ABSTRACT
The novel nitroimidazopyran agent (
S
)-PA-824 has potent antibacterial activity against
Mycobacterium tuberculosis
in vitro
and
in vivo
and is currently in phase II clinical trials for tuberculosis (TB). In contrast to
M. tuberculosis
, where (
R
)-PA-824 is inactive, we report here that both enantiomers of PA-824 show potent parasiticidal activity against
Leishmania donovani
, the causative agent of visceral leishmaniasis (VL). In leishmania-infected macrophages, (
R
)-PA-824 is 6-fold more active than (
S
)-PA-824. Both des-nitro analogues are inactive, underlining the importance of the nitro group in the mechanism of action. Although the
in vitro
and
in vivo
pharmacological profiles of the two enantiomers are similar, (
R
)-PA-824 is more efficacious in the murine model of VL, with >99% suppression of parasite burden when administered orally at 100 mg kg of body weight
−1
, twice daily for 5 days. In
M. tuberculosis
, (
S
)-PA-824 is a prodrug that is activated by a deazaflavin-dependent nitroreductase (Ddn), an enzyme which is absent in
Leishmania
spp. Unlike the case with nifurtimox and fexinidazole, transgenic parasites overexpressing the leishmania nitroreductase are not hypersensitive to either (
R
)-PA-824 or (
S
)-PA-824, indicating that this enzyme is not the primary target of these compounds. Drug combination studies
in vitro
indicate that fexinidazole and (
R
)-PA-824 are additive whereas (
S
)-PA-824 and (
R
)-PA-824 show mild antagonistic behavior. Thus, (
R
)-PA-824 is a promising candidate for late lead optimization for VL and may have potential for future use in combination therapy with fexinidazole, currently in phase II clinical trials against VL.
摘要
新型硝基咪唑并吡喃制剂 (
S
)-PA-824对结核分枝杆菌具有强效抗菌活性。
结核分枝杆菌
体外
和
体内
目前正在进行治疗结核病(TB)的 II 期临床试验。与
结核杆菌
,其中 (
R
)-PA-824没有活性,我们在此报告 PA-824 的两种对映体都对
唐氏利什曼病
的杀寄生虫活性。在利什曼原虫感染的巨噬细胞中,(
R
)-PA-824的活性是(
S
)-PA-824活性的 6 倍。两种去硝基类似物都没有活性,这突出表明了硝基在作用机制中的重要性。虽然
体外
和
体内
药理特征相似,但(
R
)-PA-824在VL小鼠模型中更有效,按每公斤体重100毫克口服时,寄生虫负荷抑制率为99%。
-1
每天两次,连续 5 天。在
结核杆菌
, (
S
)-PA-824是一种原药,由依赖于脱氮黄素的硝基还原酶(Ddn)激活。
与
与硝呋太醇和非西尼达唑的情况不同,过表达利什曼原虫硝基还原酶的转基因寄生虫对这两种药物都不过敏。
R
)-PA-824或(
S
)-PA-824都不过敏,表明这种酶不是这些化合物的主要靶标。联合用药研究
体外
表明,fexinidazole 和 (
R
)-PA-824具有相加作用,而(
S
)-PA-824和(
R
)-PA-824则表现出轻微的拮抗作用。因此,(
R
)-PA-824很有希望成为治疗VL的后期先导优化候选药物,并有可能在未来与目前正在进行的针对VL的II期临床试验中的非西尼达唑联合使用。