Cruzipain and Its Physiological Inhibitor, Chagasin, as a DNA-Based Therapeutic Vaccine Against Trypanosoma cruzi

Chagasin from Trypanosoma cruzi as a molecular scaffold to express epitopes of TSA-1 as soluble recombinant chimeras

Trypanosoma cruzi is the causative agent of Chagas disease, a global public health problem. New therapeutic drugs and biologics are needed. The TSA-1 recombinant protein of T. cruzi is one such promising antigen for developing a therapeutic vaccine. However, it is overexpressed in E. coli as inclusion bodies, requiring an additional refolding step. As an alternative, in this study, we propose the endogenous cysteine protease inhibitor chagasin as a molecular scaffold to generate chimeric proteins. These proteins will contain combinations of two of the five conserved epitopes (E1 to E5) of TSA-1 in the L4 and L6 chagasin loops. Twenty chimeras (Q1-Q20) were designed, and their solubility was predicted using bioinformatics tools. Nine chimeras with different degrees of solubility were selected and expressed in E. coli BL21 (DE3). Western blot assays with anti-6x-His and anti-chagasin antibodies confirmed the expression of soluble recombinant chimeras. Both theoretically and experimentally, the Q12 (E5-E3) chimera was the most soluble, and the Q20 (E4-E5) the most insoluble protein. Q4 (E5-E1) and Q8 (E5-E2) chimeras were classified as proteins with medium solubility that exhibited the highest yield in the soluble fraction. Notably, Q4 has a yield of 239 mg/L, well above the yield of recombinant chagasin (16.5 mg/L) expressed in a soluble form. The expression of the Q4 chimera was scaled up to a 7 L fermenter obtaining a yield of 490 mg/L. These data show that chagasin can serve as a molecular scaffold for the expression of TSA-1 epitopes in the form of soluble chimeras.

The Broad-Spectrum Antitrypanosomal Inhibitory Efficiency of the Antimetabolite/Anticancer Drug Raltitrexed

Raltitrexed is a classical antifolate drug with antimetabolite and anticancer properties. In this research, we provide its detailed antitrypanosomal inhibition against six Trypanosoma species and investigate its potential mode of action. Molecular dynamics (MD) simulations and in silico analyses were used to track the binding strength and stability. Raltitrexed showed broad-spectrum trypanocidal actions against Trypanosoma brucei brucei GUTat3.1, T. b. rhodesiense IL1501, T. b. gambiense IL1922, T. evansi Tansui, T. equiperdum IVM-t1 and T. congolense IL3000. The estimated IC50 was found to be in the range of 5.18–24.13 µg/mL, indicating inhibition of Trypanosoma in the low micromolar range. Although the co-crystallized ligand had robust hydrogen bonding and lipophilic characteristics, its docking score was only −4.6 compared to raltitrexed’s −7.78, indicating strong binding with T. brucei dihydrofolate reductase-thymidylate synthase (TbDHFR-TS). MD simulations support the strong binding of raltitrexed with TbDHFR-TS evidenced by low root mean square deviation (RMSD), low residues fluctuations, a tight radius of gyration (ROG) and an average of 3.38 ± 1.3 hydrogen bonds during 50 ns MD simulation. The prospective extended spectrum of raltitrexed against Trypanosoma species grants further research for the synthesis of raltitrexed derivatives and repurposing against other protozoa.

Assessment of a combined treatment with a therapeutic vaccine and benznidazole for the Trypanosoma cruzi chronic infection

The difficulties encountered in achieving treatments for chronic Chagas disease have promoted the investigation of new therapeutic strategies. In this study, we used two murine models of Trypanosoma cruzi chronic infection to determine the usefulness of applying a therapeutic vaccine alone or followed by benznidazole (Bz) chemotherapy. A vaccine formulation based on an N-terminal fragment of Trans-sialidase (TS) and Immunostimulant Particle Adjuvant (ISPA) - TSNt-ISPA was obtained. Firstly, the immunogenicity and protective capacity of TSNt-ISPA was demonstrated as a prophylactic formulation in an acute model of infection. Later, the formulation was assessed as a therapeutic vaccine alone or combined with (Bz) using two models of chronic infection. BALB/c mice chronically infected with Sylvio X10/4 or Tulahuen cl2 T. cruzi strains were not treated as control or treated only with the therapeutic vaccine TSNt-ISPA, with a combined treatment TSNt-ISPA+Bz (Bz applied after the vaccine), or only with Bz. The vaccination schedule consisted of TSNt-ISPA administration at days110, 120, and 130 post-infection (pi) and Bz administration was performed daily from day 140 to 170 pi. At day 273 pi, electrocardiographic (ECG) parameters, heart parasite load, myocarditis, and heart fibrosis were assessed. In both models, therapeutic administration of TSNt-ISPA reduced ECG alterations and the cardiac tissue damage observed in the chronic phase. Moreover, vaccine treatment significantly decreased heart parasite load in both Sylvio X10/4 and Tulahuen cl2 infected mice. The combined treatment, but not Bz or vaccine administration alone, allowed to restore ECG parameters in Tulahuen cl2 infected mice. The results indicate the usefulness of the therapeutic TSNt-ISPA formulation in BALB/c mice chronically infected with Sylvio X10/4 or Tulahuen cl2 strain. For the mice infected with T. cruzi Tulahuen cl2 strain, the combined treatment with the vaccine and Bz had a more positive effect on the course of heart disease than the individual treatments with the vaccine or Bz alone.

Mode of action of the sesquiterpene lactones eupatoriopicrin and estafietin on Trypanosoma cruzi

BACKGROUND

The sesquiterpene lactones (STLs) eupatoriopicrin (EP) and estafietin (ES), isolated from Stevia alpina Griseb. (Asteraceae) and Stevia maimarensis (Hieron.) Cabrera (Asteraceae) respectively, have previously showed promising trypanocidal activity, both in vitro and in vivo.

PURPOSE

In this work, using biochemical studies and electron microscopy, we aimed at characterizing the mode of action of both STLs on Trypanosoma cruzi.

METHODS

The interaction of STLs with hemin was examined by measuring modifications in the Soret absorption band of hemin; the thiol groups interaction was determined spectrophotometrically through its reaction with 5,5'-dithiobis-2-nitrobenzoate; the effect on cruzipain activity was also assayed by spectrophotometry. The synthesis of sterols were qualitatively and quantitatively tested by TLC. Mitochondrial functionality was assessed by measuring mitochondrial membrane potential and the activity of NADH-cytochrome c reductase and succinate-cytochrome c reductase enzymes. The status of the antioxidant system was assessed by quantifying the level of free thiols by spectrophotometry, together with the intracellular oxidative state by flow cytometry. Ultrastructural changes were analyzed by transmission electron microscopy.

RESULTS

EP and ES were found to impair the functionality and the redox status of the parasite. ES produced a greater decrease in the activity of succinate dehydrogenase than eupatoriopicrin, affecting the functioning of the respiratory chain and the Krebs cycle. EP increased the formation of triglycerides leading to the presence of cytoplasmic lipid droplets. By electron microscopy, alterations in the kinetoplast and the appearance of large translucent vacuoles in the cytoplasm were observed for both compounds.

CONCLUSIONS

Both sesquiterpenelactones proved to act additively on T. cruzi, supporting the hypothesis that each compound would be acting on different primary targets.. The treatment combining eupatoriopicrin and estafietin could be considered a promising alternative for the treatment of Chagas' disease.

In Vitro, In Vivo, and In Silico Studies of Cumanin Diacetate as a Potential Drug against Trypanosoma cruzi Infection

The sesquiterpene lactones cumanin, helenalin, and hymenin and their semisynthetic derivatives were evaluated against Trypanosoma cruzi epimastigotes. The cytotoxicity of the compounds was evaluated on murine splenocytes. Cumanin diacetate was one of the most active and selective compounds [IC₅₀ = 3.20 ± 0.52 μg/mL, selectivity index (SI) = 26.0]. This sesquiterpene lactone was selected for its evaluation on trypomastigote and amastigote forms of the parasite. The diacetylated derivative of cumanin showed moderate activity on trypomastigotes (IC₅₀ = 32.4 ± 5.8 μg/mL). However, this compound was able to efficiently inhibit parasite replication with an IC₅₀ value of 2.2 ± 0.05 μg/mL against the amastigote forms. Cumanin diacetate showed selectivity against the intracellular forms of Trypanosoma cruzi with an SI value of 52.7. This cumanin analogue was also active on an in vivo model of Chagas disease, leading to a reduction in the parasitemia levels in comparison with nontreated animals. Histopathological analysis of skeletal muscular tissues from treated mice showed only focal interstitial lymphocyte inflammatory infiltrates with slight myocyte necrosis; in contrast, nontreated animals showed severe lymphocyte inflammatory infiltrates with necrosis of the myocytes. A molecular docking study of cumanin and its derivatives on trypanothione reductase from T. cruzi (TcTR) was performed. The results of ΔG docking achieved let the identification of diacetylated and O-alkylated derivatives of cumanin as good inhibitors of TcTR. Cumanin diacetate could be considered a potential candidate for further studies for the development of new therapies against Chagas disease.

Oxidative stress implications for therapeutic vaccine development against Chagas disease

INTRODUCTION

Pathogenesis of Chagas disease (CD) caused by the protozoan parasite Trypanosoma cruzi (T. cruzi) involves chronic oxidative and inflammatory stress. In this review, we discuss the research efforts in therapeutic vaccine development to date and the potential challenges imposed by oxidative stress in achieving an efficient therapeutic vaccine against CD.

AREAS COVERED

This review covers the immune and nonimmune mechanisms of reactive oxygen species production and immune response patterns during T. cruzi infection in CD. A discussion on immunotherapy development efforts, the efficacy of antigen-based immune therapies against T. cruzi, and the role of antioxidants as adjuvants is discussed to provide promising insights to developing future treatment strategies against CD.

EXPERT OPINION

Administration of therapeutic vaccines can be a good option to confront persistent parasitemia in CD by achieving a rapid, short-lived stimulation of type 1 cell-mediated immunity. At the same time, adjunct therapies could play a critical role in the preservation of mitochondrial metabolism and cardiac muscle contractility in CD. We propose combined therapy with antigen-based vaccine and small molecules to control the pathological oxidative insult would be effective in the conservation of cardiac structure and function in CD.

Advances in the treatment of Chagas disease: Promising new drugs, plants and targets

Chagas disease, caused by Trypanosoma cruzi, is treated with only two drugs; benznidazole and nifurtimox. These drugs have some disadvantages, including their efficacy only in the acute or early infection phases, adverse effects during their use, and the resistance that the parasite has developed to their activity. Therefore, it is necessary to identify new, safe and effective therapeutic alternatives to treat Chagas disease, though governments and the pharmaceutical industry have shown a lack of interest in contributing to this solution. Institutions and research groups on the other hand have worked on some strategies that can help to address the problem. Some of these include the modification of conventional drug dosages, drug repurposing, and combined therapy. Plants and derived compounds with antiparasitic effects have also been studied, taking advantage of traditional medicinal knowledge. Others have studied the parasite to identify essential genes that can be used as therapeutic targets to design new, targeted drugs. Some of these studies have generated promising results, but few reach clinical phase studies. Institutions and research groups should be encouraged to unify efforts and cover all aspects of drug development according to resources and knowledge availability. In the end, this exchange of knowledge would lead to the development of new therapeutic alternatives to treat Chagas disease and benefit the populations it affects.

The Case for the Development of a Chagas Disease Vaccine: Why? How? When?

Chagas disease is a major neglected tropical disease, transmitted predominantly by triatomine insect vectors, but also through congenital and oral routes. While endemic in the Americas, it has turned into a global disease. Because of the current drug treatment limitations, a vaccine would represent a major advancement for better control of the disease. Here, we review some of the rationale, advances, and challenges for the ongoing development of a vaccine against Chagas disease. Recent pre-clinical studies in murine models have further expanded (i) the range of vaccine platforms and formulations tested; (ii) our understanding of the immune correlates for protection; and (iii) the extent of vaccine effects on cardiac function, beyond survival and parasite burden. We further discuss outstanding issues and opportunities to move Chagas disease development forward in the near future.