The effect of N-alkyl modification on the antimalarial activity of 3-hydroxypyridin-4-one oral iron chelators.

The antimalaria effect of iron chelators is attributed to their interaction with a labile iron pool within parasitised erythrocytes, and it was postulated that increased affinity to iron as well as increased lipophilicity may improve antimalarial activity. In the present study we have examined the antimalarial effect of 3-hydroxypyridin-4-ones, a family of bidentate orally effective iron chelators whose lipophilicity may be modified by altering the length of the R2 substituent on the ring nitrogen. A significant dose-related suppression of Plasmodium falciparum cultures was observed with all drugs tested in vitro at concentrations of 5 mumol/L or higher. In contrast, there was a clear segregation of the in vivo effect on P berghei in rats (300 mg/kg/d subcutaneous) into two categories: compounds CP20, 38, and 40 failed to suppress malaria, whereas CP51, 94, and 96 had a strong antimalarial effect, similar or better than deferoxamine. There was a close linear correlation between the suppression of peak parasite counts and the reduction in hepatic nonheme iron induced by the various drugs tested (r = .9837). The most lipophilic compounds were also the most effective in suppressing malaria and in depleting hepatic iron stores. These data indicate that 3-hydroxypyrydin-4-ones are able to suppress malaria in vivo and in vitro. Because lipid solubility is an important determinant of antimalarial action, our study provides useful information regarding the selection of orally effective iron-chelating compounds that may be suitable for clinical application as antimalarial agents.