Antiproliferative hydroxy-fatty acids from the fodder legume Stylosanthes guianensis.

Stylosanthes guianensis is a fodder legume native from South America and widely grown worldwide. Dried plant material was purchased on the web and taxonomically identified by light and SEM microscopy, and morphological analysis of plants germinated from seeds. The plant was extracted with dichloromethane:2-propanol (9:1). Bioguided fractionation using calcein-AM cytotoxicity assay on HeLa and A431 tumor cells allowed to isolate a lipophilic fraction, endowed with strong cytotoxicity. By means of 1- and 2-D NMR, HPLC-MS, and HR-ESIMS it could be seen that the fraction was an inseparable mixture of complex lipids, mainly consisting of esterified 3-hydroxy fatty acids. Acidic methanolysis of the mixture yielded 3-OH C10 and C12 carboxylic acids, together with palmitic, stearic, and arachidonic acids. Mass values indicate the presence of dimeric and trimeric combinations of 3-hydroxy, C10/C12 acids, and C16/C18/C20 acids, linked via ester bond. Monomeric hydroxyl-fatty acids were also observed, in particular derivatives of mono-hydroxy and di-hydroxy linolenic, linoleic, and oleic acids. 3-O-acylated, esterified fatty acids are unusual in higher plants, and recall motifs of Gram-negative endotoxin lipid A. These oxylipins are likely to be responsible for the antiproliferative activity of S. guianensis, suggesting possible use of the plant in the development of antitumor drugs.

Resveratrol induces intracellular Ca(2+) rise via T-type Ca(2+) channels in a mesothelioma cell line.

AIMS: Intracellular calcium (Ca(2+)) is known to play an important role in cancer development and growth. Resveratrol (Res) is a stilbene polyphenol occurring in several plant species and known for various possible beneficial effects, including its ability to inhibit proliferation and to induce apoptosis in cancer cells. This study was designed to determine whether Res affects Ca(2+) signaling in cancer cells. MAIN METHODS: We used the REN human mesothelioma cell line, as an in vitro cancer cell model, and the non-malignant human mesothelial MeT5A cell line, as normal cell model. Cytosolic Ca(2+) concentration was measured by the fluorescent indicator Fura-2. Immunofluorescence, Western blot, and siRNA technique were employed to assess the involvement of T-type Ca(2+) channels. Cell viability was determined by the calcein assay. KEY FINDINGS: REN cells transiently exposed to 1-10µM Res showed increasing peaks of Ca(2+) that were absent in Ca(2+)-free medium and were reduced by non-selective (Ni(2+)), and highly selective (NNC 55-0396) T-type Ca(2+) channels antagonist, and by siRNA knockout of Cav3.2T-type Ca(2+) channel gene. Dose-dependent curve of Res-induced Ca(2+) peaks showed a rightward shift in normal MeT-5A mesothelial cells (EC50=4.9µM) with respect to REN cells (EC50=2.7µM). Moreover, incubation with 3 and 10µM Res for 7days resulted in cell growth inhibition for REN, but not for MeT-5A cells. SIGNIFICANCE: Res induces Ca(2+) influx, possibly mediated through T-type Ca(2+) channels, with significant selectivity towards mesothelioma cells, suggesting a possible use as an adjuvant to chemotherapy drugs for mesothelioma clinical treatment.

Oleuropein-Enriched Olive Leaf Extract Affects Calcium Dynamics and Impairs Viability of Malignant Mesothelioma Cells.

Malignant mesothelioma is a poor prognosis cancer in urgent need of alternative therapies. Oleuropein, the major phenolic of olive tree (Olea europaea L.), is believed to have therapeutic potentials for various diseases, including tumors. We obtained an oleuropein-enriched fraction, consisting of 60% w/w oleuropein, from olive leaves, and assessed its effects on intracellular Ca(2+) and cell viability in mesothelioma cells. Effects of the oleuropein-enriched fraction on Ca(2+) dynamics and cell viability were studied in the REN mesothelioma cell line, using fura-2 microspectrofluorimetry and MTT assay, respectively. Fura-2-loaded cells, transiently exposed to the oleuropein-enriched fraction, showed dose-dependent transient elevations of cytosolic Ca(2+) concentration ([Ca(2+)]i). Application of standard oleuropein and hydroxytyrosol, and of the inhibitor of low-voltage T-type Ca(2+) channels NNC-55-0396, suggested that the effect is mainly due to oleuropein acting through its hydroxytyrosol moiety on T-type Ca(2+) channels. The oleuropein-enriched fraction and standard oleuropein displayed a significant antiproliferative effect, as measured on REN cells by MTT cell viability assay, with IC50 of 22 µg/mL oleuropein. Data suggest that our oleuropein-enriched fraction from olive leaf extract could have pharmacological application in malignant mesothelioma anticancer therapy, possibly by targeting T-type Ca(2+) channels and thereby dysregulating intracellular Ca(2+) dynamics.