Antimalarial 9-Anilinoacridine Compounds Directed at Hematin

Abstract

Antimalarial 9-anilinoacridines are potent inhibitors of parasite DNA topoisomerase II both in vitro and in situ. 3,6-Diamino substitution on the acridine ring greatly improves parasiticidal activity against Plasmodium falciparum by targeting DNA topoisomerase II. A series of 9-anilinoacridines were investigated for their abilities to inhibit β-hematin formation, to form drug-hematin complexes, and to enhance hematin-induced lysis of red blood cells. Inhibition of β-hematin formation was minimal with 3,6-diamino analogs of 9-anilinoacridine and greatest with analogs with a 3,6-diCl substitution together with an electron-donating group in the 1′-anilino position. On the other hand, the presence of a 1′-N(CH3) 2 group in the anilino ring produced compounds that strongly inhibited β-hematin formation but which did not appear to be sensitive to the nature of the substitutions in the acridine nucleus. The derivatives bound hematin, and Job's plots of UV-visible absorbance changes in drug-hematin complexes at various molar ratios indicated a stoichiometric ratio of 1:2. The drugs enhanced hematin-induced red blood cell lysis at low concentrations (<4 μM). These studies open up the novel possibility of development of 9-anilinoacridine antimalarials that target not only DNA topoisomerase II but also β-hematin formation, which should help delay the rapid onset of resistance to drugs acting at only a single site.