Biochemical disorders induced by cytotoxic marine natural products in breast cancer cells as revealed by proton NMR spectroscopy-based metabolomics

International audienceMarine plants and animals are sources of a huge number of pharmacologically active compounds, some of which exhibit antineoplastic activity of clinical relevance. However the mechanism of action of marine natural products (MNPs) is poorly understood. In this study, proton NMR spectroscopy-based metabolomics was applied to unravel biochemical disorders induced in human MCF7 breast cancer cells by 3 lead candidate anticancer MNPs: ascididemin (Asc), lamellarin-D (Lam-D), and kahalalide F (KF). Asc, Lam-D, and KF provoked a severe decrease in DNA content in MCF7 cells after 24h treatment. Asc and Lam-D provoked apoptosis, whereas KF induced non-apoptotic cell death. Metabolite profiling revealed major biochemical disorders following treatment. The response of MCF7 tumor cells to Asc involved the accumulation of citrate (×17 the control level, <0.001), testifying enzyme blockade in citrate metabolism, and the accumulation of gluconate (×9.8, <0.005), a metabolite never reported at such concentration in tumor cells, probably testifying glycolysis shutdown. The response to Lam-D involved the accumulation of aspartate (×7.2, <0.05), glutamate (×14.7, <0.05), and lactate (×2.3, <0.05), probably in relation with the targeting of the malate-aspartate shuttle, as discussed. The response to KF involved increased lipid accumulation (polyunsaturated fatty acids ×9.8, <0.05), and phospholipid and acetate derivative alterations. Altogether, this study demonstrates the potential of proton NMR spectroscopy-based metabolomics to help uncover metabolic targets and elucidate the mechanism of cytotoxicity of candidate antineoplastic MNPs

Bactericidal efficiency of UV-active TiO2 thin films on adhesion and viability of food-borne bacteria

Biofilms, containing pathogenic bacteria, represent a recurrent economic and safety problem in food industries, due to their high resistance to cleaning and sanitizing procedures. The development of photoactive surfaces with bactericidal property could facilitate the elimination of such microbial biofilms. One solution may be to deposit a photocatalyst top-layer (TiO2) on conventional materials used in food plants. Our aim is to study the photocatalytic activity of such layers on the adhesion and viability of different bacteria present on food plants, especially in pork meat factory: Listeria monocytogenes, Yersinia enterocolitica and Pseudomonas fragi. Glass substrates were coated with TiO2 thin films by radio-frequency magnetron sputtering under various deposition conditions (deposition temperature T, oxygen partial pressure PO2). The characterization of the TiO2 thin layers was performed using spectrophotometry, scanning electron microscopy and X-ray diffraction analysis. And photocatalytic activity under UVA illumination (365 nm) has been checked for all samples. Bactericidal activity has been demonstrated on the bacteria tested by enumeration of the adherent cells and in situ fluorescent labeling after three hours of contact with the thin film and a subsequent UVA illumination. Adherent bacteria with damaged bacterial cell wall were observed using a scanning electron microscopy; this can be associated with presence of oxidative stress due to the photocatalytic activity of the TiO2 thin layer. The selected TiO2 coating presents a photocatalytic activity leading to an oxidative stress. This activity provides bactericidal properties against different strains from the meat industry. This thin layer could be optimized by modifying anionic composition (band-gap reduction) during coating in order to be active under solar light so it could be used to fight against biofilms

Marine Natural Meroterpenes: Synthesis and Antiproliferative Activity

Meroterpenes are compounds of mixed biogenesis, isolated from plants, microorganisms and marine invertebrates. We have previously isolated and determined the structure for a series of meroterpenes extracted from the ascidian Aplidium aff. densum. Here, we demonstrate the chemical synthesis of three of them and their derivatives, and evaluate their biological activity on two bacterial strains, on sea urchin eggs, and on cancerous and healthy human cells

Differential modulation of Bax/Bcl-2 ratio and onset of caspase-3/7 activation induced by derivatives of Justicidin B in human melanoma cells A375.

Diphyllin and its derivatives are well known cytotoxic natural products structurally related to the anti-cancer drug podophyllotoxin. We here study their structure-activity relationship upon human melanoma cells for first time. To this end, human melanoma A375 cells were incubated with Justicidin B and its 4-methoxylated or 4-glycosylated derivatives to evaluate their selective cytotoxicity and study their effects on cell cycle distribution, caspase activation, apoptosis induction using Annexin V-FITC/PI staining, cell morphology and western blot analysis. Diphyllin methyl ether (GI50 = 3.66 μM) and Justicidin B (GI50 = 1.70 μM) caused an elevation of both early and late apoptosis populations whereas Diphyllin apioside (GI50 = 0.84 μM) and its acetate (GI50= 0.39 μM) enhanced late apoptosis population only (Annexin V-positive/PI-positive). All induced cell cycle arrest at S phase and classic morphological indicators of apoptosis (blebbing, apoptotic bodies, and nuclear fragmentation) accompanied with an elevation of cells with low DNA content (sub-G1). All compounds increased the Bax/Bcl-2 ratio by enhancing Bax expression which evidences the involvement of the mitochondria (intrinsic pathway) in the apoptotic process. These caspase-3/7 results evidence that 4-methoxylation or 4-O-glycosylation of Justicidin B -a caspase independent mitochondrial apoptosis-inducer- triggers caspase-3/7 activation at different times (24h vs. 48h, respectively). Interestingly, the methoxylation causes attenuation of Bcl-2 protein expression contrarily to Diphyllin methyl ether or the O-glycosylated derivatives. Finally, the compounds exhibited significantly less toxicity when tested in adult human dermal fibroblasts and their GI50 in melanoma Sk-Mel-5 cells was not influenced by MDR1/Pgp inhibitors. This study may inform the synthesis of future Diphyllin derivatives with different apoptosis mechanism of action towards human melanoma cells

Decarboxylation of Dialkyl Carbonates to Dialkyl Ethers over Alkali Metal-exchanged Faujasites

Non-toxic DAlCs, especially lighter dimethyl- and diethyl-carbonate, are regarded as very green alkylating reagents, particularly when coupled with metal-exchanged Y- and X-faujasites as catalysts. These reactions are selective, free from wastes or byproducts, and often require no additional solvent other than the carbonate. Nonetheless, this paper demonstrates that the operating temperature and the nature of the faujasite must be carefully chosen in order to avoid DAlC decomposition. In fact, at temperatures ranging from 150 to 240 ◦ C, faujasites can promote decarboxylation of light DAlCs to the corresponding ethers CH3OCH3 and CH3CH2OCH2CH3 plus CO2. Heavier DAlCs (dipropyl- and dioctyl-carbonate) undergo a similar decomposition pathway, followed by further reactions to the corresponding alcohols (n-propanol and n-octanol) and alkenes [propylene and octene(s)]. These transformations not only consume DAlCs, but also give rise to dangerously flammable ethers, as well as undesirable alcohols, alkenes and CO2.The present work reports an original investigation of the decarboxylation of DAlCs on faujasites with the aim of providing operative boundaries to the experimental conditions to minimise unwanted decomposition. The reaction is strongly affected by the nature of the catalyst: the more basic zeolites, NaX and CsY, are by far more active systems than NaY and LiY. However, solid K2CO3 proves to be rather inefficient. The temperature also plays a crucial role: for example, the onset of the decarboxylation of DMC requires a temperature of ~30 ◦ C lower than that for DEC and DPrC. Overall, awareness that certain zeolites cause decomposition of DAlCs under conditions similar to the ones used for DAlC-promoted alkylations allows determination of the correct experimental boundaries for a safer and more productive use of DAlCs as alkylating agent