Antimalarial Effects of Macrolactones Related to FK520 (Ascomycin) Are Independent of the Immunosuppressive Properties of the Compounds

The polyketide macrolactone FK506 inhibits the growth of Plasmodium falciparum in culture and the enzymatic (peptidyl-prolyl cis-trans isomerase [PPIase]) and chaperone activities of a recently identified P. falciparum FK506-binding protein (PfFKBP35). However, the potent immunosuppressive properties of FK506 exclude it from consideration as an antimalarial drug. We describe the antimalarial actions of the related compound FK520 and a number of its nonimmunosuppressive analogues. All compounds were shown to be strong in-hibitors of parasite growth, regardless of their immunosuppressive potency. Although some of the compounds inhibited the PPIase activity of recombinant PfFKBP35, they all inhibited the chaperone activity of this bi-functional protein. These findings suggest that the antimalarial effects of this class of drug may be mediated via inhibition of the chaperone activity rather than via the enzymatic activity of PfFKBP35. Elucidating the precise intracellular functions of PfFKBP35 may facilitate the design of more potent inhibitors that retain their specificity for parasite target protein. Malaria remains one of the most significant human diseases worldwide. It is estimated that ∼40 % of the world’s population is currently at risk of contracting the disease, resulting in an estimated 500 million clinica