Discovery of a Plasmodium falciparum Glucose-6-phosphate Dehydrogenase 6‑phosphogluconolactonase Inhibitor (<i>R</i>,<i>Z</i>)‑<i>N</i>‑((1-Ethylpyrrolidin-2-yl)methyl)-2-(2-fluorobenzylidene)-3-oxo-3,4-dihydro‑2<i>H</i>‑benzo[<i>b</i>][1,4]thiazine-6-carboxamide (ML276) That Reduces Parasite Growth in Vitro

Abstract

A high-throughput screen of the NIH’s MLSMR collection of ∼340000 compounds was undertaken to identify compounds that inhibit Plasmodium falciparum glucose-6-phosphate dehydrogenase (<i>Pf</i>G6PD). <i>Pf</i>G6PD is important for proliferating and propagating P. falciparum and differs structurally and mechanistically from the human orthologue. The reaction catalyzed by glucose-6-phosphate dehydrogenase (G6PD) is the first, rate-limiting step in the pentose phosphate pathway (PPP), a key metabolic pathway sustaining anabolic needs in reductive equivalents and synthetic materials in fast-growing cells. In P. falciparum, the bifunctional enzyme glucose-6-phosphate dehydrogenase-6-phosphogluconolactonase (<i>Pf</i>GluPho) catalyzes the first two steps of the PPP. Because P. falciparum and infected host red blood cells rely on accelerated glucose flux, they depend on the G6PD activity of <i>Pf</i>GluPho. The lead compound identified from this effort, (<i>R</i>,<i>Z</i>)-<i>N</i>-((1-ethylpyrrolidin-2-yl)­methyl)-2-(2-fluorobenzylidene)-3-oxo-3,4-dihydro-2<i>H</i>-benzo­[<i>b</i>]­[1,4]­thiazine-6-carboxamide, <b>11</b> (ML276), is a submicromolar inhibitor of <i>Pf</i>G6PD (IC₅₀ = 889 nM). It is completely selective for the enzyme’s human isoform, displays micromolar potency (IC₅₀ = 2.6 μM) against P. falciparum in culture, and has good drug-like properties, including high solubility and moderate microsomal stability. Studies testing the potential advantage of inhibiting <i>Pf</i>G6PD in vivo are in progress