Dual role of azo compounds in inhibiting Plasmodium falciparum adenosine deaminase and hemozoin biocrystallization.

Protein-ligand (GOLD) docking of the NCI compounds into the ligand-binding site of Plasmodium falciparum adenosine deaminase (PfADA) identified three most active azo compounds containing 4-[(4-hydroxy-2-oxo-1H-quinolin-3-yl) moiety. These compounds showed IC50 of 3.7-15.4 μM against PfADA, as well as inhibited the growth of P. falciparum strains 3D7 (chloroquine (CQ)-sensitive) and K1 (CQ-resistant) with IC50 of 1.8-3.1 and 1.7-3.6 μM, respectively. The identified compounds have structures similar to the backbone structure (4-N-(7-chloroquinolin-4-yl)) in CQ, and NSC45545 could mimic CQ by inhibiting the bioformation of hemozoin in parasitic food vacuole. The amount of in situ hemozoin in the ring-stage parasite was determined using a combination of synchrotron transmission Fourier transform infrared microspectroscopy and Principal Component Analysis. Stretching of the C-O bond of hemozoin propionate group measured at 1220-1210 cm-1 in untreated intraerythrocytic P. falciparum strains 3D7 and K1 was disappeared following treatment with 1.85 and 1.74 μM NSC45545, similar to those treated with 0.02 and 0.13 μM CQ, respectively. These findings indicate a novel dual function of 4-[(4-hydroxy-2-oxo-1H-quinolin-3-yl) azo compounds in inhibiting both PfADA and in situ hemozoin biocrystallization. These lead compounds hold promise for further development of new antimalarial therapeutics that could delay the onset of parasitic drug resistance.