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CRT Young Investigator Award: CRT Young Investigator Award
08:00am - 09:55am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Shana J. Sturla, Organizer, ETH Zurich; Shana J. Sturla, Presider, ETH Zurich; Christie Sayes, Presider, RTI International
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Division/Committee: [TOXI] Division of Chemical Toxicology
Sunday
Introductory Remarks
08:00am - 08:05am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid

Sunday
Vaping chemistry and the environment
08:05am - 08:30am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Robert Strongin, Presenter
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Vaping tobacco and cannabis products has become increasing popular during the past decade. This is due, in large part, to perceived harm reduction. In addition, their prevalence has benefitted from aggressive marketing campaigns and products not subject to the same advertising restrictions and regulations compared to traditional smoking. Apart from concern about their impact on user health, two of the issues concerning these products include (i) how their emissions affect indoor air quality as well as (ii) how their disposal can impact the environment. In the former case, there has been a great deal of controversy, and in the latter case, relatively little is currently known. This presentation will include an overview of how emissions from these relatively new and emerging products and formulations may lead to concerning second hand exposures. In addition, the ingredients in the increasingly popular new disposable, high nicotine content, flavored e-cigarettes will be discussed in the context of their potential impact on the environment.
Sunday
Understanding how environmental factors influence the impact of emerging contaminants
08:30am - 08:55am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Sherine Obare, Presenter, Univ. of North Carolina, Greensboro
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Anthropogenic nanoparticles are of great interest due to their importance in advanced technological applications. Increased usage of nanoparticles in industrial processes as well as in commercial products continues to raise global concerns regarding their adverse impact on the environment and on human health. A critical issue that arises in understanding the environmental health and safety concerns of nanoparticles lies in their method of preparation and the properties of the nanoparticles that arise as a result of different preparation techniques. The behavior and impact of emerging contaminants on the activity of microorganisms in the environment is affected by several factors. These factors play an important role in the persistence of microorganisms and the overall ecosystem. This presentation will focus on recent developments in our labs in which we have studied how the impact of functionalized and unfunctionalized metal and metal oxide nanoparticles on bacterial growth both in the presence and absence of dissolved organic matter. Modulation of environmental parameters on how the nanoparticles impact microorganisms was studied. The impact of emerging nanoparticle contaminants on various microorganisms will be reported.
Sunday
Intermission
08:55am - 09:05am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid

Sunday
Combination of a quantitative toxicity assessment tool and targeted disinfection byproduct screening for drinking water mixture quality evaluation and toxicity driver identification
09:05am - 09:30am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Jingyi Wu, Presenter, Cornell University; Joshua Allen; Susan Richardson, University of South Carolina; Dr. Michael J. Plewa, University of Illinois at Urbana-Champaign; Stuart Krasner; Akram Alshawabkeh; April Gu
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Quantitative Toxicity Assessment Tool and Targeted Disinfection Byproduct Screening for Drinking Water Mixture Quality
Sunday
Differential cytotoxicity of drinking water contaminant co-exposures against human intestinal and neuronal cells
09:30am - 09:55am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Christie Sayes, Presenter, RTI International; Dr. Jiaqi Liu, Baylor University; Sahar Pradhan
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Drinking water contains environmental contaminants such as disinfection byproducts (DBPs), leached metal ions, and pesticides. These chemicals are potentially harmful constituents which can cause potential adverse health effects to humans. In a series of studies, we investigated the cytotoxicity of binary mixtures of haloaromatic DBP plus lead ion, lead ion plus copper ion, and copper ion plus glyphosate, separately as well as in combination, to human epithelial colorectal adenocarcinoma (Caco-2) and neuroblastoma (SH-SY5Y) cells. Results show that the cytotoxicity of the individual constituents against Caco-2 and SH-SY5Y cells were significantly different than the cytotoxicity of binary mixtures. Haloaromatic DBP plus lead ion resulted in synergistic effects (i.e., the constituents were more toxic in combination as compared to the toxicity when inoculated separately). Lead ion plus copper ion resulted in an additive relationship (i.e., similar toxicities were observed when the constituents were inoculated in combination or separately). Copper ion plus glyphosate resulted in an antagonistic effect (i.e., the cytotoxicity decreased when the constituents were inoculated in combination as compared to toxicities induced separately). In general, constituents were more potent in neuronal cells than in gut cells at the same exposure doses. These data indicate that future prioritization of emerging drinking water contaminants must be considered in terms of their own toxicity as well as the combinatorial effects with other chemicals in water.
TOXI Founders Award Symposium:
10:30am - 12:25pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
John Essigmann, Organizer, MIT; Stephen Hecht, Organizer; John Essigmann, Presider, MIT
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Co-sponsor/Theme: Theme: Resilience of Chemistry
Division/Committee: [TOXI] Division of Chemical Toxicology
Sunday
DNA protein crosslinks: DNA lesions or epigenegic regulators?
10:30am - 10:53am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
DNA-protein crosslinks (DPCs) are exceptionally bulky, structurally diverse DNA adducts formed in cells endogenously and upon exposure to bis-electrophiles, reactive oxygen species, and ionizing radiation. We recently discovered that epigenetic marks of DNA (5-formyl-C) form reversible DNA-protein conjugates with histone proteins in the chromatin. Due to their bulky size, DPCs have the ability to block DNA transactions including transcription, replication, and repair, leading to genomic instability and cell death. DPCs can accumulate in the heart and brain tissues and are hypothesized to play a role in aging, cancer and neurodegenerative diseases. It has been proposed that the protein component of a DPC is proteolytically degraded, giving rise to smaller DNA-peptide conjugates (DpCs), which can be subject to nucleotide excision repair and replication bypass. We have developed bioconjugation reactions to generate site specific DPC and DpC lesions conjugated to various positions of DNA and introduced them into in vitro and in vivo biological systems to investigate their effects on DNA transactions. Full size DPC completely blocked DNA replication and transcription, but could be bypassed by DNA and RNA polymerases following proteolytic processing. Depending on their structure and local DNA sequence context, peptide DpC adducts induced point mutations, caused deletions, or allowed for error free lesion bypass in the presence of human lesion bypass polymerases. Replication of DpC containing vectors in human cells revealed both targeted and untargeted mutations, while transcription of 5-formylC-histone conjugates in human cells was error free. Our results suggest that exogenously induced DPCs contribute to mutational hot spots in the human genome, while 5-formylC-histone conjugates play a role in epigenetic regulation.
Sunday
Chemical biology of DNA damage and repair
10:53am - 11:16am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Dr. Deyu Li, Presenter
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
The human genome is constantly challenged by endogenous and exogenous sources, such as reactive oxygen species (ROS), ultraviolet (UV) light, and various carcinogens. Each of these DNA damaging agents forms adducts and generates unique mutational patterns, which hold promise for disease diagnosis and prevention. Our lab focuses on the mutagenesis of DNA lesions, including their formation, replication bypass and repair. By using a combination of tools from chemistry, molecular biology, and genetics, we hope to construct mutational spectra and repair/bypass maps of DNA damaging agents. These works may provide strategies to prevent diseases caused by toxins or to solve the problems of drug resistance.
Sunday
Overcoming the packaging paradox: DNA base excision repair in chromatin
11:16am - 11:39am USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Sarah Delaney, Presenter, Brown University
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
DNA damage is a fundamental molecular cause of genomic instability. To repair chemically modified DNA nucleobases, cells have the base excision repair (BER) pathway. BER can be considered to occur in two parts: (1) excision of the damaged base by a glycosylase and (2) filling the resulting “hole” with an undamaged base by downstream enzymes. BER is a prevalent DNA repair pathway because it addresses thousands of mutagenic lesions in our genome every day. However, BER in the context of chromatin, in which eukaryotic DNA is compacted through a complex hierarchy of DNA-protein interactions, remains poorly understood. At the most fundamental level of chromatin organization, DNA is packaged as a string of nucleosome core particles (NCPs) where DNA is wound around a core of histone proteins. This ubiquitous sequestration of DNA within NCPs presents a conundrum for BER enzymes, which must interact intimately with DNA, and is referred to as the “packaging paradox”. In this research we developed techniques to study the global initiation of repair on DNA packaged in NCPs. Using these techniques, we describe the global repair fingerprint of several glycosylases and identify locations in packaged DNA that are refractory to repair and those that are repaired efficiently. We also examined the role of histone variant proteins and histone tails in modulating the initiation of BER and demonstrate that the protein component of chromatin can both positively and negatively impact DNA repair. The results will be discussed in terms of structural features and dynamics of NCPs, and well as in the context of known mutational hotspots.
Sunday
Chemically induced DNA damage and mutagenesis: Genome wide patterns and sequence-specific localization
11:39am - 12:02pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Shana J. Sturla, Presenter, ETH Zurich
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Cancer risk is impacted by exposures to chemicals from food, drugs and environmental exposures. Moreover gene-environment interactions governed by deficiencies in DNA damage tolerance pathways impact individual sensitivities to chemical exposures. However, the capacity to predict individual susceptibility to chemical mutagens or the etiology of individual cancers remains a challenge. Moreover, there is a discrepancy between our low resolution understanding of the dynamic process of DNA damage formation and removal on a genome-wide level vs. our sophisticated single-base genome-wide picture of mutational landscapes of human cancers. Very recently, several strategies have emerged for addressing these issues, including base-resolution mapping of DNA damage that integrate chemical probe-based recognition and ligation strategies for tracking damage in particular genomic contexts, together with in vitro experimental models for describing mutation spectra and signatures associated with chemical exposures or chemical-gene interactions. The results of this work include new insights on chemistry-based strategies to map oxidation and alkylation damage in cells, understand how damage maps are governed by chemical sources and repair, and relate chemical exposures with in vitro mutation signatures. For example, we found that the specificity of DNA repair enzymes could be coupled with efficient click DNA ligation reactions to insert a biocompatible nucleoside probe with a locator oligonucleotide code sequence. By a complementary amplification-based strategy, we used DNA adduct-targeting synthetic nucleotide probes to locate alkylation damage in a cancer driver gene sequence. Furthermore, we coupled this polymerase-based adduct amplification strategy with a mass spectrometric quantification method to relate the quantity of synthetic amplicons with damage levels. These sequence-specific chemical probe-based strategies for tracking chemically induced DNA damage overcomes previous limitations to sequencing of DNA damage, provides information concerning the relationship between DNA repair enzyme function and mutation signatures, and could lead to new approaches for quantifying risk on the basis of early biomarkers and characterization of causative factors of individual cancers.
Sunday
Mutational spectra provide insight into the mechanisms bridging DNA damage to genetic disease
12:02pm - 12:25pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Mutations are a permanent record of past chemical and biochemical insults experienced by a cell. Each time the genome replicates, it accumulates mutations in patterns that reflect: (a) the DNA sequence context-dependent formation of damage; (b) the differential activity of DNA repair proteins, which, depending on the type of lesion, can eliminate, ignore or intensify the mutagenic consequences of the lesion; and (c) the choice of replication machinery that synthesizes the nascent genomic copy. In combination, these three factors produce a richly contoured mutational spectrum that, from appearances, is distinct for most individual forms of DNA damage. This mutational pattern, if appropriately decoded can reveal the history of genome-altering events such as chemical exposures, pathogen-stimulated base deaminations, metabolic stress, and inflammation, which in turn can provide an indication of the underlying causes and mechanisms of genetic disease. New tools help us glean a deep mechanistic understanding of the cellular factors and pathways that modulate a mutational process and, in turn, provide opportunities for better diagnostic and prognostic biomarkers, better exposure risk assessment and even actionable therapeutic targets. The goal of this talk is to present a bottom-up, lesion-centric framework of mutagenesis that integrates the contributions of lesion replication, lesion repair and lesion formation to explain the complex mutational spectra that emerge in the genome following exposure to mutagens. The mutational spectra of the well-studied hepatocarcinogen aflatoxin B1 and several alkylating agents serve as specific examples, but the implications are meant to be generalizable.
TOXI Keynote Lecture:
02:00pm - 02:50pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Dr. Patrick Breysse, Organizer; Dr Natalia Tretyakova, Organizer, University of Minnesota ; Dr Natalia Tretyakova, Presider, University of Minnesota
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Division/Committee: [TOXI] Division of Chemical Toxicology
Sunday
Introductory Remarks
02:00pm - 02:05pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid

Sunday
Biological monitoring and public health
02:05pm - 02:50pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Dr. Patrick Breysse, Presenter; Kristin Dortch, Presenter
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Biological Monitoring and Public Health
Toxicants & Cellular Aging:
04:30pm - 06:30pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Laura Niedernhofer, Organizer; Michael Trakselis, Organizer, Baylor University; Michael Trakselis, Presider, Baylor University; Laura Niedernhofer, Presider
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Division/Committee: [TOXI] Division of Chemical Toxicology
Sunday
The DNA recombination helicase, MCM8/9, stabilizes stalled forks
04:30pm - 04:53pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Michael Trakselis, Presenter, Baylor University
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Germline mutations in either MCM8 or MCM9 have been associated with primary ovarian insufficiency/failure (POI/POF), infertility, and more recently with somatic mutations in various cancers and cancer genomes. This suggests a link for the MCM8/9 complex in participating in genetic recombination processes in both meiotic and mitotic cells; however, the exact cellular or biochemical roles of MCM8/9 are not known. Knockouts of MCM8 or 9 are highly sensitive to crosslinking agents such as mitomycin-c or cisplatin, but we now find that MCM8/9 is also sensitive to and responds to the fork stalling agent hydroxyurea (HU). During fork stalling and reversal, MCM8/9 helps to protect stalled forks by loading and stabilizing Rad51 directly through the BRCA1 pathway. MCM8 or 9 deficient cells show increased degradation by Mre11 after stalling with HU; however, simultaneous knockdown of BRCA1 restores fork stability. Therefore, MCM8/9 helps to promote and stabilize reversed forks after genomic stress. These reversed forks are analogous to recombination intermediates found in meiotic and mitotic cells providing insight into their cellular functions in promoting meiotic genomic diversity and mitotic stability, impacting cellular aging.
Sunday
DNA structure induced mutation hotspots in cancer and aging
04:53pm - 05:16pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Cancer is the second leading cause of death worldwide, and is predicted to rise to ~29 million new cases by 2040. Aging plays a role in the susceptibility of cancer, and studies have shown that aging is correlated with increased genetic instability, which is a hallmark of cancer. In human genomes, cancer-associated mutation “hotspots” have been identified; however, the mechanisms involved are unclear. Interestingly, we and others have found that alternative (i.e. non-B) DNA structures formed at repetitive DNA sequences are highly enriched at mutation “hotspots” in human cancer genomes, implicating non-B DNA in cancer etiology. For example, we have found that H-DNA and Z-DNA are mutagenic both in vitro and in vivo and stimulate the formation of DNA double-strand breaks, deletions, translocations and point mutations. Interestingly, these structures are processed in a mutagenic fashion by DNA repair proteins. We found that H-DNA is processed by the nucleotide excision repair (NER) pathway, while Z-DNA is processed by proteins from both the NER (ERCC1-XPF) and the mismatch repair (MSH2-MSH3) pathways. Although we have determined that NER proteins and MSH2-MSH3 and ERCC1-XPF complexes are recruited to H-DNA and Z-DNA sequences, respectively, to process them in a mutagenic fashion, we do not know how age affects the recruitment of these proteins to these sequences and/or the mutagenic processing of non-B DNA. To test this, we developed a novel transgenic mouse model to evaluate the processing of non-B DNA sequences with age. Experiments are currently being performed on tissues from these transgenic mutation-reporter mice at 2 months and 18 months of age, and our preliminary data suggest that non-B DNA-induced mutagenesis increases with age. Results from these studies will assist in the elucidation of the mechanisms involved in the mutagenic processing of alternative DNA structures with age, and the roles of DNA structure and aging in the generation of mutation hotspots.
Sunday
Using chemoptogenetics to study cellular responses to telomere specific 8-oxoguanine damage
05:16pm - 05:39pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Telomeres are protective nucleoprotein-DNA caps at chromosome ends that profoundly influence genome stability and human health. In most human somatic cells, telomeres shorten with division, eventually triggering senescence which blocks further division and drives aging-related diseases. Critically short telomeres in pre-cancerous cells drive genetic alterations that promote carcinogenesis. Previous studies show oxidative stress caused by an excess of reactive oxygen species (ROS), accelerates telomere shortening and dysfunction. Telomere TTAGGG repeat arrays are highly susceptible to ROS-induced conversion of guanine to the common oxidative lesion 8-oxoguanine, which has been proposed to accelerate telomere dysfunction. To study cellular consequences telomere damage, wedeveloped a precision chemoptogenetic tool that selectively produces 8-oxoguanine exclusively at telomeres with high spatial and temporal control. This tool allows us to unequivocally attribute phenotypic outcomes to the telomere damage, eliminating confounding effects of damage elsewhere. We discovered that oxidative base damage at telomeres is sufficient to drive hallmarks of telomere dysfunction, generating distinct cellular consequences in human cancer cells versus non-diseased cells. Chronic formation of telomeric 8-oxoguanine in human cancer cells accelerates telomere shortening and loss, resulting in chromosome fusions and bridges. Acute telomeric 8-oxoguanine damage in human fibroblast and epithelial non-disease cells is sufficient to trigger multiple hallmarks of p53-dependent senescence. In these cells acute damage fails to shorten telomeres, but rather generates telomere fragility indicative of failures in telomere replication. Our results indicate that 8-oxoguanine damage at telomeres is sufficient to drive telomere dysfunction-induced genomic instability in cancer cells, and cellular senescence in non-diseased cells.
Sunday
Intermission
05:39pm - 05:44pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid

Sunday
Regulation of aging through chromatin-regulated stress response pathways
05:44pm - 06:07pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Weiwei Dang, Presenter
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Epigenetic markings in chromatin offer an important layer of regulation for transcription in response to metabolic changes, various stresses, and aging. In this talk, I will briefly discuss the various technologies we have developed to identify and study such pathways that discovered in recent years. In particular, I will focus on a class-II histone deacetylase, the HDA complex, regulates aging through its target of acetylated H3K18 at trehalose metabolic genes. We found that disruption of HDA results in resistance to DNA damage and osmotic stresses, as well as lifespan extension. The longevity effect of HDA is independent of the Cyc8 (Ssn6) – Tup1 repressor complex that has been previously shown to interact with HDA and coordinate transcriptional repression. Instead, we found that HDA deacetylated the promoters of genes regulating the synthesis of a storage carbohydrate, trehalose. Activation of this pathway offered protection for the cells against stresses, antagonizing aging and promoting longevity. Intriguingly, this longevity mechanism appears to be conserved in worms and fruit flies. These findings offer novel insights into how histone modifying enzymes regulate anti-aging mechanisms.
Sunday
Cellular senescence as a driver of aging and age-related diseases
06:07pm - 06:30pm USA / Canada - Eastern - August 22, 2021 | Room: B313b - B314
Dr. Laura J. Niedernhofer, MD, PhD, Presenter, University of Minnesota
Division: [TOXI] Division of Chemical Toxicology
Session Type: Oral - Hybrid
Cellular senescence is a cell fate triggered in response to numerous types of stressors, including, genotoxic stress. Indeed, many cancer therapeutics such as ionizing radiation are potent inducers of cellular senescence. Senescent cells are characterized by metabolic reprogramming, chromatin marks of chronic DNA damage, and irreversible cell cycle arrest. As such, senescence is a potent tumor suppressor mechanism. However, the down-side is that senescent cells have been shown to drive aging in mammals. Genetic or pharmacologic ablation of senescent cells in mice extends their median lifespan and attenuates a broad range of age-related diseases. This is thought to be mediated by the secretome of senescent cells, which is often pro-inflammatory and able to perturb the tissue microenvironment. Interestingly, the secretome of senescent cells can drive senescence in trans, enabling genotoxic stress to instigate aging in a cell non-autonomous mechanism. The cause and consequence of cellular senescence in particular with respect to environmental toxicants and aging will be discussed.
General Posters:
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Erin Prestwich, Organizer, University of Toledo; Ujjal Sarkar, Organizer, MIT; Grover Miller, Organizer, Dept of Biochem and Mol Biol
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person
Division/Committee: [TOXI] Division of Chemical Toxicology
Sunday
Endogenous versus exogenous sources of monohydroxy-3-butenyl and dihydroxybutyl mercapturic acid metabolites and N7-(1-hydroxy-3-buten-2-yl) guanine DNA adducts
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Caitlin Jokipii Krueger, Presenter; Erik Moran; Dr Natalia Tretyakova, University of Minnesota
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person
1,3-butadiene (BD) is a known human carcinogen found in the polymer industry, tobacco smoke, and urban air. BD is metabolically activated to electrophilic metabolite, 3,4-epoxy-1-butene (EB). EB is detoxified through glutathione conjugation and the mercapturic acid pathway to form monohydroxy-3-butenyl mercapturic acid (MHBMA) and dihydroxybutyl mercapturic acid (DHBMA). If not detoxified, EB can react with guanine bases of DNA to form N7-(1-hydroxyl-3-buten-1-yl) guanine (EB-GII) adducts. Both MHBMA and EB-GII are associated with smoking, decreasing by 80% and 34% respectively post-smoking cessation. In contrast, urinary DHBMA levels remain unchanged post-smoking cessation, suggesting that they can originate from endogenous sources. To quantify the contributions of endogenous MHBMA, DHBMA, and EB-GII to the overall MHBMA, DHBMA, and EB-GII levels, Sprague-Dawley rats were exposed to low ppm levels of isotopically labeled BD (BD -d6 , 0, 0.3, 0.5, and 3 ppm) for 6 h/day for 7 days. Following treatment, urine and target tissues (liver, pancreas, heart, lung, mammary glands, and blood) were collected. Metabolites and adducts resulting from BD-d6 exposure carry a deuterium isotope label, while endogenous metabolites and adducts are unlabeled and can be distinguished by mass spectrometry. A dose-dependent increase in MHBMA-d6, DHBMA-d5, and EB-GII-d6 was observed in urine of rats exposed to BD-d6. In addition, endogenous MHBMA, DHBMA, and EB-GII were observed in most samples and were unaffected by BD-d6 exposure. Following treatment with 3 ppm BD-d6, the levels of exogenous urinary MHBMA and EB-GII were far more prevalent than the concentrations of endogenous metabolites and adducts, suggesting that butadiene exposure was the main source of these species. In contrast, the concentrations of exogenous DHBMA were only 2.5-fold higher than that of the endogenous metabolite. This is consistent with previous studies that have shown significant amounts of DHBMA that could not be explained by BD exposures. A dose-dependent increase in genomic EB-GII-d6 was observed in the liver of rats exposed to BD-d6 in addition to endogenous levels of EB-GII that were not affected by BD-d6 exposure. Our results indicate that following sub ppm exposures to BD as experienced by smokers and city residents, endogenous sources have a major impact on the total levels of MHBMA, DHBMA, and EB-GII. Our ongoing studies aim to reveal the metabolic/dietary sources of these adducts.
Sunday
Withdrawn
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person

Sunday
Toxicity focused product development offers time, effort and money savings; defines greener processes
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Neelam N. Vaidya, Presenter, ViridisChem, Inc.
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person
Knowledge of chemical toxicity is essential while defining sustainable product development. Today, although with mandated SDS disclosures, scientists are getting more access to chemical properties, access to adequate environmental toxicological properties and knowledge about that less toxic alternatives are available is still a challenge. Many times, scientists have to rely on their past experience. But with millions of chemicals and addition of new ones every year has made this knowledge is no longer adequate.

ViridisChem offers toxicity of every known (over 95 million chemicals), proprietary chemicals, and new molecules within matter of seconds. And its "Advanced Smart Search" allows scientists to select less toxic chemicals by specifying multiple criteria that can describe their exact reaction needs. This presentation will describe the ViridisChem platform and its ability to find less toxic chemicals for your reaction needs to help you minimize the use of toxic chemicals, minimize toxic waste and most importantly allows scientists to define greener development processes so that late stages can be avoided, and process optimization can be achieved faster, shortening the go-to-market timeline.

Sunday
pH effects on oxidative modification of alkylative DNA adducts by the AlkB-family enzymes
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person
The AlkB-family enzymes have been shown to oxidize alkylative DNA adducts to different extents dependent upon the pH conditions to which they are subject in vitro. Reduced activity of enzymes such as ABH2 and ABH3 in humans, could contribute to accumulation of the cytotoxic DNA adducts, 1-methyladenine or 3-methylcytosine. This study will investigate the in vitro pH profiles of human ABH2 and ABH3 and E. coli AlkB in regard to their abilities to oxidize 1-methyladenine and 3-methylcytosine in single and double-strand contexts. All synthetic oligonucleotides were synthesized utilizing the Mermade 4 platform, and all AlkB-family enzymes were expressed and purified. The impact of pH conditions on AlkB-mediated oxidation of methylated DNA was quantified by Anion Exchange HPLC. Our findings show that pH can significantly influence the ability of these enzymes to repair DNA damage, and even alter substrate strand preferences as is the case for ABH2 when subject to more acidic pH conditions.
Sunday
Withdrawn
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person

Sunday
Sequence context effects of replication of Fapy-dG in three mutational hot spot sequences of the p53 gene in human cells
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person
Hydroxyl radical damage to DNA generates Fapy-dG and 8-OxodGuo from dG in comparable yields from a common radical intermediate. 8-OxodGuo is one of the most extensively studied DNA lesions. In contrast, much less is known about the consequences of Fapy-dG in mammalian cells, due to the lack of synthetic approaches to prepare Fapy-dG containing oligonucleotides in a desired sequence. We recently developed a robust synthetic method to prepare oligonucleotides containing Fapy-dG in any DNA sequence context, which enabled us to introduce it in three mutational hotspots of human cancers, namely codons 248 (CG*G), 249 (AG*G), and 273 (CG*T) of the p53 tumor suppressor gene. Plasmid DNA containing Fapy-dG in each of these three sequence contexts was constructed and replicated in human embryonic kidney (HEK) 293T cells. The mutation frequency (MF) induced by Fapy-dG in codons 248, 249, and 273 were 11.6%, 5.3%, and 7.3%, respectively. G→T was the dominant mutation in each case, though G→A also occurred in significant frequency in codons 248 and 249. To determine the roles of the translesion synthesis (TLS) DNA polymerases and hPol λ in Fapy-dG bypass and mutagenesis, these constructs were also replicated in TLS polymerase knockout or hPol λ-knockdown HEK 293T cell lines. TLS efficiency was reduced in each of the three sites in hPol η-, hPol i-, and hPol λ-deficient cells, suggesting that these polymerases are important for bypassing Fapy-dG. In each site, a significant increase in MF was observed in hPol i-, hPol κ-, and hPol ζ-deficient cells, whereas MF decreased upon knockdown of hPol λ. The predominant mutation in codons 248 and 249 was G→A transitions in hPol i-, hPol κ-, and hPol ζ-deficient cells, while G→T transversions were dominant in codon 273 in all cases. The results of this study suggest that in human cells not only are Fapy-dG induced mutations in codons 248, 249, and 273 of the p53 tumor suppressor gene different in types and frequencies, but the roles of the DNA polymerases are also distinct.
Sunday
Assessment of occupational exposure of firefighters to mono and polyaromatic hydrocarbons using intrinsic fluorescence
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Marcela Jaramillo, Presenter
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person
Cancer is the second leading cause of mortality and morbidity in the fire service. A recent NIOSH study of U.S. firefighters demonstrated a 14% increase in overall cancer mortality compared to the general population, and specific excesses in lung (10%), gastrointestinal (30-45%), and kidney (29%) cancer and mesothelioma (100%) deaths, with similar increases in cancer incidence. There is a significant association between fire hours and increased lung cancer incidence and mortality and between fire runs and leukemia mortality. Firefighters are exposed to hazardous bi-products of the incomplete combustion of organic materials such as mono and polyaromatic hydrocarbons, many of which are classified as either known, possible or suspected carcinogens by the EPA. We have explored the sensitivity and selectivity of fluorescence to assess exposure to mono and polyaromatic hydrocarbons in situ using a portable fluorometer. The primary goal is to develop remote exposure assessment and visualization techniques to educate, intervene and mediate the harmful effects of these chemicals. The results of lab-based assays for identifying and detecting phenanthrene, pyrene, and naphthalene will be presented.
Sunday
Characterization of phenotypic and DNA modifications of Pseudomonas aeruginosa wild-type and genomic variant strains
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person
The opportunistic pathogen Pseudomonas aeruginosa is the leading cause of death in patients with cystic fibrosis (CF), largely due to its biofilm-forming ability. P. aeruginosa forms a complex biofilm architecture of polysaccharides, proteins and extracellular DNA (eDNA) to encase and protect cells. Biofilms include niche environments due to oxygen and nutrient limitations that can induce regulatory mechanisms to promote cellular survival, resulting in different subpopulations of cells and driving the formation of genomic variants. Rugose small colony variants (RSCVs), arising from mutations and environmental changes, are associated with CF disease progression. P. aeruginosa has a complex quorum sensing network controlling virulence factors, including phenazines, which alter the pigment of culture supernatant via redox reactions and are thought to promote eDNA release via peroxide generation. Preliminary data suggests RSCVs promote higher phenazine and biomass production than wild-type (WT) cells, corresponding to their enhanced cytotoxicity. To study cellular subpopulations within a biofilm ecosystem, we developed methods to extract nucleic acids from different cell strata as well as eDNA. Virulence factors were extracted from the supernatant and monitored spectroscopically. These methods were applied to both WT and RSCVs for phenotypic characterization. DNA nucleosides were analyzed by isotope dilution LC-MS/MS to quantify epigenetic and oxidative modifications. Preliminary results suggest differences in the levels of modified DNA nucleosides between WT and RSCV strains throughout different phases of growth, potentially providing mechanistic insights into biofilm regulation and pathology.
Sunday
Withdrawn
07:00pm - 09:00pm USA / Canada - Eastern - August 22, 2021 | Room: B2 - EXHIBIT HALL
Division: [TOXI] Division of Chemical Toxicology
Session Type: Poster - In-person