Date Published: March 13, 2015
Publisher: Public Library of Science
Author(s): Jennifer Edwards, Martha Brown, Emily Peak, Barbara Bartholomew, Robert J. Nash, Karl F. Hoffmann, Timothy G. Geary. http://doi.org/10.1371/journal.pntd.0003604
Abstract: BackgroundTwo platyhelminths of biomedical and commercial significance are Schistosoma mansoni (blood fluke) and Fasciola hepatica (liver fluke). These related trematodes are responsible for the chronic neglected tropical diseases schistosomiasis and fascioliasis, respectively. As no vaccine is currently available for anti-flukicidal immunoprophylaxis, current treatment is mediated by mono-chemical chemotherapy in the form of mass drug administration (MDA) (praziquantel for schistosomiasis) or drenching (triclabendazole for fascioliasis) programmes. This overreliance on single chemotherapeutic classes has dramatically limited the number of novel chemical entities entering anthelmintic drug discovery pipelines, raising significant concerns for the future of sustainable blood and liver fluke control.Methodology/ Principle FindingsHere we demonstrate that 7-keto-sempervirol, a diterpenoid isolated from Lycium chinense, has dual anthelmintic activity against related S. mansoni and F. hepatica trematodes. Using a microtiter plate-based helminth fluorescent bioassay (HFB), this activity is specific (Therapeutic index = 4.2, when compared to HepG2 cell lines) and moderately potent (LD50 = 19.1 μM) against S. mansoni schistosomula cultured in vitro. This anti-schistosomula effect translates into activity against both adult male and female schistosomes cultured in vitro where 7-keto-sempervirol negatively affects motility/behaviour, surface architecture (inducing tegumental holes, tubercle swelling and spine loss/shortening), oviposition rates and egg morphology. As assessed by the HFB and microscopic phenotypic scoring matrices, 7-keto-sempervirol also effectively kills in vitro cultured F. hepatica newly excysted juveniles (NEJs, LD50 = 17.7 μM). Scanning electron microscopy (SEM) evaluation of adult F. hepatica liver flukes co-cultured in vitro with 7-keto-sempervirol additionally demonstrates phenotypic abnormalities including breaches in tegumental integrity and spine loss.Conclusions/ Significance7-keto-sempervirol negatively affects the viability and phenotype of two related pathogenic trematodes responsible for significant human and animal infectious diseases. This plant-derived, natural product is also active against both larval and adult developmental forms. As such, the data collectively indicate that 7-keto-sempervirol is an important starting point for anthelmintic drug development. Medicinal chemistry optimisation of more potent 7-keto-sempervirol analogues could lead to the identification of novel chemical entities useful for future combinatorial or replacement anthelmintic control.
Partial Text: Schistosomiasis and fascioliasis are Neglected Tropical Diseases (NTDs) caused by related parasitic blood (Schistosoma sp. including Schistosoma mansoni) and liver (Fasciola sp including Fasciola hepatica) flukes found within the phylum Platyhelminthes. These NTDs are responsible for chronic conditions of biomedical and veterinary significance and collectively affect a considerable proportion of the world’s human and animal populations. Globally, approximately 200 million people are currently afflicted by schistosomiasis, with this chronic disease being most prominent in tropical/subtropical regions of poverty-stricken, rural areas . While fascioliasis is one of the most important parasitic diseases of ruminant livestock animals, it also negatively impacts 2.4 to 17 million humans worldwide by inducing chronic liver pathologies in infected individuals .
Current control efforts aimed at reducing disease prevalence of schistosomiasis and fascioliasis are predominantly based on mono-chemotherapy administration of praziquantel (PZQ) and triclabendazole (TCBZ), respectively. Nevertheless, worries about the development of PZQ resistant blood flukes and the spread of TCBZ resistant liver flukes coupled to the slow progression of immunoprophylactic vaccines, have notably increased the number of new anthelmintic drug discovery projects initiated throughout the last decade. While our efforts in this area have successfully leveraged interdisciplinary techniques to identify drug targets [38–42] and to develop high-throughput drug screening methodologies , we have only recently begun characterising the detailed anthelmintic activities of defined chemical entities. Here, we report the findings from one such investigation and demonstrate that a diterpenoid (7-keto-sempervirol) derived from Lycium chinense has key properties useful in the development of a broad-spectrum agent active against both blood and liver flukes.