Marasmic acid

Background: The histidine kinase (HK) MoHik1p within the high-osmolarity glycerol (HOG) pathway is known to be the target of the fungicide fludioxonil. Treatment of the fungus with fludioxonil causes an uncontrolled hyperactivation of the pathway and cell death. In this study, we used a target-based in vivo test system with mutant strains of the rice blast fungus Magnaporthe oryzae to search for new fungicidal compounds having various target locations within the HOG pathway. Mutants with inactivated HOG signalling are resistant to fungicides having the target located in the HOG pathway. Results: The HK MoSln1p was identified as being involved in the new antifungal mode of action of marasmic acid, as single inactivation of the genes MoSLN1, MoSSK1, MoSSK2, MoPBS2 and MoHOG1 resulted in mutant strains resistant against the sesquiterpenoid, whereas the wild-type strain and the ΔMohik1 mutant were susceptible. Western blot analysis of phosphorylated MoHog1p confirmed the hypothesis that marasmic acid interferes with the HOG pathway, as a strong phosphorylation of MoHog1p was detectable after sesquiterpenoid treatment in the wild-type strain but not in the ΔMosln1 mutant. Conclusion: This study provides evidence for marasmic acid activating the HOG pathway via the HK MoSln1p, and we propose that the sesquiterpenoid has a new mode of action in M. oryzae that differs from that of known HOG inhibitors, e.g. fludioxonil. © 2016 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The neutral red absorption assay, complemented by protein determination, was used to measure the cytotoxic activity of 22 sesquiterpenoid unsaturated dialdehydes towards hamster fibroblasts in monolayer culture (cell line V79). No significant differences between the activities determined by the two assays were found for the compounds assayed, indicating that their inhibitory effects on cell growth are related to general cytotoxicity. In spite of the apparent similarity between the chemical structures of the assayed compounds, the most active was approximately 200 times more cytotoxic than the least active. Isovelleral and its derivatives are the most cytotoxic substances, but the ranking in order of general cytotoxicity within this subgroup differed from that found in a previous study of mutagenic activity. Marasmic acid and its derivatives are also potent cytotoxic agents, but two of the most cytotoxic compounds in this group have been reported to be the least mutagenic. Such differences between cytotoxic and mutagenic activities indicate that the molecular targets for these two activities differ. The cytotoxicity of polygodial found in this study is lower than that previously reported from other cytotoxicity assays, which suggests that different tests of general cytotoxicity may have different molecular targets. Because of the diverse cytotoxic activities of the unsaturated dialdehydes, it should be possible to study them in a quantitative structure-activity relationship (QSAR) multivariate analysis.

Pilatin, a new marasmane derivative, was isolated from fermentations of the cyphelloid fungus Flagelloscypha pilatii. Its structure was determined by chemical and physical methods. Pilatin inhibits the growth of bacteria and fungi at concentrations of 5-50 micrograms/ml. The compound is highly cytotoxic. The incorporation of thymidine and uridine into DNA and RNA in Ehrlich carcinoma ascitic cells is strongly inhibited by pilatin. Like marasmic acid pilatin causes frameshift mutations in Salmonella typhimurium TA98.