No abstract

Non-steroidal anti-inflammatory drugs and aureolic acid group of anti-cancer drugs belong to the class of generic drugs. Research with some members of these two groups of drugs in different laboratories has unveiled functions other than those for which they were primarily developed as drugs. Here we have reviewed the molecular mechanism behind the multiple functions of these drugs that might lead to employ them for treatment of diseases in addition to those they are presently employed.

SUMMARY The bacterial RNA polymerase (RNAP) holoenzyme consists of a catalytic core enzyme in complex with a σ factor that is required for promoter-specific transcription initiation. During initiation, members of the σ70 family of σ factors contact two conserved promoter elements, the −10 and −35 elements, that are separated by ~17 base pairs (bp). σ70 family members contain four flexibly linked domains. Two of these domains, σ2 and σ4, contain determinants for interactions with the promoter −10 and −35 elements, respectively. σ2 and σ4 also contain core-binding determinants. When bound to core the inter-domain distance between σ2 and σ4 matches the distance between promoter elements separated by ~17 bp. Prior work indicates that during early elongation the nascent RNA-assisted displacement of σ4 from core can enable the holoenzyme to adopt a configuration in which σ2 and σ4 are bound to “promoter-like” DNA elements separated by a single base pair. Here we demonstrate that holoenzyme can also adopt configurations in which σ2 and σ4 are bound to “promoter-like” DNA elements separated by 0, 2 or 3 bp. Thus, our findings suggest that displacement of σ4 from core enables the RNAP holoenzyme to adopt a broad range of “elongation-specific” configurations.

The aqueous-phase self-association of mithramycin (MTR), an aureolic acid anticancer antibiotic, has been studied using different spectroscopic techniques such as absorption, fluorescence, circular dichroism, and 1H nuclear magnetic resonance spectroscopy. Results from these studies indicate self-association of the anionic antibiotic at pH 8.0 over a concentration range from micromolar to millimolar. These results could be ascribed to the following steps of self-association: M + M left arrow over right arrow M2, M2 + M left arrow over right arrow M3, and M3 + M left arrow over right arrow M4, where M, M2, M3, and M4 represent the monomer, dimer, trimer, and tetramer of mithramycin, respectively. Dynamic light scattering and isothermal titration calorimetry studies also support aggregation. In contrast, an insignificant extent of self-association is found for the neutral drug (at pH 3.5) and the [(MTR)2Mg2+] complex (at pH 8.0). Analysis of 2D NMR spectra of 1 mM MTR suggests that the sugar moieties play a role in the self-association process. Self-association of the drug might occur either via hydrophobic interaction of the sugar residues among themselves or water-mediated hydrogen bond formation between sugar residue(s). On the other hand, absence of a significant upfield shift of the aromatic protons from 100 microM to 1 mM MTR suggests against the possibility of stacking interactions between the aromatic rings as a stabilizing force for the formation of the dimer and higher oligomers.

One of the major attributes for the biological action of the aureolic acid anticancer antibiotics chromomycin A(3) (CHR) and mithramycin (MTR) is their ability to bind bivalent cations such as Mg(II) and Zn(II) ions and form high affinity 2:1 complexes in terms of the antibiotic and the metal ion, respectively. As most of the cellular Zn(II) ion is found to be associated with proteins, we have examined the effect of MTR/CHR on the structure and function of a representative structurally well characterized Zn(II) metalloenzyme, alcohol dehydrogenase (ADH) from yeast. MTR and CHR inhibit enzyme activity of ADH with inhibitory constants of micromolar order. Results from size-exclusion column chromatography, dynamic light scattering, and isothermal titration calorimetry have suggested that the mechanism of inhibition of the metalloenzyme by the antibiotics is due to the antibiotic-induced disruption of the enzyme quaternary structure. The nature of the enzyme inhibition, the binding stoichiometry of two antibiotics per monomer, and comparable dissociation constants for the antibiotic and free (or substrate-bound) ADH imply that the association occurs as a consequence of the binding of the antibiotics to Zn(II) ion present at the structural center. Confocal microscopy shows the colocalization of the antibiotic and the metalloenzyme in HepG2 cells, thereby supporting the proposition of physical association between the antibiotic(s) and the enzyme inside the cell.

Here we have examined the association of an aureolic acid antibiotic, chromomycin A3 (CHR), with Cu(2+). CHR forms a high affinity 2:1 (CHR:Cu(2+)) complex with dissociation constant of 0.08 × 10(-10) M(2) at 25°C, pH 8.0. The affinity of CHR for Cu(2+) is higher than those for Mg(2+) and Zn(2+) reported earlier from our laboratory. CHR binds preferentially to Cu(2+) in presence of equimolar amount of Zn(2+). Complex formation between CHR and Cu(2+) is an entropy driven endothermic process. Difference between calorimetric and van't Hoff enthalpies indicate the presence of multiple equilibria, supported from biphasic nature of the kinetics of association. Circular dichroism spectroscopy show that [(CHR)(2):Cu(2+)] complex assumes a structure different from either of the Mg(2+) and Zn(2+) complex reported earlier. Both [(CHR)(2):Mg(2+)] and [(CHR)(2):Zn(2+)] complexes are known to bind DNA. In contrast, [(CHR)(2):Cu(2+)] complex does not interact with double helical DNA, verified by means of Isothermal Titration Calorimetry of its association with calf thymus DNA and the double stranded decamer (5'-CCGGCGCCGG-3'). In order to interact with double helical DNA, the (antibiotic)(2) : metal (Mg(2+) and Zn(2+)) complexes require a isohelical conformation. Nuclear Magnetic Resonance spectroscopy shows that the Cu(2+) complex adopts a distorted octahedral structure, which cannot assume the required conformation to bind to the DNA. This report demonstrates the negative effect of a bivalent metal upon the DNA binding property of CHR, which otherwise binds to DNA in presence of metals like Mg(2+) and Zn(2+). The results also indicate that CHR has a potential for chelation therapy in Cu(2+) accumulation diseases. However cytotoxicity of the antibiotic might restrict the use.

No abstract

Oenanthe javanica Blume (DC) is an aromatic medicinal herb having pharmacological properties such as antioxidant, anti-quorum sensing, anticoagulant, antitoxic, hepatoprotective, anti-hepatitis B virus and memory improvement. It is one of the most consumed vegetable throughout the year in Manipur. The present study was carried out to analyze the phytochemical constituents, antioxidant activity and total phenolic and total flavonoid content of Oenanthe javanica. Preliminary phytochemical analysis was done using standard procedure. Total phenolic, total flavonoid content and antioxidant activities were determined spectrophotometrically in crude aqueous and methanolic extracts. Preliminary phytochemical analysis indicates the presence of amino acids, carbohydrates, proteins, flavonoids, phenolic compounds, steroids and terpenoids, saponins, tannins, cardiac glycosides except alkaloids and phlobatannins. The present study demonstrates the antioxidant activity of Oenanthe javanica Blume (DC) due to the various phytochemicals present in the extract which confer their traditional uses as food and medicine.