Antituberculosis activity of polyphenols of Areca catechu.

Background: Polyphenols have been studied for their potential involvement in the prevention of various chronic diseases as well as for their antimicrobial potential. The crude extracts of arecanut have been reported to have antiinfective properties. We aimed to explore the endosperm of Areca catechu (arecanut) for the extraction of polyphenol components and to study the antituberculosis activity of these polyphenol against Mycobacterium tuberculosis H37Rv. Method: A comparative extraction was performed using microwave and Soxlet apparatus. High performance liquid chromatography (HPLC) technique was used for the estimation of the extracted polyphenols. The minimum inhibitory concentration (MIC) values against M.tuberculosis H37Rv stain, Staphylococcus aureus and Escherichia coli were estimated by resazurin microtiter assay. Results: There was a 11-fold increase in the total phenolic content by microwave assisted extraction compared to the Soxhlet extraction. The powdered extract was found to be active with MIC value of 0.975 ± 0.02 µg/mL. Fractionation and HPLC-based estimation of the extract revealed catechin, epicatechin, and epigallocatechin gallate to be the polyphenol components in the ethanol fraction. Conclusions: The bioactivity of these polyphenols confirmed their presence and complementary effect in the extract form. Because the toxic alkaloid arecoline, known to be present in arecanut, did not show any activity individually, the bioactivity of the extract was attributed to the nontoxic polyphenols present. This extract also showed selective inhibition of M. tuberculosis over other gram positive and gram-negative bacteria, thereby establishing that arecanut is an exploitable selective source of polyphenols acting against M. tuberculosis.

Design and synthesis of 5-(5-nitrothiophen-2-yl)-3-phenyl-4,5-dihydro-1H-pyrazole derivatives with improved solubility and potential antituberculosis activity.

We report the design-synthesis of several nitrothiophene containing molecules as antituberculosis agents. The molecules were designed on the basis of previously reported nitrofuran molecules in our laboratory, and the α,ß-unsaturated linker was modified to cyclized linker in order to overcome the challenge of low solubility and possible toxicity. The stereo-electronic properties such as HOMO, LUMO, and HOMO-LUMO gap along with other properties such as aqueous solvation energies and QPLogS values were studied. The designed molecules were synthesized and tested for in vitro antituberculosis activity, and some molecules were found to be highly active comparable to standard drugs. Further, the aqueous solubility was determined using visual inspection method and the designed molecules were found to be more soluble than their chalcone counterparts. Cytotoxicity studies were performed and the molecules were found to be non-cytotoxic. Electroanalytical studies proved nitro reduction as the mechanism of action for these molecules. Thus, this study provides potential nitrothiophene containing hits with improved solubility and reduced chances of toxicity.

Fragment Discovery for the Design of Nitrogen Heterocycles as Mycobacterium tuberculosis Dihydrofolate Reductase Inhibitors.

Fragment-based drug design was used to identify Mycobacterium tuberculosis (Mtb) dihydrofolate reductase (DHFR) inhibitors. Screening of ligands against the Mtb DHFR enzyme resulted in the identification of multiple fragment hits with IC50 values in the range of 38-90 µM versus Mtb DHFR and minimum inhibitory concentration (MIC) values in the range of 31.5-125 µg/mL. These fragment scaffolds would be useful for anti-tubercular drug design.

Identification of a novel class of quinoline-oxadiazole hybrids as anti-tuberculosis agents.

A series of novel quinoline-oxadiazole hybrid compounds was designed based on stepwise rational modification of the lead molecules reported previously, in order to enhance bioactivity and improve druglikeness. The hybrid compounds synthesized were screened for biological activity against Mycobacterium tuberculosis H37Rv and for cytotoxicity in HepG2 cell line. Several of the hits exhibited good to excellent anti-tuberculosis activity and selectivity, especially compounds 12m, 12o and 12p, showed minimum inhibitory concentration values<0.5µM and selectivity index>500. The results of this study open up a promising avenue that may lead to the discovery of a new class of anti-tuberculosis agents.

Design and Synthesis of a Focused Library of Diamino Triazines as Potential Mycobacterium tuberculosis DHFR Inhibitors.

We report design of a series of 2,4-diamino triazines as Mycobacterium tuberculosis (Mtb) dihydrofolate reductase inhibitors. The synthesized compounds were evaluated against Mtb (H37Rv and Dormant stage H37Ra), their cytotoxicity was assessed (HepG2 and A549 cell lines), and selectivity toward Mtb was evaluated by testing against other bacterial strains. Some derivatives showed promising activity along with low cytotoxicity. The most potent compound in the whole cell assay (MIC 0.325 µM against H37Rv) showed selectivity in the enzyme assay and exhibited synergy with second line anti-TB agent p-amino salicylic acid. This study therefore provides promising molecules for further development as antituberculosis DHFR inhibitors.

Antifolate Activity of Plant Polyphenols against Mycobacterium tuberculosis.

With the view of exploring phytochemicals as Mycobacterium tuberculosis (Mtb) dihydrofolate reductase inhibitors, known plant polyphenols from various classes were subjected to detailed docking studies. From this in-silico screening, seven polyphenols were selected and tested against Mtb H37 Rv in whole cell assays. The phytochemicals exhibited potential activity ranging from 3 to 183 µm. These molecules were then tested against the pathogenic and human enzymes in a high-throughput microtitre assay. Epigallocatechin gallate showed the best activity and selectivity. The in-silico analysis was in agreement with the assay results. Of these 7 polyphenols, 5 exhibiting minimum inhibitory concentration values of ≤15 µm were tested for synergistic activity with first line drug Ethambutol and second line folate inhibitor para-amino salicylic acid. Epigallocatechin gallate, Magnolol and Bakuchiol exhibited moderate synergistic association by lowering the minimum inhibitory concentration of these drugs. These simple phytochemicals could hence be considered as leads for further studies, or for preparation of semi-synthetic derivatives to be used in combination therapy, for increased anti-tuberculosis activity after validation in-vivo.

Rational drug design, synthesis and biological evaluation of dihydrofolate reductase inhibitors as antituberculosis agents.

BACKGROUND: A series of 2,4-diamino-s-triazines was designed, with potential for activity against Mycobacterium tuberculosis (Mtb) dihydrofolate reductase enzyme, on the basis of virtual screening results and structure-based drug design. RESULTS: The compounds were evaluated against Mtb (H37Rv) and their cytotoxicity was assessed using VERO cell lines. Of particular note, two compounds were found to have the most promising antituberculosis activity (6b minimum inhibitory concentration: 1.76 µM and 6i minimum inhibitory concentration: 1.57 µM) along with low cytotoxicity (CC50: >300 µM). The enzyme assay results of these two indicated significant inhibition of Mtb dihydrofolate reductase along with selectivity. Selected derivatives were tested against dormant tubercle bacilli in vivo and ex vivo indicating potential inhibition. CONCLUSION: This study provides promising antituberculosis dihydrofolate reductase inhibitors that can act as potential leads for further development.

E84G mutation in dihydrofolate reductase from drug resistant strains of Mycobacterium tuberculosis (Mumbai, India) leads to increased interaction with Trimethoprim.

BACKGROUND: Dihydrofolate reductase (DHFR) (dfrA gene) is an essential enzyme for cell survival and an unexplored target in Mycobacterium tuberculosis (Mtb). This study was carried out to analyze mutations in the dfrA gene amongst 20 clinical DNA samples from Mtb isolates obtained from Mumbai, India. METHODS: Sequencing of the PCR amplified dfrA gene from these DNA isolates revealed a point mutation in one strain, leading to a glutamic acid to glycine change. In silico simulation studies revealed a surface alteration in the enzyme due to this E84G mutation. The amplified mutant gene was cloned and expressed. The mutant protein was assessed against known DHFR inhibitors: Methotrexate and Trimethoprim. RESULTS: An increased affinity for inhibitor Trimethoprim and native substrate dihydrofolate was observed with the mutant. Methotrexate did not vary in its activity with both the enzyme forms. CONCLUSIONS: The Glu84Gly point mutation may lead to a variation in the strain which may cause resistance in the future.

Rational drug design based synthesis of novel arylquinolines as anti-tuberculosis agents.

A series of novel arylquinoline derivatives was designed retaining significant pharmacophoric features and three dimensional geometry of bedaquiline. In silico ADME study was performed to assess drug likeness and toxicity profiles of the designed molecules. The compounds were evaluated for activity against Mycobacterium tuberculosis H37Rv using Resazurin Microtitre Assay (REMA) plate method and cytotoxicity in VERO C1008 cell line. Several of the synthesized compounds exhibited good antituberculosis activity and selectivity, especially compounds, 12i (MIC: 5.18 µM and MIC/CC50: 152.86) and 12l (MIC: 5.59 µM and MIC/CC50: 160.57). The study opens up a new platform for the development of arylquinoline based drugs for treating tuberculosis.