Discovering the in vitro potent inhibitors against Babesia and Theileria parasites by repurposing the Malaria Box: A review

Structural variety and pharmacological potential of naphthylisoquinoline alkaloids

Naphthylisoquinoline alkaloids are a fascinating class of natural biaryl compounds. They show characteristic mono- and dimeric scaffolds, with chiral axes and stereogenic centers. Since the appearance of the last comprehensive overview on these secondary plant metabolites in this series in 1995, the number of discovered representatives has tremendously increased to more than 280 examples known today. Many novel-type compounds have meanwhile been discovered, among them naphthylisoquinoline-related follow-up products like e.g., the first seco-type (i.e., ring-opened) and ring-contracted analogues. As highlighted in this review, the knowledge on the broad structural chemodiversity of naphthylisoquinoline alkaloids has been decisively driven forward by extensive phytochemical studies on the metabolite pattern of Ancistrocladus abbreviatus from Coastal West Africa, which is a particularly "creative" plant. These investigations furnished a considerable number of more than 80-mostly new-natural products from this single species, with promising antiplasmodial activities and with pronounced cytotoxic effects against human leukemia, pancreatic, cervical, and breast cancer cells. Another unique feature of naphthylisoquinoline alkaloids is their unprecedented biosynthetic origin from polyketidic precursors and not, as usual for isoquinoline alkaloids, from aromatic amino acids-a striking example of biosynthetic convergence in nature. Furthermore, remarkable botanical results are presented on the natural producers of naphthylisoquinoline alkaloids, the paleotropical Dioncophyllaceae and Ancistrocladaceae lianas, including first investigations on the chemoecological role of these plant metabolites and their storage and accumulation in particular plant organs.

Inhibition of malaria and babesiosis parasites by putative red blood cell targeting small molecules

Background

Chemotherapies for malaria and babesiosis frequently succumb to the emergence of pathogen-related drug-resistance. Host-targeted therapies are thought to be less susceptible to resistance but are seldom considered for treatment of these diseases.

Methods

Our overall objective was to systematically assess small molecules for host cell-targeting activity to restrict proliferation of intracellular parasites. We carried out a literature survey to identify small molecules annotated for host factors implicated in Plasmodium falciparum infection. Alongside P. falciparum, we implemented in vitro parasite susceptibility assays also in the zoonotic parasite Plasmodium knowlesi and the veterinary parasite Babesia divergens. We additionally carried out assays to test directly for action on RBCs apart from the parasites. To distinguish specific host-targeting antiparasitic activity from erythrotoxicity, we measured phosphatidylserine exposure and hemolysis stimulated by small molecules in uninfected RBCs.

Results

We identified diverse RBC target-annotated inhibitors with Plasmodium-specific, Babesia-specific, and broad-spectrum antiparasitic activity. The anticancer MEK-targeting drug trametinib is shown here to act with submicromolar activity to block proliferation of Plasmodium spp. in RBCs. Some inhibitors exhibit antimalarial activity with transient exposure to RBCs prior to infection with parasites, providing evidence for host-targeting activity distinct from direct inhibition of the parasite.

Conclusions

We report here characterization of small molecules for antiproliferative and host cell-targeting activity for malaria and babesiosis parasites. This resource is relevant for assessment of physiological RBC-parasite interactions and may inform drug development and repurposing efforts.

Comparative chemical genomics in Babesia species identifies the alkaline phosphatase PhoD as a determinant of antiparasitic resistance

Babesiosis is an emerging zoonosis and widely distributed veterinary infection caused by 100+ species of Babesia parasites. The diversity of Babesia parasites and the lack of specific drugs necessitate the discovery of broadly effective antibabesials. Here, we describe a comparative chemogenomics (CCG) pipeline for the identification of conserved targets. CCG relies on parallel in vitro evolution of resistance in independent populations of Babesia spp. (B. bovis and B. divergens). We identified a potent antibabesial, MMV019266, from the Malaria Box, and selected for resistance in two species of Babesia. After sequencing of multiple independently derived lines in the two species, we identified mutations in a membrane-bound metallodependent phosphatase (phoD). In both species, the mutations were found in the phoD-like phosphatase domain. Using reverse genetics, we validated that mutations in bdphoD confer resistance to MMV019266 in B. divergens. We have also demonstrated that BdPhoD localizes to the endomembrane system and partially with the apicoplast. Finally, conditional knockdown and constitutive overexpression of BdPhoD alter the sensitivity to MMV019266 in the parasite. Overexpression of BdPhoD results in increased sensitivity to the compound, while knockdown increases resistance, suggesting BdPhoD is a pro-susceptibility factor. Together, we have generated a robust pipeline for identification of resistance loci and identified BdPhoD as a resistance mechanism in Babesia species.

Antiparasitic activity of FLLL-32 against four Babesia species, B. bovis, B. bigemina, B. divergens and B. caballi, and one Theileria species, Theileria equi in vitro, and Babesia microti in mice

Introduction: FLLL-32, a synthetic analog of curcumin, is a potent inhibitor of STAT3's constitutive activation in a variety of cancer cells, and its anticancer properties have been demonstrated both in vitro and in vivo. It is also suggested that it might have other pharmacological activities including activity against different parasites. Aim: This study therefore investigated the in vitro antiparasitic activity of FLLL-32 against four pathogenic Babesia species, B. bovis, B. bigemina, B. divergens, and B. caballi, and one Theileria species, Theileria equi. In vivo anti-Babesia microti activity of FLLL-32 was also evaluated in mice. Methods: The FLLL-32, in the growth inhibition assay with a concentration range (0.005-50 μM), was tested for it's activity against these pathogens. The reverse transcription PCR (RT-PCR) assay was used to evaluate the possible effects of FLLL-32 treatment on the mRNA transcription of the target B. bovis genes including S-adenosylhomocysteine hydrolase and histone deacetylase. Results: The in vitro growth of B. bovis, B. bigemina, B. divergens, B. caballi, and T. equi was significantly inhibited in a dose-dependent manner (in all cases, p < 0.05). FLLL-32 exhibits the highest inhibitory effects on B. bovis growth in vitro, and it's IC50 value against this species was 9.57 μM. The RT-PCR results showed that FLLL-32 inhibited the transcription of the B. bovis S-adenosylhomocysteine hydrolase gene. In vivo, the FLLL-32 showed significant inhibition (p < 0.05) of B. microti parasitemia in infected mice with results comparable to that of diminazene aceturate. Parasitemia level in B. microti-infected mice treated with FLLL-32 from day 12 post infection (pi) was reduced to reach zero level at day 16 pi when compared to the infected non-treated mice. Conclusion: The present study demonstrated the antibabesial properties of FLLL-32 and suggested it's usage in the treatment of babesiosis especially when utilized in combination therapy with other antibabesial drugs.

Evaluation of the Inhibitory Effect of Moringa oleifera Leaves Methanolic Extract against In Vitro Growth of Several Babesia Species and Theileria equi and the In Vivo Growth of Babesia microti

The current study evaluated the inhibitory effect of Moringa oleifera leaves methanolic extract (MOL) against the in vitro growth of Babesia bovis (B. bovis), B. caballi, B. bigemina, and Theileria equi (T. equi), as well as in vivo growth of B. microti in mice. Active principles of MOL extract were determined using liquid chromatography mass spectrometry (LC-MS). MOL's anti-piroplasm efficacy was assessed both in vitro and in vivo using the SYBR Green I fluorescence assay. Every 96 hours, the hematological parameters, including red blood cell count (RBCs; 104/UL), hemoglobin content (HGB; g/dl), and hematocrit percent (HCT; %), in the treated mice were monitored using a Celltac MEK6450 automated hematological analyzer. LC-MS of MOL revealed that the most abundant polyphenolic catechism found in the MOL extract was isoquercetin and rutin. MOL inhibited B. bovis, B. caballi, B. bigemina, and T. equi in vitro growth in a dose-dependent way, with IC50 values of 45.29 ± 6.14, 19.16 ± 0.45, 137.49 ± 16.07, and 9.29 ± 0.014 μg/ml, respectively. MOL's in vitro antibabesial activity was enhanced when administrated simultaneously with either diminazene aceturate (DA) or MMV665875 compound from malaria box. In mice infected by B. microti, a combination of MOL and a low dose of DA (12.5 mg·kg-1) resulted in a significant (P < 0.05) reduction in B. microti growth. These findings suggest that MOL is an effective herbal anti-piroplasm therapy, especially when combined with a low dosage of either DA or MMV665875.

Diminazene aceturate and imidocarb dipropionate-based combination therapy for babesiosis – A new paradigm

In the present study, the effect of a combination therapy consisting of diminazene aceturate (DA) and imidocarb dipropionate (ID) on the in vitro growth of several parasitic piroplasmids, and on Babesia microti in BALB/c mice was evaluated using a fluorescence-based SYBR Green I test. We evaluated the structural similarities between the regularly used antibabesial medications, DA and ID, and the recently found antibabesial drugs, pyronaridine tetraphosphate, atovaquone, and clofazimine, using atom pair fingerprints (APfp). The Chou-Talalay approach was used to determine the interactions between the two drugs. A Celltac MEK-6450 computerized hematology analyzer was used to detect hemolytic anemia every 96 hours in mice infected with B. microti and in those treated with either mono- or combination therapy. According to the APfp results, DA and ID have the most structural similarities (MSS). DA and ID had synergistic and additive interactions against the in vitro growth of Babesia bigemina and Babesia bovis, respectively. Low dosages of DA (6.25 mg kg^-1) and ID (8.5 mg kg^-1) in conjunction with each other inhibited B. microti growth by 16.5 %, 32 %, and 4.5 % more than 25 mg kg^-1 DA, 6.25 mg kg^-1 DA, and 8.5 mg kg^-1 ID monotherapies, respectively. In the blood, kidney, heart, and lung tissues of mice treated with DA/ID, the B. microti small subunit rRNA gene was not detected. The obtained findings suggest that DA/ID could be a promising combination therapy for treating bovine babesiosis. Also, such combination may overcome the potential problems of Babesia resistance and host toxicity induced by utilizing full doses of DA and ID.

Comparative chemical genomics in Babesia species identifies the alkaline phosphatase phoD as a novel determinant of resistance

Babesiosis is an emerging zoonosis and widely distributed veterinary infection caused by 100+ species of Babesia parasites. The diversity of Babesia parasites, coupled with the lack of potent inhibitors necessitates the discovery of novel conserved druggable targets for the generation of broadly effective antibabesials. Here, we describe a comparative chemogenomics (CCG) pipeline for the identification of novel and conserved targets. CCG relies on parallel in vitro evolution of resistance in independent populations of evolutionarily-related Babesia spp. ( B. bovis and B. divergens ). We identified a potent antibabesial inhibitor from the Malaria Box, MMV019266. We were able to select for resistance to this compound in two species of Babesia, achieving 10-fold or greater resistance after ten weeks of intermittent selection. After sequencing of multiple independently derived lines in the two species, we identified mutations in a single conserved gene in both species: a membrane-bound metallodependent phosphatase (putatively named PhoD). In both species, the mutations were found in the phoD-like phosphatase domain, proximal to the predicted ligand binding site. Using reverse genetics, we validated that mutations in PhoD confer resistance to MMV019266. We have also demonstrated that PhoD localizes to the endomembrane system and partially with the apicoplast. Finally, conditional knockdown and constitutive overexpression of PhoD alter the sensitivity to MMV019266 in the parasite: overexpression of PhoD results in increased sensitivity to the compound, while knockdown increases resistance, suggesting PhoD is a resistance mechanism. Together, we have generated a robust pipeline for identification of resistance loci, and identified PhoD as a novel determinant of resistance in Babesia species.

Highlights

Use of two species for in vitro evolution identifies a high confidence locus associated with resistance Resistance mutation in phoD was validated using reverse genetics in B. divergens Perturbation of phoD using function genetics results in changes in the level of resistance to MMV019266Epitope tagging reveals localization to the ER/apicoplast, a conserved localization with a similar protein in diatoms Together, phoD is a novel resistance determinant in multiple Babesia spp .

In vivo activity and atom pair fingerprint analysis of MMV665941 against the apicomplexan parasite Babesia microti, the causative agent of babesiosis in humans and rodents

The effect of MMV665941 on the growth of Babesia microti (B. microti) in mice, was investigated in this study using a fluorescence-based SYBR Green I test. Using atom Pair signatures, we investigated the structural similarity between MMV665941 and the commonly used antibabesial medicines diminazene aceturate (DA), imidocarb dipropionate (ID), or atovaquone (AV). In vitro cultures of Babesia bovis (B. bovis) and, Theileria equi (T. equi) were utilized to determine the MMV665941 and AV interaction using combination ratios ranged from 0.75 IC50 MMV665941:0.75 IC50 AV to 0.50 IC50 MMV665941:0.50 IC50 AV. The used combinations were prepared depending on the IC50 of each drug against the in vitro growth of the tested parasite. Every 96 h, the hemolytic anemia in the treated mice was monitored using a Celltac MEK-6450 computerized hematology analyzer. A single dose of 5 mg/kg MMV665941 exhibited inhibition in the B. microti growth from day 4 post-inoculation (p.i.) till day 12 p.i. MMV665941 caused 62.10%, 49.88%, and 74.23% inhibitions in parasite growth at days 4, 6 and 8 p.i., respectively. Of note, 5 mg/kg MMV665941 resulted in quick recovery of hemolytic anemia caused by babesiosis. The atom pair fingerprint (APfp) analysis revealed that MMV665941 and atovaquone (AV) showed maximum structural similarity. Of note, high concentrations (0.75 IC50) of MMV665941 and AV caused synergistic inhibition on B. bovis growth. These findings suggest that MMV665941 might be a promising drug for babesiosis treatment, particularly when combined with the commonly used antibabesial drug, AV.

Tulathromycin and Diclazuril Lack Efficacy against Theileria haneyi, but Tulathromycin Is Not Associated with Adverse Clinical Effects in Six Treated Adult Horses

Equine theileriosis, caused by Theileria haneyi and Theileria equi, leads to anemia, exercise intolerance, and occasionally, death. Theileriosis-free countries prohibit the importation of infected horses, resulting in significant costs for the equine industry. Imidocarb dipropionate is the only treatment for T. equi in the United States, but lacks efficacy against T. haneyi. The goal of this study was to assess the in vivo efficacy of tulathromycin and diclazuril against T. haneyi. Fourteen T. haneyi-infected horses were utilized. Six were treated with eight weekly 2.5 mg/kg doses of tulathromycin. Three were treated daily for eight weeks with 2.5 mg/kg diclazuril. Three were pre-treated with 0.5 mg/kg diclazuril daily for one month to determine whether low-dose diclazuril prevents infection. Following infection, the dose was increased to 2.5 mg/kg for eight weeks. Two infected horses remained untreated as controls. The horses were assessed via nested PCR, physical exams, complete blood counts, serum chemistry panels, and cytology. Tulathromycin and diclazuril failed to clear T. haneyi and the treated and control groups exhibited similar parasitemia and packed cell volume declines. To obtain additional safety data on tulathromycin use in adult horses, necropsy and histopathology were performed on tulathromycin-treated horses. No significant lesions were detected.

In Vitro Inhibitory Effects and Bioinformatic Analysis of Norfloxacin and Ofloxacin on Piroplasm

PURPOSE

The in vitro inhibitory effect of two fluroquinolone antibiotics, norfloxacin and ofloxacin, was evaluated in this study on the growth of several Babesia and Theileria parasites with highlighting the bioinformatic analysis for both drugs with the commonly used antibabesial drug, diminazene aceturate (DA), and the recently identified antibabesial drugs, luteolin, and pyronaridine tetraphosphate (PYR).

METHODS

The antipiroplasm efficacy of screened fluroquinolones in vitro and in vivo was assessed using a fluorescence-based SYBR Green I assay. Using atom Pair signatures, we investigated the structural similarity between fluroquinolones and the antibabesial drugs.

RESULTS

Both fluroquinolones significantly inhibited (P < 0.05) the in vitro growths of Babesia bovis (B. bovis), B. bigemina, B. caballi, and Theileria equi (T. equi) in a dose-dependent manner. The best inhibitory effect for both drugs was observed on the growth of T. equi. Atom Pair fingerprints (APfp) results and AP Tanimoto values revealed that both fluroquinolones, norfloxacin with luteolin, and ofloxacin with PYR, showed the maximum structural similarity (MSS). Two drug interactions findings confirmed the synergetic interaction between these combination therapies against the in vitro growth of B. bovis and T. equi.

CONCLUSION

This study helped in discovery novel potent antibabesial combination therapies consist of norfloxacin/ofloxacin, norfloxacin/luteolin, and ofloxacin/PYR.

Imidazo[1,2-a]pyridine: a Highly Potent Therapeutic Agent Clears Piroplasm Infection In Vitro

BACKGROUND AND PURPOSE

The imidazo[1,2-a] pyridines have huge applications in medicinal chemistry with potent activity against wide spectrum of infectious agents. The efficacy of imidazo[1,2-a]pyridine on the in vitro growth of different piroplasms, including Babesia bovis, B. bigemina, B. divergens, B. caballi, and Theileria equi, was investigated in this study.

METHODS

The anti-piroplasm efficacy of imidazo[1,2-a] pyridines was assessed using a fluorescence-based SYBR Green I assay. Furthermore, efficacy of imidazo[1,2-a]pyridine against piroplasms following discontinuation of treatment was also assessed using a viability assay. In vitro cultures of B. bovis and T. equi were used to assess the imidazo[1,2-a]pyridine and diminazene aceturate (DA) interaction.

RESULTS

In vitro, imidazo[1,2-a]pyridine inhibited the growth of B. bovis, B. bigemina, B. caballi, and T. equi in a dose-dependent manner. The highest inhibitory effects of imidazo[1,2-a]pyridine were detected on the growth of B. caballi with IC₅₀ value of 0.47 ± 0.07. Interestingly, the efficacy of imidazo[1,2-a]pyridine was higher against B. bigemina (IC₅₀: 1.37 ± 0.15) compared to the positive-control DA (IC₅₀: 2.29 ± 0.06). The viability test findings indicate that imidazo[1,2-a]pyridine had a long-lasting inhibitory effect on bovine Babesia parasites in vitro growth up to 4 days after treatment. Notably, when coupled with DA at 0.75 or 0.50 IC₅₀, a high concentration (0.75 IC₅₀) of imidazo[1,2-a]pyridine produced additive suppression of B. bovis growth which suggest that imidazo[1,2-a]pyridine/DA could be a promising combination therapy for the treatment of B. bovis.

CONCLUSION

The obtained encouraging findings pave the way for in vitro and in vivo efficacy trials of imidazo[1,2-a]pyridine derivatives against several piroplasmids.

Global Metabolomic Profiling of Host Red Blood Cells Infected with Babesia divergens Reveals Novel Antiparasitic Target Pathways

Babesia divergens is an apicomplexan parasite that infects human red blood cells (RBCs), initiating cycles of invasion, replication, and egress, resulting in extensive metabolic modification of the host cells. Babesia is an auxotroph for most of the nutrients required to sustain these cycles. There are currently limited studies on the biochemical pathways that support these critical processes, necessitating the high-resolution global metabolomics approach described here to uncover the metabolic interactions between parasite and host RBC. Our results reveal an extensive parasite-mediated modulation of RBC metabolite levels of all classes, including lipids, amino acids, carbohydrates, and nucleotides, with numerous metabolic species varying in proportion to the level of infection. Many of these molecules are scavenged from the host RBCs. This is in accord with the needs of a rapidly proliferating parasite with limited biosynthetic capabilities. Probing these pathways in depth, we used growth inhibition assays to quantitate parasite susceptibility to drugs targeting these pathways and stimulated emission depletion (STED) microscopy to obtain high-resolution images of drug-treated parasites to correlate changes in morphology with specific metabolic blocks in order to validate the data generated by the untargeted metabolomics platform. Thus, interruption of cholesterol scavenging from the host cell led to premature parasite egress, while chemical targeting of the hydrolysis of acyl glycerides led to the buildup of malformed parasites that could not successfully egress. This is the first report detailing the global metabolomic profile of the B. divergens-infected RBC. Besides deciphering diverse aspects of the host-parasite relationship, our results can be exploited by others to uncover further drug targets in the host-parasite biochemical network. IMPORTANCE Human babesiosis is caused by apicomplexan parasites of the Babesia genus and is associated with transfusion-transmitted illness and relapsing disease in immunosuppressed populations. Through its continuous cycles of invasion, proliferation, and egress, B. divergens radically changes the metabolic environment of the host red blood cell, allowing us opportunities to study potential chemical vulnerabilities that can be targeted by drugs. This is the first global metabolomic profiling of Babesia-infected human red blood cells, and our analysis revealed perturbation in all biomolecular classes at levels proportional to the level of infection. In particular, lipids and energy flux pathways in the host cell were altered by infection. We validated the changes in key metabolic pathways by performing inhibition assays accompanied by high-resolution microscopy. Overall, this global metabolomics analysis of Babesia-infected red blood cells has helped to uncover novel aspects of parasite biology and identified potential biochemical pathways that can be targeted for chemotherapeutic intervention.

Repurposing of the Malaria Box for Babesia microti in mice identifies novel active scaffolds against piroplasmosis

Background

An innovative approach has been introduced for identifying and developing novel potent and safe anti-Babesia and anti-Theileria agents for the control of animal piroplasmosis. In the present study, we evaluated the inhibitory effects of Malaria Box (MBox) compounds (n = 8) against the growth of Babesia microti in mice and conducted bioinformatics analysis between the selected hits and the currently used antibabesial drugs, with far-reaching implications for potent combinations.

Methods

A fluorescence assay was used to evaluate the in vivo inhibitory effects of the selected compounds. Bioinformatics analysis was conducted using hierarchical clustering, distance matrix and molecular weight correlation, and PubChem fingerprint. The compounds with in vivo potential efficacy were selected to search for their target in the piroplasm parasites using quantitative PCR (qPCR).

Results

Screening the MBox against the in vivo growth of the B. microti parasite enabled the discovery of potent new antipiroplasm drugs, including MMV396693 and MMV665875. Interestingly, statistically significant (P < 0.05) downregulation of cysteine protease mRNA levels was observed in MMV665875-treated Theileria equi in vitro culture in comparison with untreated cultures. MMV396693/clofazimine and MMV665875/atovaquone (AV) showed maximum structural similarity (MSS) with each other. The distance matrix results indicate promising antibabesial efficacy of combination therapies consisting of either MMV665875 and AV or MMV396693 and imidocarb dipropionate (ID).

Conclusions

Inhibitory and hematology assay results suggest that MMV396693 and MMV665875 are potent antipiroplasm monotherapies. The structural similarity results indicate that MMV665875 and MMV396693 have a similar mode of action as AV and ID, respectively. Our findings demonstrated that MBox compounds provide a promising lead for the development of new antibabesial therapeutic alternatives.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05430-4.

Pomegranate (Punica granatum) Peel Inhibits the In Vitro and In Vivo Growth of Piroplasm Parasites

Pomegranate (Punica granatum) peel has seen a rapid surge in attention as a medical and nutritional product over the last decade. The impact of pomegranate peel methanolic extract monotherapy and combination therapy on the in vitro growth of Babesia (B.) bovis, B. bigemina, B. divergens, B. caballi, and Theileria (T.) equi, as well as B. microti in mice, was investigated in this work. Fluorescence-based SYBR green I assay was used for evaluating the inhibitory antibabesial efficacy of pomegranate (Punica granatum) peel against the growth of several piroplasm parasites in vitro and in vivo. Celltac α MEK-6450 computerized haematology analyzer was used for monitoring the haematological parameters of treated mice every 4 days. Pomegranate peel inhibited the in vitro growth of B. bovis, B. bigemina, B. divergens, T. equi, and B. caballi in a dose-dependent manner, with IC₅₀ values of 154.45 ± 23.11, 40.90 ± 9.35, 72.71 ± 14.77, 100 ± 16.20, and 77.27 ± 16.94 μg/ml, respectively. On a B. bovis culture, the in vitro inhibitory effect of pomegranate peel was amplified when it was combined with diminazene aceturate (DA). Combination therapy of pomegranate peel and a low dose of DA (15 mg kg⁻¹) inhibited B. microti growth significantly (P < 0.05) higher than the treatment with the full dose of DA (25 mg kg⁻¹) in B. microti-infected mice. These findings suggest that pomegranate peel might be a potential medicinal plant for babesiosis treatment, especially when combined with a low dosage of DA.

Effect of methanolic extract from Capsicum annuum against the multiplication of several Babesia species and Theileria equi on in vitro cultures, and Babesia microti in mice

Background and Aim: Piroplasmosis is a serious disease that infects animals, inflicting significant economic losses in the livestock industry and animal trade worldwide. Anti-piroplasm drugs now on the market have demonstrated host toxicity and parasite resistance. As a result, developing more effective and safer anti-piroplasm drugs becomes an urgent issue. This study aimed to evaluate the inhibitory effect of Capsicum annuum methanolic extract (CA) against the growth of Babesia bovis, Babesia divergens, Babesia caballi, and Theileria equi in vitro and against B. microti in mice. Materials and Methods: Fluorescence-based SYBR Green I assay was used to evaluate CA's inhibitory effect in vitro and in vivo when used either as a monotherapy or combined with diminazene aceturate (DA). The hematological parameters (HCT, hemoglobin, and red blood cells counts) were determined in the blood of mice every 96 h using Celltac α MEK-6450 electronic hematology analyzer. Results: The in vitro growth of B. bovis, B. divergens, T. equi, and B. caballi was inhibited by CA in a dose-dependent manner with IC50 values of 4.87±1.23, 44.11±8.03, 8.23±2.54, and 1.26±0.50 mg/mL, respectively. In B. microti-infected mice, a combination therapy consisting of CA and a low dose of DA showed a significant (p<0.05) inhibition of B. microti growth nearly similar to those obtained by treatment with the full dose of DA. Conclusion: The obtained results indicate that CA might be a promising medicinal plant for treating babesiosis, especially when used with a low dose of DA.

In vivo antibabesial activity and bioinformatic analysis of compounds derived from the Medicines for Malaria Venture box against Babesia microti

Here, we have evaluated the inhibitory effects of Medicines for Malaria Venture (MMV) Malaria Box compounds that exhibited potent in vitro anti-bovine Babesia efficacy against the growth of B. microti in mice and conducted follow-up investigations of the structural similarity between the identified potent MMV compounds and the commonly used antibabesial drugs was performed using atom Pair fingerprints (APfp). Screening the Malaria Box against the in vivo growth of the B. microti parasite helped with the discovery of new, effective anti-bovine Babesia drugs, including MMV667488, MMV007285, and MMV019881. Of note, MMV019881 exhibited the highest anti-B. microti efficacy in vivo among the screened MMV compounds. The APfp results revealed that the maximum structural similarity (MSS) was observed between MMV007285, diminazene aceturate, and imidocarb dipropionate (ID). In the same way, clofazimine (CF) and MMV667488 showed the MSS with either each other based on the analysis. The distance matrix and molecular weight correlation findings highlight the possible potential antibabesial efficacy of MMV667488, ID, and CF when administrated as a combination therapy. In conclusion, in the current study new potent antibabesial drug, MMV019881 was identified. CF and MMV667488 showed the MSS with either each other based on the hierarchical clustering analysis (HCA) and such relation is confirmed by the distance matrix and molecular weight correlation findings. Such combination therapy might have a potential as a novel regime for treating animal or human babesiosis.

Discovering the Potent Inhibitors Against Babesia bovis in vitro and Babesia microti in vivo by Repurposing the Natural Product Compounds

In the present study, we screened 502 natural product compounds against the in vitro growth of Babesia (B.) bovis. Then, the novel and potent identified compounds were further evaluated for their in vitro efficacies using viability and cytotoxicity assays. The in vivo inhibitory effects of the selected compounds were evaluated using B. microti “rodent strain” in mice model. Three potent compounds, namely, Rottlerin (RL), Narasin (NR), Lasalocid acid (LA), exhibited the lowest IC₅₀ (half-maximal inhibitory concentration) as follows: 5.45 ± 1.20 μM for RL, 1.86 ± 0.66 μM for NR, and 3.56 ± 1.41 μM for LA. The viability result revealed the ability of RL and LA to prevent the regrowth of treated parasite at 4 × IC₅₀ and 2 × IC₅₀, respectively, while 4 × IC₅₀ of NR was sufficient to stop the regrowth of parasite. The hematology parameters of B. microti in vivo were different in the NR-treated groups as compared to the infected/untreated group. Interestingly, intraperitoneal administration of NR exhibiting inhibition in the growth of B. microti in mice was similar to that observed after administration of the commonly used antibabesial drug, diminazene aceturate (DA) (76.57% for DA, 74.73% for NR). Our findings indicate the richness of natural product compounds by novel potent antibabesial candidates, and the identified potent compounds, especially NR, might be used for the treatment of animal babesiosis.

Evaluation of the inhibitory effect of Zingiber officinale rhizome on Babesia and Theileria parasites

The effect of Zingiber officinale rhizome methanolic extract (ZOR) on the in vitro growth of bovine Babesia (B. bovis, B. bigemina, and B. divergens) and equine piroplasm (B. caballi, and Theileria equi) parasites and on the growth of B. microti in mice was evaluated in this study. The possible in vitro synergistic interaction between ZOR and either diminazene aceturate (DA) or potent Medicines for Malaria Venture (MMV) hits from the malaria box was also investigated. In vitro, ZOR reduced the growth of B. bovis, B. bigemina, T. equi, and B. caballi in a dose-dependent manner. B. divergens was the most susceptible parasite to the in vitro inhibitory effect of ZOR. DA and MMV compounds enhanced the in vitro inhibitory antibabesial activity of ZOR. 12.5 mg/kg DA when administrated in combination with ZOR in mice exhibited a significant inhibition (P < 0.05) in B. microti growth better than those observed after treatment with 25 mg/kg DA monotherapy. These findings suggest that ZOR could be a viable medicinal plant for babesiosis treatment, particularly when combined with a modest dose of either DA or powerful anti-B. bigemina MMV hits.

Compounds from the Medicines for Malaria Venture Box Inhibit In Vitro Growth of Babesia divergens, a Blood-Borne Parasite of Veterinary and Zoonotic Importance

Babesiosis is an infectious disease with an empty drug pipeline. A search inside chemical libraries for novel potent antibabesial candidates may help fill such an empty drug pipeline. A total of 400 compounds (200 drug-like and 200 probe-like) from the Malaria Box were evaluated in the current study against the in vitro growth of Babesia divergens (B. divergens), a parasite of veterinary and zoonotic importance. Novel and more effective anti-B. divergens drugs than the traditionally used ones were identified. Seven compounds (four drug-like and three probe-like) revealed a highly inhibitory effect against the in vitro growth of B. divergens, with IC₅₀s ≤ 10 nanomolar. Among these hits, MMV006913 exhibited an IC₅₀ value of 1 nM IC₅₀ and the highest selectivity index of 32,000. The atom pair fingerprint (APfp) analysis revealed that MMV006913 and MMV019124 showed maximum structural similarity (MSS) with atovaquone and diminazene aceturate (DA), and with DA and imidocarb dipropionate (ID), respectively. MMV665807 and MMV665850 showed MMS with each other and with ID. Of note, a high concentration (0.75 IC₅₀) of MMV006913 caused additive inhibition of B. divergens growth when combined with DA at 0.75 or 0.50 IC₅₀. The Medicines for Malaria Venture box is a treasure trove of anti-B. divergens candidates according to the obtained results.

Treatment of Human Babesiosis: Then and Now

Babesiosis is an emerging tick-borne disease caused by apicomplexan parasites of the genus Babesia. With its increasing incidence worldwide and the risk of human-to-human transmission through blood transfusion, babesiosis is becoming a rising public health concern. The current arsenal for the treatment of human babesiosis is limited and consists of combinations of atovaquone and azithromycin or clindamycin and quinine. These combination therapies were not designed based on biological criteria unique to Babesia parasites, but were rather repurposed based on their well-established efficacy against other apicomplexan parasites. However, these compounds are associated with mild or severe adverse events and a rapid emergence of drug resistance, thus highlighting the need for new therapeutic strategies that are specifically tailored to Babesia parasites. Herein, we review ongoing babesiosis therapeutic and management strategies and their limitations, and further review current efforts to develop new, effective, and safer therapies for the treatment of this disease.

Public-Private Partnerships: Compound and Data Sharing in Drug Discovery and Development

Collaborative efforts between public and private entities such as academic institutions, governments, and pharmaceutical companies form an integral part of scientific research, and notable instances of such initiatives have been created within the life science community. Several examples of alliances exist with the broad goal of collaborating toward scientific advancement and improved public welfare. Such collaborations can be essential in catalyzing breaking areas of science within high-risk or global public health strategies that may have otherwise not progressed. A common term used to describe these alliances is public-private partnership (PPP). This review discusses different aspects of such partnerships in drug discovery/development and provides example applications as well as successful case studies. Specific areas that are covered include PPPs for sharing compounds at various phases of the drug discovery process-from compound collections for hit identification to sharing clinical candidates. Instances of PPPs to support better data integration and build better machine learning models are also discussed. The review also provides examples of PPPs that address the gap in knowledge or resources among involved parties and advance drug discovery, especially in disease areas with unfulfilled and/or social needs, like neurological disorders, cancer, and neglected and rare diseases.

Impact of using pyronaridine tetraphosphate- based combination therapy in the treatment of babesiosis caused by Babesia bovis, B. caballi, and B. gibsoni in vitro and B. microti in mice

The inhibitory efficacies of pyronaridine tetraphosphate (PYR), when used in combination with two novel and potent antibabesial drugs; clofazimine (CF), and MMV396693 were evaluated in the current study against the growth of Babesia bovis, B. caballi, and B. gibsoni in vitro and B. microti in mice. The in vitro study against the selected parasites was performed using combination of PYR with either CF or MMV396693 in ratios ranged from 0.75:0.75 to 0.25:0.25. Combined application of PYR/MMV396693 revealed additive and indifferent interactions against the in vitro growth of all screened Babesia parasites. PYR in combination with CF, achieved indifferent and antagonistic interactions with all used concentration ratios against the in vitro growth of B. bovis and B. caballi. Treatment with PYR-CF combination therapy caused significant inhibition (P < 0.05) of the fluorescence values at days 12, 14, 16, 18, and 22 p.i. in comparison with control mice. Of note, treatment with combination therapy exhibited inhibition in the growth of B. microti (23.16%) greater than those caused by PYR alone. In summary, the obtained results highlight the improvement in the in vivo antibabesial efficacy of PYR when used in combination with CF rather than using PYR alone but such inhibition is still lower than those caused by either DA or CF monotherapies.

Twenty Years of Equine Piroplasmosis Research: Global Distribution, Molecular Diagnosis, and Phylogeny

Equine piroplasmosis (EP), caused by the hemoparasites Theileria equi, Theileria haneyi, and Babesia caballi, is an important tick-borne disease of equines that is prevalent in most parts of the world. Infection may affect animal welfare and has economic impacts related to limitations in horse transport between endemic and non-endemic regions, reduced performance of sport horses and treatment costs. Here, we analyzed the epidemiological, serological, and molecular diagnostic data published in the last 20 years, and all DNA sequences submitted to GenBank database, to describe the current global prevalence of these parasites. We demonstrate that EP is endemic in most parts of the world, and that it is spreading into more temperate climates. We emphasize the importance of using DNA sequencing and genotyping to monitor the spread of parasites, and point to the necessity of further studies to improve genotypic characterization of newly recognized parasite species and strains, and their linkage to virulence.

Myrrh Oil in Vitro Inhibitory Growth on Bovine and Equine Piroplasm Parasites and Babesia microti of Mice

The present experimental study was conducted for the assessment of the efficacy of in vitro inhibition of myrrh oil on the propagation of Babesia bovis, B. divergens, B. bigemina, Theileria equi, and B. caballi and in vivo efficacy on B. microti in mice through fluorescence assay based on SYBR green I. The culture of B. divergens B. bovis and was used to evaluate the in vitro possible interaction between myrrh oil and other commercial compound, such as pyronaridine tetraphosphate (PYR), diminazene aceturate (DA), or luteolin. Nested-polymerase chain reaction protocol using primers of the small-subunit rRNA of B. microti was employed to detect any remnants of DNA for studied parasitic species either in blood or tissues. Results elucidated that; Myrrh oil significantly inhibit the growth at 1% of parasitic blood level for all bovine and equine piroplasm under the study. Parasitic regrowth was inhibited subsequently by viability test at 2 µg/mL for B. bigemina and B. bovis, and there was a significant improvement in the in vitro growth inhibition by myrrh oil when combined with DA, PYR, and luteolin. At the same time; mice treated with a combination of myrrh oil/DA showed a higher inhibition in emitted fluorescence signals than the group that challenged with 25 mg/kg of diminazene aceturate at 10 and 12 days post-infection. In conclusion, this study has recommended the myrrh oil to treat animal piroplasmosis, especially in combination with low doses of DA.