RES-Seq – a barcoded library of drug-resistant Leishmania donovani allowing rapid assessment of cross-resistance and relative fitness

Visceral leishmaniasis (VL) is a parasitic disease endemic across multiple regions of the world and is fatal if untreated. New therapeutic options with diverse mechanisms of actions are required to consolidate progress towards control of this disease and combat drug resistance. Here, we describe the development of a scalable resistance library screen (RES-Seq) as a tool to facilitate the identification and prioritisation of antileishmanial compounds acting via novel mechanisms of action (MoA). We have amassed a large collection of L. donovani cell lines resistant to frontline drugs and compounds in the VL pipeline, with resistance-conferring mutations fully characterised. New phenotypic hits screened against this highly curated panel of resistant lines can determine cross-resistance and potentially shared MoA. The ability to efficiently identify compounds acting via previously established MoA is vital to maintain diversity within drug development portfolios. To expedite screening, short identifier DNA barcodes were introduced into resistant clones enabling pooling and simultaneous screening of multiple cell lines. Illumina sequencing of barcodes enables the growth kinetics and relative fitness of multiple cell lines under compound selection to be tracked. Optimal conditions allowing discrimination of resistant and sensitive clones were established (3× and 10× EC50 for 3 days) and applied to screening of a complex library with VL pre-clinical and clinical drug candidates. RES-Seq is set to play an important role in ensuring that anti-leishmanial compounds exploiting diverse mechanisms of action are developed, ultimately providing options for future drug combination strategies.