SOME PHOSPHONIC ACID ANALOGS AS INHIBITORS OF PYROPHOSPHATE-DEPENDENTPHOSPHOFRUCTOKINASE, A NOVEL TARGET IN TOXOPLASMA-GONDII

Pyrophosphate-dependent phosphofructokinase (PPi-PFK) was identified p reviously in Toxoplasma gondii as the only kinase that phosphorylates fructose-6-P to fructose-1,6-bisP. Since such an enzyme is not present in mammals, it was considered to be a good target for prospective sel ective inhibitors of the parasite. We have examined the effects of sev eral phosphonic acid derivatives, analogs of pyrophosphate, on PPi-PFK activity, as well as on the replication of T. gondii in human foreski n fibroblast (HFF) cells. The most active compound in inhibiting PPi-P FK was tetrasodium carbonyldiphosphonate. Several bisphosphonates and related arylhydrazones showed inhibition of the enzyme, but with highe r IC50 values. Although several phosphonoacetic acid derivatives also inhibited PPi-PFK, as a group they were less potent than the bisphosph onate derivatives. Comparison among the structures of various inhibito rs and their effects against PPi-PFK indicates that a carbonyl (C=O) o r imino (C=N) group between two phosphoryl moieties is associated with more potent enzyme inhibition. Tetrasodium carbonyldiphosphonate did not show a significant effect against replication of T. gondii cells, probably because, as a charged molecule, it could not cross the cell m embrane to reach the intracellular parasite. Tetraisopropyl carbonyldi phosphonate 2,4-dinitrophenylhydrazone showed some selective inhibitor y effect against replication of the parasite in the HFF cells and prot ected the mammalian cells from damage by T. gondii. The results indica te that carbonyldiphosphonic acid is a good prototype compound that is amenable to chemical manipulation, which, in turn, may optimize selec tive inhibition of T. gondii PPi-PFK and increase accessibility to the intracellular parasite.