Evaluation of anti-cancer potential of Excoecaria agallocha (L.) leaf extract on human cervical cancer (SiHa) cell line and assessing the underlying mechanism of action

Background

The incidence of cervical cancer is increasing at an alarming rate in many countries and presently, it is the most common form of malignant cancer being reported among women in India. Development of novel approach for cervical cancer therapy, sparing healthy normal cells overcoming the limitations of prevailing therapies is of prime importance. Mangroves constitute a significant repository of medicinally important plants. Thus, in this study, we aimed to determine the anticancer activity of the mangrove Excoecaria agallocha L. leaf extracts on human cervical cancer (SiHa HPV 16+) cell line with subsequent characterization of the bioactive compounds conferring the anticancer activity and studying the probable underlying mechanism of action of the purified plant extract.

Results

The plant extract was subjected to silica gel column chromatography and the fractions obtained were analyzed for cytotoxic activity against SiHa cells by MTT assay. One out of the three eluted fractions exhibited selective toxicity against SiHa cells with an IC50 value of 15.538 ± 0.577 µg/mL, while it had no cytotoxic effect on normal healthy human peripheral blood mononuclear cells. High-resolution liquid chromatography mass spectroscopy, coupled to electron spray ionization and diode array detection analysis, led to the structure elucidation and identification of a few pharmacologically important compounds, with Bergenin being present in the highest abundance. Fluorescence microscopy results revealed that the plant extract fraction induced LC3 puncta formation, in EGFP- SiHa cells indicating the onset of autophagy, with simultaneous stimulation of mitophagy. The plant extract also inhibited proliferation of the SiHa-smac-mCherry cells by second mitochondria-derived activator of caspase (SMAC)—induced cytochrome c dependent apoptosis, that was further confirmed with Caspase-3 activation by colorimetric assay. The GFP-dgn in SiHa cells was remarkably protected from proteasomal degradation that might upregulate the survivability of the cells significantly. Flow cytometry followed by Western blot analysis further asserted the ability of the plant extract fraction to cause cell cycle arrest of SiHa cells in the G2/M phase by significantly reducing protein expression levels of cyclin B1 and D1, decreasing Cdc2 level and simultaneously increasing p21 and p53 levels.

Conclusion

It could be inferred that the aqueous extract of E. agallocha successfully decreased the proliferation of SiHa cervical cancer cells through induction of autophagy and apoptosis in a concerted manner, with simultaneous stimulation of mitophagy and G2/M phase cell cycle arrest, hinting at Bergenin being the major compound conferring the anti-cancer activity of the plant extract. Thus, isolation of the identified bioactive compounds from E. agallocha and their subsequent purification for drug development might serve as a novel medicinal approach for the treatment of cervical cancer in conjugation with existing therapeutic methods.

Agallochin P, a new diterpene from Vietnamese mangrove Excoecaria agallocha L

A new diterpene (1) along with eight known compounds (2-9) were isolated from Excoecaria agallocha leaves. The structure and relative configuration of new compound were established on the basis of spectroscopic data analysis and confirmed by NMR chemical shifts calculation with DP4+ probability. Cytotoxicity of the isolated compounds were also evaluated.

Mangrove Tirucallane- and Apotirucallane-Type Triterpenoids: Structure Diversity of the C-17 Side-Chain and Natural Agonists of Human Farnesoid/Pregnane⁻X⁻Receptor

Ten new triterpenoid compounds with structure diversity of the C-17 side-chain, including nine tirucallanes, named xylocarpols A⁻E (1⁻5) and agallochols A⁻D (6⁻9), and an apotirucallane, named 25-dehydroxy protoxylogranatin B (10), were isolated from the mangrove plants Xylocarpus granatum, Xylocarpus moluccensis, and Excoecaria agallocha. The structures of these compounds were established by HR-ESIMS and extensive one-dimensional (1D) and two-dimensional (2D) NMR investigations. The absolute configurations of 1 and 2 were unequivocally determined by single-crystal X-ray diffraction analyses, conducted with Cu Kα radiation; whereas those of 4, 6⁻8 were assigned by a modified Mosher's method and the comparison of experimental electronic circular dichroism (ECD) spectra. Most notably, 5, 6, 7, and 9 displayed potent activation effects on farnesoid⁻X⁻receptor (FXR) at the concentration of 10.0 μM; 10 exhibited very significant agonistic effects on pregnane⁻X⁻receptor (PXR) at the concentration of 10.0 nM.

A New 28-Nor-oleanane Triterpene from Excoecaria agallocha

A new 28-nor-oleanane triterpene, 28- nor-olean-2α, 3β-dihydroxy-14,17-diene-16-one with a rare cyclohexa-2,5-dienone moiety, together with three known triterpenes, viz.β-amyrin (2), 3α- O - trans -coumaroyl-betulinic acid (3), 3-acetyl-aleuritolic acid (4), were isolated from the twigs of Excoecaria agallocha L.. Their structures were determined by extensive spectroscopic data analysis and comparison with previous literatures (known compounds).

Two new diterpenoids from Excoecaria acerifolia

A new tigliane diterpenoid, acerifolin A (1), and a new isopimarane diterpenoid, acerifolin B (2), together with two known compounds, were isolated from Excoecaria acerifolia. Their structures were elucidated on the basis of their spectroscopic methods, including 1D and 2D NMR techniques. All of the compounds were evaluated for cytotoxicity against five human cancer cell lines with cisplantin as a positive control.

Inhibitory effects of polyphenols toward HCV from the mangrove plant Excoecaria agallocha L

Four new polyphenols namely excoecariphenols A-D (1-4) were isolated from the Chinese mangrove plant Excoecaria agallocha L. together with 23 known phenolic compounds. The structures of new compounds were elucidated on the basis of extensive spectroscopic analyses including IR, MS, NMR, and CD data. Excoecariphenols A and B presented as the unusual flavane-based 1-thioglycosides. Part of the isolated polyphenols were tested against hepatitis C NS3-4A protease and HCV RNA in huh 7.5 cells. Excoecariphenol D, corilagin, geraniin, and chebulagic acid showed potential inhibition toward HCV NS3-4A protease with IC(50) values in a range of 3.45-9.03μM, while excoecariphenol D and corilagin inhibited HCV RNA in huh 7.5 cells significantly. A primary structure-activity relationship (SAR) is discussed.

TNF-α inhibitory diterpenoids from the Chinese mangrove plant Excoecaria agallocha L

Chemical examination of the stems and twigs of the mangrove plant Excoecaria agallocha L. resulted in the isolation of six ent-kaurane diterpenoids named agallochaols K-P (1-6), an atisane-type diterpenoid agallochaol Q (7), along with eight known diterpenoids (8-15). Their structures were elucidated on the basis of extensive spectroscopic analysis and by comparison of their NMR spectroscopic data with those reported in literature, in association with the biogenetic relationship with the X-ray structure of 9. Compounds 1, 5-7, 9-10, and 13 showed anti-inflammatory potency to suppress expression of NF-κB and AP-1 targeted genes including TNF-α and IL-6 induced by lipopolysaccharide (LPS) in mouse macrophages Raw 264.7 cells. In addition, compounds 1, 5-7, 9-10, and 13 block NF-κB activation, while compounds 1 and 7 block AP-1 activation dramatically, indicating these compounds possess an anti-inflammatory potential in vitro.