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The R enantiomer of the antitubercular drug PA-824 as a potential oral treatment for visceral Leishmaniasis.

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.

SUBMITTER: Patterson S

PROVIDER: S-EPMC3811480 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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The R enantiomer of the antitubercular drug PA-824 as a potential oral treatment for visceral Leishmaniasis.

Patterson Stephen S Wyllie Susan S Stojanovski Laste L Perry Meghan R MR Simeons Frederick R C FR Norval Suzanne S Osuna-Cabello Maria M De Rycker Manu M Read Kevin D KD Fairlamb Alan H AH

Antimicrobial agents and chemotherapy 20130715 10

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 tha ...[more]

PMID: 23856774

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Project description:BACKGROUND: With widespread resistance to antimonials in Visceral Leishmaniasis (VL) in the Indian subcontinent, Miltefosine (MIL) has been introduced as the first line therapy. Surveillance of MIL susceptibility in natural populations of Leishmania donovani is vital to preserve it and support the VL elimination program. METHODOLOGY AND PRINCIPAL FINDINGS: We measured in vitro susceptibility towards MIL and paromomycin (PMM) in L. donovani isolated from VL and PKDL, pre- and post-treatment cases, using an amastigote-macrophage model. MIL susceptibility of post-treatment isolates from cured VL cases (n?=?13, mean IC(50)±SD?=?2.43±1.44 µM), was comparable (p>0.05) whereas that from relapses (n?=?3, mean IC(50)?=?4.72±1.99 µM) was significantly higher (p?=?0.04) to that of the pre-treatment group (n?=?6, mean IC(50)?=?1.86±0.75 µM). In PKDL, post-treatment isolates (n?=?3, mean IC(50)?=?16.13±2.64 µM) exhibited significantly lower susceptibility (p?=?0.03) than pre-treatment isolates (n?=?5, mean IC(50)?=?8.63±0.94 µM). Overall, PKDL isolates (n?=?8, mean IC(50)?=?11.45±4.19 µM) exhibited significantly higher tolerance (p<0.0001) to MIL than VL isolates (n?=?22, mean IC(50)?=?2.58±1.58 µM). Point mutations in the miltefosine transporter (LdMT) and its beta subunit (LdRos3) genes previously reported in parasites with experimentally induced MIL resistance were not present in the clinical isolates. Further, the mRNA expression profile of these genes was comparable in the pre- and post-treatment isolates. Parasite isolates from VL and PKDL cases were uniformly susceptible to PMM with respective mean IC(50)?=?7.05±2.24 µM and 6.18±1.51 µM. CONCLUSION: The in vitro susceptibility of VL isolates remained unchanged at the end of MIL treatment; however, isolates from relapsed VL and PKDL cases had lower susceptibility than the pre-treatment isolates. PKDL isolates were more tolerant towards MIL in comparison with VL isolates. All parasite isolates were uniformly susceptible to PMM. Mutations in the LdMT and LdRos3 genes as well as changes in the expression of these genes previously correlated with experimental resistance to MIL could not be verified for the field isolates.

Project description:Chronic disease caused by infections, cancer or autoimmunity can result in profound immune suppression. Immunoregulatory networks are established to prevent tissue damage caused by inflammation. Although these immune checkpoints preserve tissue function, they allow pathogens and tumors to persist, and even expand. Immune checkpoint blockade has recently been successfully employed to treat cancer. This strategy modulates immunoregulatory mechanisms to allow host immune cells to kill or control tumors. However, the utility of this approach for controlling established infections has not been extensively investigated. Here, we examined the potential of modulating glucocorticoid-induced TNF receptor-related protein (GITR) on T cells to improve anti-parasitic immunity in blood and spleen tissue from visceral leishmaniasis (VL) patients infected with Leishmania donovani. We found little effect on parasite growth or parasite-specific IFN? production. However, this treatment reversed the improved anti-parasitic immunity achieved by IL-10 signaling blockade. Further investigations using an experimental VL model caused by infection of C57BL/6 mice with L. donovani revealed that this negative effect was prominent in the liver, dependent on parasite burden and associated with an accumulation of Th1 cells expressing high levels of KLRG-1. Nevertheless, combined anti-IL-10 and anti-GITR mAb treatment could improve anti-parasitic immunity when used with sub-optimal doses of anti-parasitic drug. However, additional studies with VL patient samples indicated that targeting GITR had no overall benefit over IL-10 signaling blockade alone at improving anti-parasitic immune responses, even with drug treatment cover. These findings identify several important factors that influence the effectiveness of immune modulation, including parasite burden, target tissue and the use of anti-parasitic drug. Critically, these results also highlight potential negative effects of combining different immune modulation strategies.

Dataset Information

The R enantiomer of the antitubercular drug PA-824 as a potential oral treatment for visceral Leishmaniasis.

Publications

The R enantiomer of the antitubercular drug PA-824 as a potential oral treatment for visceral Leishmaniasis.

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