Novel 4-aminoquinoline analogs highly active against the blood and sexual stages of Plasmodium in vivo and in vitro

Abstract

New drugs to treat malaria must act rapidly and be highly potent against asexual blood stages, well tolerated, and affordable to residents of regions of endemicity. This was the case with chloroquine (CQ), a 4-aminoquinoline drug used for the prevention and treatment of malaria. However, since the 1960s, Plasmodium falciparum resistance to this drug has spread globally, and more recently, emerging resistance to CQ by Plasmodium vivax threatens the health of 70 to 320 million people annually. Despite the emergence of CQ resistance, synthetic quinoline derivatives remain validated leads for new drug discovery, especially if they are effective against CQ-resistant strains of malaria. In this study, we investigated the activities of two novel 4-aminoquinoline derivatives, TDR 58845, N(1)-(7-chloro-quinolin-4-yl)-2-methyl-propane-1,2-diamine, and TDR 58846, N(1)-(7-chloro-quinolin-4-yl)-2,N(2),N(2)-trimethylpropane-1,2-diamine and found them to be active against P. falciparum in vitro and Plasmodium berghei in vivo. The P. falciparum clones and isolates tested were susceptible to TDR 58845 and TDR 58846 (50% inhibitory concentrations [IC(50)s] ranging from 5.52 to 89.8 nM), including the CQ-resistant reference clone W2 and two multidrug-resistant parasites recently isolated from Thailand and Cambodia. Moreover, these 4-aminoquinolines were active against early and late P. falciparum gametocyte stages and cured BALB/c mice infected with P. berghei. TDR 58845 and TDR 58846 at 40 mg/kg were sufficient to cure mice, and total doses of 480 mg/kg of body weight were well tolerated. Our findings suggest these novel 4-aminoquinolines should be considered for development as potent antimalarials that can be used in combination to treat multidrug-resistant P. falciparum and P. vivax.

Fig 1

Structures of the 4-aminoquinoline derivatives used in this study. (A) TDR 58845, N¹-(7-chloro-quinolin-4-yl)-2-methyl-propane-1,2-diamine; (B) TDR 58846, N¹-(7-chloro-quinolin-4-yl)-2,N²,N²-trimethylpropane-1,2-diamine; (C) chloroquine, N⁴-(7-chloro-quinolin-4-yl)-N¹,N¹-diethyl-pentane-1,4-diamine.

Fig 2

P. falciparum stage V gametocytemia (as a percentage of the control) that develops after treatment of stage I to III gametocytes with TDR 58845, TDR 58846, CQ, or DHA. P. falciparum gametocytes were treated on days 7, 8, and 9 postinoculation with 0.1 μM or 1 μM concentration of the compound, and the percentage of stage V gametocytes was calculated on day 14. CQ, TDR 58845, and TDR 58846 treatments showed significantly fewer stage V gametocytes than the control (Unt) at 1 μM (P = 0.0015). DHA (0.1 μM) was more potent and completely prevented formation of stage V gametocytes. *, statistically significant compared to the untreated control (t test).

Fig 3

P. falciparum stage V gametocytemia (as a percentage of the control) that developed after stage III to V gametocytes were treated with TDR 58845, TDR 58846, CQ, or DHA. P. falciparum (NF54) gametocytes were treated on days 11, 12, and 13 postinoculation with a 0.1 μM or 1 μM concentration of the compound, and the percentage of stage V gametocytes was calculated on day 14 postinoculation. No decrease in gametocytemia was observed in CQ-treated parasites. TDR 58845- and TDR 58846-treated gametocytes showed a decrease in stage V gametocytemia that was significant at 1.0 μM (P = 0.02 and P = 0.01). No stage V gametocytes were found in 1 μM DHA-treated cultures. *, statistically significant compared to the untreated control (Unt) by the t test.

Fig 4

Survival curves of mice untreated or treated with the 4-aminoquinoline analogs TDR 58845 and TDR 58846. (A) TDR 58845 treatment. All mice at doses of 40 and 80 mg/kg survived until the end of the experiment (day 30), although one mouse had parasitemia at day 30 and one mouse died for unknown reasons in the 160-mg/kg group on day 5. (B) TDR 58846 treatment. Recrudescence was observed only in the lower-dose group. All the mice in groups receiving 80 and 160 mg/kg survived and showed no sign of parasitemia.