Optimization of benzenesulfonyl derivatives as anti-Trypanosomatidae agents: Structural design, synthesis, and pharmacological assessment against Trypanosoma cruzi and Leishmania infantum

Leishmaniasis and Chagas disease are neglected tropical diseases caused by Trypanosomatidae parasites. Given the numerous limitations associated with current treatments, such as extended treatment duration, variable efficacy, and severe side effects, there is an urgent imperative to explore novel therapeutic options. This study details the early stages of hit-to-lead optimization for a benzenesulfonyl derivative, denoted as initial hit, against Trypanossoma cruzi (T. cruzi), Leishmania infantum (L. infantum) and Leishmania braziliensis (L. braziliensis). We investigated structure - activity relationships using a series of 26 newly designed derivatives, ultimately yielding potential lead candidates with potent low-micromolar and sub-micromolar activities against T. cruzi and Leishmania spp, respectively, and low in vitro cytotoxicity against mammalian cells. These discoveries emphasize the significant promise of this chemical class in the fight against Chagas disease and leishmaniasis.

Evaluation and discovery of novel benzothiazole derivatives as promising hits against Leishmania infantum

An early exploration of the benzothiazole class against two kinetoplastid parasites, Leishmania infantum and Trypanosoma cruzi, has been performed after the identification of a benzothiazole derivative as a suitable antileishmanial initial hit. The first series of derivatives focused on the acyl fragment of its class, evaluating diverse linear and cyclic, alkyl and aromatic substituents, and identified two other potent compounds, the phenyl and cyclohexyl derivatives. Subsequently, new compounds were designed to assess the impact of the presence of diverse substituents on the benzothiazole ring or the replacement of the endocyclic sulfur by other heteroatoms. All compounds showed relatively low cytotoxicity, resulting in decent selectivity indexes for the most active compounds. Ultimately, the in vitro ADME properties of these compounds were assessed, revealing a satisfying water solubility, gastrointestinal permeability, despite their low metabolic stability and high lipophilicity. Consequently, compounds 5 and 6 were identified as promising hits for further hit-to-lead exploration within this benzothiazole class against L. infantum, thus providing promising starting points for the development of antileishmanial candidates.

Anti-Leishmania compounds can be screened using Leishmania spp. expressing red fluorescence (tdTomato)

The main challenges associated with leishmaniasis chemotherapy are drug toxicity, the possible emergence of resistant parasites, and a limited choice of therapeutic agents. Therefore, new drugs and assays to screen and detect novel active compounds against leishmaniasis are urgently needed. We thus validated Leishmania braziliensis (Lb) and Leishmania infantum (Li) that constitutively express the tandem tomato red fluorescent protein (tdTomato) as a model for large-scale screens of anti-Leishmania compounds. Confocal microscopy of Lb and Li::tdTomato revealed red fluorescence distributed throughout the entire parasite, including the flagellum, and flow cytometry confirmed that the parasites emitted intense fluorescence. We evaluated the infectivity of cloned promastigotes and amastigotes constitutively expressing tdTomato, their growth profiles in THP-1 macrophages, and susceptibility to trivalent antimony, amphotericin, and miltefosine in vitro. The phenotypes of mutant and wild-type parasites were similar, indicating that the constitutive expression of tdTomato did not interfere with the evaluated parameters. We applied our validated model to a repositioning strategy and assessed the susceptibility of the parasites to eight commercially available drugs. We also screened 32 natural plant and fungal extracts and 10 pure substances to reveal new active compounds. The infectivity and Glucantime treatment efficacy of BALB/c mice and golden hamsters infected with Lb and Li::tdTomato mutant lines, respectively, were very similar compared to animals infected with wild-type parasites. Standardizing our methodology would offer more rapid, less expensive, and easier assays to screen of compounds against L. braziliensis and L. infantum in vitro and in vivo. Our method could also enhance the discovery of active compounds for treating leishmaniasis.

Hit-to-lead optimization of a pyrazinylpiperazine series against Leishmania infantum and Leishmania braziliensis

An early hit-to-lead optimization of a novel pyrazinylpiperazine series against L. infantum and L. braziliensis has been performed after an extensive SAR focusing on the benzoyl fragment of hit (4). Deletion of the meta-Cl of (4) led to the obtention of the para-hydroxyl derivative (12), on which the design of most monosubstituted derivatives of the SAR was based. Further optimization of the series, involving disubstituted benzoyl fragments and the hydroxyl substituent of (12), allowed the obtention of a total of 15 compounds with increased antileishmanial potency (IC₅₀ < 10 μM), nine of which displayed activity in the low micromolar range (IC₅₀ < 5 μM). This optimization ultimately identified the ortho, meta-dihydroxyl derivative (46) as an early lead for this series (IC₅₀ (L. infantum) = 2.8 μM, IC₅₀ (L. braziliensis) = 0.2 μM). Additional assessment of some selected compounds against other trypanosomatid parasites revealed that this series is selective towards Leishmania parasites, and in silico ADMET predictions revealed satisfactory profiles for these compounds, allowing further lead optimization of the pyrazinylpiperazine class against Leishmania.

Brucella abortus nitric oxide metabolite regulates inflammasome activation and IL-1β secretion in murine macrophages

NLRP3 inflammasome is a protein complex crucial to caspase-1 activation and IL-1β and IL-18 maturation. This receptor participates in innate immune responses to different pathogens, including the bacteria of genus Brucella. Our group recently demonstrated that Brucella abortus-induced IL-1β secretion involves NLRP3 inflammasome and it is partially dependent on mitochondrial ROS production. However, other factors could be involved, such as P2X7-dependent potassium efflux, membrane destabilization, and cathepsin release. Moreover, there is increasing evidence that nitric oxide acts as a modulator of NLRP3 inflammasome. The aim of this study was to unravel the mechanism of NLRP3 inflammasome activation induced by B. abortus, as well as the involvement of bacterial nitric oxide (NO) as a modulator of this inflammasome pathway. We demonstrated that NO produced by B. abortus can be used by the bacteria to modulate IL-1β secretion in infected murine macrophages. Additionally, our results suggest that B. abortus-induced IL-1β secretion depends on a P2X7-independent potassium efflux, lysosomal acidification, cathepsin release, mechanisms clearly associated to NLRP3 inflammasome. In summary, our results help to elucidate the molecular mechanisms of NLRP3 activation and regulation during an intracellular bacterial infection.