Anu Arya

Characterization of 7-amino-4-methylcoumarin as an effective antitubercular agent: structure–activity relationships

OBJECTIVES The objective of the present study was to evaluate the antitubercular activity of amino and acyl amino derivatives of coumarins when used alone and in combination with isoniazid, rifampicin, streptomycin or ethambutol, and to decipher the mode of action of the most effective agent. METHODS A series of amino and acyl amino coumarins were synthesized and screened for activity against the Mycobacterium tuberculosis H37Rv strain. These compounds were further evaluated by standard assay procedures to determine their MBCs, fractional inhibitory concentration index values and cytotoxicities. The MICs for a susceptible and a multidrug-resistant clinical isolate of M. tuberculosis were also determined. Electron and fluorescence microscopy of the test compound-treated mycobacterial samples were also carried out in an attempt to find out the target of action. RESULTS 7-Amino-4-methylcoumarin (7-amino-4-methyl-2H-chromen-2-one; NA5) displayed the lowest MIC of 1 mg/L against not only H37Rv but also the susceptible as well as the multidrug-resistant clinical isolates. Certain acyl amino coumarins were also found to inhibit the aforementioned strains and isolates with MICs in the range of 1.0-3.5 mg/L. They were also found to act in synergy with isoniazid/rifampicin. Electron microscopy revealed the cell-wall-attacking characteristic of these compounds, while fluorescence microscopy indicated that mycolic acid might be the target of action. CONCLUSIONS The present study clearly demonstrated the in vitro antitubercular potential of the novel drug candidate NA5. Further studies are warranted to establish the in vivo efficacy and therapeutic potential of NA5.

Cytotoxic and Radio-sensitizing Effects of Polyphenolic Acetates in a Human Glioma Cell Line (BMG-1)

BACKGROUND AND AIMS Polyphenolic acetates (PAs) have antioxidant/ pro-oxidant properties and can also acetylate proteins (enzymes) by a novel acetoxy drug: calreticulin transacetylase acetylation system. While PAs have been investigated as pharmacological agents for the treatment of various diseases, their potential as anti-cancer agents or their efficacy as an adjuvant in anti-cancer therapeutics remains to be explored. In the present study we investigated the cytotoxic and radio-sensitizing effects of 7, 8- diacetoxy-4-methyl coumarin (DAMC) and 7- acetoxy-4-methyl coumarin (7-AMC) in a human glioma cell line (BMG-1). METHODS Cytotoxic and radio-sensitizing effects were investigated by studying reactive oxygen species (ROS) levels, metabolic viability, clonogenic survival, growth inhibition, cell cycle perturbation, DNA repair and cytogenetic damage, besides analyzing the histone (H3) acetylation. RESULTS Exposure of cells to DAMC and 7-AMC for 24 h showed a dose dependent increase in toxicity as indicated by reduced metabolic viability, clonogenic survival and cell proliferation, with DAMC being more toxic than 7-AMC. The degree of radiosensitization by DAMC was also higher as compared to 7-AMC as reflected by a decrease in the clonogenicity, enhanced radiation-induced cell cycle perturbation and apoptosis. DAMC impaired the removal of radiation-induced DNA double stranded breaks (measured by γH2AX immuno- fluorescence) and enhanced the cytogenetic damage (micronuclei formation), leading to an increase in mitotic death. While DAMC alone induced pan nuclear γH2AX fluorescence, both pan nuclear and spatially restricted foci was observed with the combined treatment (DAMC + Radiation) suggesting a complex nature of DNA damage and repair. DAMC- induced cytotoxic and radio-sensitizing effects were independent of its pro-oxidant activity, whereas histone H3 lysine (9/14) hyperacetylation appeared to be a potential target, regulating cellular responses to ionizing radiation (IR). CONCLUSIONS The polyphenolic acetate 7, 8- diacetoxy-4-methyl coumarin (DAMC) demonstrates both anticancer effects and radiosensitizing potential under in vitro conditions.

Chemoenzymatic synthesis of 3'-deoxy-3'-(4-substituted-triazol-1-YL)-5-methyluridine.

An efficient protocol has been developed for the synthesis of a small library of 3′-deoxy-3′-(4-substituted-triazol-1-yl)-5-methyluridine using Cu(I)-catalyzed Huisgen–Sharpless–Meldal 1,3-dipolar cycloaddition reaction of 3′-azido-3′-deoxy-5-methyluridine with different alkynes under optimized condition in an overall yields of 76%–92%. Here, the azido precursor compound, i.e., 3′-azido-3′-deoxy-5-methyluridine was chemoenzymatically synthesized from D-xylose in good yield. Some of the alkynes used in cycloaddition reaction were synthesized by the reaction of hydroxycoumarins or naphthols with propargyl bromide in acetone using K2CO3in excellent yields. All synthesized compounds were unambiguously identified on the basis of their spectral (IR, 1H-, 13C NMR spectra, and high-resolution mass spectra) data analysis.

7, 8-diacetoxy-4-methylcoumarin induced cell death in human tumor cells is influenced by calreticulin.

Calreticulin (CRT), an endoplasmic reticulum resident protein demonstrates transacetylase activity in presence of 7, 8 diacetoxy-4-methyl coumarin (DAMC) in vitro. To investigate the possible role of CRT and DAMC mediated protein acetylation in cells, we investigated the effects of DAMC in tumor cells with different levels of CRT. DAMC was more toxic (clonogenicity, metabolic viability and proliferation) to human glioma cells (BMG-1) expressing low endogenous CRT level as compared to head and neck carcinoma cells (KB) with a high CRT level. The cytotoxicity was accompanied by loss of mitochondrial membrane potential in both the cells, which correlated with corresponding changes in the levels of pro-apoptotic (Bax) and anti-apoptotic (NFkB) regulators. Manipulation of CRT protein level in KB cells by application of small RNA interference enhanced the sensitivity by four folds while over expression of CRT in BMG-1 cells reduced their sensitivity to DAMC by ~20% strongly suggesting the influence of CRT on DAMC induced cytotoxicity. The partial rescue of CROE cells from DAMC induced toxicity was accompanied by changes in NFkB levels and over all protein acetylation status, besides increase in the NADPH-cytochrome c reductase activity related to its well known antioxidant property. Since CRT is over-expressed in cancer cells, which are generally resistant to radio- and chemotherapy; targeting CRT transacetylase system, may be an attractive approach for increasing the efficacy of anticancer therapies.

Correction of Mars Colour Camera images for identification of spectral classes

Mars Colour Camera on-board the Mars Orbital Mission makes use of a Bayer pattern detector. Spectral response of RGB (red, green and blue) pixels of Bayer detector shows large overlap which reduces the spectral information content of the image. In the present paper, a simple method is suggested to correct the data for spectral overlap. It is shown that correction process significantly increases the spectral information content of the image and enhances the ability of the sensor to identify different target types like dust clouds and water ice clouds.