The protozoan toxin climacostol and its derivatives: cytotoxicity studies on 10 species of free-living ciliates

Climacostol (5-(Z)-non-2-enyl-benzene-1,3-diol) is a natural toxin isolated from the freshwater ciliated protozoan Climacostomum virens and belongs to resorcinolic lipids, a group of compounds that show antimicrobial, antiparasitic, and anticancer activities. We investigated the cytotoxic activity of the chemically synthesized toxin and its alkyl and alkynyl derivatives on C. virens and nine other common species of free-living freshwater ciliates. Our results show that the cytotoxic potency of climacostol can be modulated by the substitution of the double bond present in the aliphatic chain of the toxin with a single or a triple one that was previously obtained during the synthesis of the unsaturated and saturated derivatives of the parent molecule. We demonstrated that the cytotoxicity level of the molecules considered in this study appears to be inversely correlated to the unsaturation level of their aliphatic chains, and that the potency of their action is also related to the target organism.