Addressing the Intracellular Vestibule of the Plasmodial Lactate Transporter PfFNT by p‑Substituted Inhibitors Amplifies In Vitro Activity

Inhibition of the lactate transporter PfFNT is a valid
novel mode
of action against malaria parasites. Current pyridine-substituted
pentafluoro-3-hydroxy-pent-2-en-1-ones act as substrate analogs with
submicromolar EC50 in vitro, and >99.7% activity in
mice.
The recently solved structure of a PfFNT-inhibitor complex visualized
the binding mode. Here, we extended the inhibitor layout by series
of amine- and anilide-linked pyridine p-substituents to generate additional
interactions in the cytoplasmic vestibule. Virtual docking indicated
hydrogen bonding to Tyr31 and Ser102. Fluorescence cross-correlation
spectroscopy yielded respectively enhanced target affinity. Strikingly,
the in vitro activity increased by 1 order of magnitude to 14.8 nM
at negligible cytotoxicity. While p-amine substitutions
were rapidly metabolized, the more stable p-acetanilide
cleared 99.7% of parasites at 4 × 50 mg kg–1 in a mouse malaria model. Future stabilization of the p-substitution
against metabolism may translate the gain in in vitro potency to the
in vivo situation.