Attenuation of Cytotoxic Natural Product DNA Intercalating Agents by Caffeine

Many anti-tumor drugs function by intercalating into DNA. The xanthine alkaloid caffeine can also intercalate into DNA as well as form π-π molecular complexes with other planar alkaloids and anti-tumor drugs. The presence of caffeine could interfere with the intercalating anti-tumor drug by forming π-π molecular complexes with the drug, thereby blocking the planar aromatic drugs from intercalating into the DNA and ultimately lowering the toxicity of the drug to the cancer cells. The cytotoxic activities of several known DNA intercalators (berberine, camptothecin, chelerythrine, doxorubicin, ellipticine, and sanguinarine) on MCF-7 breast cancer cells, both with and without caffeine present (200 μg/mL) were determined. Significant attenuation of the cytotoxicities by caffeine was found. Computational molecular modeling studies involving the intercalating anti-tumor drugs with caffeine were also carried out using density functional theory (DFT) and the recently developed M06 functional. Relatively strong π–π interaction energies between caffeine and the intercalators were found, suggesting an “interceptor” role of caffeine protecting the DNA from intercalation

Determination of in silico rules for predicting small molecule binding behavior to nucleic acids in vitro.

The vast knowledge of nucleic acids is evolving and it is now known that DNA can adopt highly complex, heterogeneous structures. Among the most intriguing are the G-quadruplex structures, which are thought to play a pivotal role in cancer pathogenesis. Efforts to find new small molecules for these and other physiologically relevant nucleic acid structures have generally been limited to isolation from natural sources or rationale synthesis of promising lead compounds. However, with the rapid growth in computational power that is increasingly becoming available, virtual screening and computational approaches are quickly becoming a reality in academia and industry as an efficient and economical way to discover new lead compounds. These computational efforts have historically almost entirely focused on proteins as targets and have neglected DNA. We present research here showing that not only can software be utilized for targeting DNA, but that selectivity metrics can be developed to predict the binding mechanism of a small molecule to a DNA target. The software Surflex and Autodock were chosen for evaluation and were demonstrated to be able to accurately reproduce the known crystal structures of several small molecules that bind by the most common nucleic acid interacting mechanisms of groove binding and intercalation. These software were further used to rationalize known affinity and selectivity data of a 67 compound library of compounds for a library of nucleic acid structures including duplex, triplex and quadruplexes. Based upon the known binding behavior of these compounds, in silica metrics were developed to classify compounds as either groove binders or intercalators. These rules were subsequently used to identify new triplex and quadruplex binding small molecules by structure and ligand-based virtual screening approaches using a virtual library consisting of millions of commercially available small molecules. The binding behavior of the newly discovered triplex and quadruplex binding compounds was empirically validated using a number of spectroscopic, fluorescent and thermodynamic equilibrium techniques. In total, this research predicted the binding behavior of these test compounds in silica and subsequently validated these findings in vitro. This research presents a novel approach to discover lead compounds that target multiple nucleic acid morphologies

Discovery of novel triple helical DNA intercalators by an integrated virtual and actual screening platform

Virtual Screening is an increasingly attractive way to discover new small molecules with potential medicinal value. We introduce a novel strategy that integrates use of the molecular docking software Surflex with experimental validation by the method of competition dialysis. This integrated approach was used to identify ligands that selectively bind to the triplex DNA poly(dA)-[poly(dT)]2. A library containing ∼2 million ligands was virtually screened to identify compounds with chemical and structural similarity to a known triplex intercalator, the napthylquinoline MHQ-12. Further molecular docking studies using compounds with high structural similarity resulted in two compounds that were then demonstrated by competition dialysis to have a superior affinity and selectivity for the triplex nucleic acid than MHQ-12. One of the compounds has a different chemical backbone than MHQ-12, which demonstrates the ability of this strategy to ‘scaffold hop’ and to identify small molecules with novel binding properties. Biophysical characterization of these compounds by circular dichroism and thermal denaturation studies confirmed their binding mode and selectivity. These studies provide a proof-of-principle for our integrated screening strategy, and suggest that this platform may be extended to discover new compounds that target therapeutically relevant nucleic acid morphologies

تخليق وتقييم إمكانات مضادات الليباز والالتحام الجزيئي لـلمركب الجديد N \u27- (2-Hydroxy-5-nitrobenzylidene) naphthalene-2-sulfonohydrazide

N’-(2-Hydroxy-5-nitrobenzylidene) naphthalene-2-sulfonohydrazide (SB) was prepared by condensation reaction, of naphthalene-2-sulfonylchloride with 2-Hydroxy-5-nitrobenzaldehyde. The Schiff base product (SB) was isolated, purified and then spectrally characterized via UV-Vis, FT-IR, 1H and 13C NMR analysis, where strong evidences confirmed the formation of the desired product. Pancreatic porcine lipase inhibition of the Schiff base product was evaluated and compared with the reference “Orlistat”. The product was an active as a lipase enzyme inhibitor with IC50 42.65±0.97 mcg/ml. The molecular docking of the compound with porcine pancreatic lipase was investigating, the results of theoretical docking explained the experimental one since several hydrogen bonds between the Schiff base compound and amino acids in lipase were detected. Antimicrobial activity of SB product was also evaluated in vitro against several types of bacteria such as: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumonia and MRSA by Minimum Inhibitory Concentration (MIC) test using tetracycline (TE) as a standard antibiotic. Results showed a bacteriostatic effect of this compound against bacteria such as MRSA, P. aeruginosa and K. pneumoniae

Docking of indolo- and pyrrolo-pyrimidines to DNA. New DNA-interactive polycycles from amino-indoles/pyrroles and BMMA.

New indolo- and pyrrolo-pyrimidines of type 1-4 were studied for their ability to form stable complexes with DNA fragments. The calculated free energies of binding were found in the range -8.39 ÷ -16.72 Kcal/mol. The docking studies revealed a common binding mode with the chromophore intercalated between GC base pairs whereas the side chain lies along the minor groove

Selective Cytotoxicity of Rhodium Metalloinsertors in Mismatch Repair-Deficient Cells

Mismatches in DNA occur naturally during replication and as a result of endogenous DNA damaging agents, but the mismatch repair (MMR) pathway acts to correct mismatches before subsequent rounds of replication. Rhodium metalloinsertors bind to DNA mismatches with high affinity and specificity and represent a promising strategy to target mismatches in cells. Here we examine the biological fate of rhodium metalloinsertors bearing dipyridylamine ancillary ligands in cells deficient in MMR versus those that are MMR-proficient. These complexes are shown to exhibit accelerated cellular uptake which permits the observation of various cellular responses, including disruption of the cell cycle, monitored by flow cytometry assays, and induction of necrosis, monitored by dye exclusion and caspase inhibition assays, that occur preferentially in the MMR-deficient cell line. These cellular responses provide insight into the mechanisms underlying the selective activity of this novel class of targeted anticancer agents

Programing strand displacement reaction pathways using small molecular DNA binders

DNA has been used in nature as carriers of heredity information for billions of years. The last four decades have witnessed the success of DNA nanotechnology, an interdisciplinary research area in which DNA is used as a synthetic engineering tool rather than a carrier of genetic information. The growth of DNA nanotechnology crosses the boundaries between physics, chemistry, biology and computer science and enables DNA to function as an electronic component, substrate, drug delivery vector and data storage unit. The hybridization of DNA strictly follows the by Watson-Crick rule; thus, DNA base pairs are the most reliable and predictable building block in the true nanometer range. New methods and designs for controlling DNA hybridization have always provided the most essential momentum for the development of DNA nanotechnology. When small molecules bind to the double helical structure of DNA, either through intercalation or minor groove binding, the stability and functionality of DNA may be significantly altered, which is a fundamental basis for many therapeutic and sensing applications. Herein, we reveal, for the first time, that small molecular DNA binders may also be used to program the reaction pathways of toehold-mediated DNA strand displacement, an elementary building block in DNA nanotechnology