Report of Workshop on Euthanasia for Zebrafish-A Matter of Welfare and Science.

The increasing importance of zebrafish as a biomedical model organism is reflected by the steadily growing number of publications and laboratories working with this species. Regulatory recommendations for euthanasia as issued in Directive 2010/63/EU are, however, based on experience with fish species used for food production and do not take the small size and specific physiology of zebrafish into account. Consequently, the currently recommended methods of euthanasia in the Directive 2010/63/EU are either not applicable or may interfere with research goals. An international workshop was held in Karlsruhe, Germany, March 9, 2017, to discuss and propose alternative methods for euthanasia of zebrafish. The aim was to identify methods that adequately address the physiology of zebrafish and its use as a biomedical research model, follow the principles of the 3Rs (Replacement, Reduction, and Refinement) in animal experimentation and consider animal welfare during anesthesia and euthanasia. The results of the workshop are summarized here in the form of a white paper.

The plakotenins: biomimetic Diels-Alder reactions, total synthesis, structural investigations, and chemical biology.

The total synthesis of plakotenin, a cytotoxic marine natural product, using a biomimetic Diels-Alder reaction is described in detail. Two approaches were used, whereby the Diels-Alder reaction occurs at different stages of the synthesis. Homo- and nor-plakotenin, related natural products, were also prepared, as well as iso-plakotenin, a diastereoisomer of plakotenin. The syntheses prove the relative and absolute stereochemistry of the latter. The chemical biology of the plakotenins was investigated on selected compounds.

LiCl induces TNF-α and FasL production, thereby stimulating apoptosis in cancer cells.

BACKGROUND: The incidence of cancer in patients with neurological diseases, who have been treated with LiCl, is below average. LiCl is a well-established inhibitor of Glycogen synthase kinase-3, a kinase that controls several cellular processes, among which is the degradation of the tumour suppressor protein p53. We therefore wondered whether LiCl induces p53-dependent cell death in cancer cell lines and experimental tumours. RESULTS: Here we show that LiCl induces apoptosis of tumour cells both in vitro and in vivo. Cell death was accompanied by cleavage of PARP and Caspases-3, -8 and -10. LiCl-induced cell death was not dependent on p53, but was augmented by its presence. Treatment of tumour cells with LiCl strongly increased TNF-α and FasL expression. Inhibition of TNF-α induction using siRNA or inhibition of FasL binding to its receptor by the Nok-1 antibody potently reduced LiCl-dependent cleavage of Caspase-3 and increased cell survival. Treatment of xenografted rats with LiCl strongly reduced tumour growth. CONCLUSIONS: Induction of cell death by LiCl supports the notion that GSK-3 may represent a promising target for cancer therapy. LiCl-induced cell death is largely independent of p53 and mediated by the release of TNF-α and FasL.Key words: LiCl, TNF-α, FasL, apoptosis, GSK-3, FasL.