Rick Tarleton Archives - Page 3 of 4 - Center for Tropical and Emerging Global Diseases

Strain-specific genome evolution in Trypanosoma cruzi, the agent of Chagas disease

Donna Huber on January 28, 2021

The protozoan Trypanosoma cruzi almost invariably establishes life-long infections in humans and other mammals, despite the development of potent host immune responses that constrain parasite numbers. The consistent, decades-long persistence of T. cruzi in human hosts arises at least in part from the remarkable level of genetic diversity in multiple families of genes encoding the primary target antigens of anti-parasite immune responses. However, the highly repetitive nature of the genome-largely a result of these same extensive families of genes-have prevented a full understanding of the extent of gene diversity and its maintenance in T. cruzi. In this study, we have combined long-read sequencing and proximity ligation mapping to generate very high-quality assemblies of two T. cruzi strains representing the apparent ancestral lineages of the species. These assemblies reveal not only the full repertoire of the members of large gene families in the two strains, demonstrating extreme diversity within and between isolates, but also provide evidence of the processes that generate and maintain that diversity, including extensive gene amplification, dispersion of copies throughout the genome and diversification via recombination and in situ mutations. Gene amplification events also yield significant copy number variations in a substantial number of genes presumably not required for or involved in immune evasion, thus forming a second level of strain-dependent variation in this species. The extreme genome flexibility evident in T. cruzi also appears to create unique challenges with respect to preserving core genome functions and gene expression that sets this species apart from related kinetoplastids.

Wang W, Peng D, Baptista RP, Li Y, Kissinger JC, Tarleton RL (2021) Strain-specific genome evolution in Trypanosoma cruzi, the agent of Chagas disease. PLoS Pathog 17(1): e1009254. https://doi.org/10.1371/journal.ppat.1009254

Rick Tarleton elected AAAS Fellow

Donna Huber on November 30, 2020

University of Georgia researcher Rick Tarleton has been elected as a 2020 American Association for the Advancement of Science (AAAS) Fellow by the AAAS Council “for distinguished contributions to the field of biological sciences, particularly for his research contributions and leadership to control Chagas Disease.”

Tarleton is a Regents Professor in the Department of Cellular Biology and UGA Athletic Association Distinguished Professor in Biological Sciences.

“It is indeed an honor to be acknowledged in this way – it reflects the strong efforts of many past and present members of the lab,” stated Tarleton, founder of the Center for Tropical and Emerging Global Diseases.

Since his undergraduate days, Tarleton’s research has focused on Trypanosoma cruzi infection, which causes the potentially fatal illness Chagas Disease. Historically, Tarleton’s research has attempted to answer broad questions such as how is immune control initiated and maintained during the infection, how does T. cruzi manage to avoid immune clearance and maintain an infection of decades in host, and what is the relationship between immunity, parasite persistence, and disease development. In an effort to answer these questions and more, Tarleton’s research group has developed tools to better study T. cruzi. They pioneered the use of the gene editing tool CRISPR in T. cruzi. Recently, they applied light sheet fluorescent microscopy to view infection in whole mouse organs. The Tarleton Research Group is also actively pursuing drug discovery for T. cruzi infection in a number of animal models including rodent, dog, and nonhuman primates. Their recent discovery of a dormancy stage in T. cruzi infections has revolutionized their drug treatment research, bringing them one step closer to finding a cure for this infection that affects at least 6 million people.

Tarleton’s work has largely been funded by the National Institutes of Health, the Wellcome Trust, the Burroughs Wellcome Fund, and partnerships with several pharmaceutical groups.

In addition to establishing the Center for Tropical and Emerging Global Diseases at UGA, he has been instrumental in organizing the Chagas Drug Discovery Consortium, which brings together U.S.-based laboratories with international groups. Tarleton is also the founder and current president of The Chagas Disease Foundation. He has been honored with a number of awards, including the Lamar Dodd Outstanding Researcher Award and being named a Burroughs Wellcome Fund Scholar in Molecular Parasitology. In 2017, he was elected as a Fellow of the American Academy of Microbiology.

“Rick’s election as a Fellow of AAAS is recognition of his immense contributions to the study of T. cruzi,” said Dennis Kyle, director of the Center for Tropical and Emerging Global Diseases. “His research has advanced our understanding of immune response to the pathogen, has developed new molecular approaches to study the parasite, and has accelerated drug discovery for Chagas Disease.”

Stronger, less frequent treatments could cure Chagas disease [video]

Donna Huber on November 17, 2020

Video by UGA Research Communications

Outbreak News Today Interviews Rick Tarleton

Donna Huber on November 9, 2020

Recently, Dr. Rick Tarleton was interviewed by Outbreak News Today about his recently published study in Science Translational Medicine.

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Stronger treatments could cure Chagas disease

Donna Huber on October 30, 2020

Research shows stronger but less frequent drug doses could be key

Researchers in the University of Georgia’s Center for Tropical and Emerging Global Diseases have found that a more intensive, less frequent drug regimen with currently available therapeutics could cure the infection that causes Chagas disease, a potentially life-threatening illness affecting up to 300,000 people in the United States.

Trypanosoma cruzi is a single-celled parasitic organism that causes Chagas disease. At least 6 million people are infected by T. cruzi, mostly in South America. Current drug therapies have been ineffective in completely clearing the infection and are associated with severe adverse side effects.

A single dose of benznidazole has been shown to be highly effective in killing more than 90% of parasites. However, after a CTEGD team found some of the parasites enter into a dormancy stage, the researchers hypothesized that an intermittent treatment schedule could be effective.

Photo credit: Peter Frey/UGA

“Current human trials are only looking at giving lower doses over a shorter time period, which is the exact opposite of what we show works.” — Rick Tarleton

“In this system we can see what a single dose of drug does,” said Rick Tarleton, Regents’ Professor in UGA’s department of cellular biology. “Does it make sense to give a drug twice daily when the remaining dormant parasites are insensitive to it?”

The investigators found that giving as little as two-and-a-half times the typical daily dose of benznidazole, once per week for 30 weeks, completely cleared the infection, whereas giving the standard daily dose once a week for a longer period did not.

“Current human trials are only looking at giving lower doses over a shorter time period, which is the exact opposite of what we show works,” said Tarleton.

Since Tarleton’s team worked with a mouse model, how this change in treatment regimen will translate in humans is yet unknown, as are any potential side effects of the higher doses. Adverse reactions already are a problem with current treatments; the hope is that side effects from a less frequent dosage would be more tolerable.

Significant challenge

Assessing the success of treatments in Chagas disease is a significant challenge. Tissue samples from infected organisms might not be representative of the entire organ or animal, since low numbers of persistent, dormant parasites can be difficult to detect. Therefore, Tarleton’s group used light sheet fluorescence microscopy to view intact whole organs from infected mice.

“With light sheet fluorescence microscopy, you have a broad view of potentially any tissue in the mouse that allows for dependable assessment of parasite load and persistence,” said Tarleton. “It gives you an incredible view of the infection.”

Using this technology, they learned something new about the dormant parasites: Some were still susceptible to drug treatment. This provides hope that new drug therapies could be developed to target these parasites.

“Discovery of new drugs should continue,” Tarleton said. “We still need better drugs.”

Co-led by assistant research scientist Juan Bustamante and research professional Fernando Sanchez-Valdez in Tarleton’s research group, the study’s findings appear in Science Translational Medicine.

A modified drug regimen clears active and dormant trypanosomes in mouse models of Chagas disease

Donna Huber on October 28, 2020

A major contributor to treatment failure in Chagas disease, caused by infection with the protozoan parasite Trypanosoma cruzi, is that current treatment regimens do not address the drug insensitivity of transiently dormant T. cruzi amastigotes. Here, we demonstrated that use of a currently available drug in a modified treatment regimen of higher individual doses, given less frequently over an extended treatment period, could consistently extinguish T. cruzi infection in three mouse models of Chagas disease. Once per week administration of benznidazole at a dose 2.5 to 5 times the standard daily dose rapidly eliminated actively replicating parasites and ultimately eradicated the residual, transiently dormant parasite population in mice. This outcome was initially confirmed in “difficult to cure” mouse infection models using immunological, parasitological, and molecular biological approaches and ultimately corroborated by whole organ analysis of optically clarified tissues using light sheet fluorescence microscopy (LSFM). This tool was effective for monitoring pathogen load in intact organs, including detection of individual dormant parasites, and for assessing treatment outcomes. LSFM-based analysis also suggested that dormant amastigotes of T. cruzi may not be fully resistant to trypanocidal compounds such as benznidazole. Collectively, these studies provide important information on the phenomenon of dormancy in T. cruzi infection in mice, demonstrate methods to therapeutically override dormancy using a currently available drug, and provide methods to monitor alternative therapeutic approaches for this, and possibly other, low-density infectious agents.

Juan M. Bustamante, Fernando Sanchez-Valdez, Angel M. Padilla, Brooke White, Wei Wang and Rick L. Tarleton. Science Translational Medicine 28 Oct 2020: Vol. 12, Issue 567, eabb7656. DOI: 10.1126/scitranslmed.abb7656

Cutting Edge: Augmenting Muscle MHC Expression Enhances Systemic Pathogen Control at the Expense of T Cell Exhaustion

Donna Huber on June 26, 2020

Myocytes express low levels of MHC class I (MHC I), perhaps influencing the ability of CD8⁺ T cells to efficiently detect and destroy pathogens that invade muscle. Trypanosoma cruzi infects many cell types but preferentially persists in muscle, and we asked if this tissue-dependent persistence was linked to MHC expression. Inducible enhancement of skeletal muscle MHC I in mice during the first 20 d of T. cruzi infection resulted in enhanced CD8-dependent reduction of parasite load. However, continued overexpression of MHC I beyond 30 d ultimately led to a collapse of systemic parasite control associated with immune exhaustion, which was reversible in part by blocking PD-1:PD-L1 interactions. These studies demonstrate a surprisingly strong and systemically dominant effect of skeletal muscle MHC expression on maintaining T cell function and pathogen control and argue that the normally low MHC I expression in skeletal muscle is host protective by allowing for pathogen control while preventing immune exhaustion.

Angela D. Pack and Rick L. Tarleton. J Immunol. 2020 Jun 26;ji2000218. doi: 10.4049/jimmunol.2000218.

New Scheme of Intermittent Benznidazole Administration in Patients Chronically Infected With Trypanosoma cruzi: Clinical, Parasitological and Serological Assessment After Three Years of Follow-Up

Donna Huber on June 22, 2020

Introduction. In a pilot study, we showed that intermittent administration of benznidazole in chronic Chagas disease patients resulted in a low rate of treatment suspension and therapeutic failure, as assessed by qPCR at the end of treatment. Herein, a three-year post-treatment follow-up study of the same cohort of patients is presented.

Methods. The treatment scheme consisted of 12 doses of benznidazole at 5 mg/kg/day in two daily doses every 5 days. Parasite load, T. cruzi-specific antibodies and serum chemokine levels were measured prior to treatment and after a median follow-up of 36 months post-treatment by kDNA and SatDNA qPCR methods, conventional serological techniques and a Luminex-based assay with recombinant T. cruzi protein, and a cytometric bead array, respectively.

Results. At the end of follow-up, 14 of 17 (82%) patients had negative qPCR findings, whereas three of 17 (18%) had detectable nonquantifiable findings by at least one of the qPCR techniques. A decline in parasite-specific antibodies at 12 months post-treatment was confirmed by conventional serological tests and the Luminex assays. Monocyte chemoattractant protein-1 (MCP-1) levels increased after treatment, whereas monokine induced by gamma interferon (MIG) levels decreased. New post-treatment electrocardiographic abnormalities were observed in only one patient who had cardiomyopathy prior to treatment.

Conclusions. Altogether, these data strengthen our previous findings by showing that the intermittent administration of benznidazole results in a low rate of treatment suspension, with comparable treatment efficacy to that of a daily dose of 5mg/kg for 60 days.

María Gabriela Álvarez, Juan Carlos Ramírez, Graciela Bertocchi, Marisa Fernández, Yolanda Hernández, Bruno Lococo, Constanza Lopez-Albizu, Alejandro Schijman, Carolina Cura, Marcelo Abril, Susana Laucella, Rick L Tarleton, María Ailen Natale, Melisa Castro Eiro, Sergio Sosa-Estani, Rodolfo Viotti. Antimicrob Agents Chemother. 2020 Jun 22;AAC.00439-20. doi: 10.1128/AAC.00439-20.

Chagas Disease Drug Discovery: Multiparametric Lead Optimization against Trypanosoma cruzi in Acylaminobenzothiazole Series

Donna Huber on November 18, 2019

Acylaminobenzothiazole hits were identified as potential inhibitors of Trypanosoma cruzi replication, a parasite responsible for Chagas disease. We selected compound 1 for lead optimization, aiming to improve in parallel its anti-T. cruzi activity (IC₅₀ = 0.63 μM) and its human metabolic stability (human clearance = 9.57 mL/min/g). A total of 39 analogues of 1 were synthesized and tested in vitro. We established a multiparametric structure-activity relationship, allowing optimization of antiparasite activity, physicochemical parameters, and ADME properties. We identified compound 50 as an advanced lead with an improved anti-T. cruzi activity in vitro (IC₅₀ = 0.079 μM) and an enhanced metabolic stability (human clearance = 0.41 mL/min/g) and opportunity for the oral route of administration. After tolerability assessment, 50 demonstrated a promising in vivo efficacy.

Charlotte Fleau, Angel Padilla, Juan Miguel-Siles, Maria T. Quesada-Campos, Isabel Saiz-Nicolas, Ignacio Cotillo, Juan Cantizani Perez, Rick L. Tarleton, Maria Marco, Gilles Courtemanche. J Med Chem. 2019. doi: 10.1021/acs.jmedchem.9b01429.

Visiting Scholar Fellow: Fernando Sanchez-Valdéz

Donna Huber on August 28, 2019

Fellow: Fernando Sanchez Valdez Dr. Fernando Sanchez-Valdéz, from Salta, Argentina, completed a Ph.D. in Molecular Biology at the Faculty of Pharmacy and Biochemistry at the University of Buenos Aires, Argentina in 2014. After his Ph.D., he completed a postdoctoral fellowship in Dr. Rick Tarleton´s laboratory at University of Georgia. In 2018, he obtained a Research Scientist position in the career pathway of the National Research Council in Argentina (CONICET). Earlier this year, he was awarded a fellowship from the CTEGD-Janssen Visiting Scholars Program, which enabled him to return to the Tarleton Research Group.

What is your primary research focus? Why are you interested in this subject?

The main focus of my research has been to uncover the mechanism of drug resistance in the Chagas disease agent, Trypanosoma cruzi. The main question we are trying to answer is why the treatment with highly effective drugs like Benznidazole (the current available treatment for Chagas disease) often fails to cure Chagas disease. By combining ex vivo luminescence assays and tissue-clearing techniques we were able to report, for the first time, the presence of dormant non-replicating amastigotes forms in the chronic phase of the disease. Dormant amastigotes were uniquely resistant to extended drug treatment in vivo and in vitro and could re-establish a flourishing infection after treatment interruption. T. cruzi‘s capacity to become dormant makes them transiently drug-resistant, suggesting that this phenomenon accounts for the failure of the otherwise highly active compounds such Benznidazole (Sanchez-Valdéz, et al eLife 2018).

Why did you choose UGA?

I returned to Athens in February 2019 to continue working on the findings we made during my postdoctoral training in the Tarleton Laboratory. I initially decided to come UGA based on a colleague’s recommendations and the fact that Tarleton´s lab is one of the reference centers for Chagas disease research. It’s a really motivating environment to do science since the scientific and technical level here is really high as well as diverse including areas as immunology, drug discovery, genetic manipulation, genomics, diagnostics, etc. Also the amount of resources available is impressive not only from the lab but also from the Biomedical Microscopy Core, Cytometry Shared Resource Laboratory and the animal facility at UGA.

What has been your research project while at UGA?

Currently, we are expanding our knowledge about T. cruzi dormancy and trying to interfere T. cruzi dormancy using new compounds or the conventional drugs but in a different treatment schedule. One of the approaches we are testing now involves the evaluation of drug doses and treatment schemes able to kill dormant parasites. For this purpose, we are optimizing a robust platform to detect low levels of parasites in whole clarified mice organs using light-sheet fluorescent microscopy. This technique will allow us the specific detection of low levels of persistent dormant parasites.

How has the CTEGD-Janssen Visiting Scholar Fellowship and your time at UGA impacted your research and professional goals?

I am so glad about the opportunity to continue working on T. cruzi dormancy with such experienced and renowned scientists and particularly using state-of-the-art microscopy techniques currently unavailable in South America. This experience will definitely have a positive impact on my career development and probably in the Chagas disease research field.

Tag: Rick Tarleton