BackgroundPlant derived components have attracted particular attention as an alternative source to battle several diseases including cancer. The variation in the climate, the geographical location and the rich ethnomedicinal traditions has made the Darjeeling Himalayas an abode of invaluable repository of traditional medicinal plants. In this study, we explored the in vitro anticancer properties of traditionally used medicinal plants from the Darjeeling hills against different human cancer cell lines.MethodsThe ethanolic leaf extracts of 30 medicinal plants were tested for their cytotoxicity against human breast adenocarcinoma cell line (MCF 7), human hepatocarcinoma cell line (HepG2) and human cervix adenocarcinoma cell line (HeLa). The cytotoxicity was evaluated by performing MTT assay, trypan blue exclusion assay and morphological assessment under phase contrast inverted microscope. For the extracts which tested positive, IC50 (the concentration that inhibited cell growth by 50%) was calculated. The extract(s) were further subjected to Thin Layer Chromatography (TLC) to determine their phytochemical profile.ResultsOut of the 30 plant extracts tested, five plants, Artemisia indica, Eupatorium odoratum, Eupatorium adenophorum, Maesa macrophylla and Phlogacanthus thyrsiformis showed a > 50% growth inhibition of cancer cell lines at a concentration of 50 μg/ml. The sensitivity to different extracts varied according to the cell type under investigation. Of these plants, Maesa macrophylla, exhibited the most potent cytotoxicity against HeLa and MCF7 cell with IC50 values of 9.55 μg/ml and 16.19 μg/ml respectively. Phytochemical analysis revealed the presence of coumarins, flavonoids, tannins, saponins, steroids and terpenes.ConclusionsThis is perhaps the first report of screening of traditional medicinal plants from Darjeeling district in West Bengal, India, for their cytotoxic activity against three human cancerous cell lines MCF7, HeLa and HepG2. The extracts of Maesa macrophylla significantly inhibited the growth of HeLa and MCF7 cancerous cell lines and constituted of multiple known biologically active compounds. The present study may provide the landmark for further exploration of M. macrophylla for its potent anticancer constituents.Electronic supplementary materialThe online version of this article (doi:10.1186/s12906-015-0543-5) contains supplementary material, which is available to authorized users.

Quorum sensing (QS) is a process mediated via small molecules termed autoinducers (AI) that allow bacteria to respond and adjust according to the cell population density by altering the expression of multitudinous genes. Since QS governs numerous bioprocesses in bacteria, including virulence, its inhibition promises to be an ideal target for the development of novel therapeutics. We found that the aqueous leaf extract of Psidium guajava (GLE) exhibited anti-QS properties as evidenced by inhibition of violacein production in Chromobacterium violaceum and swarming motility of Pseudomonas aeruginosa. The gram-negative bacterium, C. violaceum is a rare pathogen with high mortality rate. In this study, perhaps for the first time, we identified the target genes of GLE in C. violaceum MTCC 2656 by whole transcriptome analysis on Ion Torrent. Our data revealed that GLE significantly down-regulated 816 genes at least three fold, with p value≤0.01, which comprises 19% of the C. violaceum MTCC 2656 genome. These genes were distributed throughout the genome and were associated with virulence, motility and other cellular processes, many of which have been described as quorum regulated in C. violaceum and other gram negative bacteria. Interestingly, GLE did not affect the growth of the bacteria. However, consistent with the gene expression pattern, GLE treated C. violaceum cells were restrained from causing lysis of human hepatoma cell line, HepG2, indicating a positive relationship between the QS-regulated genes and pathogenicity. Overall, our study proposes GLE as a QS inhibitor (QSI) with the ability to attenuate virulence without affecting growth. To the best of our knowledge, this is the first report which provides with a plausible set of candidate genes regulated by the QS system in the neglected pathogen C. violaceum.

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