In vitro Screening of Antileishmanial Activity of Natural Product Compounds: Determination of IC50, CC50 and SI Values.

Neglected tropical diseases gain the scientific interest of numerous research programs in an attempt to achieve their effective control or elimination. In this attempt, more cutting-edge public health policies and research are needed for the discovery of new, safer and effective drugs originated from natural products. Here, we describe protocols for the in vitro screening of a natural product-derived compound required for the determination of its antileishmanial potency. For this purpose, the Total Phenolic Fraction (TPF) derived from extra virgin olive oil is evaluated through the in vitro cell culture method against extracellular promastigote and intracellular amastigote Leishmania spp. forms. The aim of this article is to describe a step-by-step procedure that can be easily applied to accurately estimate the 50% inhibitory concentration (IC50), the 50% cytotoxic concentration (CC50) and the selectivity index (SI) via the resazurin reduction assay. These protocols are based on the ability of resazurin (oxidized blue form) to be irreversibly reduced by enzymes in viable cells and generate a red fluorescent resorufin product and can be easily expanded to the investigation of the antimicrobial activity in other microorganisms.