Human clinical trials are expensive, and when they fail, they create the impression that a problem is intractable, thus depressing interest in future attempts. For neglected tropical diseases, where there are likely limited numbers of “shots on goal”, such failures need to be assiduously avoided. Chagas disease drug discovery efforts have experienced more than its share of human clinical trial failures. Here Here are some guidelines, many specific for Chagas, but some which might also have application for other neglected tropical diseases. Chagas disease has major challenges (e.g., the lack of a definitive test of cure) but also has outstanding advantages, among these the unmatched multi-species natural infection systems that can be exploited to de-risk compounds before human trials. Fully utilizing these advantages while frankly acknowledging and addressing the challenges should bring better options to patients, sooner.
Trypanosoma cruzi naturally infects a wide variety of wild and domesticated mammals, in addition to humans. Depending on the infection dose and other factors, the acute infection can be life-threatening, and in all cases, the risk of chagasic heart disease is high in persistently infected hosts. Domestic, working, and semi-feral dogs in the Americas are at significant risk of T. cruzi infection and in certain settings in the southern United States, the risk of new infections can exceed 30% per year, even with the use of vector control protocols. In this study, we explored whether intermittent low-dose treatment with the trypanocidal compound benznidazole (BNZ) during the transmission season, could alter the number of new infections in dogs in an area of known, intense transmission pressure. Preliminary studies in mice suggested that twice-weekly administration of BNZ could prevent or truncate infections when parasites were delivered at the mid-point between BNZ doses. Pre-transmission season screening of 126 dogs identified 53 dogs (42.1%) as T. cruzi infection positive, based upon blood PCR and Luminex-based serology. Serial monitoring of the 67 uninfected dogs during the high transmission season (May to October) revealed 15 (22.4%) new infections, 6 in the untreated control group and 9 in the group receiving BNZ prophylaxis, indicating no impact of this prophylaxis regimen on the incidence of new infections. Although these studies suggest that rigorously timed and more potent dosing regimen may be needed to achieve an immediate benefit of prophylaxis, additional studies would be needed to determine if drug prophylaxis reduced disease severity despite this failure to prevent new infections.
Juan M Bustamante, Angel M Padilla, Brooke White, Lisa D Auckland, Rachel E Busselman, Stephanie Collins, Elizabeth L Malcolm, Briana F Wilson, Ashley B Saunders, Sarah A Hamer, Rick L Tarleton. PLoS Negl Trop Dis. 2022 Oct 31;16(10):e0010688. doi: 10.1371/journal.pntd.0010688.
The skeletal muscle of a mouse infected with Trypanosoma cruzi is shown under a microscope. (Submitted by Fernando Sanchez)
The condition affects tens of millions across the Americas but lacks effective treatments
Researchers from the University of Georgia have discovered a potential treatment for Chagas disease, marking the first medication with promise to successfully and safely target the parasitic infection in more than 50 years.
Human clinical trials of the drug, an antiparasitic compound known as AN15368, will hopefully begin in the next few years.
Distinguished Research Professor Dr. Rick Tarleton of the Center for Tropical and Emerging Global Diseases at the Paul D. Coverdell Center for Biomedical and Health Sciences on Thursday, May 8, 2008. Dr. Tarleton is researching the effects of drug treatments on Chagas’ disease.
“I’m very optimistic,” said Rick Tarleton, corresponding author of the study and a UGA Athletic Association Distinguished Professor in the Franklin College of Arts and Sciences and member of the Center for Tropical and Emerging Global Diseases. “I think it has a really strong chance of being a real solution, not just a stand-in for something that works better than the drugs we currently have.”
The new drug works by targeting the parasite that causes the disease, Trypanosoma cruzi, also known as T. cruzi.
Nearly all people infected with the parasite experience flu-like symptoms such as fever, headaches and vomiting. However, after their immune response kicks in, their symptoms may subside.
But for 30% to 40% of patients, the infection can result in severe heart damage that can be both debilitating and life-threatening.
New drug is 100% effective in eliminating T. cruzi
Published in Nature Microbiology, the study found the new medication was 100% effective in curing mice, as well as non-human primates that were naturally infected by the parasite at a research facility in Texas. The animals also experienced no significant side effects from exposure to the drug.
Over the past several decades, previous treatment candidates went straight from experimental infections in mice to human clinical trials, where they failed to cure the infection. The new drug’s efficacy in non-human primates bodes well for how it will perform in humans.
“We’ve got something that is as close to effective as it can be in what is as close to a human as it could be, and there aren’t any side effects. That really de-risks it by a lot going into humans,” Tarleton said. “It doesn’t make it fail-safe, but it moves it much further along.”
Current medications to treat T. cruzi infection not ideal
T. cruzi is carried by blood-sucking insects known as kissing bugs. The insects can be found throughout North, Central and South America.
In addition to a nasty bite, the creatures carry the T. cruzi parasite, which is transmitted through their fecal matter. Victims can become infected when they unknowingly rub the insect’s feces into their eyes, nose or an open wound.
The infection may also be transmitted through organ transplants, from a pregnant person to their fetus or through contaminated food. However, infections from these pathways are less common.
The go-to medications used to treat Chagas aren’t terrible, Tarleton said, but they’re not ideal. They can pack some serious side effects and they’re not reliably effective, but they’re currently the only treatment option.
Patients also have to take the drugs for two months. And even the common but mild side effects like headache or nausea get old after a few weeks. As a result, about one in five people being treated for the disease stop taking their medications before they have a chance to cure the infection.
“Plus they have variable efficacy, and it’s not predictable,” Tarleton said. “I think most physicians in Latin America have to say, ‘We have a drug. It’s going to make you feel bad, and two months later after we finish it, we’re not really going to be able to tell you if it worked or not.’
“It’s really not a good inducement to take the medication.”
Chagas disease common in Latin American countries
Tens of millions of people across the Americas are infected with the parasite that causes Chagas disease. But it doesn’t get much media attention.
It’s most common in Latin American countries, particularly in low-income areas where housing isn’t ideal. Some of the countries with the highest rates of the disease include Bolivia, Venezuela, Argentina, Chile, Mexico and Brazil.
In homes with thatched roofs, mud walls or inadequate protection from the elements, kissing bugs thrive, making infection more likely.
Chagas disease poses significant risk to pets
The Centers for Disease Control and Prevention estimates around 300,000 people infected with the parasite currently live in the U.S. But because the condition isn’t a huge threat in places with good housing options, Chagas disease treatment and prevention doesn’t get much research funding.
There is growing concern about the T. cruzi infection rate among outdoor pets in the U.S., however. Working dogs and other pets that spend extended periods of time outside are contracting the parasite at an alarming rate.
“There are areas where the infection rates are 20% to 30% new infections per year,” Tarleton said. “Those tend to be severe infections where the dogs either die or develop a disease that makes them unable to work.”
Tarleton hopes to partner with veterinary pharmaceutical companies in the future to create a drug to treat the infection in pets as a means of funding diagnostics and medication purchases in Latin America.
For the present study, Tarleton partnered with colleagues at Anacor Pharmaceuticals, Texas A&M University, the University of Texas, the University of Kansas and Pfizer. Angel Padilla, Wei Wang, Dylan Orr, Brooke White, Arlene George and Huifeng Shen from UGA’s Center for Tropical and Emerging Global Diseases and the Department of Cellular Biology are co-authors on the paper.
Rick Tarleton and colleagues recently published their new study, “Discovery of an orally active benzoxaborole prodrug effective in the treatment of Chagas disease in non-human primates” in Nature Microbiology. Check out these news stories about the study.
Behind the paper: New Hope for Treatment of a Very Neglected, Neglected Tropical Disease (Nature Microbiology)
Possible new treatment identified for neglected tropical disease (Science.org)
Researchers discover potential treatment for Chagas disease (Mirage News)
Researchers discover potential treatment for Chagas disease (Science Daily)
Researchers discover potential treatment for Chagas disease (Medical Xpress)
Chagas disease potential treatment: ‘I think it has a really strong chance of being a real solution’ (Outbreak News Today)
Promising New Drug May Effectively Treat Chagas Disease (Technology Networks)
Researchers discover potential treatment for Chagas disease (Newswise)
Trypanosoma cruzi, the agent of Chagas disease, probably infects tens of millions of people, primarily in Latin America, causing morbidity and mortality. The options for treatment and prevention of Chagas disease are limited and underutilized. Here we describe the discovery of a series of benzoxaborole compounds with nanomolar activity against extra- and intracellular stages of T. cruzi. Leveraging both ongoing drug discovery efforts in related kinetoplastids, and the exceptional models for rapid drug screening and optimization in T. cruzi, we have identified the prodrug AN15368 that is activated by parasite carboxypeptidases to yield a compound that targets the messenger RNA processing pathway in T. cruzi. AN15368 was found to be active in vitro and in vivo against a range of genetically distinct T. cruzi lineages and was uniformly curative in non-human primates (NHPs) with long-term naturally acquired infections. Treatment in NHPs also revealed no detectable acute toxicity or long-term health or reproductive impact. Thus, AN15368 is an extensively validated and apparently safe, clinically ready candidate with promising potential for prevention and treatment of Chagas disease.
Angel M. Padilla, Wei Wang, Tsutomu Akama, David S. Carter, Eric Easom, Yvonne Freund, Jason S. Halladay, Yang Liu, Sarah A. Hamer, Carolyn L. Hodo, Gregory K. Wilkerson, Dylan Orr, Brooke White, Arlene George, Huifeng Shen, Yiru Jin, Michael Zhuo Wang, Susanna Tse, Robert T. Jacobs & Rick L. Tarleton. Nat Microbiol (2022). https://doi.org/10.1038/s41564-022-01211-y
Chagas disease is a neglected pathology that affects millions of people worldwide, mainly in Latin America. The Chagas disease agent, Trypanosoma cruzi(T. cruzi), is an obligate intracellular parasite with a diverse biology that infects several mammalian species, including humans, causing cardiac and digestive pathologies. Reliable detection of T. cruzi in vivo infections has long been needed to understand Chagas disease’s complex biology and accurately evaluate the outcome of treatment regimens. The current protocol demonstrates an integrated pipeline for automated quantification of T. cruzi-infected cells in 3D-reconstructed, cleared organs. Light-sheet fluorescent microscopy allows for accurately visualizing and quantifying of actively proliferating and dormant T. cruzi parasites and immune effector cells in whole organs or tissues. Also, the CUBIC-HistoVision pipeline to obtain uniform labeling of cleared organs with antibodies and nuclear stains was successfully adopted. Tissue clearing coupled with 3D immunostaining provides an unbiased approach to comprehensively evaluate drug treatment protocols, improve the understanding of the cellular organization of T. cruzi-infected tissues, and is expected to advance discoveries related to anti-T. cruzi immune responses, tissue damage, and repair in Chagas disease.
Fernando Sanchez-Valdez, Ángel M Padilla, Juan M Bustamante, Caleb W D Hawkins, Rick L Tarleton. J Vis Exp. 2022 Jun 23;(184). doi: 10.3791/63919.
Background: Antibodies against SARS-CoV-2 can be detected by various testing platforms, but a detailed understanding of assay performance is critical. Methods: We developed and validated a simple enzyme-linked immunosorbent assay (ELISA) to detect IgG binding to the receptor-binding domain (RBD) of SARS-CoV-2, which was then applied for surveillance. ELISA results were compared to a set of complimentary serologic assays using a large panel of clinical research samples. Results: The RBD ELISA exhibited robust performance in ROC curve analysis (AUC> 0.99; Se=89%, Sp=99.3%). Antibodies were detected in 23/353 (6.5%) healthcare workers, 6/9 RT-PCR-confirmed mild COVID-19 cases, and 0/30 non-COVID-19 cases from an ambulatory site. RBD ELISA showed a positive correlation with neutralizing activity (p = <0.0001, R2 = 0.26). Conclusions: We applied a validated SARS-CoV-2-specific IgG ELISA in multiple contexts and performed orthogonal testing on samples. This study demonstrates the utility of a simple serologic assay for detecting prior SARS-CoV-2 infection, particularly as a tool for efficiently testing large numbers of samples as in population surveillance. Our work also highlights that precise understanding of SARS-CoV-2 infection and immunity at the individual level, particularly with wide availability of vaccination, may be improved by orthogonal testing and/or more complex assays such as multiplex bead assays.
Amy C. Sherman, Teresa Smith, Yerun Zhu, Kaitlin Taibl, Jessica Howard-Anderson, Taylor Landay, Nora Pisanic, Jennifer Kleinhenz, Trevor W. Simon, Daniel Espinoza, Skyler Hammond, Nadine Rouphael, Huifeng Shen, Jessica K. Fairley, Jaime A. Cardona-Ospina, Alfonso J. Rodriguez-Morales, Lakshmanane Premkumar, Jens Wrammert, Rick Tarleton, Scott Fridkin, Christopher D. Heaney, Erin M. Scherer and Matthew H. Collins. Frontiers in Public Health, Oct. 2021, doi: 10.3389/fpubh.2021.744535
In chronic Chagas disease, Trypanosoma cruzi-specific T-cell function decreases over time, and alterations in the homeostatic IL-7/IL-7R axis are evident, consistent with a process of immune exhaustion. IL-27 is an important immunoregulatory cytokine that shares T-cell signaling with IL-7 and other cytokines of the IL-12 family and might be involved in the transcriptional regulation of T-cell function. Here, we evaluated the expression and function of IL-27R in antigen-experienced T cells from subjects with chronic Chagas disease and assessed whether in vitro treatment with IL-27 and IL-7 might improve T. cruzi-specific polyfunctional T-cell responses. In vitro exposure of PBMCs to T. cruzi induced a downregulation of IL-27R in CD4+ T cells and an upregulation in CD8+ T cells in subjects without heart disease, while IL-27R expression remained unaltered in subjects with more severe clinical stages. The modulation of IL-27R was associated with functional signaling through STAT3 and STAT5 and induction of the downstream genes TBX21, EOMES and CXCL9 in response to IL-27. In vitro treatment of PBMCs with IL-27 and IL-7 improved monofunctional and polyfunctional Th1 responses, accompanied by the induction of IL-10 and Bcl-2 expression in subjects without heart disease but did not improve those in subjects with cardiomyopathy. Our findings support the process of desensitization of the IL-27/IL-27R pathway along with disease severity and that the pro-inflammatory and immunomodulatory mechanisms of IL-27 might be interconnected.
María Ailén Natale, Todd Minning, María Cecilia Albareda, Melisa Daiana Castro Eiro, María Gabriela Álvarez, Bruno Lococo, Gonzalo Cesar, Graciela Bertocchi, María Josefina Elias, María Belén Caputo, Rick Lee Tarleton, Susana Adriana Laucella. PLoS Negl Trop Dis. 2021 Jun 1;15(6):e0009473. doi: 10.1371/journal.pntd.0009473.
Trypanosoma cruzi, the causative agent of human Chagas disease, is endemic to the southern region of the United States where it routinely infects many host species. The indoor/outdoor housing configuration used in many non-human primate research and breeding facilities in the southern of the USA provides the opportunity for infection by T. cruzi and thus provides source material for in-depth investigation of host and parasite dynamics in a natural host species under highly controlled and restricted conditions. For cynomolgus macaques housed at such a facility, we used a combination of serial blood quantitative PCR (qPCR) and hemoculture to confirm infection in >92% of seropositive animals, although each method alone failed to detect infection in >20% of cases. Parasite isolates obtained from 43 of the 64 seropositive macaques were of 2 broad genetic types (discrete typing units, (DTU’s) I and IV); both within and between these DTU groupings, isolates displayed a wide variation in growth characteristics and virulence, elicited host immune responses, and susceptibility to drug treatment in a mouse model. Likewise, the macaques displayed a diversity in T cell and antibody response profiles that rarely correlated with parasite DTU type, minimum length of infection, or age of the primate. This study reveals the complexity of infection dynamics, parasite phenotypes, and immune response patterns that can occur in a primate group, despite being housed in a uniform environment at a single location, and the limited time period over which the T. cruzi infections were established.
Padilla AM, Yao PY, Landry TJ, Cooley GM, Mahaney SM, Ribeiro I, VandeBerg JL. Tarleton RL. (2021) High variation in immune responses and parasite phenotypes in naturally acquired Trypanosoma cruzi infection in a captive non-human primate breeding colony in Texas, USA. PLoS Negl Trop Dis 15(3): e0009141. https://doi.org/10.1371/journal.pntd.0009141
Background: Interruption of benznidazole therapy due to the appearance of adverse effects, which is presumed to lead to treatment failure, is a major drawback in the treatment of chronic Chagas disease.
Methods: Trypanosoma cruzi-specific humoral and T cell responses, T cell phenotype and parasite load were measured to compare the outcome in 33 subjects with chronic Chagas disease treated with an incomplete benznidazole regimen and 58 subjects treated with the complete regimen, during a median follow-up period of 48 months.
Results: Both treatment regimens induced a reduction in the T. cruzi-specific antibody levels and similar rates of treatment failure when evaluated using quantitative PCR. Regardless of the regimen, polyfunctional CD4+ T cells increased in the subjects, with successful treatment outcome defined as a decrease of T. cruzi-specific antibodies. Regardless of the serological outcome, naive and central memory T cells increased after both regimens. A decrease in CD4+ HLA-DR+ T cells was associated with successful treatment in both regimens. The cytokine profiles of subjects with successful treatment showed fewer inflammatory mediators than those of the untreated T. cruzi-infected subjects. High levels of T cells expressing IL-7 receptor and low levels of CD8+ T cells expressing the programmed cell death protein 1 at baseline were associated with successful treatment following benznidazole interruption.
Conclusions: These findings challenge the notion that treatment failure is the sole potential outcome of an incomplete benznidazole regimen and support the need for further assessment of the treatment protocols for chronic Chagas disease.
Melisa D Castro Eiro, María A Natale, María G Alvarez, Huifeng Shen, Rodolfo Viotti, Bruno Lococo, Jacqueline Bua, Myriam Nuñez, Graciela L Bertocchi, María C Albareda, Gonzalo Cesar, Rick L Tarleton, Susana A Laucella. J Antimicrob Chemother. 2021 Mar 7;dkab054. doi: 10.1093/jac/dkab054
