Anticancer activities of enniatin and beauvericin

In recent years there has been substantial progress in development of new anticancer drugs. However, tumours frequently develop resistance to often even structurally and mechanistically unrelated drugs. This acquired resistance to chemotherapy is a major obstacle to successful cancer treatment and encourages the research for new and better anticancer drugs. Currently, cyclic depsipeptides are in the focus of interest as new anticancer drugs and some of them already in preclinical trials. Recently, the two cyclic hexadepsipeptidic Fusarium metabolites enniatin (ENN) and beauvericin (BEA) were shown to possess potential quality for the use as anticancer drugs. This was indicated by the proof of cytotoxic activities in the low micro-molar range against several cancer cell lines and comparable insensitivity of normal cells. Moreover, ATP-binding cassette transporters frequently involved in multidrug resistance during chemotherapy did not affect the cytotoxic potential of ENN and BEA. Even long term of carcinoma cells to stepwise increasing ENN and BEA concentrations did not result in resistant cell models. So far, the precise mechanisms underlying ENN- and BEA-induced cytotoxicity are not exactly defined. However, to judge the pharmacological potential of these two substances as lead anticancer compounds the knowledge on their molecular modes of action is of utmost importance. Consequently, the presented project aims to gain more insights into the ENN- and BEA-mediated signal transduction and cell death. Overall, we will investigate the impact of ENN and BEA on genome wide gene expression with a special focus on stress signals and signals known to result in activated cell death pathways in cancer cells. Moreover, since ENN- and BEA-induced cell death is suggested to be based on disruption of intracellular Ca2+ homeostatis, key components of intracellular signalling networks which are closely connected to modifications of the intracellular Ca2+ levels are of interest. In addition, the impact of the apoptosis- and cell cycle-regulation proteins p53 and p21 will be investigated. Since ENN was shown to induce the cyclin-dependent kinase inhibitor p21 independent of the p53 status, histone deacetylase inhibitory effects are suggested and thus matter of the ongoing project. Moreover, preliminary studies revealed that BEA exerts antiangiogenic activities. To gain more insights into the antiangiogenic properties we will investigate the impact of the test substances on the most important angiogenesis pathways by using diverse test systems in vitro and in vivo including the Chick Chorioallantoic Membrane angiogenesis assay. In addition, in vitro and in vivo investigations of ENN and BEA as single drugs or in combination regimens with diverse targeted drugs and chemotherapeutics against human cancer xenografts will support the rational planning of successful clinical application of the two test substances. Taken together, the intended project could break new ground in the evaluation of the two cyclic hexadepsipeptides ENN and BEA as new anticancer drugs for use in clinical oncology. Moreover, the obtained toxicological data will also help in assessing the risk of ENN and BEA to human and animal health as food contaminants.

There is unchallenged evidence that during the last decades substantial progress has been made in developing cancer chemotherapy, which is effective against a wide variety of tumours. However, tumours frequently develop resistance mechanisms against several often structurally and mechanistically unrelated drugs. Thus, it is of predominant interest to overcome drug resistance and to encourage the research for new and better chemotherapeutic drugs. It is noteworthy, that nature provides a rich source for bioactive natural products as lead compounds for drug discovery. Amongst them are cyclic depsipeptides like enniatins (Enn), beauvericin (Bea), destruxins A, B, and E (Dtx A, B, and E), which have been identified from plants, fungi and marine organisms. These are polypeptides, in which one or more amino acid is replaced by a hydroxy acid, resulting in the formation of at least one ester bond in the core ring structure. At the beginning of our research studies, only a few data about the effect and the toxicological impact of these cyclodepsipeptidic secondary metabolites were published and at the beginning of the project, we only focused on Enn B and Bea but in the meantime also the interesting group of Dtx was included in our investigations. Thanks to this Hertha Firnberg project, we have made remarkable headway bringing to light the anticancer properties of these little-studied cyclodepsipeptides. For instance, we could demonstrate antiangiogenic properties for Enn B, Bea and Dtx indicated by a strong inhibition of human endothelial cell migration and tube formation further reflecting their anticancer potential. Moreover, our in vivo experiments of Enn B and Bea with mice suggested a favourable tolerability of both substances, as no toxicological signs during lifetime or pathological changes were observed. Additionally, investigations of their pharmacological behaviour demonstrated the molecules tendency to bioaccumulate in lipophilic tissues and that both fusariotoxins were spread over all tissues (also tumour tissues) and serum but not found in urine. Although tumour enrichment and the therapeutic margin of Enn and Bea still needs to be improved, our observations suggest further preclinical development of this natural compounds as anticancer agents. Remarkably, combination studies of Enn B and Bea with the clinically approved multi-kinase inhibitor Sorafenib (Sora) revealed profound synergistic anticancer effects against cervical cancer cells in vitro, which could be confirmed for Enn B in a KB-3-1 cervix carcinoma xenograft model, so far. Comparable in vivo experiments for Bea are currently under progress. However, the mechanism underlying the synergistic anticancer activity of the cyclic depsipeptides with Sora seems to be quite complex and multifaceted and were suggested to be based for Enn B on interference with the p38 MAPK and the ERK signalling pathways. For Bea the synergism was assumed to be based on a multifarious disturbance of the ERK/p38 MAPK and PI3K-Akt-mTOR signalling. To conclude, our findings demonstrated Dtx, Enn B and Bea as promising single anticancer agents. For the two latter ones also an encouraging new combination strategy with Sorafenib for cervix cancer treatment was suggested.