Researchers from Harvard Medical School and the University of California, Davis, blocked the progression of cancer growth caused by environmental carcinogens and food contaminants by resolving an eicosanoid/cytokine storm triggered by cell debris.
The research, from the laboratories of physician-researcher Dipak Panigrahy of Harvard Medical School and UC Davis distinguished professor Bruce Hammock, is published in the current edition of the Proceedings of the National Academy of Sciences.
“We advanced the hypothesis that cell debris from chemotherapy, resection of tumors and even immunotherapy can make these therapies a double-edged sword stimulating cancer growth and metastasis while treating it,” said Hammock, who holds a joint appointment in the UC Davis Department of Entomology and Nematology and the UC Davis Comprehensive Cancer Center.
In their paper, “Resolution of Eicosanoid/Cytokine Storm Prevents Carcinogen and Inflammation-Initiated Hepatocellular Cancer Progression,” the scientists covered the potent environmental carcinogen and food contaminant aflatoxin. Aflatoxins are toxins produced by certain fungi that are found in such agricultural crops as corn, peanuts, cottonseed, and nuts.
“Not only is this fungal metabolite genotoxic but it is also a tumor promoter,” said Hammock, defining a genotoxic agent as “a chemical that damages cellular DNA, resulting in mutations or cancer.”
Lead authors Anna Fishbein of Harvard University, a recently enrolled medical student in the Georgetown University School of Medicine, and Weicang Wang, a postdoctoral scholar in the Hammock lab, said aflatoxin exerts some of its cancer-promoting effects by generating cell debris which activate a pathway leading to eicosanoid and cytokine storms. These two classes of natural chemical mediators, they explained, control many of our defenses against pathogens, but when out of control, these storms lead to growth and metastasis of liver cancer.
“We demonstrated that debris generated by aflatoxin B1accelerates tumor dormancy escape in liver cancer models by stimulating a macrophage-derived eicosanoid and cytokine storm of pro-inflammatory mediators,” said Fishbein. “Thus, targeting a single inflammatory mediator or eicosanoid pathway is unlikely to prevent carcinogen-induced tumor progression.”
The researchers showed that the inhibition of the soluble epoxide hydrolase (sEH) pathway or the combined inhibition sEH and cyclooxygenase-2 (COX-2) pathways prevented the carcinogen debris-induced storm of both cytokines and lipid mediators by macrophages--specialized detect-and-destroy cells.
In animal models, the dual COX-2/sEH inhibitor PTUPB prevented the onset of debris-stimulated liver cancer. The dual inhibition of COX-2/sEH pathways may be “a novel approach” to control cancer of the liver, the researchers said.
“We also showed that carcinogen-generated debris stimulates an endoplasmic reticulum (ER) stress response which may promote HCC progression. Importantly, PTUPB prevents the ER stress response,” Wang added. “We created a novel model of debris-stimulated liver cancer designed to study new strategies for the prevention and treatment of carcinogen-induced cancers with tremendous potential to translate to the clinic.”
From a nutritional standpoint, aflatoxin is a common food contaminant, Wang said. “But good agricultural practice and post-harvest technology keep the levels very low. However, in much of the world, aflatoxin levels are so high that many crops are discarded. In other cases, these contaminated grain and nut crops enter the human food chain, where they cause acute toxicity, severe anemia and of course later lead to cancer.”
UC Davis co-author and nutritional scientist Yuxin Wang (who is the wife of Weicang Wang) said that “finding a way to modulate the events that lead to the eicosanoid storm would have a major effect on children's health in many developing countries.”
Fishbein and Allison Gartung of the Panigrahy lab not only used the soluble epoxide hydrolase inhibitors from the Hammock lab but also used some prototype drugs synthesized by chemist Sung Hee Hwang of the UC Davis School of Veterinary Medicine “which proved to be even better,” Hammock said.
“These compounds are a synthetic combination of cyclooxygenase inhibitors like celebrex with epoxide hydrolase inhibitors,” Hammock said. “Since epoxide hydrolase inhibitors stabilize the endoplasmic reticulium stress response and transcriptionally down regulate inflammatory cyclooxygenase we expected them to synergize with cyclooxygenase inhibitors. We were surprised and pleased with the dramatic interaction of these inhibitors when combined in the same molecule in reducing the cytokine and eicosanoid production by in response to cell debris.”
“The observations from Harvard show that by inhibiting soluble epoxide hydrolase, we can block the activation of these inflammatory cascades leading to tumor promotion, growth and metastasis,” Hammock said. “We have a compound in human clinical trials that inhibits sEH, which should be clinically available in a few years. In addition. we have found natural inhibitors of the epoxide hydrolase in a variety of plants, including crop plants. This may allow us to reduce the cancer risk and block the gastrointestional erosion and bleeding caused by dietary aflatoxin using natural means.”
Other members of the 15-member team are UC Davis researchers Jun Yang, Yuxin Wang and Sung Hee Hwang; Harvard researchers Haixia Yang, Victoria Hallisey, Jianjun Deng, Sanne Verheul, Allison Gartung, Diane Bielenberg and Mark Kiernan (now of Bristol-Myers Squibb); and Sui Huang, Institute for Systems Biology, Seattle. Hammock and Panigrahy are the corresponding authors.
The research drew strong financial support as the Panigrahy's laboratory is generously supported by the Credit Unions Kids at Heart Team, the CJ Buckley Pediatric Brain Tumor Fund, and the Joe Andruzzi Foundation; and Hammock's UC Davis grants from the National Institute of Environmental Health (NIEHS) Superfund Research Program, and the NIEHS RIVER Award (Revolutionizing Innovative, Visionary, Environmental Health Research).
Hammock, a member of the UC Davis faculty since 1980, has directed the UC Davis Superfund Research Program for nearly four decades. It supports scores of pre- and postdoctoral scholars in interdisciplinary research in five different colleges and graduate groups on campus. Last year Hammock received a $6 million, eight-year “Outstanding Investigator” federal grant for his innovative and visionary environmental health research: The award is part of the Revolutionizing Innovative, Visionary Environmental Health Research (RIVER) Program of NIEHS.
“Toxic environmental carcinogens promote cancer via genotoxic and nongenotoxic pathways, but nongenetic mechanisms remain poorly characterized. Carcinogen-induced apoptosis may trigger escape from dormancy of microtumors by interfering with inflammation resolution and triggering an endoplasmic reticulum (ER) stress response. While eicosanoid and cytokine storms are well-characterized in infection and inflammation, they are poorly characterized in cancer. Here, we demonstrate that carcinogens, such as aflatoxin B1 (AFB1), induce apoptotic cell death and the resulting cell debris stimulates hepatocellular carcinoma (HCC) tumor growth via an ‘eicosanoid and cytokine storm.' AFB1-generated debris up-regulates cyclooxygenase-2 (COX-2), soluble epoxide hydrolase (sEH), ER stress-response genes including BiP, CHOP, and PDI in macrophages. Thus, selective cytokine or eicosanoid blockade is unlikely to prevent carcinogen-induced cancer progression. Pharmacological abrogation of both the COX-2 and sEH pathways by PTUPB prevented the debris-stimulated eicosanoid and cyto- kine storm, down-regulated ER stress genes, and promoted macrophage phagocytosis of debris, resulting in suppression of HCC tumor growth. Thus, inflammation resolution via dual COX-2/sEH inhibition is an approach to prevent carcinogen-induced cancer.”
A team of nine researchers, including UC Davis biologist Scott Carroll, analyzed data over a six-year period and concluded that crop rotation works well in battling the notorious pest that annually causes $800 million in yield loss and $200 million in treatment costs.
“Answering this question was important not only to grower success but the agricultural economy, said Carroll, an associate of the UC Davis Department of Entomology and Nematology and owner of the Davis-based Institute for Contemporary Evolution. “Bt crops are far-and-away the single most important factor reducing soil and crop insecticide applications in the United States at present.”
When Bacillus thuringiensis (Bt) corn was introduced in 2003, the pest seemed under control. The genetically engineered corn is a transgenic, insecticidal crop that kills rootworm larvae but is harmless to humans.
However, when the pest began developing resistance to the Bt corn toxins, the U.S. Department of Agriculture recommended crop rotation as a method of control. Crop rotation, an age-old agricultural tactic, is a consistent and economical means of controlling rootworms the season following an outbreak. It reduces rootworm densities, and is considered more effective than insecticides.
“Corn rootworm is one of the nation's most devastating pests, giving a sense of urgency to protecting the efficacy of industrial pest control approaches with reduced non-target effects,” said Carroll, who studies basic and applied aspects of evolutionary biology. “Transgenic insecticidal Bt crops in the United States are cultivated under a very interesting socio-evolutionary model of resistance management that is mandated by the U.S. Environmental Protection Agency. Individual growers must implement resistance management--usually by devoting a small acreage to planting a 'refuge' of non-Bt crops in order to nurture a local reservoir population of Bt-susceptible pest insects.”
Carroll pointed out that the “outstanding productivity of Bt corn has led a portion of growers to reduce or eliminate their required refuge planting. Moreover, many time-tested practices for integrated pest management have fallen by the wayside as growers have found they could rely solely on the genetics of the seemingly invulnerable Bt varieties.”
“As predicted, Bt resistance evolution in corn rootworm has accelerated. In response to this dire risk, in 2016 EPA began mandating crop rotation as a complementary means of reducing the damage to Bt corn fields caused by resistant corn rootworms. Our working group analyzed the success of this traditional agricultural tactic to help sustain the efficacy of the high-tech Bt tactic.”
Carroll said that under the leadership of his colleague Yves Carrière at the University of Arizona, “our team analyzed six years of field data from 25 crop reporting districts in Illinois, Iowa and Minnesota—three states facing some of the most severe rootworm damage to Bt cornfields.
“The answer we found is that traditional crop rotation is working to protect the Bt corn fields from rootworm damage, including in areas that have seen the evolution of behavioral resistance to crop-rotation by rootworms.”
The bottom line, said Carrière, is this: "Farmers have to diversify their Bt crops and rotate. Diversify the landscape and the use of pest control methods. No one technology is the silver bullet.”
The project also included scientists from North Carolina State and McGill University, along with Carroll's colleague, Peter Jørgensen of the Stockholm Resistance Center.
While Jorgensen was pursuing his master's degree program at the University of Copenhagen and studying at UC Davis, he worked with Carroll and Sharon Strauss of the Department of Evolution and Ecology.
“This PNAS paper,” Carroll said, “is one of several that have developed from a pursuit Peter and I organized on 'Living with Resistance' at the National Socio-Environmental Synthesis Center in Annapolis, with the aim to explore more sustainable approaches to managing evolutionary challenges to health and food security.”
"Transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt) can suppress pests and reduce insecticide sprays, but their efficacy is reduced when pests evolve resistance. Although farmers plant refuges of non-Bt host plants to delay pest resistance, this tactic has not been sufficient against the western corn rootworm, Diabrotica virgifera virgifera. In the United States, some populations of this devastating pest have rapidly evolved practical resistance to Cry3 toxins and Cry34/35Ab, the only Bt toxins in commercially available corn that kill rootworms. Here, we analyzed data from 2011 to 2016 on Bt corn fields producing Cry3Bb alone that were severely damaged by this pest in 25 crop reporting districts of Illinois, Iowa, and Minnesota. The annual mean frequency of these problem fields was 29 fields (range 7 to 70) per million acres of Cry3Bb corn in 2011 to 2013, with a cost of $163 to $227 per damaged acre. The frequency of problem fields declined by 92% in 2014 to 2016 relative to 2011 to 2013 and was negatively associated with rotation of corn with soybean. The effectiveness of corn rotation for mitigating Bt resistance problems did not differ significantly between crop-reporting districts with versus without prevalent rotation-resistant rootworm populations. In some analyses, the frequency of problem fields was positively associated with planting of Cry3 corn and negatively associated with planting of Bt corn producing both a Cry3 toxin and Cry34/35Ab. The results highlight the central role of crop rotation for mitigating impacts of D. v. virgifera resistance to Bt corn."
Crowley-Gall's project, “Examining Pathogen-Induced Changes in Floral Chemistry and Assessing Impacts on Plant-Pollinator Interactions,” will focus on the effects of a plant pathogen on chemical signals that pollinators use when foraging. “Specifically, I will examine changes in nectar chemistry and floral volatile cues as a result of infection and resulting effects on pollinator behavior,” she said. “This proposal will utilize the Erwinia-pear system and the commercially utilized pollinator, honey bees.”
In his project, “The Role of Nectar Trait Plasticity and Nectar-Inhabiting Microbes in Sunflower Pollination,” McMunn will explore the interaction among sunflowers, nectar-inhabiting microbes, and bees in determining sunflower pollination success. “The results of this project will reduce the cost of sunflower production by testing new management strategies involving the introduction of beneficial nectar microbes,” he predicts.
“Globally approximately 16 percent of crops are lost a year due to pathogens,” Crowley-Gall wrote in her project proposal summary. “Plant pathogens can manipulate chemical cues emitted from their hosts to attract potential vectors. Pollinator insects rely heavily on these chemical cues when selecting potential host plants and there is evidence that pollinators can contribute to pathogen spread in agricultural systems. Pollination is widely used in agricultural systems and even crops that are not commercially supplied with pollinators are often exposed to some level of pollination. However, little is known about the effects of pathogens on pollinator behavior or the role of pollinators in pathogen transmission in agricultural systems.
“The purpose of this proposal is to examine the effects of pathogen infection on plant chemical cues and associated effects on pollinator behavior,” she wrote. This proposal will focus on Erwinia amylovora a widely spread pathogen that causes fire blight disease in Rosaceous plants. Effects of Erwinia across plant species will be experimentally tested using in vitro assays to examine effects on nectar chemistry and volatiles as well as pollinator neurophysiological and behavioral responses. Pathogen effects in natural systems will be examined in pear, an agricultural crop valued at $429 million in 2018 in the United States. Changes in nectar chemistry as well as nectar/floral volatiles will be characterized throughout the asymptomatic period of blossom infection. Pollinator behavioral responses and contribution to pathogen transmission will be assessed. This proposal will provide an increased understanding of pathogen affects on pollination in agricultural systems and enhance current pollinator management.”
Crowley-Gall, who joined the Vannette lab in 2019 as a postdoctoral researcher, has published her work in Journal of Hereditary, Ecology and Evolution, and Proceedings of the Royal Society B, among others. She guest-lectured this year in Vannette's chemical ecology course.
A native of Cincinnati, Ohio, Amber holds a bachelor of science degree in biological sciences in 2012 from Wright State University, Dayton, Ohio, where she focused on nematodes for her honor thesis, “Genetic Analysis of Hybrid Male Lethality in Caenorhabditis." The University of Cincinnati awarded her a doctorate in 2019: her dissertation: “Mechanisms Underlying Host Shift in Cactophilic Drosophila. Amber also received the J. Robie Vestal Award for Outstanding Doctoral Student.
“Production of many crop plants remains dependent on insect pollination, which occurs as a result of insect attraction to the nectar and pollen within flowers,” McMunn related. “Recent advances in pollination biology have demonstrated that nectar traits are frequently altered by nectar-inhabiting microbes (bacteria and yeast), leading to changes in bee visitation rates. Despite the central role of nectar traits in crop pollination, there is limited information on nectar traits that have known effects on bee preference.”
“The goal of this project is to explore the interaction among sunflowers, nectar-inhabiting microbes, and bees in determining sunflower pollination success,” he said. This will be accomplished through three objectives:
- characterize sunflower nectar traits and nectar-inhabiting microbes using a comparative field study
- assay bee preference for microbially inoculated nectar in a lab study and
- measure change in sunflower nectar traits and bee visitation following microbial inoculation in an experimental field study. The results of this project will reduce the cost of sunflower production by testing new management strategies involving the introduction of beneficial nectar microbes.
As a National Science Foundation Postdoctoral Research Fellow in Biology (August 2018 to July 2020) at UC Santa Cruz and UC Davis, McMunn is co-advised by faculty members Rachel Vannette of UC Davis, and Stacy Philpott of UC Santa Cruz.
Marshall, a native of Jackson, Mich., received his doctorate in population biology in June 2018 from UC Davis, and his bachelor's degree in ecology and evolutionary biology in 2009 from the University of Michigan, Ann Arbor. A 2018 UC Davis Professors for the Future Fellow, he has published his work in the journals Environmental Entomology, Arthropod-Plant Interactions, Ecological Entomology, and Ecology, among others. He served as a UC Davis teaching assistant for four years, and in 2016, taught at the UC Davis Bio Bootcamp 2.0, a weeklong research summer camp for high school students.
Vannette, a community ecologist, assistant professor and Hellman fellow, now has three graduate students, two postdoctoral scholars (another to start in September) and three undergraduates and a junior specialist working in her lab. (See their projects here.)
Igwe who joined the UC Davis doctoral program in 2015, anticipates receiving her PhD in microbiology in September 2020. Her thesis: “Microbial Community Contribution to Plant Abiotic Stress Tolerance: A Case Study in Serpentine Soils.” Igwe focuses her research on plant-microbe associations, microbial ecology, environmental microbiology and bioinformatics.
“Plant-microbe associations impact plant phenotype, distribution and biodiversity and range in their effects on a continuum from costly parasitic to beneficial mutualistic interactions,” she wrote in her successful proposal. “These mutualistic relationships also range from loose and facultative to endosymbiotic and obligate. The relationship between nitrogen-fixing bacteria and plants is especially important ecologically. Research into these associations have traditionally focused on endosymbiotic relationships within the nodules of legumes. I propose to explore the impact of strong selective soil pressures on microbial local adaptation and mutualism using free-living nitrogen-fixers and non-legumes.“
“My study,” she wrote, “will utilize serpentine ecosystems because serpentine soils are naturally high in heavy metals and deficient in plant nutrients which contributes to low plant productivity and presents strong selective pressures. The system also includes a free-living nitrogen-fixer, Microvirga spp., and plants that can grow on both serpentine and nonserpentine soils (serpentine-indifferent), allowing tractable manipulations across stress environments. Research with this system can be useful for disentangling the relative influence of soil and plant type on the establishment of mutualistic relationships and its impact on plant performance.”
She seeks a career as an environmental microbiologist to “scientifically and commercially address problems related to environmental degradation and food security.”
“Allie has initiated exciting research directions during her time in the lab: examining how rhizosphere microbes influence plant survival and growth on serpentine soils,” said Vannette, a UC Davis Hellman Fellow. “She has funded this work through several successful grant applications during her graduate career at UC Davis. Her creative research suggests previously unrecognized ways that plants are able to successfully establish and grow on harsh soils. She has also found that the composition of soil microbes can affect seedling establishment and also change when plants flower!"
“Her findings are novel and they are already making an impact on the field,” Vannette pointed out. “Allie has published a first-author paper and co-authored two additional papers on how soil microbial communities are shaped by soil characteristics and plant species Allie has taken an active role in mentoring students in our lab. She has worked closely with and trained at least five undergraduate students in techniques ranging from DNA extraction and library prep, isolating and identifying soil bacteria, bioinformatics analysis and root imaging analysis. She has accompanied students to national meetings and supported their career goals even after they had left the lab.“
Vannette, who joined the UC Davis Department of Entomology and Nematology in 2015 after serving as a postdoctoral fellow at Stanford University's biology department, also praised Allie for “taking an active role in mentoring students in our lab. She has worked closely with and trained at least five undergraduate students in techniques ranging from DNA extraction and library prep, isolating and identifying soil bacteria, bioinformatics analysis and root imaging analysis. She has accompanied students to national meetings and supported their career goals even after they had left the lab.”
“Allie has not only strong academic achievements, excellent leadership ability and but also the ability to translate these skills into meaningful research, impactful mentoring, and effective recruitment and retention of underrepresented students,” Vannette said. “Allie has accomplished a lot here at Davis and I am excited to watch her career unfold. Her achievements have been recognized with a prestigious NSF Postdoctoral fellowship.”
“I am the first to go to graduate school and will be the first doctor in the family, although not the type they likely expected,” she quipped. “I've always been interested in the natural world and participated in science fairs growing up. My first project was a survey of all the bugs in my front yard. My mom and I collected, identified, and mounted them. She told me that she could always find me in some mud or looking under a rock or collecting snails. I always had an interest in the environmental field--it just took a little nudge from amazing mentors for me to pursue it.”
Allie received her bachelor's degree in biology in 2013 from Howard University, Washington, D.C., where she submitted her honors thesis: “Elemental Defense in Alyssum murale: Effects on Plant-Herbivore Interactions.” She holds a master of science degree in soil science in December 2015 from Texas A&M (TAMU), where she presented her thesis on “Phytoremediation of Hydrocarbon-Contaminated Soil Using Phenolic-Exuding Horticultural Plants.”
At TAMU, Allie designed greenhouse experiment to identify rhizosphere microbial composition of horticulture plants growing in soil contaminated with polycyclic aromatic hydrocarbons.
The UC Davis doctoral student co-authored “Organic Management Promotes Natural Pest Control through Altered Plant Resistance to Insects,” published May 15 in the journal Nature Plants, with Vannette and several other co-authors.
Igwe served as the lead author of the Igwe-Vannette research, “Bacterial Communities Differ Between Plant Species and Soil Type, and Differentially Influence Seedling Establishment on Serpentine Soils,” published June 26, 2010 in the journal Plant and Soil.
At UC Davis, she has helped other students succeed. She served as a teaching assistant from September 2016 to- December 2019 in the UC Davis Career Discovery Group. She mentored a group of 10-20 freshmen in career exploration activities and professional communication. In addition, she recruited industry professionals to participate in student networking events, and coordinated on-site visits with working professionals for career exploration trips. Igwe also was a success coach in the UC Davis Success Coaching and Learning Strategies for a year.
Boudinot will return to the United States in 2023.
While at UC Davis, Boudinot excelled in academics, leadership, public service activities, professional activities, and publications. “A highly respected scientist, teacher and leader with a keen intellect, unbridled enthusiasm, and an incredible penchant for public service, Brendon maintains a 4.00 grade point average; has published 12 outstanding publications on insect systematics (some are landmarks or ground-breaking publications); and engages in exceptional academic, student and professional activities,” wrote nominator Steve Nadler, professor and chair of the UC Davis Department of Entomology and Nematology. (Update: As of June 14, Boudinot has now published 16 peer-reviewed papers.)
Despite being at an early stage of his academic career, Boudinot had already published several landmark papers on insect systematics, wrote Phil Ward in 2019. "This includes a remarkable article, just published in Arthropod Structure & Development, in which Brendon presents a comprehensive theory of genital homologies across all Hexapoda (Boudinot 2018). Based on careful comparative morphological study and conducted within a phylogenetic framework, this paper is a major contribution to the field and is destined to become a “classic." This could have been a decade-long study by any investigator, and yet it is just one chapter of Brendon's thesis!"
His exit seminar on March 4 drew a standing room-only crowd in 122 Briggs. His abstract: "It is widely yet loosely agreed that the study of morphology--body form, structure and function--is undergoing a post-genomic revival, cautiously labeled 'phenomics' among active practitioners. I argue that the full reality of phenomics has yet to be realized, and that functional anatomy is the linchpin for the meaningful use of morphological data to understand evolution. In this seminar, I will present two case studies from my dissertation. The first will focus on reproductive anatomy in the context of the major transitions of insects from a marine, crustacean ancestor to the epically abundant diversity of wing-bearing species. The second and ongoing study combines more than 300,000 point-observations of morphology for 431 extinct and extant species with genomic sequence data to reconstruct the sequence of evolution leading to the living ants. I will introduce the audience to several extinct lineages of ants, including a new family of wasp-ant intermediates, and present functional morphological reconstructions of the ancestors of all ants, living and extinct." (Listen to the exit seminar here; access is free.)
Active in PBESA and ESA, Boudinot received multiple “President's Prize” awards for his research presentations at national ESA meetings. He organized the ESA symposium, “Evolutionary and Phylogenetic Morphology,” at the 2018 meeting in Vancouver, B.C. , and delivered a presentation on “Male Ants: Past, Present and Prospects” at the 2016 International Congress of Entomology meeting in Orlando, Fla.
Boudinot served on—and anchored—three of the UC Davis Linnaean Games teams that won national or international ESA championships. The Linnaean Games, now known as the Entomology Games, are a lively question-and-answer, college bowl-style competition on entomological facts played between university-sponsored student teams.
Boudinot served as president of the UC Davis Entomology Graduate Student Association from 2006 to 2019, and co-chaired the department's Picnic Day celebration (with forensic entomologist Robert Kimsey) for three years.