– Cylindrospermopsin, a tricyclic uracil derivative, is a cyanobacterial toxin that was first discovered in an algal bloom contaminating a local drinking supply on Palm Island in Queensland, Australia after an outbreak of a mysterious disease. Cylindrospermopsin targets protein and glutathione synthesis in hepatocytes (IC50s = 1.3 and 2.4 &#181M, respectively), leading to cell death. [1] It has been shown to inhibit the activity of the uridine monophosphate synthase complex with a Ki value of 10 &#181M.[2] Cylindrospermopsin is genotoxic, inducing DNA damage as evidenced by double strand breaks and reducing cell viability in HepG2 cells at 0.1-0.5 &#181g/ml.[3]