Date Published: September 23, 2016
Publisher: Public Library of Science
Author(s): Víctor M. Castillo-Acosta, Luis M. Ruiz-Pérez, Juan Etxebarria, Niels C. Reichardt, Miguel Navarro, Yasuhiro Igarashi, Sandra Liekens, Jan Balzarini, Dolores González-Pacanowska, David Sacks.
Current treatments available for African sleeping sickness or human African trypanosomiasis (HAT) are limited, with poor efficacy and unacceptable safety profiles. Here, we report a new approach to address treatment of this disease based on the use of compounds that bind to parasite surface glycans leading to rapid killing of trypanosomes. Pradimicin and its derivatives are non-peptidic carbohydrate-binding agents that adhere to the carbohydrate moiety of the parasite surface glycoproteins inducing parasite lysis in vitro. Notably, pradimicin S has good pharmaceutical properties and enables cure of an acute form of the disease in mice. By inducing resistance in vitro we have established that the composition of the sugars attached to the variant surface glycoproteins are critical to the mode of action of pradimicins and play an important role in infectivity. The compounds identified represent a novel approach to develop drugs to treat HAT.
Human African trypanosomiasis or sleeping sickness is a neglected disease caused by the protozoan parasite Trypanosoma brucei. Treatments are largely insufficient and unsatisfactory and new approaches for drug design are highly necessary.
In this study we have explored the trypanocidal activity of pradimicins and the mode of action of these non-peptidic CBAs in order to provide an insight into the potential of these highly novel antiparasitics. Pradimicins are low-molecular-weight antibiotics (~ 900 Da) that exhibit antiviral and antifungal properties mediated by lectin-mimic binding to surface glycans [11, 12, 14, 17, 31]. We show that these CBAs exhibit a remarkable trypanocidal activity in vitro in the low micromolar range, in particular PRM-A and its highly water-soluble derivative PRM-S proved most active. Extraordinarily, PRM-S also exhibits a potent trypanocidal effect in vivo, resulting in a parasitological cure in acute models of African trypanosomiasis using both the T. brucei rhodesiense and T. brucei brucei species. These findings are a continuation of previous work conducted in our laboratory where we identified a series of plant lectins such as HHA, UDA, GNA, NPA and EHA, that exhibit strong inhibitory activity against T. brucei . Our observations were in contrast to the general belief that most lectins are not toxic for T. brucei bloodstream forms since rapid internalization and degradation of the surface glycoprotein-lectin complex would result in a lack of toxicity . Although the dissociation constant of the PRM-A-VSG221 or PRM-S-VSG221 complexes could not be determined in detail due to the existence of multiple binding sites in the VSG molecule, we provide multiple evidence that the mode of action of pradimicins is indeed due to tight binding to surface VSGs and perturbation of the endocytic pathway resulting in a rapid parasite death. Defects in endocytosis of a similar fashion have been observed earlier upon formation of VSG-specific nanobody complexes (Nsbs) and have been reported to play an essential role in the nanobody’s cytotoxic action .