NRF2 Activation in Trp53;p16-deficient Mice Drives Oral Squamous Cell Carcinoma

Aberrant activation of the NRF2/NFE2L2 transcription factor commonly occurs in head and neck squamous cell carcinomas (HNSCC). Mouse model studies have shown that NRF2 activation alone does not result in cancer. When combined with classic oncogenes and at the right dose, NRF2 activation promotes tumor initiation and progression. Here we deleted the tumor suppressor genes p16INK4A and p53 (referred to as CP mice), which are commonly lost in human HNSCC, in the presence of a constitutively active NRF2E79Q mutant (CPN mice). NRF2E79Q expression in CPN mice resulted in squamous cell hyperplasia or dysplasia with hyperkeratosis in the esophagus, oropharynx, and forestomach. In addition, CPN mice displayed oral cavity squamous cell carcinoma (OSCC); CP mice bearing wild-type NRF2 expression did not develop oral cavity hyperplasia, dysplasia or OSCC. In both CP and CPN mice, we also observed predominantly abdominal sarcomas and carcinomas. Our data show that in the context of p53 and p16 tumor suppressor loss, NRF2 activation serves oncogenic functions to drive OSCC. CPN mice represent a new model for OSCC that closely reflects the genetics of human HNSCC.

SIGNIFICANCE

Human squamous cancers frequently show constitutive NRF2 activation, associated with poorer outcomes and resistance to multiple therapies. Here, we report the first activated NRF2-driven and human-relevant mouse model of squamous cell carcinoma that develops in the background of p16 and p53 loss. The availability of this model will lead to a clearer understanding of how NRF2 contributes to the initiation, progression, and therapeutic response of OSCC.

SMARCB1 Loss in Poorly Differentiated Chordomas Drives Tumor Progression

Poorly differentiated (PD) chordoma, a rare, aggressive tumor originating from notochordal tissue, shows loss of SMARCB1 expression, a core component of the Switch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complexes. To determine the impact of SMARCB1 re-expression on cell growth and gene expression, two SMARCB1-negative PD chordoma cell lines with an inducible SMARCB1 expression system were generated. After 72 hours of induction of SMARCB1, both SMARCB1-negative PD chordoma cell lines continued to proliferate. This result contrasted with those observed with SMARCB1-negative rhabdoid cell lines in which SMARCB1 re-expression caused the rapid inhibition of growth. We found that the lack of growth inhibition may arise from the loss of CDKN2A (p16INK4A) expression in PD chordoma cell lines. RNA-sequencing of cell lines after SMARCB1 re-expression showed a down-regulation for rRNA and RNA processing as well as metabolic processing and increased expression of genes involved in cell adhesion, cell migration, and development. Taken together, these data establish that SMARCB1 re-expression in PD chordomas alters the repertoire of SWI/SNF complexes, perhaps restoring those associated with cellular differentiation. These novel findings support a model in which SMARCB1 inactivation blocks the conversion of growth-promoting SWI/SNF complexes to differentiation-inducing ones, and they implicate SMARCB1 loss as a late event in tumorigenic progression. Importantly, the absence of growth inhibition after SMARCB1 restoration creates a unique opportunity to identify therapeutic vulnerabilities.

TP53, CDKN2A/P16, and NFE2L2/NRF2 regulate the incidence of pure- and combined-small cell lung cancer in mice

Studies have shown that Nrf2^E79Q/+ is one of the most common mutations found in human tumors. To elucidate how this genetic change contributes to lung cancer, we compared lung tumor development in a genetically-engineered mouse model (GEMM) with dual Trp53/p16 loss, the most common mutations found in human lung tumors, in the presence or absence of Nrf2^E79Q/+. Trp53/p16-deficient mice developed combined-small cell lung cancer (C-SCLC), a mixture of pure-SCLC (P-SCLC) and large cell neuroendocrine carcinoma. Mice possessing the LSL-Nrf2^E79Q mutation showed no difference in the incidence or latency of C-SCLC compared with Nrf2^+/+ mice. However, these tumors did not express NRF2 despite Cre-induced recombination of the LSL-Nrf2^E79Q allele. Trp53/p16-deficient mice also developed P-SCLC, where activation of the NRF2^E79Q mutation associated with a higher incidence of this tumor type. All C-SCLCs and P-SCLCs were positive for NE-markers, NKX1-2 (a lung cancer marker) and negative for P63 (a squamous cell marker), while only P-SCLC expressed NRF2 by immunohistochemistry. Analysis of a consensus NRF2 pathway signature in human NE⁺-lung tumors showed variable activation of NRF2 signaling. Our study characterizes the first GEMM that develops C-SCLC, a poorly-studied human cancer and implicates a role for NRF2 activation in SCLC development.

Pilot Study to Detect Genes Involved in DNA Damage and Cancer in Humans: Potential Biomarkers of Exposure to E-Cigarette Aerosols

There is a paucity of data on how gene expression enables identification of individuals who are at risk of exposure to carcinogens from e-cigarette (e-cig) vaping; and how human vaping behaviors modify these exposures. This pilot study aimed to identify genes regulated from acute exposure to e-cig using RT-qPCR. Three subjects (2M and 1F) made three visits to the lab (n_TOT = 9 visits); buccal and blood samples were collected before and immediately after scripted vaping 20 puffs (n_TOT = 18 samples); vaping topography data were collected in each session. Subjects used their own e-cig containing 50:50 propylene glycol (PG):vegetable glycerine (VG) +3-6 mg/mL nicotine. The tumor suppressor TP53 was significantly upregulated in buccal samples. TP53 expression was puff volume and flow rate dependent in both tissues. In blood, the significant downregulation of N-methylpurine DNA glycosylase (MPG), a base excision repair gene, was consistent across all subjects. In addition to DNA repair pathway, cell cycle and cancer pathways were the most enriched pathways in buccal and blood samples, respectively. This pilot study demonstrates that vaping 20 puffs significantly alters expression of TP53 in human tissues; vaping behavior is an important modifier of this response. A larger study is needed to confirm these relationships.

Abstract 1628: Activation of the Nrf2E79Q mutation in mouse lung accelerate development of lung squamous dysplasia

NFE2-related factor 2 (Nrf2) is a transcription factor that regulates more than 500 genes in human cells to protect them from oxidative damage. Somatic mutations in NRF2 resulting in constitutively Nrf2 signaling have been implicated as driver mutations in cancer, especially lung cancer. However, the mechanisms by which NRF2 activating mutations drive tumor development remains unresolved. Therefore, we used a novel genetically engineered mouse model (GEMM), LSL-Nrf2E79Q/+, to understand the role of this activating mutation (one of the most common mutations found in human tumors) in the development of lung tumors. We compared tumor development in two groups of mice: p53fl/fl; p16fl/fl; LSL-Nrf2+/+ (WT, n=38) and p53fl/fl; p16fl/fl; Nrf2E79Q/+ (Het, n=37). We used intranasal instillation of Adenoviral Cre at 6-8 weeks of age to activate the Nrf2E79Q allele and inactivate p53 and p16. Among other tumors, lung tumors were the most common tumors that were found in the GEMM, with major subtypes of lung squamous dysplasia (LSD: pre-malignant lesions of lung squamous cell carcinoma (LSCC)) and lung adenocarcinoma (LADC). Additionally, Het mice showed significantly higher LSD (30%) compared to WT mice (11%) implicating Nrf2E79Q/+ in LSD initiation. However, no significant difference in LADC was observed in Het mice compared to WT mice. Immunohistochemistry (IHC) including Nrf2, TTF1, CK7 and p63 was used to differentiate lung tumors. LADC of WT and Het mice showed negative Nrf2 staining despite the presence of the recombined Nrf2E79Q/+ allele in the Het tumors. However, LSDs developed by Het mice showed positive Nrf2 staining, while those in WT mice were negative, suggesting the mutant Nrf2 increased the frequency of LSDs. LADC of both groups was positive for TTF1 (A primary-non small lung cancer marker, mostly LADC) and CK7 (Cytokeratin7: a marker of epithelial cells). However, LSD lesions were also positive for TTF1. No p63 (a marker of LSCC) stain was shown for LADC of both groups; while p63 was negative to mildly positive in the case of LSD. Results of this study appear consistent with TCGA results where LADC predominantly contained Keap1 loss, while Nrf2 mutations frequently appeared in LSCC. This is the first study to show that a common activating mutation of Nrf2 promotes initiation of LSD that could further develop into LSCC.

Citation Format: Samera H. Hamad, Stephanie Montgomery, Brittany Bowman, Ryan Murphy, Ben Major, Bernard Weissman. Activation of the Nrf2E79Q mutation in mouse lung accelerate development of lung squamous dysplasia [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1628.

ROS production and gene expression in alveolar macrophages exposed to PM(2.5) from Baghdad, Iraq: Seasonal trends and impact of chemical composition

The objective of this study was to assess the impact of changes in atmospheric particulate matter (PM) composition on oxidative stress markers in an in-vitro alveolar macrophage (AM) model. Fifty-three PM2.5 samples were collected during a year-long PM sampling campaign in Baghdad, Iraq, a semi-arid region of the country. Monthly composites were analyzed for chemical composition and for biological activity using in-vitro measurements of ROS production and gene expression in the AM model. Twelve genes that were differentially expressed upon PM exposure were identified and their co-associations with the composition of PM2.5 were examined. Ten of those genes were up-regulated in January and April composites; samples which also exhibited high ROS activity and relatively high PM mass concentration. ROS production was statistically correlated with total PM2.5 mass, levoglucosan (a wood burning tracer) and several trace elements of the PM (especially V and Ni, which are associated with oil combustion). The expression of several cytokine genes was found to be moderately associated with PM mass, crustal materials (indication of dusty days or dust storms) and certain metals (e.g. V, Fe and Ni) in the PM. Thus, the ROS activity association with PM2.5, may, in part, be driven by redox-active metals. The antioxidant response genes (Nqo1 and Hmox1) were moderately associated with polyaromatic hydrocarbons (PAHs) and showed a good correlation (r-Pearson of >0.7) with metals linked to vehicle-related emissions (i.e. Cu, Zn and Sb). Examining these associations in a larger sample pool (e.g. daily samples) would improve the power of the analysis and may strengthen the implication of these chemicals in the oxidative stress of biological systems, which could aid in the development of new metrics of PM toxicity.

Risk assessment of total and bioavailable potentially toxic elements (PTEs) in urban soils of Baghdad-Iraq

The solubility of soil-associated potentially toxic elements (PTEs) in surrogate biological fluids provides valuable information about their potential health hazard. This work addresses the concentrations and bioaccessibility of nine PTEs (As, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn) in thirty eight agricultural land and playground soils collected from a semi-arid urban area of Baghdad-Iraq. Two surrogate biological fluids (SBFs), macrophage vacuole (MS) and gastric (GS) solutions, were used to extract the metals to simulate the biological availability of the PTEs via inhalation and ingestion exposure routes. ICP/AES was used to quantify PTEs in both strong acid digests (for total concentration), and in the SBF extracts. Soil contamination factors showed that some sites exhibited elevated levels of As (36 ± 10 mg/kg), however, these levels of As are not likely to have significant human health impacts whether the particulate arsenic is ingested or/and inhaled. Soil-geochemical variables (including: pH, EC, CO3(=), soil organic carbon (SOC)) and major elements (e.g. Al, Ca, and Fe) were used to interpret the lability of PTEs in the soils. Hazardous index (HI) based non-cancer risk of inhalation and ingestion of PTEs was estimated to be 2-fold higher for that based on total element concentrations compared with that for bioavailable fractions for both children and adults. A similar conclusion was reached for the estimated cancer risk (which was lower than the threshold level of concern for children and adults). A sensitivity analysis showed that there is a 97% chance for children and 90% for adults to have hazardous indices of the total PTEs >1 (the acceptable value); the corresponding metrics for the bioavailable fraction of the elements were 39% for children, and 3% for adults; these results were sensitive to the concentrations of "airborne" soil particles.

Particulate metals and organic compounds from electronic and tobacco-containing cigarettes: comparison of emission rates and secondhand exposure

In recent years, electronic cigarettes have gained increasing popularity as alternatives to normal (tobacco-containing) cigarettes. In the present study, particles generated by e-cigarettes and normal cigarettes have been analyzed and the degree of exposure to different chemical agents and their emission rates were quantified. Despite the 10-fold decrease in the total exposure to particulate elements in e-cigarettes compared to normal cigarettes, specific metals (e.g. Ni and Ag) still displayed a higher emission rate from e-cigarettes. Further analysis indicated that the contribution of e-liquid to the emission of these metals is rather minimal, implying that they likely originate from other components of the e-cigarette device or other indoor sources. Organic species had lower emission rates during e-cigarette consumption compared to normal cigarettes. Of particular note was the non-detectable emission of polycyclic aromatic hydrocarbons (PAHs) from e-cigarettes, while substantial emission of these species was observed from normal cigarettes. Overall, with the exception of Ni, Zn, and Ag, the consumption of e-cigarettes resulted in a remarkable decrease in secondhand exposure to all metals and organic compounds. Implementing quality control protocols on the manufacture of e-cigarettes would further minimize the emission of metals from these devices and improve their safety and associated health effects.

Microbiological and biochemical studies on Gergoush fermentation

According to the results obtained, three steps in Gergoush fermentation were identified. Step one is the primary starter preparation and comprises a 12-15 h propagation of the natural thermotolerant bacterial flora of the legume ingredient of Gergoush using the legume and boiled milk as a propagation medium. This primary starter is then used in step two to inoculate a wheat flour dough to produce the adapted starter in a 1-2-h fermentation time. The adapted starter is finally used in step three to raise the main Gergoush dough. In all of the three steps of Gergoush fermentation, three genera of bacteria dominated. They were tentatively identified as lactic acid bacteria, Bacillus spp. and Clostridium spp. Their counts reached a maximum in the primary starter stage of 2.2 x 10(7), 2.8 x 10(8) and 7.3 x 10(7) CFU/g, respectively. These bacteria produced lactic, acetic and butyric acids. The concentrations of the acids were maximum in the primary starter and reached values of 0.6%, 0.4% and 0.5%, respectively, and the pH decreased from 6.1 to 4.1. Baked Gergoush has a pH of about 5 and contains about 59% starch, 16% protein, 18% fat, 6.5% water and 0.5% ash.

Characterization of the bacterial flora of Sudanese sorghum flour and sorghum sourdough

The microflora of a Sudanese sorghum flour, a spontaneously fermented sourdough and a long-term sourdough produced in a Sudanese household by consecutive re-inoculations, was studied. The dominant contaminants of sorghum flour were Gram-negative, catalase-positive, rod-shaped bacteria with counts of about 10(5) cfu g-1. The spontaneously fermented sorghum sourdough showed a bacterial succession from Gram-negative, catalase-positive contaminants to Enterococcus faecalis, Lactococcus lactis, Lactobacillus fermentum and Lact. reuteri. The total bacterial count reached about 10(10) cfu g-1 and the pH dropped from 6.4 to 3.35 in about 42 h. In this phase, only the Latter two species remained dominant in a ratio of 1:1. From the Sudanese long-term dough, seven strains of Lactobacillus were isolated, representing the dominant flora. Sequence comparison of partial 16S rRNA gene sequences were used to clarify their phylogenetic positions. Five strains were classified as Lact. vaginalis and could be regarded as heterogeneous biovars of this species. The other two strains could be assigned to Lact. helveticus. RAPD-PCR and sugar fermentation patterns were useful in differentiation of these strains.