Acanthamoeba castellanii Neff: In vitro activity against the trophozoite stage of a natural sesquiterpene and a synthetic cobalt(II)–lapachol complex Carmen M. Martín-Navarro a , Atteneri López-Arencibia a , Jacob Lorenzo-Morales a , Sandra Oramas-Royo b,c , Rita Hernández-Molina d , Ana Estévez-Braun b,c , Ángel G. Ravelo b,c , Basilio Valladares a , José E. Piñero a, * a University Institute of Tropical Diseases and Public Health of the Canary Islands, University of La Laguna, Avda. Astrofísico Fco. Sánchez, S/N 38203 La Laguna, Tenerife, Canary Islands, Spain b Instituto Universitario de Bio-Orgánica ‘‘Antonio González”, Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez 2, 38206, La Laguna, Tenerife, Canary Islands, Spain c Instituto Canario de Investigación del Cáncer (ICIC) 1 , Avenida Astrofisico Fco. Sanchez, S/N 38204 La Laguna, Tenerife, Canary Islands, Spain d Departamento de Química Inorgánica, Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez S/N, 38206, La Laguna, Tenerife, Canary Islands, Spain article info Article history: Received 2 October 2009 Accepted 23 December 2009 Available online 4 January 2010 Keywords: Acanthamoeba Lapachol Sesquiterpene Cyperotundone Chemotherapy abstract In this study, the in vitro activities of a natural sesquiterpene, a-cyperotundone, isolated from the root bark of Maytenus retusa and a cobalt(II)-complex of a natural occurring prenyl hydroxynaphthoquinone (lapachol) were evaluated against the trophozoite stage of Acanthamoeba castellanii Neff using a previ- ously developed colorimetric 96-well microtiter plate assay, based on the oxido-reduction of Alamar Blue Ò . The obtained activities showed that these two compounds were able to inhibit the in vitro growth of the amoebae at relatively low concentrations. Further identification of the molecular targets of these products and their effects on acanthamoebae should be determined to evaluate their possible therapeutic use. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Acanthamoeba species are opportunistic causal agents of dis- seminated infections (mostly cutaneous and nasopharyngeal infec- tions), such as a sight-threatening ulceration of the cornea called amoebic keratitis and a fatal Acanthamoeba Granulomatous Encephalitis (AGE) (Marciano-Cabral and Cabral, 2003; Clarke and Niederkorn, 2006; Khan, 2006). Present therapeutic measures for Acanthamoeba keratitis rely on topical applications of antimicrobials including a combination of propamidine isothionate and neomycin or chlorhexidine. The length of these treatments makes the process arduous. Further- more, as present treatments are poorly effective against cystic stages of the protozoan, residual infection often remains even after treatment. No treatment against AGE has been established although therapeutic measures have been used with apparent ef- fect as an adjunct to surgery (Schuster and Visvesvara, 2004; Khan, 2003, 2006; Martín-Navarro et al., 2008). Terpenes represent one of the largest and most diverse classes of secondary metabolites, with over 55,000 members isolated to date. The terpene cyclase enzymes used in nature convert simple, linear hydrocarbon phosphates into an exotic array of chiral, carbo- cyclic skeletons. Further oxidation and rearrangement results in an almost endless number of conceivable structures. The enormous structural diversity presented by this class of natural products en- sures a broad range of biological properties—ranging from anti- cancer and anti-malarial activities to tumour promotion and ion- channel binding (Paduch et al., 2007; Patoc ˇka, 2003). The marked structural differences of terpenes also largely thwart the develop- ment of any truly general strategies for their synthetic construction (Maimone and Baran, 2007). Furthermore, several sesquiterpenes have shown to be promising for the treatment of infections due to parasitic protozoa such as Plasmodium, Leishmania and Trypano- soma (Karioti et al., 2007; Schmidt et al., 2009). In this work, the in vitro activity of a natural sesquiterpene and a synthetic cobal- t(II)–lapachol complex against the trophozoite stage of Acantha- moeba castellanii Neff is reported. The first molecule is a patchoulane-type sesquiterpene, a-cypertundone (Neraldi et al., 1965), isolated from the root bark of Maytenus retusa. The second molecule tested is a cobalt(II)-complex of lapachol. Lapachol is a prenyl hydroxynaphthoquinone with interesting bio- logical properties such as antitumoural and antibiotic (Ravelo et al., 2004). Unfortunately, it has serious negative side effects 0014-4894/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.exppara.2009.12.015 * Corresponding author. Address: Instituto Universitario de Enfermedades Trop- icales y Salud Pública de Canarias, Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez, S/N 38203 La Laguna, Canary Islands, Spain. Fax: +34 922318514. E-mail address: jmlorenz@ull.es (J.E. Piñero). 1 http://www.icic.es Experimental Parasitology 126 (2010) 106–108 Contents lists available at ScienceDirect Experimental Parasitology journal homepage: www.elsevier.com/locate/yexpr