Efficacy of pyrvinium pamoate against Cryptosporidium parvum infection in vitro and in a neonatal mouse model

In Vitro and Ex Vivo Synergistic Effect of Pyrvinium Pamoate Combined with Miltefosine and Paromomycin against Leishmania

One of the major drawbacks of current treatments for neglected tropical diseases is the low safety of the drugs used and the emergence of resistance. Leishmaniasis is a group of neglected diseases caused by protozoa of the trypanosomatidae family that lacks preventive vaccines and whose pharmacological treatments are scarce and unsafe. Combination therapy is a strategy that could solve the above-mentioned problems, due to the participation of several mechanisms of action and the reduction in the amount of drug necessary to obtain the therapeutic effect. In addition, this approach also increases the odds of finding an effective drug following the repurposing strategy. From the previous screening of two collections of repositioning drugs, we found that pyrvinium pamoate had a potent leishmanicidal effect. For this reason, we decided to combine it separately with two clinically used leishmanicidal drugs, miltefosine and paromomycin. These combinations were tested in axenic amastigotes of Leishmania infantum obtained from bone marrow cells and in intramacrophagic amastigotes obtained from primary cultures of splenic cells, both cell types coming from experimentally infected mice. Some of the combinations showed synergistic behavior, especially in the case of the combination of pyrvinium pamoate with paromomycin, and exhibited low cytotoxicity and good tolerability on intestinal murine organoids, which reveal the potential of these combinations for the treatment of leishmaniasis.

Metabolic modulation of mitochondrial mass during CD4+ T cell activation

Mitochondrial biogenesis initiates within hours of T cell receptor (TCR) engagement and is critical for T cell activation, function, and survival; yet, how metabolic programs support mitochondrial biogenesis during TCR signaling is not fully understood. Here, we performed a multiplexed metabolic chemical screen in CD4+ T lymphocytes to identify modulators of metabolism that impact mitochondrial mass during early T cell activation. Treatment of T cells with pyrvinium pamoate early during their activation blocks an increase in mitochondrial mass and results in reduced proliferation, skewed CD4+ T cell differentiation, and reduced cytokine production. Furthermore, administration of pyrvinium pamoate at the time of induction of experimental autoimmune encephalomyelitis, an experimental model of multiple sclerosis in mice, prevented the onset of clinical disease. Thus, modulation of mitochondrial biogenesis may provide a therapeutic strategy for modulating T cell immune responses.

Pyrvinium Pamoate: Past, Present, and Future as an Anti-Cancer Drug

Pyrvinium, a lipophilic cation belonging to the cyanine dye family, has been used in the clinic as a safe and effective anthelminthic for over 70 years. Its structure, similar to some polyaminopyrimidines and mitochondrial-targeting peptoids, has been linked with mitochondrial localization and targeting. Over the past two decades, increasing evidence has emerged showing pyrvinium to be a strong anti-cancer molecule in various human cancers in vitro and in vivo. This efficacy against cancers has been attributed to diverse mechanisms of action, with the weight of evidence supporting the inhibition of mitochondrial function, the WNT pathway, and cancer stem cell renewal. Despite the overwhelming evidence demonstrating the efficacy of pyrvinium for the treatment of human cancers, pyrvinium has not yet been repurposed for the treatment of cancers. This review provides an in-depth analysis of the history of pyrvinium as a therapeutic, the rationale and data supporting its use as an anticancer agent, and the challenges associated with repurposing pyrvinium as an anti-cancer agent.

Pyrvinium pamoate potentiates levofloxacin against levofloxacin-resistant Staphylococcus aureus

Background: Drug repurposing is a viable approach to expediting the tedious conventional drug discovery process, given rapidly increasing bacterial resistance. In this context, we have repurposed pyrvinium pamoate (PP) for its antibacterial activity against Staphylococcus aureus. Methods: US FDA-approved non-antibiotics were screened against clinically relevant bacterial pathogens to identify antibacterials. The hits were further evaluated utilizing a variety of preclinical parameters, following which in vivo efficacy was estimated in isolation and in combination in a murine neutropenic thigh infection model. Result: The screening identified PP exhibiting potent activity against S. aureus along with concentration-dependent killing. PP also showed a post-antibiotic effect of >22 h and significantly eradicated preformed S. aureus biofilms and intracellular S. aureus at 1× and 5× MIC, respectively. PP synergized with levofloxacin both in vitro and in vivo, resulting in ∼1.5 and ∼0.5 log10 CFU/g reduction against susceptible and resistant S. aureus infections, respectively, as compared with untreated control. Conclusion: Pyrvinium potentiates levofloxacin against levofloxacin-resistant S. aureus.

Activity of (1-benzyl-4-triazolyl)-indole-2-carboxamides against Toxoplasma gondii and Cryptosporidium parvum

Parasitic diseases such as toxoplasmosis and cryptosporidiosis remain serious global health challenges, not only to humans but also to domestic animals and wildlife. With only limited treatment options available, Toxoplasma gondii and Cryptosporidium parvum (the causative agents of toxoplasmosis and cryptosporidiosis, respectively) constitute a substantial health threat especially to young children and immunocompromised individuals. Herein, we report the synthesis and biological evaluation of a series of novel (1-benzyl-4-triazolyl)-indole-2-carboxamides and related compounds that show efficacy against T. gondii and C. parvum. Closely related analogs 7c (JS-2-30) and 7e (JS-2-44) showed low micromolar activity with IC50 indices ranging between 2.95 μM and 7.63 μM against both T. gondii and C. parvum, whereas the compound representing (1-adamantyl)-4-phenyl-triazole, 11b (JS-2-41), showed very good activity with an IC50 of 1.94 μM, and good selectivity against T. gondii in vitro. Importantly, compounds JS-2-41 and JS-2-44 showed appreciable in vivo efficacy in decreasing the number of T. gondii cysts in the brains of Brown Norway rats. Together, these results indicate that (1-benzyl-4-triazolyl)-indole-2-carboxamides and (1-adamantyl)-4-phenyl-triazoles are potential hits for medicinal chemistry explorations in search for novel antiparasitic agents for effective treatment of cryptosporidiosis and toxoplasmosis.

Pyrvinium Pamoate and Structural Analogs Are Early Macrofilaricide Leads

Onchocerciasis and lymphatic filariasis are neglected tropical diseases caused by infection with filarial worms. Annual or biannual mass drug administration with microfilaricidal drugs that kill the microfilarial stages of the parasites has helped reduce infection rates and thus prevent transmission of both infections. However, success depends on high population coverage that is maintained for the duration of the adult worm's lifespan. Given that these filarial worms can live up to 14 years in their human hosts, a macrofilaricidal drug would vastly accelerate elimination efforts. Here, we have evaluated the repurposed drug pyrvinium pamoate as well as newly synthesized analogs of pyrvinium for their efficacy against filarial worms in vitro and in vivo. We found that pyrvinium pamoate, tetrahydropyrvinium and one of the analogs were highly potent in inhibiting worms in in vitro whole-worm screening assays, and that all three compounds reduced female worm fecundity and inhibited embryogenesis in the Brugia pahangi-gerbil in vivo model of infection.

Anti-protozoal activity of Thymol and a Thymol ester against Cryptosporidium parvum in cell culture

Cryptosporidium parvum is a protozoan parasite that infects intestinal epithelial cells causing malabsorption and severe diarrhea. The monoterpene thymol has been reported to have antifungal and antibacterial properties but less is known about the antiparasitic effect of this compound. Terpenes are sometimes unsuitable for therapeutic and food applications because of their instability. Esterification of terpenes eliminates this disadvantage. The present study evaluates the effects of thymol (Th) and a thymol ester, thymol octanoate (TO), against C. parvum infectivity in vitro. The cytotoxicity IC50 value for TO after 24 h of treatment was 309.6 μg/mL, significantly higher than that of Th (122.5 μg/mL) in a human adenocarcinoma cell line (HCT-8). In the same way, following 48 h of treatment, the cytotoxicity IC50 value for TO was significantly higher (139 μg/mL) than that of Th (75.5 μg/mL). These results indicate that esterification significantly reduces Th cytotoxicity. Dose-dependent effects were observed for TO and Th when both parasite invasion and parasite growth assays were evaluated. When evaluated for their activity against C. parvum growth cultured in vitro in HCT-8 cells, the anti-cryptosporidial IC50 values were 35.5 and 7.5 μg/mL, for TO and Th, respectively. Together, these findings indicate that esterified thymol has anti-cryptosporidial effect comparable with its parental compound thymol, but with improved safety margins in mammalian cells and better physicochemical properties that could make it more suitable for diverse applications as an antiparasitic agent.

Novel acyl carbamates and acyl / diacyl ureas show in vitro efficacy against Toxoplasma gondii and Cryptosporidium parvum

Toxoplasma gondii and Cryptosporidium parvum are protozoan parasites that are highly prevalent and opportunistically infect humans worldwide, but for which completely effective and safe medications are lacking. Herein, we synthesized a series of novel small molecules bearing the diacyl urea scaffold and related structures, and screened them for in vitro cytotoxicity and antiparasitic activity against T. gondii and C. parvum. We identified one compound (GMG-1-09), and four compounds (JS-1-09, JS-2-20, JS-2-35 and JS-2-49) with efficacy against C. parvum and T. gondii, respectively, at low micromolar concentrations and showed appreciable selectivity in human host cells. Among the four compounds with efficacy against T. gondii, JS-1-09 representing the diacyl urea scaffold was the most effective, with an anti-Toxoplasma IC50 concentration (1.21 μM) that was nearly 53-fold lower than its cytotoxicity IC50 concentration, indicating that this compound has a good selectivity index. The other three compounds (JS-2-20, JS-2-35 and JS-2-49) were structurally more divergent from JS-1-09 as they represent the acyl urea and acyl carbamate scaffold. This appeared to correlate with their anti-Toxoplasma activity, suggesting that these compounds' potency can likely be enhanced by selective structural modifications. One compound, GMG-1-09 representing acyl carbamate scaffold, depicted in vitro efficacy against C. parvum with an IC50 concentration (32.24 μM) that was 14-fold lower than its cytotoxicity IC50 concentration in a human intestinal cell line. Together, our studies unveil a series of novel synthetic acyl/diacyl urea and acyl carbamate scaffold-based small molecule compounds with micromolar activity against T. gondii and C. parvum that can be explored further for the development of the much-needed novel anti-protozoal drugs.

Anti-protozoal activity of extracts from chicory (Cichorium intybus) against Cryptosporidium parvum in cell culture

Cryptosporidium spp. are responsible for severe public health problems and livestock production losses. Treatment options are limited to only one drug available for human and bovine cryptosporidiosis, respectively, and both drugs exhibit only partial efficacy. Sesquiterpene lactones (SL) are plant bioactive compounds that function as a defence mechanism against herbivores. SL have demonstrated anti-parasitic properties against a range of parasitic taxa but knowledge about their anti-Cryptosporidium efficacy is limited. The effect of SL-rich leaf and root extracts from chicory (Cichorium intybus cv. Spadona) was investigated using human colon adenocarcinoma (HCT-8) cells infected with Cryptosporidium parvum. C. parvum oocysts were inoculated onto the cell monolayer and i) incubated for 4 hours with extracts (leaf and root extracts 300, 150, 75, 37.5, 18.75 and 9.375 μg/mL) in triplicates followed by incubation in bioactive free media (sporozoite invasion assays) or ii) incubated for 4 hours in bioactive free media followed by 48-hours incubation with extracts (growth inhibition assays). Extract toxicity on HCT-8 cells was assessed via water-soluble tetrazolium (WST)-1 assay prior to quantifying parasitic growth via immunofluorescence. Both extracts demonstrated dose-dependent inhibition in the growth inhibition assays (p = < 0.0001 for both extracts) but not in the invasion assays. Anti-parasitic activity did not appear to be solely related to SL content, with the extract with lower SL content (leaf) exhibiting higher inhibition at 300 μg/ml. However, given the limited treatment options available for Cryptosporidium spp., our study encourages further investigation into the use of chicory extracts to identify novel active compound(s) inhibiting these protozoa.

Antileishmanial effect of rapamycin as an alternative approach to control Leishmania tropica infection

Cutaneous leishmaniosis (CL) is a parasitic disease in animals and human with no satisfactory treatments and vaccination. Rapamycin is a potent inhibitor of mammalian target of rapamycin (mTOR) with various applications. Here, the effect of rapamycin alone or in combination with two other drugs, namely amphotericin B (AmB) and glucantime, was investigated against Leishmania tropica infection. In vitro viability and electron microscopy evaluation of the parasites showed detrimental changes in their appearance and viability. Treatment with clinically relevant dose of rapamycin (10.2 μg/dose) is able to control the parasite load in BALB/c mice infected with L. tropica. Furthermore, the cytokine profiles showed significant polarization towards Th1 immune response. Surprisingly, combination therapy with either AmB or glucantime was not efficient. Rapamycin is showed an effective alternative therapy against leishmaniosis caused by L. tropica.

Novel lactate dehydrogenase inhibitors with in vivo efficacy against Cryptosporidium parvum

Cryptosporidium parvum is a highly prevalent zoonotic and anthroponotic protozoan parasite that causes a diarrheal syndrome in children and neonatal livestock, culminating in growth retardation and mortalities. Despite the high prevalence of C. parvum, there are no fully effective and safe drugs for treating infections, and there is no vaccine. We have previously reported that the bacterial-like C. parvum lactate dehydrogenase (CpLDH) enzyme is essential for survival, virulence and growth of C. parvum in vitro and in vivo. In the present study, we screened compound libraries and identified inhibitors against the enzymatic activity of recombinant CpLDH protein in vitro. We tested the inhibitors for anti-Cryptosporidium effect using in vitro infection assays of HCT-8 cells monolayers and identified compounds NSC158011 and NSC10447 that inhibited the proliferation of intracellular C. parvum in vitro, with IC₅₀ values of 14.88 and 72.65 μM, respectively. At doses tolerable in mice, we found that both NSC158011 and NSC10447 consistently significantly reduced the shedding of C. parvum oocysts in infected immunocompromised mice’s feces, and prevented intestinal villous atrophy as well as mucosal erosion due to C. parvum. Together, our findings have unveiled promising anti-Cryptosporidium drug candidates that can be explored further for the development of the much needed novel therapeutic agents against C. parvum infections.

Cryptosporidium parvum is a protozoan parasite that can cause a life-threatening gastrointestinal disease in children and in immunocompromised adults. The only approved drug for treatment of Cryptosporidium infections in humans is nitazoxanide, but it is not effective in immunocompromised individuals or in children with malnutrition. C. parvum possesses a unique lactate dehydrogenase (CpLDH) enzyme that it uses for generating metabolic energy (ATP) via the glycolytic pathway to fuel its growth and proliferation in the host. We have identified novel inhibitors for the enzymatic activity of CpLDH. Further, we have demonstrated that two of the CpLDH inhibitors effectively block the growth, proliferation and pathogenicity of C. parvum at tolerable doses in immunocompromised mice. Together, our findings have unveiled novel CpLDH inhibitors that can be explored for the development of efficacious therapeutic drugs against C. parvum infections.

Efficacy of chitosan, a natural polysaccharide, against Cryptosporidium parvum in vitro and in vivo in neonatal mice

Cryptosporidiosis is a zoonotic disease caused by species in the genus Cryptosporidium. In young ruminants, Cryptosporidium parvum causes economically significant disease with mild to severe clinical signs and occasional death. The typical clinical course in animals aged 1-3 weeks old is acute diarrhoea. Currently there are no available treatments that are fully effective against cryptosporidiosis in either humans or animals. Therefore there is a critical need for the development of new therapeutic agents. We adapted two in vitro culture systems (HCT-8 and Caco-2 cell lines) for C. parvum infection to investigate the "anticryptosporidial" activity of two chitosans; Chitosan NAG and Chitosan Mix. Chitosan-a naturally-occurring polysaccharide compound-has been found to be active against a variety of diseases, possessing both antimicrobial and anticancer properties. We investigated both chitosan's toxicity and effects on C. parvum in the two in vitro models. To evaluate chitosan's effects on oocyst shedding in vivo, CD-1 neonate mice were orally inoculated with C. parvum oocysts (Iowa strain), treated with chitosan, and compared to infected non-treated animals. Paromomycin, a classical drug used in veterinary medicine, was used as a reference compound. Immunofluorescence techniques were used to analyse the parasites. Our results showed significant reductions in Cryptosporidium oocyst viability (>95%) after oocyst pre-incubation with either paromomycin (P < 0.001), Chitosan Mix or Chitosan NAG (P < 0.001), for 24 h at 37 °C. Additionally, paromomycin, Chitosan Mix, and Chitosan NAG significantly inhibited C. parvum multiplication in HCT-8 and Caco-2 cell lines (P < 0.005). These effects were dose-dependent. In in vivo studies, treatment with both chitosans (Chitosan NAG, Chitosan Mix) or paromomycin sulfate significantly reduced parasite shedding in infected treated newborn mice (-56%, -34.5% and -58%, respectively). In conclusion, these findings provide the first in vitro and in vivo evidence of the anticryptosporidial activities of this natural polysaccharide.

Identification of Agents Active against Methicillin-Resistant Staphylococcus aureus USA300 from a Clinical Compound Library

Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat for effective treatment of several difficult-to-treat infections in humans. To identify potential new treatment options for MRSA infections, we screened a clinical compound library consisting of 1524 compounds using a growth inhibition assay in 96-well plates. We identified 34 agents which are either bacteriostatic or bactericidal against log-phase clinical MRSA strain USA300. Among them, 9 candidates (thonzonium, cetylpyridinium, trilocarban, benzododecinium, bithionol, brilliant green, chlorquinaldol, methylbenzethonium and green violet) are known antiseptics, 11 candidates are known antibiotics currently recommended for the treatment of MRSA. We identified 9 new drug candidates, 5 of which (thiostrepton, carbomycin, spiramycin, clofazimine and chloroxine) are antibiotics used for treating other infections than S. aureus infections; 4 of which (quinaldine blue, closantel, dithiazanine iodide and pyrvinium pamoate) are drugs used for treating parasitic diseases or cancer. We ranked these new drug candidates according to their MICs against the MRSA strain USA300. Our findings may have implications for more effective treatment of MRSA infections.

Drug Targeting to Macrophages With Solid Lipid Nanoparticles Harboring Paromomycin: an In Vitro Evaluation Against L. major and L. tropica

Leishmaniasis is a worldwide disease that leads to high mortality and morbidity in human populations. Today, leishmaniasis is managed via drug therapy. The drugs that are already in clinical use are limited to a number of toxic chemical compounds and their parasite drug resistance is increasing. It is therefore essential, in order to circumvent the current difficulties, to design a new anti-leishmanial drug treatment strategy. Besides producing new, active anti-leishmanial entities, another promising strategy could be developing novel delivery systems and formulations of the existing pharmaceutical ingredients to improve drug efficacy. In the present study, paromomycin sulfate (PM), as one of the promising anti-leishmanial drugs, was formulated in solid lipid nanoparticles (SLN), and its in vitro efficacy was investigated against different strains of Leishmania using a MTT test, Parasite-Rescue-Transformation-Assay, SYTO Green staining, and fluorescent microscope imaging. The results show that PM-loaded SLN is significantly more effective than PM in inhibiting parasite propagation (P < 0.05) and that cytotoxicity of PM-SLN formulations is size dependent. According to our results, delivery of the drugs to the macrophages via nanoparticle utilization seems to be an accessible and practical approach.

Oleylphosphocholine (OlPC) arrests Cryptosporidium parvum growth in vitro and prevents lethal infection in interferon gamma receptor knock-out mice

Cryptosporidium parvum is a species of protozoa that causes cryptosporidiosis, an intestinal disease affecting many mammals including humans. Typically, in healthy individuals, cryptosporidiosis is a self-limiting disease. However, C. parvum can cause a severe and persistent infection that can be life-threatening for immunocompromised individuals, such as AIDS patients. As there are no available treatments for these patients that can cure the disease, there is an urgent need to identify treatment options. We tested the anti-parasitic activity of the alkylphosphocholine oleylphosphocholine (OlPC), an analog of miltefosine, against C. parvum in in vitro and in vivo studies. In vitro experiments using C. parvum infected human ileocecal adenocarcinoma cells (HCT-8 cells) showed that OlPC has an EC₅₀ of 18.84 nM. Moreover, no cell toxicity has been seen at concentrations ≤50 μM. C57BL/6 interferon gamma receptor knock-out mice, were infected by gavage with 4000 C. parvum oocysts on Day 0. Oral treatments, with OlPC, miltefosine, paromomycin or PBS, began on Day 3 post-infection for 10 days. Treatment with OlPC, at 40 mg/kg/day resulted in 100% survival, complete clearance of parasite in stools and a 99.9% parasite burden reduction in the intestines at Day 30. Doses of 30 and 20 mg/kg/day also demonstrated an increased survival rate and a dose-dependent parasite burden reduction. Mice treated with 10 mg/kg/day of miltefosine resulted in 50% survival at Day 30. In contrast, control mice, treated with PBS or 100 mg/kg/day of paromomycin, died or had to be euthanized between Days 6 and 13 due to severe illness. Results of parasite burden were obtained by qPCR and cross-validated by both flow cytometry of stool oocysts and histological sections of the ileum. Together, our results strongly support that OlPC represents a potential candidate for the treatment of C. parvum infections in immunocompromised patients.

Wnt blockers inhibit the proliferation of lung cancer stem cells

Background

Previous study has confirmed that the occurrence of Wnt pathway activation is associated with risk of non-small-cell lung cancer recurrence. However, whether the pharmacologic blocking of the Wnt signaling pathway could provide therapeutic possibility remains unknown. The aim of the present study was to evaluate the therapeutic functions of the Wnt signaling pathway inhibitor pyrvinium pamoate (PP) on lung cancer stem cells (LCSCs) in vitro.

Methods

Colony formation and sphere culture were performed to enrich LCSCs from three lung cancer cell lines: PC9, SPC-A1, and A549. After confirming stemness by immunofluorescence, PP was employed for cell viability assay by comparison with three other kinds of Wnt signaling inhibitor: salinomycin, ICG-001, and silibinin. The effect of PP on LCSCs was further verified by colony formation assay and gene expression analysis.

Results

LCSCs were successfully generated by sphere culture from SPC-A1 and PC9 cells, but not A549 cells. Immunofluorescence assay showed that LCSCs could express pluripotent stem cell markers, including NANOG, Oct4, KLF5, and SOX2, and Wnt signaling pathway molecules β-catenin and MYC. Half-maximal inhibitory concentrations of PP on SPC-A1, PC9, and A549 were 10 nM, 0.44 nM, and 0.21 nM, respectively, which are much lower than those of salinomycin, ICG-001, and silibinin. Moreover, significantly decreased colony formation and downregulation of pluripotent stem cell signaling pathway were observed in lung cancer cells after treatment with PP.

Conclusion

Wnt signaling inhibitor PP can inhibit proliferation of LCSCs, and the Wnt signaling pathway could be considered a promising therapeutic or interventional target in lung adenocarcinoma.

Gametocytocidal screen identifies novel chemical classes with Plasmodium falciparum transmission blocking activity

Discovery of transmission blocking compounds is an important intervention strategy necessary to eliminate and eradicate malaria. To date only a small number of drugs that inhibit gametocyte development and thereby transmission from the mosquito to the human host exist. This limitation is largely due to a lack of screening assays easily adaptable to high throughput because of multiple incubation steps or the requirement for high gametocytemia. Here we report the discovery of new compounds with gametocytocidal activity using a simple and robust SYBR Green I- based DNA assay. Our assay utilizes the exflagellation step in male gametocytes and a background suppressor, which masks the staining of dead cells to achieve healthy signal to noise ratio by increasing signal of viable parasites and subtracting signal from dead parasites. By determining the contribution of exflagellation to fluorescent signal and using appropriate cutoff values, we were able to screen for gametocytocidal compounds. After assay validation and optimization, we screened an FDA approved drug library of approximately 1500 compounds, as well as the 400 compound MMV malaria box and identified 44 gametocytocidal compounds with sub to low micromolar IC₅₀s. Major classes of compounds with gametocytocidal activity included quaternary ammonium compounds with structural similarity to choline, acridine-like compounds similar to quinacrine and pyronaridine, as well as antidepressant, antineoplastic, and anthelminthic compounds. Top drug candidates showed near complete transmission blocking in membrane feeding assays. This assay is simple, reproducible and demonstrated robust Z-factor values at low gametocytemia levels, making it amenable to HTS for identification of novel and potent gametocytocidal compounds.

Validation of IMP dehydrogenase inhibitors in a mouse model of cryptosporidiosis

Cryptosporidium parasites are a major cause of diarrhea and malnutrition in the developing world, a frequent cause of waterborne disease in the developed world, and a potential bioterrorism agent. Currently, available treatment is limited, and Cryptosporidium drug discovery remains largely unsuccessful. As a result, the pharmacokinetic properties required for in vivo efficacy have not been established. We have been engaged in a Cryptosporidium drug discovery program targeting IMP dehydrogenase (CpIMPDH). Here, we report the activity of eight potent and selective inhibitors of CpIMPDH in the interleukin-12 (IL-12) knockout mouse model, which mimics acute human cryptosporidiosis. Two compounds displayed significant antiparasitic activity, validating CpIMPDH as a drug target. The best compound, P131 (250 mg/kg of body weight/day), performed equivalently to paromomycin (2,000 mg/kg/day) when administered in a single dose and better than paromomycin when administered in three daily doses. One compound, A110, appeared to promote Cryptosporidium infection. The pharmacokinetic, uptake, and permeability properties of the eight compounds were measured. P131 had the lowest systemic distribution but accumulated to high concentrations within intestinal cells. A110 had the highest systemic distribution. These observations suggest that systemic distribution is not required, and may be a liability, for in vivo antiparasitic activity. Intriguingly, A110 caused specific alterations in fecal microbiota that were not observed with P131 or vehicle alone. Such changes may explain how A110 promotes parasitemia. Collectively, these observations suggest a blueprint for the development of anticryptosporidial therapy.

The antihelmintic drug pyrvinium pamoate targets aggressive breast cancer

WNT signaling plays a key role in the self-renewal of tumor initiation cells (TICs). In this study, we used pyrvinium pamoate (PP), an FDA-approved antihelmintic drug that inhibits WNT signaling, to test whether pharmacologic inhibition of WNT signaling can specifically target TICs of aggressive breast cancer cells. SUM-149, an inflammatory breast cancer cell line, and SUM-159, a metaplastic basal-type breast cancer cell line, were used in these studies. We found that PP inhibited primary and secondary mammosphere formation of cancer cells at nanomolar concentrations, at least 10 times less than the dose needed to have a toxic effect on cancer cells. A comparable mammosphere formation IC50 dose to that observed in cancer cell lines was obtained using malignant pleural effusion samples from patients with IBC. A decrease in activity of the TIC surrogate aldehyde dehydrogenase was observed in PP-treated cells, and inhibition of WNT signaling by PP was associated with down-regulation of a panel of markers associated with epithelial-mesenchymal transition. In vivo, intratumoral injection was associated with tumor necrosis, and intraperitoneal injection into mice with tumor xenografts caused significant tumor growth delay and a trend toward decreased lung metastasis. In in vitro mammosphere-based and monolayer-based clonogenic assays, we found that PP radiosensitized cells in monolayer culture but not mammosphere culture. These findings suggest WNT signaling inhibition may be a feasible strategy for targeting aggressive breast cancer. Investigation and modification of the bioavailability and toxicity profile of systemic PP are warranted.

Pyrvinium targets autophagy addiction to promote cancer cell death

Autophagy is a cellular catabolic process by which long-lived proteins and damaged organelles are degradated by lysosomes. Activation of autophagy is an important survival mechanism that protects cancer cells from various stresses, including anticancer agents. Recent studies indicate that pyrvinium pamoate, an FDA-approved antihelminthic drug, exhibits wide-ranging anticancer activity. Here we demonstrate that pyrvinium inhibits autophagy both in vitro and in vivo. We further demonstrate that the inhibition of autophagy is mammalian target of rapamycin independent but depends on the transcriptional inhibition of autophagy genes. Moreover, the combination of pyrvinium with autophagy stimuli improves its toxicity against cancer cells, and pretreatment of cells with 3-MA or siBeclin1 partially protects cells from pyrvinium-induced cell death under glucose starvation, suggesting that targeted autophagy addiction is involved in pyrvinium-mediated cytotoxicity. Finally, in vivo studies show that the combination therapy of pyrvinium with the anticancer and autophagy stimulus agent, 2-deoxy-𝒟-glucose (2-DG), is significantly more effective in inhibiting tumor growth than pyrvinium or 2-DG alone. This study supports a novel cancer therapeutic strategy based on targeting autophagy addiction and implicates using pyrvinium as an autophagy inhibitor in combination with chemotherapeutic agents to improve their therapeutic efficacy.

Synergistic effects of combined Wnt/KRAS inhibition in colorectal cancer cells

Activation of Wnt signalling due to inability to degrade β-catenin is found in >85% of colorectal cancers. Approximately half of colon cancers express a constitutively active KRAS protein. A significant fraction of patients show both abnormalities. We previously reported that simultaneous down-regulation of both β-catenin and KRAS was necessary to induce significant cell death and tumor growth inhibition of colorectal cancer cells. Although attractive, an RNAi-based therapeutic approach is still far from being employed in the clinical setting. Therefore, we sought to recapitulate our previous findings by the use of small-molecule inhibitors of β-catenin and KRAS. We show here that the β-catenin inhibitors PKF115-584 and pyrvinium pamoate block β-catenin-dependent transcriptional activity and synergize with the KRAS inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS, salirasib) in colon cancer cells driven by Wnt and KRAS oncogenic signals, but not in cells carrying BRAF mutations. The combined use of these compounds was superior to the use of any drug alone in inducing cell growth arrest, cell death, MYC and survivin down-modulation, and inhibition of anchorage-independent growth. Expression analysis of selected cancer-relevant genes revealed down-regulation of CD44 as a common response to the combined treatments. These data provide a proof of principle for a combination therapeutic strategy in colorectal cancer.

Reprofiling a classical anthelmintic, pyrvinium pamoate, as an anti-cancer drug targeting mitochondrial respiration

Pyrvinium pamoate (PP) is an FDA-approved classical anthelmintic, but is now attracting particular attention as an anti-cancer drug after recent findings of its potent cytotoxicity against various cancer cell lines only during glucose starvation, as well as its anti-tumor activity against hypovascular pancreatic cancer cells transplanted in mice. The molecular mechanisms by which PP promotes such preferential toxicity against cancer cells are currently under extensive investigation. PP suppressed the NADH-fumarate reductase system that mediates a reverse reaction of the mitochondrial electron-transport chain complex II in anaerobic organisms such as parasitic helminthes or mammalian cells under tumor microenvironment-mimicking hypoglycemic/hypoxic conditions, thereby inhibiting efficient ATP production. PP also inhibited the unfolded protein response induced by glucose starvation, thereby inhibiting the proliferation of pancreatic cancer cells. Even under normoglycemic/normoxic conditions, PP suppressed the mitochondrial electron-transport chain complex I and thereby STAT3, inhibiting the proliferation of myeloma/erythroleukemia cells. Here, we review accumulating knowledge on its working mechanisms and evaluate PP as a novel anti-cancer drug that targets mitochondrial respiration.

An anticancer agent, pyrvinium pamoate inhibits the NADH-fumarate reductase system--a unique mitochondrial energy metabolism in tumour microenvironments

Increased glycolysis is the principal explanation for how cancer cells generate energy in the absence of oxygen. However, in actual human tumour microenvironments, hypoxia is often associated with hypoglycemia because of the poor blood supply. Therefore, glycolysis cannot be the sole mechanism for the maintenance of the energy status in cancers. To understand energy metabolism in cancer cells under hypoxia-hypoglycemic conditions mimicking the tumour microenvironments, we examined the NADH-fumarate reductase (NADH-FR) system, which functions in parasites under hypoxic condition, as a candidate mechanism. In human cancer cells (DLD-1, Panc-1 and HepG2) cultured under hypoxic-hypoglycemic conditions, NADH-FR activity, which is composed of the activities of complex I (NADH-ubiquinone reductase) and the reverse reaction of complex II (quinol-FR), increased, whereas NADH-oxidase activity decreased. Pyrvinium pamoate (PP), which is an anthelmintic and has an anti-cancer effect within tumour-mimicking microenvironments, inhibited NADH-FR activities in both parasites and mammalian mitochondria. Moreover, PP increased the activity of complex II (succinate-ubiquinone reductase) in mitochondria from human cancer cells cultured under normoxia-normoglycemic conditions but not under hypoxia-hypoglycemic conditions. These results indicate that the NADH-FR system may be important for maintaining mitochondrial energy production in tumour microenvironments and suggest its potential use as a novel therapeutic target.

Protein kinase CK1α regulates erythrocyte survival

Protein kinase CK1 (casein kinase 1) isoforms are involved in the regulation of various physiological functions including apoptosis. The specific CK1 inhibitor D4476 may either inhibit or foster apoptosis. Similar to apoptosis of nucleated cells, eryptosis, the suicidal death of erythrocytes, is paralleled by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increase of cytosolic Ca(2+) activity following energy depletion (removal of glucose) or oxidative stress (exposure to the oxidant tert-butyl hydroperoxide [TBOOH]). Western blotting was utilized to verify that erythrocytes express the protein kinase CK1α, and FACS analysis to determine whether the CK1 inhibitor D4476 and CK1α activator pyrvinium pamoate modify forward scatter (reflecting cell volume), annexin V binding (reflecting phosphatidylserine exposure), and Fluo3 fluorescence (reflecting cytosolic Ca(2+) activity). As a result, both, human and murine erythrocytes express CK1 isoform α. Glucose depletion (48 hours) and exposure to 0.3 mM TBOOH (30 minutes) both decreased forward scatter, increased annexin V binding and increased Fluo3 fluorescence. CK1 inhibitor D4476 (10 μM) significantly blunted the decrease in forward scatter, the increase in annexin V binding and the increase in Fluo 3 fluorescence. (R)-DRF053, another CK1 inhibitor, similarly blunted the increase in annexin V binding upon glucose depletion. The CK1α specific activator pyrvinium pamoate (10 μM) significantly enhanced the increase in annexin V binding and Fluo3 fluorescence upon glucose depletion and TBOOH exposure. In the presence of glucose, pyrvinium pamoate slightly but significantly increased Fluo3 fluorescence. In conclusion, CK1 isoform α participates in the regulation of erythrocyte programmed cell death by modulating cytosolic Ca(2+) activity.

Novel and promising compounds to treat Cryptosporidium parvum infections

No fully effective approved drug therapy exists for Cryptosporidium infections of immunocompetent and immunocompromised patients. Here, we investigated 11 benzimidazole derivatives carrying substituted thioalkyl and thiobenzyl groups at position 2 of benzimidazole nucleus and additional substituents at the benzene part of benzimidazole for inhibition of the in vitro growth of the intestinal protozoan parasite, Cryptosporidium parvum. Three of them, i.e., 5-carboxy-2-(4-nitrobenzylthio)-1H-benzimidazole, 5,6-dichloro-2-(4-nitrobenzylthio)-1H-benzimidazole, and 4,6-dichloro-2-(4-nitrobenzylthio)-1H-benzimidazole, (compounds 5, 7, and 8) were the most active (IC(50) 28-31 μM). The concentration of compounds 5, 7, and 8 that caused 50% growth inhibition in human enterocytic HCT-8 cells by a quantitative alkaline phosphatase immunoassay was comparable with those obtained for paromomycin.

Efficacy of antiamebic drugs in a mouse model

Nitroimidazole antibiotics are the mainstay of treatment of invasive amebiasis; however, few comparative studies of applicable antibiotics are available. Evidence of sporadic clinical failure and rare reports of metronidazole resistance have led to the investigation of novel antiamebic therapeutics. The goal of this study was to examine drug efficacy in both in vitro and in vivo models of intestinal amebiasis. We studied six current and three novel drugs. Many drugs, including metronidazole, nitazoxanide, and nitazoxanide derivatives, were shown to be potently inhibitory in vitro. However, metronidazole remained the most effective in vivo, both in preventative and curative regimens, underscoring the value of animal models in evaluating future therapies.

Finding promiscuous old drugs for new uses

From research published in the last six years we have identified 34 studies that have screened libraries of FDA-approved drugs against various whole cell or target assays. These studies have each identified one or more compounds with a suggested new bioactivity that had not been described previously. We now show that 13 of these drugs were active against more than one additional disease, thereby suggesting a degree of promiscuity. We also show that following compilation of all the studies, 109 molecules were identified by screening in vitro. These molecules appear to be statistically more hydrophobic with a higher molecular weight and AlogP than orphan-designated products with at least one marketing approval for a common disease indication or one marketing approval for a rare disease from the FDA's rare disease research database. Capturing these in vitro data on old drugs for new uses will be important for potential reuse and analysis by others to repurpose or reposition these or other existing drugs. We have created databases which can be searched by the public and envisage that these can be updated as more studies are published.

In silico repositioning of approved drugs for rare and neglected diseases

One approach to speed up drug discovery is to examine new uses for existing approved drugs, so-called 'drug repositioning' or 'drug repurposing', which has become increasingly popular in recent years. Analysis of the literature reveals many examples of US Food and Drug Administration-approved drugs that are active against multiple targets (also termed promiscuity) that can also be used to therapeutic advantage for repositioning for other neglected and rare diseases. Using proof-of-principle examples, we suggest here that with current in silico technologies and databases of the structures and biological activities of chemical compounds (drugs) and related data, as well as close integration with in vitro screening data, improved opportunities for drug repurposing will emerge for neglected or rare/orphan diseases.

Small-molecule inhibition of Wnt signaling through activation of casein kinase 1α

Wnt/β-catenin signaling is critically involved in metazoan development, stem cell maintenance and human disease. Using Xenopus laevis egg extract to screen for compounds that both stabilize Axin and promote β-catenin turnover, we identified an FDA-approved drug, pyrvinium, as a potent inhibitor of Wnt signaling (EC(50) of ∼10 nM). We show pyrvinium binds all casein kinase 1 (CK1) family members in vitro at low nanomolar concentrations and pyrvinium selectively potentiates casein kinase 1α (CK1α) kinase activity. CK1α knockdown abrogates the effects of pyrvinium on the Wnt pathway. In addition to its effects on Axin and β-catenin levels, pyrvinium promotes degradation of Pygopus, a Wnt transcriptional component. Pyrvinium treatment of colon cancer cells with mutation of the gene for adenomatous polyposis coli (APC) or β-catenin inhibits both Wnt signaling and proliferation. Our findings reveal allosteric activation of CK1α as an effective mechanism to inhibit Wnt signaling and highlight a new strategy for targeted therapeutics directed against the Wnt pathway.

A screening pipeline for antiparasitic agents targeting cryptosporidium inosine monophosphate dehydrogenase

Background

The protozoan parasite Cryptosporidium parvum is responsible for significant disease burden among children in developing countries. In addition Cryptosporidiosis can result in chronic and life-threatening enteritis in AIDS patients, and the currently available drugs lack efficacy in treating these severe conditions. The discovery and development of novel anti-cryptosporidial therapeutics has been hampered by the poor experimental tractability of this pathogen. While the genome sequencing effort has identified several intriguing new targets including a unique inosine monophosphate dehydrogenase (IMPDH), pursuing these targets and testing inhibitors has been frustratingly difficult.

Methodology and Principal Findings

Here we have developed a pipeline of tools to accelerate the in vivo screening of inhibitors of C. parvum IMPDH. We have genetically engineered the related parasite Toxoplasma gondii to serve as a model of C. parvum infection as the first screen. This assay provides crucial target validation and a large signal window that is currently not possible in assays involving C. parvum. To further develop compounds that pass this first filter, we established a fluorescence-based assay of host cell proliferation, and a C. parvum growth assay that utilizes automated high-content imaging analysis for enhanced throughput.

Conclusions and Significance

We have used these assays to evaluate C. parvum IMPDH inhibitors emerging from our ongoing medicinal chemistry effort and have identified a subset of 1,2,3-triazole ethers that exhibit excellent in vivo selectivity in the T. gondii model and improved anti-cryptosporidial activity.

Persistent diarrhea is a leading cause of illness and death among impoverished children, and a growing share of this disease burden can be attributed to the parasite Cryptosporidium. There are no vaccines to prevent Cryptosporidium infection, and the treatment options are limited and unreliable. Critically, no effective treatment exists for children or adults suffering from AIDS. Cryptosporidium presents many technical obstacles for drug discovery; perhaps the most important roadblock is the difficulty of monitoring drug action. Here we have developed a set of methods to accelerate the drug discovery process for cryptosporidiosis. We exploit the opportunities for experimental manipulation in the related parasite Toxoplasma to genetically engineer a Cryptosporidium model. This new model parasite mirrors the metabolism of Cryptosporidium for a particularly promising drug target that supplies the building blocks for DNA and RNA. Drug effectiveness can be assayed through simple fluorescence measurements for many candidates. Using this assay as an initial filter, and adapting other assays to a high throughput format, we identify several novel chemical compounds that exhibit markedly improved anti-cryptosporidial activity and excellent selectivity.

In vitro activity of pyrvinium pamoate against Entamoeba histolytica and Giardia intestinalis using radiolabelled thymidine incorporation and an SYBR Green I-based fluorescence assay

OBJECTIVES

To assess the in vitro activity of the FDA-approved antihelminthic drug pyrvinium pamoate against Entamoeba histolytica and Giardia intestinalis.

METHODS

A head-to-head comparison of a standard radiolabelled thymidine incorporation assay and the SYBR Green I-based fluorescence assay for determination of in vitro inhibition by pyrvinium and metronidazole was performed.

RESULTS

The 50% inhibitory concentration (IC(50)) for treatment of E. histolytica with pyrvinium was 4-5 microM for both assays compared with 1-2 microM for metronidazole. For pyrvinium treatment of G. intestinalis, an IC(50) of approximately 12 microM was determined by the radiolabelled thymidine assay alone, with maximum inhibition around 60%. In contrast, the IC(50) for metronidazole treatment using this assay was approximately 2 microM.

CONCLUSIONS

Pyrvinium is a potential gut lumen agent for treatment of intestinal amoebiasis, but possibly not for giardiasis. SYBR Green I is an alternative screening method for E. histolytica, but not G. intestinalis.