Center for Tropical and Emerging Global Diseases
University of Georgia
Dennis Kyle is the Director of CTEGD and the GRA Eminent Scholar in Antiparasitic Drug Discovery in the Departments of Cellular Biology and Infectious Diseases.
Brain-eating amoeba: Will the warming climate bring more cases? (MSN)
The increase in research funding for the development of antimalarials since 2000 has led to a surge of new chemotypes with potent antimalarial activity. High-throughput screens have delivered several thousand new active compounds in several hundred series, including the 4,7-diphenyl-1,4,5,6,7,8-hexahydroquinolines, hereafter termed dihydropyridines (DHPs). We optimized the DHPs for antimalarial activity. Structure-activity relationship studies focusing on the 2-, 3-, 4-, 6-, and 7-positions of the DHP core led to the identification of compounds potent (EC50 < 10 nM) against all strains of P. falciparum tested, including the drug-resistant parasite strains K1, W2, and TM90-C2B. Evaluation of efficacy of several compounds in vivo identified two compounds that reduced parasitemia by >75 % in mice 6 days post-exposure following a single 50 mg/kg oral dose. Resistance acquisition experiments with a selected dihydropyridine led to the identification of a single mutation conveying resistance in the gene encoding for Plasmodium falciparum multi-drug resistance protein 1 (PfMDR1). The same dihydropyridine possessed transmission blocking activity. The DHPs have the potential for the development of novel antimalarial drug candidates.
Kurt S Van Horn, Yingzhao Zhao, Prakash T Parvatkar, Julie Maier, Tina Mutka, Alexis Lacrue, Fabian Brockmeier, Daniel Ebert, Wesley Wu, Debora R Casandra, Niranjan Namelikonda, Jeanine Yacoub, Martina Sigal, Spencer Knapp, David Floyd, David Waterson, Jeremy N Burrows, James Duffy, Joseph L DeRisi, Dennis E Kyle, R Kiplin Guy, Roman Manetsch. Eur J Med Chem. 2024 Jun 18:275:116599. doi: 10.1016/j.ejmech.2024.116599.
Radical cure of Plasmodium vivax malaria must include elimination of quiescent ‘hypnozoite’ forms in the liver; however, the only FDA-approved treatments are contraindicated in many vulnerable populations. To identify new drugs and drug targets for hypnozoites, we screened the Repurposing, Focused Rescue, and Accelerated Medchem (ReFRAME) library and a collection of epigenetic inhibitors against P. vivax liver stages. From both libraries, we identified inhibitors targeting epigenetics pathways as selectively active against P. vivax and P. cynomolgi hypnozoites. These include DNA methyltransferase (DNMT) inhibitors as well as several inhibitors targeting histone post-translational modifications. Immunofluorescence staining of Plasmodium liver forms showed strong nuclear 5-methylcystosine signal, indicating liver stage parasite DNA is methylated. Using bisulfite sequencing, we mapped genomic DNA methylation in sporozoites, revealing DNA methylation signals in most coding genes. We also demonstrated that methylation level in proximal promoter regions as well as in the first exon of the genes may affect, at least partially, gene expression in P. vivax. The importance of selective inhibitors targeting epigenetic features on hypnozoites was validated using MMV019721, an acetyl-CoA synthetase inhibitor that affects histone acetylation and was previously reported as active against P. falciparum blood stages. In summary, our data indicate that several epigenetic mechanisms are likely modulating hypnozoite formation or persistence and provide an avenue for the discovery and development of improved radical cure antimalarials.
S. P. Maher, M. A. Bakowski, A. Vantaux, E. L. Flannery, C. Andolina, M. Gupta, Y. Antonova-Koch, M. Argomaniz, M. Cabrera-Mora, B. Campo, A. T. Chao, A. K. Chatterjee, W. T. Cheng, E. Chuenchob, C. A. Cooper, K. Cottier, M. R. Galinski, A. Harupa-Chung, H. Ji, S. B. Joseph, T. Lenz, S. Lonardi, J. Matheson, S. A. Mikolajczak, T. Moeller, A. Orban, V. Padín-Irizarry, K. Pan, J. Péneau, J. Prudhomme, C. Roesch, A. A. Ruberto, S. S. Sabnis, C. L. Saney, J. Sattabongkot, S. Sereshki, S. Suriyakan, R. Ubalee, Y. Wang, P. Wasisakun, J. Yin, J. Popovici, C. W. McNamara, C. J. Joyner, F. Nosten, B. Witkowski, K. G. Le Roch, D. E. Kyle. 2024. eLife13:RP98221, https://doi.org/10.7554/eLife.98221.1
Background: Like other oviparous organisms, the gonotrophic cycle of mosquitoes is not complete until they have selected a suitable habitat to oviposit. In addition to the evolutionary constraints associated with selective oviposition behavior, the physiological demands relative to an organism’s oviposition status also influence their nutrient requirement from the environment. Yet, studies that measure transmission potential (vectorial capacity or competence) of mosquito-borne parasites rarely consider whether the rates of parasite replication and development could be influenced by these constraints resulting from whether mosquitoes have completed their gonotrophic cycle.
Methods: Anopheles stephensi mosquitoes were infected with Plasmodium berghei, the rodent analog of human malaria, and maintained on 1% or 10% dextrose and either provided oviposition sites (‘oviposited’ herein) to complete their gonotrophic cycle or forced to retain eggs (‘non-oviposited’). Transmission potential in the four groups was measured up to 27 days post-infection as the rates of (i) sporozoite appearance in the salivary glands (‘extrinsic incubation period’ or EIP), (ii) vector survival and (iii) sporozoite densities.
Results: In the two groups of oviposited mosquitoes, rates of sporozoite appearance and densities in the salivary glands were clearly dependent on sugar availability, with shorter EIP and higher sporozoite densities in mosquitoes fed 10% dextrose. In contrast, rates of appearance and densities in the salivary glands were independent of sugar concentrations in non-oviposited mosquitoes, although both measures were slightly lower than in oviposited mosquitoes fed 10% dextrose. Vector survival was higher in non-oviposited mosquitoes.
Conclusions: Costs to parasite fitness and vector survival were buffered against changes in nutritional availability from the environment in non-oviposited but not oviposited mosquitoes. Taken together, these results suggest vectorial capacity for malaria parasites may be dependent on nutrient availability and oviposition/gonotrophic status and, as such, argue for more careful consideration of this interaction when estimating transmission potential. More broadly, the complex patterns resulting from physiological (nutrition) and evolutionary (egg-retention) trade-offs described here, combined with the ubiquity of selective oviposition behavior, implies the fitness of vector-borne pathogens could be shaped by selection for these traits, with implications for disease transmission and management. For instance, while reducing availability of oviposition sites and environmental sources of nutrition are key components of integrated vector management strategies, their abundance and distribution are under strong selection pressure from the patterns associated with climate change.
Justine C Shiau, Nathan Garcia-Diaz, Dennis E Kyle, Ashutosh K Pathak. Parasit Vectors. 2024 May 23;17(1):236. doi: 10.1186/s13071-024-06317-2.
Testing Plasmodium vivax antimicrobial sensitivity is limited to ex vivo schizont maturation assays, which preclude determining the IC50s of delayed action antimalarials such as doxycycline. Using Plasmodium cynomolgi as a model for P. vivax, we determined the physiologically significant delayed death effect induced by doxycycline [IC50(96 h), 1,401 ± 607 nM]. As expected, IC50(96 h) to chloroquine (20.4 nM), piperaquine (12.6 µM), and tafenoquine (1,424 nM) were not affected by extended exposure.
Peter Christensen, Rosy Cinzah, Rossarin Suwanarusk, Adeline Chiew Yen Chua, Osamu Kaneko, Dennis E Kyle, Htin Lin Aung, Jessica Matheson, Pablo Bifani, Laurent Rénia, Gregory M Cook, Georges Snounou, Bruce Russell. Antimicrob Agents Chemother. 2024 Apr 8:e0028024. doi: 10.1128/aac.00280-24.
Jessica Kissinger and Dennis Kyle received the Lamar Dodd Creative Research Award during UGA’s Honors Week. The award recognizes established investigators whose overall scholarly body of work has had a major impact on the field of study and has established the investigator’s international reputation as a leader in the field.
Jessica Kissinger, Distinguished Research Professor in the Franklin College of Arts and Sciences’ genetics department and former director of the UGA Institute of Bioinformatics, has focused her interdisciplinary career on the question of how parasites evolve. She has been a driving force behind the groundbreaking effort to create and maintain novel bioinformatics databases covering omics data for hundreds of dangerous pathogens. The Eukaryotic Pathogen, Vector, and Host Informatics Resources knowledgebase (VEuPathDB.org) is an integrated, centralized resource for data mining on more than 500 organisms. Databases searches are free, permitting researchers to gain insights into and test hypotheses that may pave the way for new approaches to treating or preventing diseases such as malaria and Cryptosporidium (a waterborne parasite). Kissinger has used the databases and other bioinformatics tools to make remarkable discoveries.
Dennis E. Kyle, professor of cellular biology and infectious diseases in the Franklin College of Arts and Sciences and the College of Veterinary Medicine, is one of the top parasitologists in the world. Kyle serves as director of the Center for Tropical and Emerging Global Diseases, and some of his most recent work focuses on discovery of new drugs that eliminate dormant vivax malaria that can linger in the liver. His group has discovered new drug series that target the dormant liver stages and is moving these novel therapeutics through preclinical studies. He also works on Naegleria fowleri, a rare but deadly parasite known as “brain-eating amoebae.” More than 97% of people infected with these amoebae die within two weeks. Kyle has conducted research into that pathogen, leading to effective repurposed drugs and the first rapid, sensitive diagnostic method.
First appeared in 2024 Research Awards
Trichothecenes (TCNs) are a large group of tricyclic sesquiterpenoid mycotoxins that have intriguing structural features and remarkable biological activities. Herein, we focused on three TCNs (anguidine, verrucarin A, and verrucarol) and their ability to target both the blood and liver stages of Plasmodium species, the parasite responsible for malaria. Anguidine and verrucarin A were found to be highly effective against the blood and liver stages of malaria, while verrucarol had no effect at the highest concentration tested. However, these compounds were also found to be cytotoxic and, thus, not selective, making them unsuitable for drug development. Nonetheless, they could be useful as chemical probes for protein synthesis inhibitors due to their direct impact on parasite synthesis processes.
Prakash T Parvatkar, Steven P Maher, Yingzhao Zhao, Caitlin A Cooper, Sagan T de Castro, Julie Péneau, Amélie Vantaux, Benoît Witkowski, Dennis E Kyle, Roman Manetsch. J Nat Prod. 2024 Jan 23. doi: 10.1021/acs.jnatprod.3c01019.
Director Dennis Kyle was interviewed about CTEGD and his research as part of Georgia Trend’s feature article “Moving Innovation Beyond the Walls”. Read the article now.
Ingestion of an additional blood meal(s) by a hematophagic insect can accelerate development of several vector-borne parasites and pathogens. Most studies, however, offer blood from the same vertebrate host species as the original challenge (for e.g., human for primary and additional blood meals). Here, we show a second blood meal from bovine and canine hosts can also enhance sporozoite migration in Anopheles stephensi mosquitoes infected with the human- and rodent-restricted Plasmodium falciparum and P. berghei, respectively. The extrinsic incubation period (time to sporozoite appearance in salivary glands) showed more consistent reductions with blood from human and bovine donors than canine blood, although the latter’s effect may be confounded by the toxicity, albeit non-specific, associated with the anticoagulant used to collect whole blood from donors. The complex patterns of enhancement highlight the limitations of a laboratory system but are nonetheless reminiscent of parasite host-specificity and mosquito adaptations, and the genetic predisposition of An. stephensi for bovine blood. We suggest that in natural settings, a blood meal from any vertebrate host could accentuate the risk of human infections by P. falciparum: targeting vectors that also feed on animals, via endectocides for instance, may reduce the number of malaria-infected mosquitoes and thus directly lower residual transmission. Since endectocides also benefit animal health, our results underscore the utility of the One Health framework, which postulates that human health and well-being is interconnected with that of animals. We posit this framework will be further validated if our observations also apply to other vector-borne diseases which together are responsible for some of the highest rates of morbidity and mortality in socio-economically disadvantaged populations.
Ashutosh K Pathak, Justine C Shiau, Rafael C S Freitas, Dennis E Kyle. One Health. 2023 Jun 9:17:100582. doi: 10.1016/j.onehlt.2023.100582. eCollection 2023 Dec.
My name is Victoria Mendiola and I am a PhD candidate in Dennis Kyle’s lab studying drug-induced dormancy in Plasmodium falciparum, the parasite responsible for malaria. I have been at UGA for four years but originally received my BSc in Biology and MSc of Integrative Biology from Kennesaw State University in Kennesaw, GA.
My interest in infectious diseases stems from an NSF REU research internship where I was first introduced to the complexities of parasite-host interactions on an organismal level by studying hookworm infections in South American fur seals (SAFS) in the Gottdenker Lab at UGA’s College of Veterinary Medicine.
During my REU, I fell in love with Athens and the scientific community in the area but the large number of tropical disease parasitologists solidified my reason for choosing UGA to continue my studies.
My doctoral research focuses on developing novel high-content imaging assays to incorporate Artemisinin-induced dormant Plasmodium falciparum recovery into the current understanding of drug treatment, therapeutics, and prevention. Of the species of Plasmodium that infect humans, P. falciparum is the deadliest and, unfortunately, is becoming resistant to current treatment options.
In August 2023, I received the CTEGD Training in Tropical and Emerging Global Diseases fellowship. In addition to providing up to two years of funding, there is also the opportunity for a capstone experience. I plan to use the capstone project opportunity to gain essential in-field, on-site training to complement my current wet lab skillset.
My long-term career goal is to utilize my diverse training in physiology, developmental biology, cellular biology, and infectious diseases to design, optimize, and implement phenotypic and behavioral assays in the context of drug discovery and parasite homeostasis.
For students who are interested in joining the Center for Tropical and Emerging Global Diseases, I suggest they take every opportunity to talk to other researchers in and out of their field and organism of study. The sense of community within the CTEGD is unparalleled and should be utilized at every given opportunity. The friends I have made in and outside of the lab is one of my favorite things about being here at UGA (but the local festivals are really fun too).
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