Importance of secondary screening with clinical isolates for anti-leishmania drug discovery

The growing drug resistance (DR) raises major concerns for the control of visceral leishmaniasis (VL), a neglected disease lethal in 95 percent of the cases if left untreated. Resistance has rendered antimonials (SSG) obsolete in the Indian Sub-Continent (ISC) and the first miltefosine-resistant Leishmania donovani were isolated. New chemotherapeutic options are needed and novel compounds are being identified by high-throughput screening (HTS). HTS is generally performed with old laboratory strains such as LdBOB and we aimed here to validate the activity of selected compounds against recent clinical isolates. In this academic/industrial collaboration, 130 compounds from the GSK “Leishbox” were screened against one SSG-sensitive and one SSG-resistant strain of L. donovani recently isolated from ISC patients, using an intracellular assay of L. donovani-infected THP1-derived macrophages. We showed that only 45% of the compounds were active in both clinical isolates and LdBOB. There were also different compound efficiencies linked to the SSG susceptibility background of the strains. In addition, our results suggested that the differential susceptibility profiles were chemical series-dependent. In conclusion, we demonstrate the potential value of including clinical isolates (as well as resistant strains) in the HTS progression cascade.