Development of anEx VivoLymph Node Explant Model for Identification of Novel Molecules Active against Leishmania major

Leishmaniasis is a vector-borne zoonotic infection affecting people in tropical and subtropical regions of the world. Current treatments for cutaneous leishmaniasis are difficult to administer, toxic, expensive, and limited in effectiveness and availability. Here we describe the development and application of a medium-throughput screening approach to identify new drug candidates for cutaneous leishmaniasis using ane x vivo l ymph nodee xplantc ulture (ELEC) derived from the draining lymph nodes ofLeishmania major -infected mice. The ELEC supported intracellular amastigote proliferation and contained lymph node cell populations (and their secreted products) that enabled the testing of compounds within a system that mimicked the immunopathological environment of the infected host, which is known to profoundly influence parasite replication, killing, and drug efficacy. The activity of known antileishmanial drugs in the ELEC system was similar to the activity measured in peritoneal macrophages infectedin vitro withL. major . Using the ELEC system, we screened a collection of 334 compounds, some of which we had demonstrated previously to be active againstL. donovani , and identified 119 hits, 85% of which were confirmed to be active by determination of the 50% effective concentration (EC50 ). We found 24 compounds (7%) that had ani nv itrot herapeutici ndex (IVTI; 50% cytotoxic/effective concentration [CC50 ]/EC50 ) > 100; 19 of the compounds had an EC50 below 1 μM. According to PubChem searchs, 17 of those compounds had not previously been reported to be active againstLeishmania . We expect that this novel method will help to accelerate discovery of new drug candidates for treatment of cutaneous leishmaniasis.