Mode of interaction of altretamine with calf thymus DNA: biophysical insights.

Insights into drug-DNA interactions have importance in medicinal chemistry as it has a major role in the evolution of new therapeutic drugs. Therefore, binding studies of small molecules with DNA are of significant interest. Spectroscopy, coupled with measurements of viscosity and molecular docking studies were employed to obtain mechanistic insights into the binding of altretamine with calf thymus DNA (CT-DNA). The UV-visible spectroscopic measurements study confirmed altretamine-CT-DNA complex formation with affinity constant ([15.68 ± 0.04] × 103 M-1), a value associated with groove binding phenomenon. The associated thermodynamic signatures suggest enthalpically driven interactions. The values of standard molar free energy change (ΔGmo) -(23.93 ± 0.23) kJ mol-1, enthalpy change (ΔvHHmo) -(50.84 ± 0.19) kJ mol-1 and entropy change (ΔSmo) -(90.29 ± 0.12) JK-1 mol-1 indicate the binding is thermodynamically favorable and an important role of the hydrogen bonds and Van der Waals interactions in the binding of altretamine with CT-DNA. Circular dichroism spectroscopy indicated insignificant conformational changes in the DNA backbone upon interaction with altretamine suggesting no distortion and/or unstacking of the base pairs in the DNA helix. UV-melting study suggested that the thermal stability of the DNA backbone is not affected by the binding of the drug. Competitive displacement assays with ethidium bromide, Hoechst-33258 and DAPI established the binding of altretamine with CT-DNA in the minor groove. The mode of binding was further confirmed by viscosity and molecular docking studies. Molecular docking further ascertained binding of altretamine in the minor groove of the CT-DNA, preferably with the A-T rich sequences.[Formula: see text]HighlightsAltretamine binds CT-DNA which is enthalpically driven with Ka of the order of 103Insignificant conformational change is observed due to DNA-altretamine complexationAltretamine binds favorably with A-T rich sequences in the minor groove of CT-DNAMechanistic insights obtained based on thermodynamic signaturesCommunicated by Ramaswamy H. Sarma.

Painkiller Isoxicam and Its Copper Complex Can Form Inclusion Complexes with Different Cyclodextrins: A Fluorescence, Fourier Transform Infrared Spectroscopy, and Nuclear Magnetic Resonance Study.

The interaction of a painkiller Isoxicam, belonging to the oxicam group of nonsteroidal anti-inflammatory drugs (NSAIDs) and its copper complex with different cyclodextrins (ß-CD, γ-CD, HPßCD, and HPγCD), has been investigated in both solution and the solid state. Steady state and time-resolved fluorescence spectroscopy, fluorescence anisotropy, 1H NMR, and FTIR spectroscopy are used. Both the drug and its copper complex form a host-guest inclusion complex with all CDs. Fluorescence spectroscopy is used to determine binding constants and stoichiometries of the host-guest complex. The strongest binding is seen for γ-CD. 1H NMR study showed that Isoxicam penetrates into the CD cavity from the more accessible wider side. For ß- and γ-CD, Isoxicam showed one type of binding, i.e., formation of an inclusion complex, whereas, for HPßCD and HPγCD, it showed two types of binding, i.e., inclusion in the CD cavities and interaction with the outer surface of the CD molecules mainly near the hydroxy propyl group. Deeper penetration occurred into the larger diameter cavity of γ-CD and HPγCD compared to ß-CD and HPßCD. From FTIR and 1H NMR study, it is seen that predominantly the π-electron-rich benzene part of the drug and its complex penetrate into the host cavity.

Interaction of a common painkiller piroxicam and copper-piroxicam with chromatin causes structural alterations accompanied by modulation at the epigenomic/genomic level.

BACKGROUND: NSAIDs are the most common class of painkillers and anti-inflammatory agents. They also show other functions like chemoprevention and chemosuppression for which they act at the protein but not at the genome level since they are mostly anions at physiological pH, which prohibit their approach to the poly-anionic DNA. Complexing the drugs with bioactive metal obliterate their negative charge and allow them to bind to the DNA, thereby, opening the possibility of genome level interaction. To test this hypothesis, we present the interaction of a traditional NSAID, Piroxicam and its copper complex with core histone and chromatin. METHODS: Spectroscopy, DLS, and SEM studies were applied to see the effect of the interaction on the structure of histone/chromatin. This was coupled with MTT assay, immunoblot analysis, confocal microscopy, micro array analysis and qRT-PCR. RESULTS: The interaction of Piroxicam and its copper complex with histone/chromatin results in structural alterations. Such structural alterations can have different biological manifestations, but to test our hypothesis, we have focused only on the accompanied modulations at the epigenomic/genomic level. The complex, showed alteration of key epigenetic signatures implicated in transcription in the global context, although Piroxicam caused no significant changes. We have correlated such alterations caused by the complex with the changes in global gene expression and validated the candidate gene expression alterations. CONCLUSION AND GENERAL SIGNIFICANCE: Our results provide the proof of concept that DNA binding ability of the copper complexes of a traditional NSAID, opens up the possibility of modulations at the epigenomic/genomic level.

Spectroscopic studies on the interaction of DNA with the copper complexes of NSAIDs lornoxicam and isoxicam.

Non Steroidal Anti-inflammatory Drugs (NSAIDs) form the most common class of anti-inflammatory and analgesic agents. They also show anticancer properties for which they exert their effects by interacting at the protein but not at the genomic level. This is because most NSAIDs are anions at physiological pH, which prohibit their approach to the polyanionic DNA backbone. Complexing NSAIDs with bioactive metal like copper obliterates this disadvantage. Here, copper complexes of two oxicam NSAIDs, Lornoxicam (Lx) and Isoxicam (Isx) have been chosen to study their interaction with calf thymus (ct) DNA and have been synthesized as per reported protocols. UV-vis absorption showed that DNA binding to Cu(II)-Lx complex alters the absorption spectra indicating changes in the electronic environment of the complex, whereas, for Cu(II)-Isx there was only small changes. Hence, UV-vis absorption was used to determine the binding constant, stoichiometry and thermodynamic parameters of Cu(II)-Lx. However, UV-melting studies and CD difference spectra showed that both Cu(II)-Lx and Cu(II)-Isx can interact with the DNA backbone albeit with different binding modes. The probable binding mode was determined by kinetics of EtBr displacement and viscosity measurements. Our results point to an intercalative mode of binding for Cu(II)-Lx and external groove binding for Cu(II)-Isx.