Structural modifications of plumieride isolated from Plumeria bicolor and the effect of these modifications on in vitro anticancer activity

Organosilicon Compounds, SILA-409 and SILA-421, as Doxorubicin Resistance-Reversing Agents in Human Colon Cancer Cells

Multidrug resistance (MDR) that occurs in cancer cells constitutes one of the major reasons for chemotherapy failure. The main molecular mechanism of MDR is overexpression of protein transporters from the ATP-binding cassette (ABC) superfamily, such as ABCB1 (multidrug resistance protein 1 (MDR1), P-glycoprotein). At the expense of ATP hydrolysis, ABCB1 pumps a diverse range of substrates (including anticancer drugs) out of the cell, thereby reducing their intracellular concentration. In the present study, the ability of two patented disiloxanes (SILA-409 and SILA-421) to reverse drug resistance in human colon adenocarcinoma cell lines LoVo and LoVo/Dx was investigated. It was demonstrated that both compounds in concentrations of 0.5-1 µM strongly increased the sensitivity of LoVo/Dx cells to doxorubicin. By means of an accumulation test in which rhodamine 123 was used as an ABCB1 substrate analogue, both organosilicon compounds were also shown to inhibit ABCB1 transport activity. The intracellular accumulation of doxorubicin was also increased, and more drug entered the cellular nuclei of resistant cells in the presence of the studied compounds. In conclusion, both SILA-409 and SILA-421 were demonstrated to be effective MDR reversal agents in resistant human colon cancer cells.

Biological Activity and Isolation of Compounds from Stem Bark of Plumeria acutifolia

Background:

Plumeria acutifolia (Apocynaceae) is an ornamental plant, used in the traditional medicine and known to have a variety of constituents as alkaloids, flavonoids, and iridoids. Extracts of this plant were proved to have antimicrobial and anticancer activities.

Objectives:

This research was conducted for the evaluation of the biological activities of P. acutifolia stem bark and isolation and structural elucidation of various chemical compounds from the biologically active fractions.

Materials and Methods:

Methanol extract of stem bark of P. acutifolia was successively fractionated with petroleum ether, dichloromethane, ethyl acetate, and n-butanol. The fractions were evaluated for their antimicrobial, cytotoxic, and antioxidant activities. Fractions with promising biological activities were subjected to chromatographic techniques for the isolation of compounds, followed by structural elucidation using several spectroscopic techniques.

Results:

P. acutifolia stem bark showed a significant antimicrobial activity, where the ethyl acetate fraction was active against Syncephalastrum racemosum (7.81 μg/ml) and Escherichia coli (3.9 μg/ml). The cytotoxic activity against HEPG-2, HCT-116, and MCF-7 cell lines was highest in the petroleum ether fraction, using concentrations of 1, 2.5, 5, and 10 μl/ml. The antioxidant activity was concentration dependent; ethyl acetate fraction showed the most predominant effect, with an IC₅₀ of 197.1 μg/ml. Five compounds were identified as narcissin (1), quercitrin (2), sweroside (3), gaertneroside (4), and plumieride (5).

Conclusion:

P. acutifolia was proved to have significant antimicrobial, cytotoxic, and antioxidant activities; the isolated compounds were flavonoids, iridoids, and secoiridoid, some of which were reported for the first time in genus Plumeria and/or family Apocynaceae.

SUMMARY

P. acutifolia stem bark showed a significant antimicrobial activity, where the ethyl acetate fraction was active against Syncephalastrum racemosum and Escherichia coli. The cytotoxic activity against HEPG-2, HCT-116, and MCF-7 cell lines was highest in the petroleum ether fraction. The antioxidant activity was concentration dependent; ethyl acetate fraction showed the most predominant effect. Five compounds were identified as narcissin (1), quercitrin (2), sweroside (3), gaertneroside (4), and plumieride (5).

Abbreviations used: mp: Melting point, NMR: Nuclear magnetic resonance, s: Singlet, d: Double, t: Triplet, q: Quartet, dd: Double-double, m: Multiplet, br: Broad.

Immunostimulatory activity of plumieride an iridoid in augmenting immune system by targeting Th-1 pathway in balb/c mice

Plumieride, an iridoid glucoside isolated from Plumieria acutifolia leaves was investigated for its immunostimulatory activity on humoral, cell mediated and intracellular cytokine levels in sensitized and unsensitised balb/c mice. Plumieride restores the suppressed cell mediated, humoral immune response and also enhances the release of TNF- α, IFN-γ, and IL-2 (Th-1) in immune compromised cyclosporine and cyclophosphamide treated balb/c mice. It does not stimulate the IL-4 (Th-2) expression. Plumieride demonstrates significant augmentation of Th-1 response in immunosuppressed balb/c mice. Results of the present study suggested that plumieride can be developed as an immunostimulatory adjuvant to treat the immune suppression in various disease condition(s).

Antioxidant Potential of Plumieride against CCl₄-Induced Peroxidative Damage in Rats

In search of a new potent as an antioxidant from natural sources, plumieride—an iridoid isolated from the methanol extract of the bark of Plumeria bicolor (family Apocynaceae) was evaluated for its antioxidant potential against CCl₄-induced peroxidative damage in liver of rats. The antioxidant potential was evaluated by using hepatic tissue for SOD (superoxide dismutase), CAT (catalase), GSH (reduced glutathione), GPx (glutathione peroxidase), GR (glutathione reductase) and LPO (lipid peroxidation) alongwith the concomitant blood serum for AST & ALT (aspartate and alanine transaminases), GGT (gamma glutamyl transpeptidase), ALP (alkaline phosphatase), total bilirubin and total protein contents. All the biochemical parameters were significantly (p ≤ 0.001) altered by CCl₄ (0.3 mL/kg body weight/twice a week, intra-peritoneally for 30 days). Simultaneously, oral treatment with plumieride (5, 10 and 20 mg/kg body weight/day for 30 days), restored all the parameters towards a normal level, remarkably. The histological findings of liver sections further corroborated the antioxidant potential of plumieride compared with standard drug-silymarin. In conclusion, plumieride consists of sugar molecules, which have alcoholic groups. Therefore, the alcoholic groups of sugar increase its antioxidant potential through intermolecular hydrogen bonding along with the thiol(SH) group of non-protein thiols and enzymes resulting in the restoration of the antioxidant system. Therefore, it might be considered a natural antioxidant against peroxidative damage in rats.

Anti-mycobacterial activity of plumericin and isoplumericin against MDR Mycobacterium tuberculosis

BACKGROUND AND OBJECTIVES

Because of the developing resistance of Mycobacterium species against currently available anti-mycobacterial drugs, there is an urgent need for new drug development. In this study, we have evaluated the in vitro anti-mycobacterial activity of Plumeria bicolor extract and its phytoconstituents - plumericin and isoplumericin against multi-drug resistance Mycobacterium tuberculosis.

METHODS

The in vitro anti-mycobacterial activity of chloroform extract of P. bicolor, plumericin and isoplumericin were tested against M. tuberculosis (H37Rv) and four multi-drug resistant (MDR) clinical isolates by measuring the minimum inhibitory concentration (MIC) using MTT (Tetrazolium bromide [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide]) assay. The extract and both compounds were further evaluated by standard assay procedures to determine their minimum bactericidal concentration (MBC). Cytotoxicity of these compounds was performed against J774G8 murine macrophage cell lines. The activity was represented in the mean (±SD) of duplicate samples from three independent assays.

RESULTS

Plumericin showed better activity against pan sensitive as well as four MDR strains of M. tuberculosis with MIC values of 2.1 ± 0.12, 1.3 ± 0.15, 2.0 ± 0.07, 1.5 ± 0.13 & 2.0 ± 0.14 μg/mL and MBC values of 3.6 ± 0.22, 2.5 ± 0.18, 3.8 ± 0.27, 2.9 ± 0.20 & 3.7 ± 0.32 μg/mL than isoplumericin, respectively. Interestingly, both isolated active compounds showed an advantage over rifampicin (80 times) and isoniazid (8 times) by being highly active against the MDR strains. The extract and both compounds were found to be non-toxic against J774G8 macrophages up to the used concentrations.

CONCLUSION

Plumericin showed more potent activity than isoplumericin. The excellent activity of these compounds against MDR strains opens a possibility of obtaining new anti-mycobacterial drug candidate in near future.

Antiparasitic activity of plumericin & isoplumericin isolated from Plumeria bicolor against Leishmania donovani

BACKGROUND & OBJECTIVES

The severe toxicity, exorbitant cost and emerging resistance of Leishmania species against most of the currently used drugs underscores the urgent need for the alternative drugs. The present study evaluates in vitro anti-leishmanial activity of Plumeria bicolor and its isolated compounds.

METHODS

The in vitro anti-parasitic activity of chloroform extract of Plumeria bicolor, plumericin and isoplumericin were tested alongwith appropriate controls against promastigote and amastigote forms of Leishmania donovani using 96 well microtiter plate. The concentration used for assessing the anti-leishmanial activity of extract of Plumeria bicolor and both isolated compounds were 100 μg/ml and 15 μM, respectively. The viability of the cells was assessed by MTT assay. The cytotoxicity of these compounds was performed against J774G8 murine macrophage cells lines at the concentration of 30 μM.

RESULTS

The Plumeria bicolor extract showed activity with the IC 50 of 21±2.2 and 14±1.6 μg/ml against promastigote and amastigote forms of L. donovani, respectively. Plumericin consistently showed high activity with the IC 50 of 3.17±0.12 and 1.41±0.03 μM whereas isoplumericin showed the IC50 of 7.2±0.08 μM and 4.1±0.02 μM against promastigote and amastigote forms, respectively. Cytotoxic effect of the chloroform extract of P. bicolor, plumericin and isoplumericin was evaluated in murine macrophage (J774G8) model with CC50 value of 75±5.3 μg/ml, 20.6±0.5 and 24±0.7 μM, respectively.

INTERPRETATION & CONCLUSIONS

Our results indicated that plumericin showed more potent activity than isoplumericin and might be a promising anti-leishmanial agent against L. donovani.

Antifungal Activity of Plumericin and Isoplumericin

This study evaluated the in vitro antifungal activity of the chloroform extract of Plumeria bicolor and its phytoconstituents plumericin and isoplumericin against Candida species and Cryptococcus neoformans by measuring the Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC). Plumericin's consistently high activity against Candida albicans, C. krusei, C. glabrata, C. tropicalis and Cryptococcus neoformans was more potent than isoplumericin and the standard antifungal drug nystatin suggesting its potential as a drug candidate for candidiasis and cryptococcosis.

Antiproliferative effect of a traditional remedy, Himatanthus articulatus bark, on human cancer cell lines

ETHNOPHARMACOLOGICAL RELEVANCE

Himatanthus articulatus (Vahl) Woodson (Apocynaceae) is a tree occurring in the Amazon region. The local population uses its bark against to external tumors and cancer.

AIM OF THE STUDY

Evaluated the antiproliferative activity of the crude extract and their fractions against human tumors cells.

MATERIALS AND METHODS

The antiproliferative responses of the crude extract and their fractions were colorimetrically evaluated by sulforhodamine B (SRB) assay against HT-29 (colon adenocarcinoma); NCI-H460 (non-small cell lung carcinoma); MCF-7 (breast cancer); OVCAR-3 (ovarian adenocarcinoma) and RXF-393 (renal cell carcinoma) as well as against NIH-3T3 (mouse embryo fibroblast cell).

RESULTS

The cytotoxicity data from the crude extract allowed considering active only in the NCI-H460 cell line. However, the antiproliferative activity was much more pronounced at the chloroformic fraction in all cell lines tested. The butanolic fraction demonstrated activity against to HT-29, MCF-7, RXF-393 and OVCAR-3 cells. The ethyl acetate fraction demonstrated activity only in RXF-393 and the aqueous residue did not present antiproliferative effect.

CONCLUSIONS

Through the popular use we find that the crude extracts of Himatanthus articulatus bark displayed weak cytotoxic. However, the butanolic fraction showed to be active only against to tumor cell lines while chloroformic fraction possesses high activity being similar to the positive control. Both fractions have been selected for future bio-guided fractionation and isolation of active compounds.

Complete NMR spectral assignments of two new iridoid diastereoisomers from the flowers of Plumeria rubra L. cv. acutifolia

Two new iridoid diastereoisomers (1, 2), together with five known compounds, were isolated from the flowers of Plumerian rubra L. cv. acutifolia. Their structures were elucidated by the means of in-depth spectroscopic and mass-spectrometric analyses, particularly 1D and 2D NMR spectroscopy.

Revision of the Absolute Configuration of Plumericin and Isoplumericin fromPlumeria rubra

The absolute configurations of plumericin (1) and isoplumericin (2), isolated from Plumeria rubra, were re-assigned based on a combination of X-ray crystal-structure determination and quantum-mechanical calculations of their circular dichroism (CD) spectra. The experimental CD spectra showed an excellent match with those calculated for the (1S,5R,8R,9R,10R) absolute configuration (corresponding to ent-1 and ent-2, resp.), opposite to that generally accepted and published in the literature. Since the (false) plumericin configuration has been often used to derive the absolute configuration of related iridoids by chemical correlation, their absolute configurations also have to be reconsidered.