From the initially selected 70 nitroimidazoles belonging to four chemical sub-classes, VL-2098 was identified as a very potent and safe molecule and was selected for in-depth evaluation of its efficacy, pharmacokinetic, and early safety profile on the basis of these preliminary results. This compound is potent against L. donovani in vitro and shows efficacy in acute and chronic VL animal models after oral dosing. Toxicology and pharmacokinetic studies were completed in 2014 and a batch of high purity active pharmaceutical ingredient (API) successfully manufactured.

Results performed in three animal species indicated a link between dose, length of treatment, and testicular toxicity. Further studies of longer duration were undertaken in the animal model most sensitive to the therapeutic window in order to determine the safety margin, as a result of which the decision was taken not to move the candidate forward.