Novel molecular hybrids of cinnamic acids and guanylhydrazones as potential antitubercular agents

In an attempt to identify potential new agents active against tuberculosis, 20 novel phenylacrylamide derivatives incorporating cinnamic acids and guanylhydrazones were synthesized using microwave assisted synthesis. Activity of the synthesized compounds was evaluated using resazurin microtitre plate assay (REMA) against Mycobacterium tuberculosis H37Rv. Based on empirical structure–activity relationship data it was observed that both steric and electronic parameters play major role in the activity of this series of compounds. Compound 7s (2E)-N-((-2-(3,4-dimethoxybenzylidene) hydrazinyl) (imino) methyl)-3-(4-methoxyphenyl) acrylamide showed MIC of 6.49 μM along with good safety profile of >50-fold in VERO cell line. Thus, this compound could act as a potential lead for further antitubercular studies.     

Characterization of glyceraldehyde-3-phosphate dehydrogenase as a novel transferrin receptor

A majority of cells obtain of transferrin (Tf) bound iron via transferrin receptor 1 (TfR1) or by transferrin receptor 2 (TfR2) in hepatocytes. Our study establishes that cells are capable of acquiring transferrin iron by an alternate pathway via GAPDH.These findings demonstrate that upon iron depletion, GAPDH functions as a preferred receptor for transferrin rather than TfR1 in some but not all cell types. We utilized CHO-TRVb cells that do not express TfR1 or TfR2 as a model system. A knockdown of GAPDH in these cells resulted in a decrease of not only transferrin binding but also associated iron uptake. The current study also demonstrates that, unlike TfR1 and TfR2 which are localized to a specific membrane fraction, GAPDH is located in both the detergent soluble and lipid raft fractions of the cell membrane. Further, transferrin uptake by GAPDH occurs by more than one mechanism namely clathrin mediated endocytosis, lipid raft endocytosis and macropinocytosis. By determining the kinetics of this pathway it appears that GAPDH-Tf uptake is a low affinity, high capacity, recycling pathway wherein transferrin is catabolised. Our findings provide an explanation for the detailed role of GAPDH mediated transferrin uptake as an alternate route by which cells acquire iron.     

IL-6 inhibits IFN-γ induced autophagy in Mycobacterium tuberculosis H37Rv infected macrophages

The significance of IL-6 production in tuberculosis is yet to be fully elucidated, although it is known for quite some time that IL-6 interferes with IFN-γ induced signal. In order to know which cellular process induced by IFN-γ is actually counteracted by IL-6, we studied the role of IL-6 on IFN-γ induced autophagy formation in virulent Mycobacterium tuberculosis infection in THP-1 cells, since it is well characterized that induction of autophagy by IFN-γ eliminates intracellular mycobacterium by overcoming the phagosome maturation block imposed by bacilli. We report here that IL-6 inhibits both IFN-γ and starvation induced autophagy in M. tuberculosis H37Rv infected cells. M. tuberculosis H37Rv infection results in time dependent production of IL-6 in THP-1 cells and neutralization of this endogenous IL-6 by anti-IL-6 antibody significantly enhances the IFN-γ mediated killing of the intracellular bacteria. IL-6 time dependently lowers Atg12-Atg5 complex and therefore inhibits autophagosome biogenesis rather than autophagolysosome formation. IL-6 also affects IFN-γ mediated stimulation of mTOR, p-38 and JNK pathways. These results clearly indicate that virulent mycobacteria strategically upregulate IL-6 production to combat innate immunity.     

Evaluation of in vitro inhibitory potential of small interfering RNAs directed against various regions of foot-and-mouth disease virus genome

India is endemic for foot-and-mouth disease and it continues to be a major threat to the livestock industry despite vaccination programmes. In the present study, the ability of specific small interfering (si)RNAs directed against different genomic regions of foot-and-mouth disease virus (FMDV) to inhibit virus replication in BHK-21 cells was examined. For preliminary evaluation of possible siRNA-mediated FMDV inhibition, a cocktail of several unique populations of 12-30bp siRNAs were successfully produced corresponding to three target regions located at structural (VP3-VP1), non-structural (2A-2C), and non-structural-untranslated (3D-3'UTR) region of serotype Asia1. Once the populations of siRNAs generated were found to reduce the virus titre significantly, two highly conserved 21bp siRNA duplexes were designed by analysing all FMDV sequence entries available in public-domain databases. In virus titration assay, more than 99% inhibition of virus yield for all the four serotypes (type Asia1, O, A, and C) could be demonstrated in cells transfected with each of the FMDV-specific siRNAs at 24h post-infection, compared to control cells transfected with scrambled siRNA. This was well supported by reduction in OD values in FMDV-specific sandwich ELISA. Although 100-fold reduction in virus titre with siRNA1 is substantial considering the transfection efficiency and fixed level of input siRNA, siRNA2 emerged to be a better choice as target where more than 300-fold reduction was observed and its inhibitory effect extended up to 48 h post-infection against all the serotypes. Interestingly, in the present study type A virus (IND 17/77) had a single mismatch at position 2 in the siRNA2 target region but it did not abrogate the inhibitory effect.     

Targeting the ICB2 site of the topoisomerase IIα promoter with a formamido-pyrrole–imidazole–pyrrole H-pin polyamide

The synthesis, DNA binding characteristics and biological activity of an N-formamido pyrrole- and imidazole-containing H-pin polyamide (f-PIP H-pin, 2) designed to selectively target the ICB2 site on the topoIIα promoter, is reported herein. Thermal denaturation, circular dichroism, isothermal titration calorimetry, surface plasmon resonance and DNase I footprinting studies demonstrated that 2 maintained the selectivity of the unlinked parent monomer f-PIP (1) and with a slight enhancement in binding affinity (K_eq = 5 × 10⁵ M^?1) to the cognate site (5′-TACGAT-3′). H-pin 2 also exhibited comparable ability to inhibit NF-Y binding to 1, as demonstrated by gel shift studies. However, in stark contrast to monomer 1, the H-pin did not affect the up-regulation of topoisomerase IIα (topoIIα) in cells (Western blot), suggesting that the H-pin does not enter the nucleus. This study is the first to the authors’ knowledge that reports such a markedly different cellular response between two compounds of almost identical binding characteristics.     

Effects of Small Molecule Calcium-Activated Chloride Channel Inhibitors on Structure and Function of Accessory Cholera Enterotoxin (Ace) of Vibrio cholerae

Cholera pathogenesis occurs due to synergistic pro-secretory effects of several toxins, such as cholera toxin (CTX) and Accessory cholera enterotoxin (Ace) secreted by Vibrio cholerae strains. Ace activates chloride channels stimulating chloride/bicarbonate transport that augments fluid secretion resulting in diarrhea. These channels have been targeted for drug development. However, lesser attention has been paid to the interaction of chloride channel modulators with bacterial toxins. Here we report the modulation of the structure/function of recombinant Ace by small molecule calcium-activated chloride channel (CaCC) inhibitors, namely CaCC_inh-A01, digallic acid (DGA) and tannic acid. Biophysical studies indicate that the unfolding (induced by urea) free energy increases upon binding CaCC_inh-A01 and DGA, compared to native Ace, whereas binding of tannic acid destabilizes the protein. Far-UV CD experiments revealed that the α-helical content of Ace-CaCC_inh-A01 and Ace-DGA complexes increased relative to Ace. In contrast, binding to tannic acid had the opposite effect, indicating the loss of protein secondary structure. The modulation of Ace structure induced by CaCC inhibitors was also analyzed using docking and molecular dynamics (MD) simulation. Functional studies, performed using mouse ileal loops and Ussing chamber experiments, corroborate biophysical data, all pointing to the fact that tannic acid destabilizes Ace, inhibiting its function, whereas DGA stabilizes the toxin with enhanced fluid accumulation in mouse ileal loop. The efficacy of tannic acid in mouse model suggests that the targeted modulation of Ace structure may be of therapeutic benefit for gastrointestinal disorders.     

Synthesis, in vivo and in vitro biological activity of novel azaline B analogs

Several azaline B analogs (2-10) were synthesized and evaluated for their ability to antagonize GnRH in vitro and for duration of action in inhibiting luteinizing hormone secretion in a castrated male rat assay in vivo. Analogs, 8 (IC(50) = 1.85 nM), and 9 (IC(50) = 1.78 nM), are equipotent with azaline B (1, IC(50) = 1.36 nM) in vitro. Whereas 9 is short acting, 8 is as long acting as azaline B. Other analogs have IC(50) greater than 2.0 nM and are all short acting.