A nanotherapy strategy significantly enhances anticryptosporidial activity of an inhibitor of bifunctional thymidylate synthase-dihydrofolate reductase from Cryptosporidium

Prodrug nanotherapy demonstrates in vivo anticryptosporidial efficacy in a mouse model of chronic Cryptosporidium infection

The gastrointestinal disease cryptosporidiosis, caused by the genus Cryptosporidium, is a common cause of diarrheal diseases in children, particularly in developing countries and frequently fatal in immunocompromised individuals. Cryptosporidium hominis (Ch)-specific bifunctional dihydrofolate reductase-thymidylate synthase (DHFR-TS) has been a molecular target for inhibitor design. (Note that this bifunctional enzyme has also been referred to as TS-DHFR in previous literature since the functional biochemical reaction first involves the conversion of methylene tetrahydrofolate to dihydrofolate at the TS site.) While nanomolar inhibitors of Ch DHFR-TS have been identified at the biochemical level, effective delivery of these compounds to achieve anticryptosporidial activity in cell culture and in vivo models of parasite infection remains a major challenge in developing new therapies. Previous studies, using a nanotherapy approach, have shown a promising Ch DHFR-TS inhibitor, 906, that can successfully target Cryptosporidium parasites in cell culture with nanomolar anticryptosporidial activity. This formulation utilized poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) loaded with 906 (NP-906) and conjugated with a Cryptosporidium monoclonal antibody (MAb) on the nanoparticle surface to specifically target the glycoprotein GP25-200 in excysting oocysts. However, a limitation for in vivo use is antibody susceptibility to gastric acidity. To address this gap, a prodrug diethyl ester form of 906 (MAb-NP-Prodrug) was synthesized that allowed higher compound loading in the MAb-coated PLGA nanoparticles. An oral formulation was prepared by loading lyophilized MAb-NP-Prodrug into gelatin capsules with an enteric coating for gastric stability. Proof-of-concept studies with this oral formulation demonstrated antiparasitic activity in a chronic mouse model of Cryptosporidium infection. Efficacy was observed after a low daily dose of 2 × 8 mg kg-1 for 5 days, when examined 6 and 20 days postinfection, offering a new avenue of drug delivery to be further explored.

Medical prospects of cryptosporidiosis in vivo control using biofabricated nanoparticles loaded with Cinnamomum camphora extracts by Ulva fasciata

Background and Aim

Global efforts are continuing to develop preparations against cryptosporidiosis. This study aimed to investigate the efficacy of biosynthesized Ulva fasciata loading Cinnamomum camphora oil extract on new zinc oxide nanoparticles (ZnONPs shorten to ZnNPs) and silver nanoparticles (AgNPs) as alternative treatments for Cryptosporidium parvum experimental infection in rats.

Materials and Methods

Oil extract was characterized by gas chromatography-mass spectrometry, loaded by U. fasciata on ionic-based ZnO and NPs, and then characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. Biosafety and toxicity were investigated by skin tests. A total of 105 C. parvum oocysts/rat were used (n = 81, 2-3 W, 80-120 g, 9 male rats/group). Oocysts shedding was counted for 21 d. Doses of each preparation in addition to reference drug were administered daily for 7 d, starting on post-infection (PI) day (3). Nitazoxanide (100 mg) was used as the reference drug. After 3 weeks, the rats were sacrificed for postmortem examination and histopathological examination. Two blood samples/rat/group were collected on the 21st day. Ethylenediaminetetraacetic acid blood samples were also used for analysis of biochemistry, hematology, immunology, micronucleus prevalence, and chromosomal abnormalities.

Results

C. camphora leaves yielded 28.5 ± 0.3 g/kg oil and 20 phycocompounds were identified. Spherical and rod-shaped particles were detected at 10.47-30.98 nm and 18.83-38.39 nm, respectively. ZnNPs showed the earliest anti-cryptosporidiosis effect during 7-17 d PI. Other hematological, biochemical, immunological, histological, and genotoxicity parameters were significantly fruitful; hence, normalized pathological changes induced by infestation were observed in the NPs treatments groups against the infestation-free and Nitazoxanide treated group.

Conclusion

C. camphora, U. fasciata, ZnNPs, and AgNPs have refluxed the pathological effects of infection as well as positively improved host physiological condition by its anticryptosporidial immunostimulant regenerative effects with sufficient ecofriendly properties to be proposed as an alternative to traditional drugs, especially in individuals with medical reactions against chemical commercial drugs.

Use of nanoparticles, a modern means of drug delivery, against cryptosporidiosis

Cryptosporidium is a primary cause of waterborne epidemics, despite being previously considered only an opportunistic pathogen. The disease is associated with significant economic losses in humans and animals that are brought on by diarrhea, which frequently causes dehydration. Contact with diseased people or animals, as well as polluted water, is the major cause of infection. Different drugs are used to control the parasites. Nitazoxanide (NTZ), which is an anti-protozoan and anti-viral drug, can be used to control helminths, viruses, and protozoan parasites as a broad-spectrum antibiotic and has been approved by the food and drug authority (FDA). However, the problem is the development of resistance over a period of time in these parasites. Nanoparticles have received significant attention as possible anti-parasitic agents in recent years. By directing medications to specific cellular locations, targeted drug delivery minimizes the side effects of medications. Nanoparticles have demonstrated effectiveness against different Cryptosporidium species. Nanoparticles loaded with NTZ are found to be an effective remedy for C. parvum in young ones and decrease the oocyst count shed in the stools. Additionally, silver nanoparticles have proven to be effective against C. parvum by releasing silver ions that breach the cell wall of the oocyst, causing the escape of intracellular contents and the destruction of sporozoites within the oocyst. Implementing tiny particles for the purification of consuming water from Cryptosporidium is an economical and environmentally sustainable process. However, the use of nanoparticles in medicine requires more research.

Diagnosis and control of cryptosporidiosis in farm animals

Cryptosporidium is a pathogenic protozoan parasite infecting the gastrointestinal epithelium of human and animal hosts. In farm animals, cryptosporidiosis causes significant economic losses including deaths in newborn animals, retarded growth, increased labor involved and high cost of drugs. The detection of Cryptosporidium oocysts in fecal samples is traditionally dependent on examination of stained slides by light microscope or by advanced microscopical tools such as: electron microscopy and phase contrast microscopy. Immunological diagnosis using either antibody or antigen detection could offer high sensitivity and specificity. Examples for these tests are Enzyme Linked Immunosorbent Assay (ELISA), Immunochromatographic tests, Immunochromatographic lateral flow (ICLF), Immunofluorescence assays (IFA) and Flow cytometry coupled with cell sorting. Molecular methods could differentiate species and genotypes of Cryptosporidium and help in studying the epidemiological features of this parasite with rapid, simple and sensitive procedures. Nanotechnology-based platforms could improve the sensitivity and specificity of other detection methods like: ELISA, ICLF, IFA and polymerase chain reaction. As the available prophylactic and therapeutic drugs or natural products treatments are insufficient and no approved vaccines are available, the best approach to control this parasite is by following firm hygienic measures. Many vaccine attempts were performed using hyperimmune colostrum, live or attenuated vaccines, recombinant and Deoxyribonucleic acid vaccines. Also, Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 technology could help in Cryptosporidium genome editing to improve drug and vaccine discovery. Another approach that could be useful for assigning drug targets is metabolomics. Probiotics were also used successfully in the treatment of acute diarrhea and they proved a limiting effect on cryptosporidiosis in animal models. In addition, nanotherapy-based approaches could provide a good strategy for improving the potency of any type of drugs against Cryptosporidium and give good anti-cryptosporidial effects. In conclusion, accurate diagnosis using advanced techniques is the key to the control and prevention of cryptosporidiosis.

Comparative proteomics reveals Cryptosporidium parvum manipulation of the host cell molecular expression and immune response

Cryptosporidium is a life-threating protozoan parasite belonging to the phylum Apicomplexa, which mainly causes gastroenteritis in a variety of vertebrate hosts. Currently, there is a re-emergence of Cryptosporidium infection; however, no fully effective drug or vaccine is available to treat Cryptosporidiosis. In the present study, to better understand the detailed interaction between the host and Cryptosporidium parvum, a large-scale label-free proteomics study was conducted to characterize the changes to the proteome induced by C. parvum infection. Among 4406 proteins identified, 121 proteins were identified as differentially abundant (> 1.5-fold cutoff, P < 0.05) in C. parvum infected HCT-8 cells compared with uninfected cells. Among them, 67 proteins were upregulated, and 54 proteins were downregulated at 36 h post infection. Analysis of the differentially abundant proteins revealed an interferon-centered immune response of the host cells against C. parvum infection and extensive inhibition of metabolism-related enzymes in the host cells caused by infection. Several proteins were further verified using quantitative real-time reverse transcription polymerase chain reaction and western blotting. This systematic analysis of the proteomics of C. parvum-infected HCT-8 cells identified a wide range of functional proteins that participate in host anti-parasite immunity or act as potential targets during infection, providing new insights into the molecular mechanism of C. parvum infection.

Cryptosporidium parvum is an emerging zoonotic pathogen transmitted via the fecal–oral route, and is considered a leading cause of moderate-to-severe diarrheal disease in young children in resource limited areas. After infection, C. parvum parasitizes intestinal epithelial cells and evokes an inflammatory immune response, leading to severe damage of the intestinal mucosa. The infection can be lethal to immunosuppressed individuals. However, no fully effective drug or vaccine is available for cryptosporidiosis, and the pathogenesis and immune mechanisms during C. parvum infection are obscure. Thus, an in-depth understanding of host-parasite interaction is needed. Hence, we established a C. parvum-infected HCT-8 cell model and performed comparative quantitative proteomic analyses to profile global host-parasite interactions and determine the molecular mechanisms that are activated during infection, aiming to offer new insights into the treatment of Cryptosporidium.

Targeting the TS dimer interface in bifunctional Cryptosporidium hominis TS-DHFR from parasitic protozoa: Virtual screening identifies novel TS allosteric inhibitors

Effective therapies are lacking to treat gastrointestinal infections caused by the genus Cryptosporidium, which can be fatal in the immunocompromised. One target of interest is Cryptosporidium hominis (C. hominis) thymidylate synthase-dihydrofolate reductase (ChTS-DHFR), a bifunctional enzyme necessary for DNA biosynthesis. Targeting the TS-TS dimer interface is a novel strategy previously used to identify inhibitors against the related bifunctional enzyme in Toxoplasma gondii. In the present study, we target the ChTS dimer interface through homology modeling and high-throughput virtual screening to identifying allosteric, ChTS-specific inhibitors. Our work led to the discovery of methylenedioxyphenyl-aminophenoxypropanol analogues which inhibit ChTS activity in a manner that is both dose-dependent and influenced by the conformation of the enzyme. Preliminary results presented here include an analysis of structure activity relationships and a ChTS-apo crystal structure of ChTS-DHFR supporting the continued development of inhibitors that stabilize a novel pocket formed in the open conformation of ChTS-TS.

Genetic ablation of purine salvage in Cryptosporidium parvum reveals nucleotide uptake from the host cell

The apicomplexan parasite Cryptosporidium is a leading global cause of severe diarrheal disease and an important contributor to early-childhood mortality. Waterborne outbreaks occur frequently, even in countries with advanced water treatment capabilities, and there is currently no fully effective treatment. Nucleotide pathways are attractive targets for antimicrobial development, and several laboratories are designing inhibitors of these enzymes as potential treatment for Cryptosporidium infections. Here we take advantage of newly available molecular genetics for Cryptosporidium parvum to investigate nucleotide biosynthesis by directed gene ablation. Surprisingly, we found that the parasite tolerates the loss of classical targets including dihydrofolate reductase-thymidylate synthase (DHFR-TS) and inosine monophosphate dehydrogenase (IMPDH). We show that thymidine kinase provides a route to thymidine monophosphate in the absence of DHFR-TS. In contrast, only a single pathway has been identified for C. parvum purine nucleotide salvage. Nonetheless, multiple enzymes in the purine pathway, as well as the adenosine transporter, can be ablated. The resulting mutants are viable under normal conditions but are hypersensitive to inhibition of purine nucleotide synthesis in their host cell. Cryptosporidium might use as-yet undiscovered purine transporters and salvage enzymes; however, genetic and pharmacological experiments led us to conclude that Cryptosporidium imports purine nucleotides from the host cell. The potential for ATP uptake from the host has significant impact on our understanding of parasite energy metabolism given that Cryptosporidium lacks oxidative phosphorylation and glycolytic enzymes are not constitutively expressed throughout the parasite life cycle.

Novel treatment strategies and drugs in development for cryptosporidiosis

INTRODUCTION

Cryptosporidium is a protozoan pathogen that can cause diarrheal disease in healthy and immunosuppressed individuals, worldwide. Recent studies have highlighted the impact of cryptosporidiosis on children in resource-limited countries. Nitazoxanide is the only Food and Drug Administration approved treatment, but it is not consistently effective therapy for cryptosporidiosis in the most vulnerable populations. Areas covered: This review focused on recent published studies evaluating novel drugs and new compounds for the treatment of cryptosporidiosis. Expert commentary: Combinations of approved drugs have demonstrated some activity. Broad screens have demonstrated activity against Cryptosporidium for a number of available drugs, including statins and clofazimine, and the latter has advanced into clinical trials. Cryptosporidium calcium-dependent protein kinase 1 (CDPK1) has been identified as an attractive target for treatment, and bumped kinase inhibitors have been developed which inhibit CDPK1 and are active against Cryptosporidium growth both in vitro and in vivo. Inhibition of Plasmodium lipid kinase PI(4)K8 of Cryptosporidium by KDU731 greatly reduced oocyst shedding and improved diarrhea in calves with limited effects on the human PI(4)K. Another novel potent inhibitor MMV665917 was efficacious in mouse models with cidal activity against Cryptosporidium. Additional compounds have proved active in vitro. So far, only clofazimine has entered human trials.

Understanding the molecular mechanism of substrate channeling and domain communication in protozoal bifunctional TS-DHFR

Most species, such as humans, have monofunctional forms of thymidylate synthase (TS) and dihydrofolate reductase (DHFR) that are key folate metabolism enzymes making critical folate components required for DNA synthesis. In contrast, several parasitic protozoa, including Leishmania major (Lm), Plasmodium falciparum (Pf), Toxoplasma gondii (Tg) and Cryptosporidium hominis (Ch), contain a unique bifunctional thymidylate synthase-dihydrofolate reductase (TS-DHFR) having the two sequential catalytic activities contained on a single polypeptide chain. It has been suggested that the bifunctional nature of the two catalytic activities may enable substrate channeling. The 3D structures for each of these enzymes reveals distinct features for each species. While three of the four species (Pf, Tg and Ch) contain a junctional region linking the two domains, this is lacking in Lm. The Lm and Pf contain N-terminal amino acid extensions. A multidisciplinary approach using structural studies and transient kinetic analyses combined with mutational analysis has investigated the roles of these unique structural features for each enzyme. Additionally, the possibility of substrate channeling behavior was explored. These studies have identified unique, functional regions in both the TS and DHFR domains that govern efficient catalysis for each species. Surprisingly, even though there are structural similarities among the species, each is regulated in a distinct manner. This structural and mechanistic information was also used to exploit species-specific inhibitor design.

Recent developments in drug discovery against the protozoal parasites Cryptosporidium and Toxoplasma

Apicomplexan parasites cause some of the most devastating human diseases, including malaria, toxoplasmosis, and cryptosporidiosis. New drug discovery is imperative in light of increased resistance. In this digest article, we briefly explore some of the recent and promising developments in new drug discovery against two apicomplexan parasites, Cryptosporidium and Toxoplasma.

Perturbation of genome integrity to fight pathogenic microorganisms

BACKGROUND

Resistance against antibiotics is unfortunately still a major biomedical challenge for a wide range of pathogens responsible for potentially fatal diseases.

SCOPE OF REVIEW

In this study, we aim at providing a critical assessment of the recent advances in design and use of drugs targeting genome integrity by perturbation of thymidylate biosynthesis.

MAJOR CONCLUSION

We find that research efforts from several independent laboratories resulted in chemically highly distinct classes of inhibitors of key enzymes within the routes of thymidylate biosynthesis. The present article covers numerous studies describing perturbation of this metabolic pathway in some of the most challenging pathogens like Mycobacterium tuberculosis, Plasmodium falciparum, and Staphylococcus aureus.

GENERAL SIGNIFICANCE

Our comparative analysis allows a thorough summary of the current approaches to target thymidylate biosynthesis enzymes and also include an outlook suggesting novel ways of inhibitory strategies. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.