Genetic and phenotypic features of visceral Leishmania species exposed to miltefosine. Towards understanding therapeutic failure
16 juni 2017
UAntwerpen - Campus Drie Eiken - Gebouw Q - Promotiezaal - Universiteitsplein 1 - 2610 Antwerpen (Wilrijk) (route: UAntwerpen, Campus Drie Eiken
16 - 18 uur
Guy Caljon, Paul Cos
Doctoraatsverdediging Annelies Mondelaers - Departement Farmaceutische Wetenschappen
Abstract Mondelaers Annelies: Genetic and phenotypic features of visceral Leishmania species exposed to miltefosine-towards understanding therapeutic failure
Visceral leishmaniasis is a ‘neglected’ tropical disease that is spread through the bite of infected sandflies and for which treatment is still fully based on chemotherapy to avoid lethality. The initial first- line treatment option with pentavalent antimonials was not only threatened by severe side effects but also by the emergence of treatment failures due to drug-resistance. Introduction of miltefosine (MIL) as the first highly effective oral drug circumvented these difficulties for a large part. However, relapses upon MIL-treatment are now increasingly being reported. While the multifactorial nature of treatment failure, involving host-, parasite- and drug-related factors, has clearly been established, this PhD research specifically focused on the elucidation of parasite factors that may contribute to MIL-treatment failure by performing a full phenotypic and genotypic characterization of parasites that were repeatedly exposed to MIL. An in vitro selection protocol in which intracellular amastigotes are exposed to successive selection cycles of MIL was developed to more closely mimic the in vivo field situation. Since intrinsic parasite resistance is only partially responsible for treatment failure, additional (epi)-phenotypic features included genomic studies complemented with transcriptomic and phenotypic assays.
First, a general description on the disease leishmaniasis is presented with attention to the visceral clinical form and the mode-of action of current antileishmanial drugs together with their proposed resistance mechanisms (Chapter II). Next, the state-of-the-art on therapeutic failure and drug resistance in Leishmania is outlined in detail with particular reference to MIL (Chapter III).
Chapters IV and V describe the full characterization of parasites having an intermediate or fully resistant phenotype, hereby exploring the role of the MIL-transporter complex (MT/ROS3) as well as the validity of an in vitro amastigote resistance selection model as a proxy to study MIL-resistance in the field (Chapter V).
Next, the defined MIL-resistant strains were assessed for cross-resistance towards amphotericin B since both drugs share a fairly similar mechanism of leishmanicidal activity. These findings may be important when designing combination therapies (Chapter VI).
Further, in the context of very low post-treatment parasite burdens, a novel qPCR technique for detecting DNA and RNA was developed and applied as a tool to assess homogeneity of infection and post- treatment parasite burdens in the target organs liver and spleen. Quantification of amastigote burdens was compared with those obtained by the standard microscopy method (Chapter VII).
Finally, the last chapter (Chapter VIII) includes a general discussion and points out specific approaches to safeguard the effectiveness of MIL and delay the onset and spread of drug resistance in general.