N7 and N6 atoms of the piperazinium moiety. Non covalent interaction (NCI) calculations were carried out to identify the weak non-covalent interactions from the topological analysis and reduced gradient of the electron density of complex 1. Our results revealed significant inter- and intramolecular non-covalent interactions between the naI− and [Ag(pip)2]2+ units. Furthermore, an analysis of Hirshfeld surfaces and fingerprint plots were carried out to ascertain a comparison between intermolecular interactions which provide interesting supramolecular architectures involving combinations of N–H⋯O, O–H⋯O and C–H⋯O linkages into a two-dimensional framework. In vitro binding studies of 1 with ct-DNA and tRNA revealed higher binding propensity for tRNA which was evidenced from its higher intrinsic binding constant, Kb and binding constant, K values and the mode of binding was found to be groove binding in nature. The catalytic activity of topoisomerase I enzyme in the presence of complex 1 was ascertained by gel electrophoretic assay which demonstrated significant inhibitory effects at a low concentration of 25 μM. The cytotoxicity activity of 1 was determined by SRB assay on MIA-PA-CA-2, HepG2, HeLa and MCF7 human cancer cell lines; these results exhibited specific and selective antitumor activity for the MIA-PA-CA-2 cancer cell line with a GI50 value <10.

Multispectroscopic insight, morphological analysis and molecular docking studies of CuII based chemotherapeutic drug entity with Human Serum Albumin (HSA) and Bovine Serum Albumin (BSA)

Abstract The interaction studies of CuII nalidixic acid–DACH chemotherapeutic drug entity, [C36H50N8O6Cu] with serum albumin proteins, viz., human serum albumin (HSA) and bovine serum albumin (BSA) employing UV–vis, fluorescence, CD, FTIR and molecular docking techniques have been carried out. Complex [C36H50N8O6Cu] demonstrated strong binding affinity towards serum albumin proteins via hydrophobic contacts with binding constants, K = 3.18 × 105 and 7.44 × 104 M–1 for HSA and BSA, respectively implicating a higher binding affinity for HSA. The thermodynamic parameters ΔG, ΔH and ΔS at different temperatures were also calculated and the interaction of complex [C36H50N8O6Cu] with HSA and BSA was found to be enthalpy and entropy favoured, nevertheless, complex [C36H50N8O6Cu] demonstrated higher binding affinity towards HSA than BSA evidenced from its higher binding constant values. Time resolved fluorescence spectroscopy (TRFS) was carried out to validate the static quenching mechanism of HSA/BSA fluorescence. The collaborative results of spectroscopic studies indicated that the microenvironment and the conformation of HSA and BSA (α–helix) were significantly perturbed upon interaction with complex [C36H50N8O6Cu]. Hirshfeld surfaces analysis and fingerprint plots revealed various intermolecular interactions viz., N–H····O, O–H····O and C–H····O linkages in a 2–dimensional framework that provide crucial information about the supramolecular architectures in the complex. Molecular docking studies were carried out to ascertain the preferential binding mode and affinity of complex [C36H50N8O6Cu] at the target site of HSA and BSA. Furthermore, only for Transmission electroscopy microscopy micrographs of HSA and BSA in presence of complex [C36H50N8O6Cu] revealed major protein morphological transitions and aggregation which validates efficient delivery of complex by serum proteins to the target site. Communicated by Ramaswamy H. Sarma Graphical Abstract

Exploring the intermolecular interactions and contrasting binding of flufenamic acid with hemoglobin and lysozyme: A biophysical and docking insight

The intermolecular interaction of flufenamic acid (Hfluf) with two model proteins i.e., hemoglobin and lysozyme was explored using fluorescence, UV-vis, circular dichroism, DLS, and molecular docking techniques. The corroborative spectroscopic techniques suggested efficient binding of Hfluf to both the proteins. The S-V plot in Hb-Hfluf system showed positive deviation highlighting the presence of both static and dynamic quenching. Hence, ground state complex model and sphere of action quenching model were used for the study. In Lyz-Hfluf system, a linear S-V plot was obtained indicating the presence of a single quenching mechanism. FRET study suggested a high probability of energy transfer from Hb/Lyz to Hfluf. Our thermodynamic results revealed that binding reaction in both the systems was exothermic and spontaneous. The UV-vis spectroscopy demonstrated that the binding of Hfluf affected the globin, Soret and oxy-bands of Hb along with globin band and polypeptide backbone of Lyz. CD spectra revealed the enhancement of ɑ-helicity in Lyz and decrease in case of Hb whereas the Rh values of proteins from DLS experiment corroborated the CD findings. 3-D fluorescence spectra highlighted the conformational changes upon binding whereas docking studies predicted the active binding site of both the proteins as the binding site of Hfluf.