A New Nonpolar N -Hydroxy Imidazoline Lead Compound with Improved Activity in a Murine Model of Late-Stage Trypanosoma brucei brucei Infection Is Not Cross-Resistant with Diamidines

Abstract

Treatment of late-stage sleeping sickness requires drugs that can cross the blood-brain barrier (BBB) to reach the parasites located in the brain. We report here the synthesis and evaluation of four new N-hydroxy and 12 new N-alkoxy derivatives of bisimidazoline leads as potential agents for the treatment of late-stage sleeping sickness. These compounds, which have reduced basicity compared to the parent leads (i.e., are less ionized at physiological pH), were evaluated in vitro against Trypanosoma brucei rhodesiense and in vivo in murine models of first-and second-stage sleeping sickness. Resistance profile, physicochemical parameters, in vitro BBB permeability, and microsomal stability also were determined. The N-hydroxy imidazoline analogues were the most effective in vivo, with 4-((1-hydroxy-4,5-dihydro-1H-imidazol-2-yl)amino)-N-(4-((1-hydroxy-4,5-dihydro-1H-imidazol-2-yl)amino)phenyl)benzamide (14d) showing 100% cures in the first-stage disease, while 15d, 16d, and 17d appeared to slightly improve survival. In addition, 14d showed weak activity in the chronic model of central nervous system infection in mice. No evidence of reduction of this compound with hepatic microsomes and mitochondria was found in vitro, suggesting that N-hydroxy imidazolines are metabolically stable and have intrinsic activity against T. brucei. In contrast to its unsubstituted parent compound, the uptake of 14d in T. brucei was independent of known drug transporters (i.e., T. brucei AT1/P2 and HAPT), indicating a lower predisposition to cross-resistance with other diamidines and arsenical drugs. Hence, the N-hydroxy bisimidazolines (14d in particular) represent a new class of promising antitrypanosomal agents.

Synthesis and in Vitro Studies of a Series of Carborane-Containing Boron Dipyrromethenes (BODIPYs)

“…All other BODIPYs display BBB permeabilities higher than that reported for phenytoin, which has been used as a marker for medium BBB permeability. 33,35 Among the new BODIPYs, 1b , 2b , and 6b showed higher permeability than 3b , 20 which displays a slightly higher P e value than phenytoin. These results show that both the MW and amphiphilicity of the BODIPYs influence their permeability across the BBB and that small amphiphilic carboranyl-BODIPYs of MW < 400 Da and log P < 1.7, such as 1b and 2b , are the most efficient at diffusing across the BBB by passive diffusion.…”

Positively selected modifications in the pore of TbAQP2 allow pentamidine to enterTrypanosoma brucei

“…Stilbamidine and the short-linker analogues FR39 and CRMI8 (Ríos Martínez et al, 2015) displayed low binding affinity (Table 1). Diminazene also displayed similar low affinity (K i = 63 µM), and [ 3 H]-diminazene uptake can only just be detected in procyclic T. b. brucei , i.e.…”

Lowering the p K a of a bisimidazoline lead with halogen atoms results in improved activity and selectivity against Trypanosoma brucei in vitro

“…In most cases, fluoro derivatives had approximately 2-fold lower EC 50 values than chloro analogues except for 5a (R 4 On the other hand, a chlorine atom in ortho to the imidazoline ring (2a, 5a) seemed to be favoured. The incorporation of a pyridyl ring (6) led to a small decrease in activity. These data show that the introduction of a fluorine, chlorine or nitrogen atom on the phenyl rings has a moderate effect on the in vitro activity (either positive or negative) of the parent compound 1.…”

“…The basicity of several leads was reduced by approximately two pK a units [6,7] resulting in one compound ( Fig. 1, 1a) with weak activity in a mouse model of late-stage HAT [6]. In the present work, we have tested a different strategy to reduce the pK a of lead 1.…”

“…Hence, we turned our attention to a strategy consisting in reducing the pK a of the molecules through the derivatization of the NÀ1 nitrogen of the imidazoline rings with OR groups to improve their BBB permeability (R ¼ H, alkyl) [5]. The basicity of several leads was reduced by approximately two pK a units [6,7] resulting in one compound ( Fig. 1, 1a) with weak activity in a mouse model of late-stage HAT [6].…”