Altered membrane rigidity via enhanced endogenous cholesterol synthesis drives cancer cell resistance to destruxins.

Destruxins, secondary metabolites of entomopathogenic fungi, exert a wide variety of interesting characteristics ranging from antiviral to anticancer effects. Although their mode of action was evaluated previously, the molecular mechanisms of resistance development are unknown. Hence, we have established destruxin-resistant sublines of HCT116 colon carcinoma cells by selection with the most prevalent derivatives, destruxin (dtx)A, dtxB and dtxE. Various cell biological and molecular techniques were applied to elucidate the regulatory mechanisms underlying these acquired and highly stable destruxin resistance phenotypes. Interestingly, well-known chemoresistance-mediating ABC efflux transporters were not the major players. Instead, in dtxA- and dtxB-resistant cells a hyper-activated mevalonate pathway was uncovered resulting in increased de-novo cholesterol synthesis rates and elevated levels of lanosterol, cholesterol as well as several oxysterol metabolites. Accordingly, inhibition of the mevalonate pathway at two different steps, using either statins or zoledronic acid, significantly reduced acquired but also intrinsic destruxin resistance. Vice versa, cholesterol supplementation protected destruxin-sensitive cells against their cytotoxic activity. Additionally, an increased cell membrane adhesiveness of dtxA-resistant as compared to parental cells was detected by atomic force microscopy. This was paralleled by a dramatically reduced ionophoric capacity of dtxA in resistant cells when cultured in absence but not in presence of statins. Summarizing, our results suggest a reduced ionophoric activity of destruxins due to cholesterol-mediated plasma membrane re-organization as molecular mechanism underlying acquired destruxin resistance in human colon cancer cells. Whether this mechanism might be valid also in other cell types and organisms exposed to destruxins e.g. as bio-insecticides needs to be evaluated.

The Natural Fungal Metabolite Beauvericin Exerts Anticancer Activity In Vivo: A Pre-Clinical Pilot Study.

Recently, in vitro anti-cancer properties of beauvericin, a fungal metabolite were shown in various cancer cell lines. In this study, we assessed the specificity of this effect by comparing beauvericin cytotoxicity in malignant versus non-malignant cells. Moreover, we tested in vivo anticancer effects of beauvericin by treating BALB/c and CB-17/SCID mice bearing murine CT-26 or human KB-3-1-grafted tumors, respectively. Tumor size and weight were measured and histological sections were evaluated by Ki-67 and H/E staining as well as TdT-mediated-dUTP-nick-end (TUNEL) labeling. Beauvericin levels were determined in various tissues and body fluids by LC-MS/MS. In addition to a more pronounced activity against malignant cells, we detected decreased tumor volumes and weights in beauvericin-treated mice compared to controls in both the allo- and the xenograft model without any adverse effects. No significant differences were detected concerning percentages of proliferating and mitotic cells in tumor sections from treated and untreated mice. However, a significant increase of necrotic areas within whole tumor sections of beauvericin-treated mice was found in both models corresponding to an enhanced number of TUNEL-positive, i.e., apoptotic, cells. Furthermore, moderate beauvericin accumulation was detected in tumor tissues. In conclusion, we suggest beauvericin as a promising novel natural compound for anticancer therapy.

Mouse tissue distribution and persistence of the food-born fusariotoxins Enniatin B and Beauvericin.

The fusariotoxins Enniatin B (Enn B) and Beauvericin (Bea) have recently aroused interest as food contaminants and as potential anticancer drugs. However, limited data are available about their toxic profile. Aim of this study was to investigate their pharmacological behavior in vivo and their persistence in mice. Therefore, liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to analyze the distribution of Enn B and Bea in selected tissue samples and biological fluids originating from mice treated intraperitoneally with these cyclohexadepsipeptides. Overall, no toxicological signs during life time or pathological changes were observed. Moreover, both fusariotoxins were found in all tissues and serum but not in urine. Highest amounts were measured in liver and fat demonstrating the molecules tendency to bioaccumulate in lipophilic tissues. While for Bea no metabolites could be detected, for Enn B three phase I metabolites (dioxygenated-Enn B, mono- and di-demethylated-Enn B) were found in liver and colon, with dioxygenated-Enn B being most prominent. Consequently, contribution of hepatic as well as intestinal metabolism seems to be involved in the overall metabolism of Enn B. Thus, despite their structural similarity, the metabolism of Enn B and Bea shows distinct discrepancies which might affect long-term effects and tolerability in humans.

Disruptive environmental chemicals and cellular mechanisms that confer resistance to cell death.

Cell death is a process of dying within biological cells that are ceasing to function. This process is essential in regulating organism development, tissue homeostasis, and to eliminate cells in the body that are irreparably damaged. In general, dysfunction in normal cellular death is tightly linked to cancer progression. Specifically, the up-regulation of pro-survival factors, including oncogenic factors and antiapoptotic signaling pathways, and the down-regulation of pro-apoptotic factors, including tumor suppressive factors, confers resistance to cell death in tumor cells, which supports the emergence of a fully immortalized cellular phenotype. This review considers the potential relevance of ubiquitous environmental chemical exposures that have been shown to disrupt key pathways and mechanisms associated with this sort of dysfunction. Specifically, bisphenol A, chlorothalonil, dibutyl phthalate, dichlorvos, lindane, linuron, methoxychlor and oxyfluorfen are discussed as prototypical chemical disruptors; as their effects relate to resistance to cell death, as constituents within environmental mixtures and as potential contributors to environmental carcinogenesis.

The naturally born fusariotoxin enniatin B and sorafenib exert synergistic activity against cervical cancer in vitro and in vivo.

During the last decades substantial progress has been made in developing systemic cancer therapy. However, tumors are frequently intrinsically resistant against structurally and mechanistically unrelated drugs. Thus, it is of predominant interest to overcome drug resistance and to encourage the research for novel chemotherapeutic approaches. Recently, we have introduced enniatins, naturally occurring cyclohexadepsipeptides produced by filamentous fungi of the genus Fusarium, as potential anticancer drugs. Here, we expend this approach by demonstrating antiangiogenic properties for enniatin B (Enn B) indicated by a strong inhibition of human endothelial cell migration and tube formation. Moreover, combination of Enn B with the clinically approved multi-kinase inhibitor sorafenib (Sora) displayed profound synergistic in vitro and in vivo anticancer effects against cervical cancer. Subsequent studies showed that this strong synergism is accompanied by a marked increase in mitochondrial injury and apoptosis induction reflected by mitochondrial membrane depolarization, caspase-7 activation, and subsequent cleavage of PARP. Additionally, cells were shown to stop DNA synthesis and accumulate in S and G2/M phase of the cell cycle. The multifaceted characteristics underlying this strong synergism were suggested to be based on interference with the p38 MAPK as well as the ERK signaling pathways. Finally, also in vivo studies revealed that the combination treatment is distinctly superior to single drug treatments against the KB-3-1 cervix carcinoma xenograft model. Taken together, our data confirm the anticancer benefits of the naturally occurring fusariotoxin Enn B and further present Enn B/Sora as a novel combination strategy especially for the treatment of cervical cancer.