Expression of Stem Cell Markers in High-LET Space Radiation-Induced Intestinal Tumors in Apc1638N/+ Mouse Intestine

Estimation of cancer risk among astronauts planning to undertake future deep-space missions requires understanding the quantitative and qualitative differences in radiogenic cancers after low- and high-LET radiation exposures. Previously, we reported a multifold higher RBE for high-LET radiation-induced gastrointestinal (GI) tumorigenesis in Apc1638N/+ mice. Using the same model system, i.e., Apc1638N/+ mice, here, we report qualitative differences in the cellular phenotype of low- and high-LET radiation-induced GI tumors. Stem cell (SC) phenotypes were identified using BMI1, ALDH1, CD133, DCLK1, MSI1, and LGR5 markers in low (γ-rays)- and high (56Fe)-LET radiation-induced and spontaneous tumors. We also assessed the expression of these markers in the adjacent normal mucosa. All six of these putative SC markers were shown to be overexpressed in tumors compared to the adjacent normal intestinal tissue. A differential SC phenotype for spontaneous and radiogenic intestinal tumors in Apc1638N/+ mice was observed, where the ALDH1, BMI1, CD133, MSI1, and DCLK1 expressing cells were increased, while LGR5 expressing cells were decreased in 56Fe-induced tumors compared to γ-ray-induced and spontaneous tumors. Furthermore, higher β-catenin activation (marked by nuclear localization) was observed in 56Fe-induced tumors compared to γ and spontaneous tumors. Since differential tumor cell phenotype along with activated β-catenin may very well affect malignant progression, our findings are relevant to understanding the higher carcinogenic risk of high-LET radiation. This study has implications for the assessment of GI-cancer risk among astronauts, as well as for the estimation of secondary cancer risk among patients receiving hadron therapy, considering that our results indicate increased stemness properties after radiation.

High-LET-Radiation-Induced Persistent DNA Damage Response Signaling and Gastrointestinal Cancer Development

Ionizing radiation (IR) dose, dose rate, and linear energy transfer (LET) determine cellular DNA damage quality and quantity. High-LET heavy ions are prevalent in the deep space environment and can deposit a much greater fraction of total energy in a shorter distance within a cell, causing extensive DNA damage relative to the same dose of low-LET photon radiation. Based on the DNA damage tolerance of a cell, cellular responses are initiated for recovery, cell death, senescence, or proliferation, which are determined through a concerted action of signaling networks classified as DNA damage response (DDR) signaling. The IR-induced DDR initiates cell cycle arrest to repair damaged DNA. When DNA damage is beyond the cellular repair capacity, the DDR for cell death is initiated. An alternative DDR-associated anti-proliferative pathway is the onset of cellular senescence with persistent cell cycle arrest, which is primarily a defense mechanism against oncogenesis. Ongoing DNA damage accumulation below the cell death threshold but above the senescence threshold, along with persistent SASP signaling after chronic exposure to space radiation, pose an increased risk of tumorigenesis in the proliferative gastrointestinal (GI) epithelium, where a subset of IR-induced senescent cells can acquire a senescence-associated secretory phenotype (SASP) and potentially drive oncogenic signaling in nearby bystander cells. Moreover, DDR alterations could result in both somatic gene mutations as well as activation of the pro-inflammatory, pro-oncogenic SASP signaling known to accelerate adenoma-to-carcinoma progression during radiation-induced GI cancer development. In this review, we describe the complex interplay between persistent DNA damage, DDR, cellular senescence, and SASP-associated pro-inflammatory oncogenic signaling in the context of GI carcinogenesis.

Low dose radiation upregulates Ras/p38 and NADPH oxidase in mouse colon two months after exposure

BACKGROUND

Exposure to ionizing is known to cause persistent cellular oxidative stress and NADPH oxidase (Nox) is a major source of cellular oxidant production. Chronic oxidative stress is associated with a myriad of human diseases including gastrointestinal cancer. However, the roles of NADPH oxidase in relation of long-term oxidative stress in colonic epithelial cells after radiation exposure are yet to be clearly established.

METHODS AND RESULTS

Mice were exposed either to sham or to 0.5 Gy γ radiation, and NADPH oxidase, oxidative stress, and related signaling pathways were assessed in colon samples 60 days after exposure. Radiation exposure led to increased expression of colon-specific NADPH oxidase isoform, Nox1, as well as upregulation of its modifiers such as Noxa1 and Noxo1 at the mRNA and protein level. Co-immunoprecipitation experiments showed enhanced binding of Rac1, an activator of NADPH oxidase, to Nox1. Increased 4-hydroxynonenal, 8-oxo-dG, and γH2AX along with higher protein carbonylation levels suggest increased oxidative stress after radiation exposure. Immunoblot analysis demonstrates upregulation of Ras/p38 pathway, and Gata6 and Hif1α after irradiation. Increased staining of β-catenin, cyclinD1, and Ki67 after radiation was also observed.

CONCLUSIONS

In summary, data show that exposure to a low dose of radiation was associated with upregulation of NADPH oxidase and its modifiers along with increased Ras/p38/Gata6 signaling in colon. When considered along with oxidative damage and proliferative markers, our observations suggest that the NADPH oxidase pathway could be playing a critical role in propagating long-term oxidative stress after radiation with implications for colon carcinogenesis.

Simulated galactic cosmic radiation (GCR)-induced expression of Spp1 coincide with mammary ductal cell proliferation and preneoplastic changes in ApcMin/+ mouse

Female astronauts inevitably exposed to galactic cosmic radiation (GCR) are considered at a greater risk for mammary cancer development. The purpose of this study is to assess the status of mammary cancer-associated preneoplasia markers after GCR and γ-ray irradiation using a mouse model of human mammary cancer. Female Apc^Min/+ mice were irradiated to 50 cGy of either γ-ray (¹³⁷Cs) or full-spectrum simulated galactic cosmic radiation (GCR) (33-beam), and at 110 - 120 days post-irradiation mice were euthanized, and normal-appearing mammary tissues were analyzed for histological and molecular markers of preneoplasia. Whole-mount staining, hematoxylin and eosin-based histological assessment, and Cyclin D1 immunohistochemistry (IHC) were performed to analyze ductal outgrowth and cell proliferation. Additionally, mRNA expression of known mammary preneoplasia markers (Muc1, Exo1, Foxm1, Depdc1a, Nusap1, Spp1, and Rrm2) was analyzed using qPCR, and their respective protein expression was validated using immunohistochemistry. A significant increase in ductal outgrowth and cell proliferation in mammary tissues of GCR-irradiated mice was noted which indicates a higher risk of mammary cancer, relative to γ-rays. Increased mRNA and protein expression of Spp1 was observed in the GCR group, relative to γ-rays. This study demonstrates the plausibility of Spp1 as a preneoplasia marker in the early detection of mammary cancer after space radiation exposure.

Targeted Inhibition of Upregulated Sodium-Calcium Exchanger in Rat Inferior Colliculus Suppresses Alcohol Withdrawal Seizures

The inferior colliculus (IC) is critical in initiating acoustically evoked alcohol withdrawal-induced seizures (AWSs). Recently, we reported that systemic inhibition of Ca2+ entry via the reverse mode activity of the Na+/Ca2+ exchanger (NCXrev) suppressed AWSs, suggesting remodeling of NCX expression and function, at least in the IC, the site of AWS initiation. Here, we probe putative changes in protein expression in the IC of NCX isoforms, including NCX type 1 (NCX1), 2 (NCX2), and 3 (NCX3). We also evaluated the efficacy of targeted inhibition of NCX1rev and NCX3rev activity in the IC on the occurrence and severity of AWSs using SN-6 and KB-R943, respectively. We used our well-characterized alcohol intoxication/withdrawal model associated with enhanced AWS susceptibility. IC tissues from the alcohol-treated group were collected 3 h (before the onset of AWS susceptibility), 24 h (when AWS susceptibility is maximal), and 48 h (when AWS susceptibility is resolved) following alcohol withdrawal; in comparison, IC tissues from the control-treated group were collected at 24 h after the last gavage. Analysis shows that NCX1 protein levels were markedly higher 3 and 24 h following alcohol withdrawal. However, NCX3 protein levels were only higher 3 h following alcohol withdrawal. The analysis also reveals that bilateral microinjections of SN-6 (but not KB-R7943) within the IC markedly suppressed the occurrence and severity of AWSs. Together, these findings indicate that NCX1 is a novel molecular target that may play an essential role in the pathogenesis and pathophysiology of AWSs.

Heavy-ion radiation-induced colitis and colorectal carcinogenesis in Il10-/- mice display co-activation of β-catenin and NF-κB signaling

Space radiation-induced gastrointestinal (GI) cancer risk models for future interplanetary astronauts are being developed that primarily rely on quantitative animal model studies to assess radiation-quality effects of heavy-ion space radiation exposure in relation to γ-rays. While current GI-cancer risk estimation efforts are focused on sporadic GI-cancer mouse models, emerging in-vivo data on heavy-ion radiation-induced long-term GI-inflammation are indicative of a higher but undetermined risk of GI-inflammation associated cancers, such as colitis-associated cancer (CAC). Therefore, we aimed to assess radiation quality effects on colonic inflammation, colon cancer incidence, and associated signaling events using an in-vivo CAC model i.e., Il10-/- mice. Male Il10-/- mice (8-10 weeks, n = 12/group) were irradiated with either sham, γ-rays or heavy-ions (28Si or 56Fe), and histopathological assessments for colitis and CAC were conducted at 2.5 months post-exposure. qPCR analysis for inflammation associated gene transcripts (Ptges and Tgfb1), and in-situ staining for markers of cell-proliferation (phospho-histone H3), oncogenesis (active-β-catenin, and cyclin D1), and inflammation (phospho-p65NF-κB, iNOS, and COX2) were performed. Significantly higher colitis and CAC frequency were noted after heavy-ion exposure, relative to γ and control mice. Higher CAC incidence after heavy-ion exposure was associated with greater activation of β-catenin and NF-κB signaling marked by induced expression of common downstream inflammatory (iNOS and COX2) and pro-proliferative (Cyclin D1) targets. In summary, IR-induced colitis and CAC incidence in Il10-/- mice depends on radiation quality and display co-activation of β-catenin and NF-κB signaling.

Predominant contribution of the dose received from constituent heavy-ions in the induction of gastrointestinal tumorigenesis after simulated space radiation exposure

Gastrointestinal (GI) cancer risk among astronauts after encountering galactic cosmic radiation (GCR) is predicted to exceed safe permissible limits in long duration deep-space missions. Current predictions are based on relative biological effectiveness (RBE) values derived from in-vivo studies using single-ion beams, while GCR is essentially a mixed radiation field composed of protons (H), helium (He), and heavy ions. Therefore, a sequentially delivered proton (H) → Helium (He) → Oxygen (O) → Silicon (Si) beam was designed to simulate simplified-mixed-field GCR (Smf-GCR), and Apc^1638N/+ mice were total-body irradiated to sham or γ (¹⁵⁷Cs) or Smf-GCR followed by assessment of GI-tumorigenesis at 150 days post-exposure. Further, GI-tumor data from equivalent doses of heavy-ions (i.e., 0.05 Gy of O and Si) in 0.5 Gy of Smf-GCR were compared to understand the contributions of heavy-ions in GI-tumorigenesis. The Smf-GCR-induced tumor and carcinoma count were significantly greater than γ-rays, and male preponderance for GI-tumorigenesis was consistent with our earlier findings. Comparison of tumor data from Smf-GCR and equivalent doses of heavy ions revealed an association between higher GI-tumorigenesis where dose received from heavy-ions contributed to > 95% of the total GI-tumorigenic effect observed after Smf-GCR. This study provides the first experimental evidence that cancer risk after GCR exposure could largely depend on doses received from constituent heavy-ions.

Countermeasure development against space radiation-induced gastrointestinal carcinogenesis: Current and future perspectives

A significantly higher probability of space radiation-induced gastrointestinal (GI) cancer incidence and mortality after a Mars mission has been projected using biophysical and statistical modeling approaches, and may exceed the current NASA mandated limit of less than 3% REID (risk of exposure-induced death). Since spacecraft shielding is not fully effective against heavy-ion space radiation, there is an unmet need to develop an effective medical countermeasure (MCM) strategy against heavy-ion space radiation-induced GI carcinogenesis to safeguard astronauts. In the past, we have successfully applied a GI cancer mouse model approach to understand space radiation-induced GI cancer risk and associated molecular signaling events. We have also tested several potential MCMs to safeguard astronauts during and after a prolonged space mission. In this review, we provide an updated summary of MCM testing using the GI cancer mouse model approach, lessons learned, and a perspective on the senescence signaling targeting approach for desirable protection against space radiation-induced GI carcinogenesis. Furthermore, we also discuss some of the advanced senotherapeutic candidates/combinations as a potential MCM for space radiation-induced GI carcinogenesis.

Total body proton and heavy-ion irradiation causes cellular senescence and promotes pro-osteoclastogenic activity in mouse bone marrow

Low-LET photon radiation-induced persistent alterations in bone marrow (BM) cells are well documented in total-body irradiated (TBI) rodents and also among radiotherapy patients. However, the late effects of protons and high-LET heavy-ion radiation on BM cells and its implications in osteoclastogenesis are not fully understood. Therefore, C57BL6/J female mice (8 weeks; n = 10/group) were irradiated to sham, and 1 Gy of the proton (0.22 keV/μm), or high-LET ⁵⁶Fe-ions (148 keV/μm) and at 60 d post-exposure, mice were sacrificed and femur sections were obtained for histological, cellular and molecular analysis. Cell proliferation (PCNA), cell death (active caspase-3), senescence (p16), osteoclast (RANK), osteoblast (OPG), osteoblast progenitor (c-Kit), and osteoclastogenesis-associated secretory factors (like RANKL) were assessed using immunostaining. While no change in cell proliferation and apoptosis between control and irradiated groups was noted, the number of BM megakaryocytes was significantly reduced in irradiated mice at 60 d post-exposure. A remarkable increase in p16 positive cells indicated a persistent increase in cell senescence, whereas increased RANKL/OPG ratio, reductions in the number of osteoblast progenitor cells, and osteocalcin provided clear evidence that exposure to both proton and ⁵⁶Fe-ions promotes pro-osteoclastogenic activity in BM. Among irradiated groups, ⁵⁶Fe-induced alterations in the BM cellularity and osteoclastogenesis were significantly greater than the protons that demonstrated a radiation quality-dependent effect. This study has implications in understanding the role of IR-induced late changes in the BM cells and its involvement in bone degeneration among deep-space astronauts, and also in patients undergoing proton or heavy-ion radiotherapy.

Effects of dietary aspirin on high-LET radiation-induced prostaglandin E2 levels and gastrointestinal tumorigenesis in Apc1638N/+ mice

Inevitable exposure to high-LET ionizing radiation (IR) present in galactic cosmic radiation (GCR) could enhance gastrointestinal (GI) cancer incidence among astronauts undertaking deep space exploration and GI-cancer mortality has been predicted to far exceed NASA's limit of < 3% REID (Radiation exposure-induced death) from cancer. Therefore, the development of countermeasure agents against high-LET radiation-induced GI cancer is needed to safeguard astronauts during and after an outer space mission. The cyclooxygenase-2/prostaglandin E2 (COX2/PGE2) mediated activation of pro-inflammatory and oncogenic signaling has been reported to play an important role in persistent inflammation and GI-tumorigenesis after high-LET radiation exposure. Therefore, aspirin, a well-known inhibitor of the COX/PGE2 pathway, was evaluated as a potential countermeasure against ²⁸Si-induced PGE2 and tumorigenesis in Apc^1638N/+, a murine model of human GI-cancer. Animals were fed either standard or aspirin supplemented diet (75, 150, or 300 mg/day of human equivalent dose) starting at the age of 4 weeks and continued till the end of the study, while mice were exposed to ²⁸Si-ions (300 MeV/n; 69 keV/μm) at the age of 8 weeks. Serum PGE2 level, GI tumor size (>2mm²), number, and cluster (>5 adjoining tumors) were analyzed at 150 days post-exposure. Aspirin led to a significant reduction in PGE2 in a dose-dependent manner but did not reduce ²⁸Si-induced GI tumorigenesis even at the highest (300 mg/day) dose. In summary, this study suggests that aspirin could reduce high-LET IR-induced pro-inflammatory PGE2 levels, however, lacks the ability to reduce high-LET IR-induced GI tumorigenesis in Apc^1638N/+ mice.

Abstract 3059: Heavy ion radiation exposure perturbs intestinal stem cell homeostasis and induces accelerated tumorigenesis in apc mutant mouse intestine

In a previous study, we demonstrated long-term decreased intestinal epithelial cell migration after low-dose heavy ion iron radiation, and this was associated with increased senescence-associated secretory phenotype (SASP) signaling. However, we know very little about the long-term effects of low dose space radiation on intestinal stem cell (ISC) senescence and SASP that have implications for intestinal homeostasis. Male Lgr5+ (Lgr5-EGFP-IRES-creERT) mice or Lgr5+/APC1638N/+ were exposed to 0.5 Gy of sham, γ-rays, or 28Si (69 keV/μm) radiation and were euthanized 60 or 150 days after irradiation. ISCs were FACS sorted for oxidative stress analysis and assessed for senescence and SASP signaling in tissue sections by immunostaining. Greater cellROX or mitoSOX staining was observed after 28Si indicating higher oxidative stress compared to γ-rays or control Lgr5 positive cells. β-gal co-staining with Lgr5, lysozyme, IL1R, or ILβ showed highest staining in 28Si irradiated compared to controls ISCs samples. γ-H2AX staining showed greater foci numbers in 28Si relative to γ-rays or control group. Higher expression of secretory cytokines IL8 and IL15 was observed in 28Si irradiated ISCs relative to γ-rays or control group at both time points. Elevated expression of DKK2 and activation of NF-κB and p38 MAPK were observed in senescent stem cells of 28Si irradiated relative to γ-rays or control group at these time points. A higher GI tumor count was observed in 28Si compared to γ-irradiated or control Lgr5+/APC1638N/+ mice. In summary, our results demonstrate low dose heavy ion exposure induces ongoing DNA damage, persistent oxidative stress, senescence and acquisition of the SASP in ISCs. Higher levels of oxidative stress, senescence and SASP were observed at 150 compared to the 60-day timepoint. Overall, space radiation-induced oxidative stress, senescence, SASP, and activated p38MAPK/NF-κB pathway may very well have implications in GI carcinogenesis, accelerated aging, and pathological conditions, such as intestinal dysfunction, in astronauts during deep space flights. Since similar effects have been seen in our studies with other particle beams including carbon ions, this has potential relevance to particle radiotherapy as well. This work was supported by NASA NNX15AI21G

Citation Format: Santosh Kumar, Shubhankar Suman, Kamal Datta, Albert J. Fornace. Heavy ion radiation exposure perturbs intestinal stem cell homeostasis and induces accelerated tumorigenesis in apc mutant mouse intestine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3059.

Heavy ion space radiation triggers ongoing DNA base damage by downregulating DNA repair pathways

Long-duration space missions outside low earth orbit will expose astronauts to a cumulative dose of high-energy particle radiation especially to highly damaging heavy ion radiation, which poses considerable risk to astronauts' health. The purpose of the current study was to quantitatively identify oxidatively induced DNA base modifications and assess status of the repair pathways involved in removing the modified bases in mouse intestinal cells after exposure to γ-rays and iron radiation. Mice (C57BL/6J; 6 to 8 weeks; female) were exposed to 0.5 Gy of either γ-rays or iron radiation and control mice were sham-irradiated. Intestinal tissues were collected 2 months after radiation. DNA base lesions were measured using gas chromatography-tandem mass spectrometry with isotope‑dilution. Base excision repair (BER) and nucleotide excision repair (NER) pathways were assessed using PCR and immunoblotting. Effects of iron radiation were compared to γ-rays and sham-irradiated controls. Exposure to iron radiation resulted in significantly higher levels of several DNA base lesions relative to control animals and those exposed to γ radiation. Assessment of BER and NER showed downregulation of pathway factors both at the RNA as well as at the protein levels. Our results not only provide important insight into DNA damage pattern in intestinal cells in response to iron radiation, but they also confirm our previous immunohistochemistry data on oxidatively induced DNA damage. We suggest that downregulation of the BER and NER pathways is contributing to ongoing DNA base damages long time after radiation exposure and has implications for chronic diseases including gastrointestinal diseases after heavy ion radiation exposure during space travel.

Intestinal stem cells acquire premature senescence and senescence associated secretory phenotype concurrent with persistent DNA damage after heavy ion radiation in mice

Heavy ion radiation, prevalent in outer space and relevant for radiotherapy, is densely ionizing and poses risk to stem cells that are key to intestinal homeostasis. Currently, the molecular spectrum of heavy ion radiation-induced perturbations in intestinal stem cells (ISCs), that could trigger intestinal pathologies, remains largely unexplored. The Lgr5-EGFP-IRES-creERT mice were exposed to 50 cGy of iron radiation. Mice were euthanized 60 d after exposure and ISCs were sorted using fluorescence activated cell sorting. Reactive oxygen species (ROS) and mitochondrial superoxide were measured using fluorescent probes. Since DNA damage is linked to senescence and senescent cells acquire senescence-associated secretory phenotype (SASP), we stained ISCs for both senescence markers p16, p21, and p19 as well as SASP markers IL6, IL8, and VEGF. Due to potential positive effects of SASP on proliferation, we also stained for PCNA. Data show increased ROS and ongoing DNA damage, by staining for γH2AX, and 53BP1, along with accumulation of senescence markers. Results also showed increased SASP markers in senescent cells. Collectively, our data suggest that heavy-ion-induced chronic stress and ongoing DNA damage is promoting SASP in a fraction of the ISCs, which has implications for gastrointestinal function, inflammation, and carcinogenesis in astronauts and patients.

AB1231 2019 LUPUS CLASSIFICATION CRITERIA SCORE PREDICTS FUTURE LUPUS HOSPITAL ADMISSION

Background:

There are several validated tools to quantitate lupus disease activity, end-organ damage and overall fragility. An algorithm to predict the hospitalization risk in lupus patients was proposed by Li et al1. That algorithm was able to effectively screen patients at increased risk of hospitalization using EHR information only. Recently, the new 2019 Lupus classification criteria score has been noted to accurately predict 10 year mortality2.

Objectives:

To test the above 2 algorithms with potential to predict lupus related hospital admissions.

First, we attempted to validate the existing algorithm from the index study of Li et al to predict lupus hospitalization.

Second, we tested the 2019 lupus clinical classification score for its ability to predict hospitalizations.

Methods:

A retrospective chart review was performed using EHR data collected from 2013 to 2018 at University of Kentucky (UK) Medical Center. Inclusion criteria were 18 years or older at first outpatient rheumatology appointment at UK, at least 3 outpatient rheumatology visits at UK, and ICD 9/10 code for Lupus. A total of 217 patients met inclusion criteria. Variables similar to the index study were extracted from patients’ first outpatient rheumatology visit at UK. Additionally, 2019 Lupus Classification Criteria score was calculated. Patients who were subsequently hospitalized, manual chart review was done to determine if the hospitalization was attributable to lupus or not.

Results:

Table 1 shows differences between the variables predicting hospitalization in patients in this study (UK) and the Ohio State University (OSU) cohort from whom the admission predicting algorithm was derived1. All the risk factors that were found to predict lupus hospitalization in the index study, failed to achieve a statistical significance in our validation study.

Table 1.

Differences in the variables predicting hospitalization between Index and Validation Cohort

Variables predicting Lupus HospitalizationIndex Study (Ohio State),% of patients(n=226)Validation Study(University of Kentucky)% of patients; (n=217)African American33%18%Creatinine > 1.217%7%Hemoglobin < 11g/dl79%18%Platelets < 180 / uL75%22%High Risk immunosuppression35%9. 2%Missed appointment27%25%

There was more success predicting lupus hospitalization using the 2019 lupus classification criteria score (CCS) (Figure 1). A CCS >=19 predicted higher risk of lupus related hospitalization vs CCS < 19 over the ensuing 2 years (p-0.05).

Figure 1.

Kaplan- Meier Survival Analysis comparing the risk of hospitalization between the groups with 2019 Lupus classification criteria score (CCS) of less than 19 (red) and more/equal to 19 (blue). A time-dependent effect, with the admission free survival curves crossing at two years (Figure 1), indicated a 1 out of 3 chance of lupus related admission during the first 6 months for a high CCS score > =19.

Conclusion:

We failed to validate the EHR algorithm identifying patients at high risk for lupus hospitalization in our less severely affected cohort with fewer admission events to analyze. Nonetheless, “criteria counting” using the weightings of the 2019 lupus classification criteria was granular enough to make these case finding criteria themselves prognostic for future hospitalization risk. It is likely that existing EHRs, using protocols based upon classification criteria scores, are now capable of predicting survival, costs, and admissions automatically.

References:

[1]D Li et al. Determining risk factors that increase hospitalizations in patients with systemic lupus erythematosus, Lupus (2018) 27, 1321–1328

[2]Carneiro et al. A comparison of three classification criteria sets for Systemic Lupus Erythematosus – a study looking at links to outcome and mortality; Arthritis Care Res (Hoboken). 2019 Sep 10. doi: 10.1002/acr.24061

Disclosure of Interests:

Saurav Suman: None declared, Mervat Eissa: None declared, Heidi Rogers: None declared, Aleksander Lenert: None declared, Arnold Stromberg: None declared, william roberts Shareholder of: Own Stocks of Pfizer and Novartis

Possible Role of Myoglobin in Regulating Calpain-1 Activity in Postmortem Beef Muscle

ObjectivesPrevious research revealed a relationship between meat color and beef tenderness and indicated that myoglobin can inhibit calpain-1 in solution. The objective of this study was to determine the extent to which myoglobin and beef color are associated with calpain activity and beef tenderness.Materials and MethodsBeef Longissimus dorsi samples from the left side of Holstein beef carcasses (n = 21) were collected immediately post exsanguination on the processing floor for 0 h analyses. Muscle temperature and pH was measured at 0, 24, and 48 h postmortem. After USDA quality and yield grade determination, steaks (n = 6) were removed from the right side of each carcass (n = 21) at 48 h for analyses at 48 and 336 h postmortem. Color (L*, a*, and b* values), surface myoglobin redox forms, metmyoglobin reducing activity (MRA), total myoglobin concentrations, slice shear force (SSF), Warner-Bratzler shear force (WBSF) were measured. Calpain-1 concentrations and autolysis were determined via Western blot at 0, 48, and 336 h.ResultsDecline in muscle pH was 6.4, 5.8, and 5.6 at 0, 24, and 48 h, respectively. Shear force values at 48 h were 73.19 N for WBSF and 384.21 N for SSF and at 336 h were 48.75 N for WBSF and 260.47 N for SSF. Myoglobin reducing activity at 336 h was positively correlated to WBSF at 48 h and negatively correlated to calpain-1 concentration at 0 h (P < 0.05; Table 9). Color measurements of L* and b* at 48 h were moderately correlated with WBSF at 336 h (P < 0.05; Table 9). The b* measurement at 336 h showed a moderate relationship to calpain-1 concentration at 0 h (P < 0.05; Table 9).ConclusionModerate correlations between color and tenderness measurements taken at 48 h with those taken at 336 h were discovered indicating that myoglobin may impact calpain-1 in vivo.Table 9Correlations (P-values) between selected color and tenderness measurements (n = 21)

Comparison of Lipid and Protein Oxidation Products and their Impact on Colour Stability in Bison Longissimus Lumborum and Psoas Major Muscles

ObjectivesTo compare lipid (malondialdehyde [MDA], 4-hydroxy-2-nonenal [HNE]) and protein (carbonyl content [CAR]) oxidation products and determine their influence on color stability in two bison muscles (longissimus lumborum [LL; color stable] and psoas major [PM; color labile]).Materials and MethodsA total of 10 longissimus lumborun (LL) and 10 psoas major (PM) from five A1 grade bison carcasses were obtained from a commercial slaughter plant within 48 h post-mortem. From each muscle, a 10-cm thick piece was removed and subsampled for evaluation of pH, MDA (by thiobarbituric acid assay), HNE (by ELISA) and CAR (by 2,4-dinitrophenylhydrazine). These measurements allowed the establishment of a baseline for the different oxidation products. The remainder of the muscles were cut into two equal portions, and each portion was vacuum-packaged and assigned to an ageing period of 7 and 14 d at 2°C. At the end of each ageing period, each muscle portion was removed from their packages, pH measured, and steaks obtained for sensory (muscle and discoloration scores) and instrumental color measurements (L*, a* and b*) over 5 d of retail display, and for estimation of MDA, HNE and CAR. After 5 d in retail display and following color and pH measurements the steaks were removed and collected for MDA, HNE and CAR determination. Data were analyzed as a completely randomized design with a split-split plot arrangement. Additionally, correlation and regression analysis were performed to identify the influence of the measured attributes on color.ResultsRegardless of the ageing time, LL showed greater redness and lower surface discoloration by instrumental (a* value; P = 0.04) and sensory (P < 0.01) color evaluation than PM at the end of the retail display. Furthermore, LL exhibited lower MDA, HNE and CAR content compared to PM (P < 0.05). A three-way interaction (muscle × ageing time × retail day display) was detected on MDA content, where PM presented a higher level of MDA with increasing ageing time and retail display than LL (P = 0.02). The pH was not different between LL and PM (P > 0.05) steaks.In both muscles, Pearson (r) and Spearman (rs) correlation coefficients indicated that MDA was the oxidation compound showing the highest correlation to a* (r = –0.78; P < 0.01) and discoloration (rs = 0.81; P < 0.01) scores, followed by a moderate correlation with HNE and CAR (r or rs < 0.7; P < 0.01). The pH did not exhibit correlation with color traits, except for lightness, in both muscles. For the stepwise regression analysis, the main variable entered into the equation for predicting a*, color and discoloration score in PM muscle was MDA with an R2 of 0.72, 0.75 and 0.78, respectively, while for LL muscle, MDA presented an R2 of 0.62, 0.68 and 0.66;, respectively. The pH, HNE and CAR only explained an additional 2% of the variation in those attributes.ConclusionThe results of color attributes corroborated that bison LL is a color-stable muscle due to the lower level of protein and lipid oxidation products developed during storage and retail display compared to PM muscle, which is considered color-labile muscle. The MDA seemed to have remarkable importance in the color deterioration than HNE and CAR, particularly in bison PM muscle.

Myoglobin Modeling to Study Species-Specific Differences in the Distance Between Heme Iron and Proximal and Distal Histidines

ObjectivesSpecies-specific differences in amino acid sequence influence myoglobin redox properties. Previous studies reported that the number and location of histidine residues can influence myoglobin redox stability. However, limited knowledge is currently available on the species-specific differences in the distances between the proximal (His 93) and distal (His 64) histidines and the heme iron in myoglobin. The objective of the current research was to utilize homology-based modeling to determine the distances between the proximal and distal histidines and the heme iron in the myoglobins from beef, pork, goat, bison, sheep, water-buffalo, venison, and emu.Materials and MethodsThe homology-based modeling was conducted using the Iterative Threading Assembly Refinement server (I-TASSER), which identifies the homologous structure models of myoglobins (beef, pork, goat, bison, sheep, water-buffalo, venison, and emu) from Protein Data Bank (PDB) using an algorithm named Local Meta-Threading-Server. The secondary structure of the target protein was predicted based on sequence information from the Protein Secondary Structure PREDiction algorithm. The lowest free energy conformations of the proteins were determined by SPICKER (a clustering approach to identify near-native protein folds). Refinement of the low free energy conformations were done by using Fragment Guided Molecular Dynamics simulations and ModRefiner. Prediction of the ligand-binding site of the target proteins were made by COACH algorithm. The distances between histidines (His 64 and His 93) and the iron in the heme group in the predicted structure of eight different species were determined using PyMOL, a computer software used for molecular visualization.ResultsThe homology-based modeling has shown that despite having 80% sequence similarity and conserved histidine residues (His 64 and His 93), the distance between the distal histidine (His 64) and heme iron varied between 4.3–5.5 Angstrom. Pork myoglobin has the shortest distance, and beef myoglobin has the longest distance. The distance between the proximal histidine (His 93) to the heme varied between 1.9 to 3 Angstrom; sheep myoglobin had the shortest and bison had the longest.ConclusionThe results suggest that in addition to the inherent differences in muscle biochemistry, variations in myoglobin structure also contributes to species-specific differences in meat color.

Fractionated and Acute Proton Radiation Show Differential Intestinal Tumorigenesis and DNA Damage and Repair Pathway Response in ApcMin/+ Mice

PURPOSE

Proton radiation is a major component of the radiation field in outer space and is used clinically in radiation therapy of resistant cancers. Although epidemiologic studies in atom bomb survivors and radiologic workers have established radiation as a risk factor for colorectal cancer (CRC), we have yet to determine the risk of CRC posed by proton radiation owing to a lack of sufficient human or animal data. The purpose of the current study was to quantitatively and qualitatively characterize differential effects of acute and fractionated high-energy protons on colorectal carcinogenesis.

METHODS AND MATERIALS

We used Apc^Min/+ mice, a well-studied CRC model, to examine acute versus fractionated proton radiation-induced differences in intestinal tumorigenesis and associated signaling pathways. Mice were exposed to 1.88 Gy of proton radiation delivered in a single fraction or in 4 equal daily fractions (0.47 Gy × 4). Intestinal tumor number and grade were scored 100 to 110 days after irradiation, and tumor and tumor-adjacent normal tissues were harvested to assess proliferative β-catenin/Akt pathways and DNA damage response and repair pathways relevant to colorectal carcinogenesis.

RESULTS

Significantly higher intestinal tumor number and grade, along with decreased differentiation, were observed after acute radiation relative to fractionated radiation. Acute protons induced upregulation of β-catenin and Akt pathways with increased proliferative marker phospho-histone H3. Increased DNA damage along with decreased DNA repair factors involved in mismatch repair and nonhomologous end joining were also observed after exposure to acute protons.

CONCLUSIONS

We show increased γH2AX, 53BP1, and 8-oxo-dG, suggesting that increased ongoing DNA damage along with decreased DNA repair factors and increased proliferative responses could be triggering a higher number of intestinal tumors after acute relative to fractionated proton exposures in Apc^Min/+ mice. Taken together, our data suggest greater carcinogenic potential of acute relative to fractionated proton radiation.

Abstract 3728: Inverse effect of 28Si and 56Fe radiation on intestinal tumorigenesis vs. carcinogenesis in APC1638N/+ mice

Space radiation is a major risk factor for gastrointestinal (GI) cancer in astronauts and is a matter of concern. Earlier we have reported higher relative effects for intestinal tumorigenesis in APC1638N/+ mice after exposure to different heavy ion radiation spanning a range of LET values. The purpose of the current study was to histologically grade intestinal tumors into adenoma vs. adenocarcinoma and assess relative effects of different heavy ion radiation on tumorigenesis vs carcinogenesis. Tumors from male APC1638N/+ mice 150 d after exposure to whole-body sham, γ (0.3 keV/μm), 12C (13 keV/μm), 28Si (70 keV/μm), or 56Fe (148 keV/μm) radiation were harvested, fixed, paraffin embedded, and sectioned. Radiation doses were 0.1 Gy, 0.5 Gy and a equitoxic dose of 2.0 Gy γ-rays. H&E stained tumor sections from at least 50 tumors per study group were used for histological grading into adenoma and adenocarcinoma. Hotspot mutations for p53 and Kras genes were assessed using targeted PCR followed by amplicon sequencing in 20 tumors per study group. Our previous published data showed that among the three LETs tested relative intestinal tumorigenic effects (relative to γ-rays) peaked at a LET of 70 keV/μm (28Si) with 13 keV/μm (12C) showing the least effect and 148 keV/μm (56Fe) showing an intermediate effect. In contrast, the current study demonstrates that the frequency of adenocarcinoma peaked after 56Fe with the least effect after 12C and an intermediate effect after 28Si. Relative to γ-rays, the carcinoma frequencies were 42.4+0.9, 13.2+0.61 and 8.0+1.14 higher after 56Fe at doses of 0.1, 0.5 and 2.0 Gy respectively. Whereas the relative carcinoma frequencies of 34.2+1.35, 14.0+0.95 and 9.0+2.25 were observed after 28Si at doses of 0.1, 0.5 and 2.0 Gy respectively. While Kras mutation analysis of tumors did not show any difference among radiation types, p53 mutation analysis demonstrate a higher number of mutations in exon 5 in 56Fe relative to 28Si samples. Collectively, our data show that while LET-dependent tumorigenic effects followed a parabolic shape, carcinogenic effects followed a more linear-like pattern with highest adenocarcinoma percentage and frequency at 148 keV/μm (56Fe). Although inverse effects of LET on tumorigenesis vs. carcinogenesis could in part be attributed to the beams’ differential physical properties, our mutation data on p53 supports differential effects of the beams on tumor suppressor mutation.

Citation Format: Santosh Kumar, Shubhankar Suman, Bhaskar V.s. Kallakury, Bo-Hyun Moon, Albert J. Fornace, Kamal Datta. Inverse effect of 28Si and 56Fe radiation on intestinal tumorigenesis vs. carcinogenesis in APC1638N/+ mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3728.

Abstract 3729: Heavy-ion space radiation exposure is a potential risk factor for gastrointestinal tumorigenesis even at extremely low doses

Heavy-ion radiation (HZE)-induced carcinogenesis is a major concern in astronauts planning to undertake long-term deep space exploration, such as a mission to the Mars. Due to high-LET (linear energy transfer) characteristics of HZE ions present in deep space environment, the Mars mission is expected to substantially enhance gastrointestinal cancer risk in astronauts, relative to low-LET radiation. Previously, using three different mouse models of human colorectal cancer (APCmin/+, APC1638N/+ and IL10-/- mouse) we have unequivocally demonstrated a significantly higher risk of intestinal and colonic tumorigenesis after exposure to energetic heavy ions. This study aims to obtain quantitative GI-tumorigenesis data at space relevant doses (5-50 cGy) of heavy ions covering a broad-spectrum of linear energy transfer (2-148 keV/μm), relative to γ-radiation.

The APC1638N/+ mouse was used due to its best signal-to-noise ratio among all previously studied mouse models of human gastrointestinal cancer. Both female and male APC1638N/+ mice (6-8 weeks, n=20) were whole-body exposed to sham-radiation, γ-rays, 4He (2 keV/μm), 12C (13 keV/μm), 16O (22 keV/μm), 28Si (69 keV/μm), and 56Fe (148 keV/μm) -ion radiation at 5, 10, and 50 cGy dose at the NASA Space Radiation Laboratory (NSRL) in Brookhaven National Laboratory. Mice were euthanized at 150 d after radiation exposure and intestinal and colon tumor frequency and size were scored and analyzed as a function of dose, LET, and gender.

The highest increase in tumor frequency was observed after 28Si followed by 56Fe, 16O, 12C, and 4He radiation, and male preponderance for tumorigenesis was evident for each radiation type and dose. At 50 cGy dose, no significant difference in tumorigenesis was observed between γ and 4He. However, at lower doses (5 and 10 cGy) significantly higher tumorigenesis was noted after 4He exposure. Furthermore, calculation of relative biological effectiveness (RBE) for tumorigenesis showed the highest value with 28Si and lower doses showed greater RBE relative to higher doses. No statistical difference in tumorigenesis pattern was evident between 16O and 12C at all studied doses. In addition no significant change in tumorigenesis pattern was evident between 28Si and 56Fe in female mice. Analysis showed greater tumorigenesis per unit of radiation (per cGy) at lower doses suggesting radiation-induced tumorigenesis reaching a saturation point at higher doses.

The lack of understanding on radiation quality effects is one of the major uncertainties in space radiation exposure-associated cancer risk prediction. Using a broad-spectrum of HZE-ions we have demonstrated the dependence of gastrointestinal tumorigenesis on radiation quality even at very low doses, which has implications in cancer risk prediction for astronauts and also for accessing secondary cancer risks after particle radiotherapy.

Citation Format: Shubhankar Suman, Santosh Kumar, Bo-Hyun Moon, Jerry Angdisen, Bhaskar VS Kallakury, Albert J. Fornace, Kamal Datta. Heavy-ion space radiation exposure is a potential risk factor for gastrointestinal tumorigenesis even at extremely low doses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3729.

Elevated lipolysis in adipose tissue by doxorubicin via PPARα activation associated with hepatic steatosis and insulin resistance

Adipose dysfunction is tightly associated with hepatic insulin resistance and steatosis condition. Doxorubicin would disturb the lipid metabolism both in adipose and liver. Here we projected that doxorubicin would impede lipogenesis and elevated lipolysis in adipose tissue would elevate the circulatory lipid profile and leads to insulin resistance. Further exacerbated lipid profile in circulation would impair the lipid metabolism in hepatic tissue which leads to fatty liver condition and consequently related disease during doxorubicin treatment. Doxorubicin impairs the lipogenesis through PPARγ and augments lipolysis and fatty acid oxidation through ATGL and PPARα in adipose tissue. Increased fatty acid level by adipose tissue in circulation would translocate into the liver and dysregulates AHR, PXR, PPARγ, ATGL and Apo B,which further develop insulin resistance and hepatic steatosis condition. The findings add to the mechanistic role of association between adipose tissue dysfunction and hepatic dysfunction.

The effect of carbon irradiation is associated with greater oxidative stress in mouse intestine and colon relative to γ-rays

Carbon irradiation due to its higher biological effectiveness relative to photon radiation is a concern for toxicity to proliferative normal gastrointestinal (GI) tissue after radiotherapy and long-duration space missions such as mission to Mars. Although radiation-induced oxidative stress is linked to chronic diseases such as cancer, effects of carbon irradiation on normal GI tissue have not been fully understood. This study assessed and compared chronic oxidative stress in mouse intestine and colon after different doses of carbon and γ radiation, which are qualitatively different. Mice (C57BL/6J) were exposed to 0.5 or 1.3 Gy of γ or carbon irradiation, and intestinal and colonic tissues were collected 2 months after irradiation. While part of the tissues was used for isolating epithelial cells, tissue samples were also fixed and paraffin embedded for 4 µm thick sections as well as frozen for biochemical assays. In isolated epithelial cells, reactive oxygen species and mitochondrial status were studied using fluorescent probes and flow cytometry. We assessed antioxidant enzymes and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in tissues and formalin-fixed tissue sections were stained for 4-hydroxynonenal, a lipid peroxidation marker. Data show that mitochondrial deregulation, increased NADPH oxidase activity, and decreased antioxidant activity were major contributors to carbon radiation-induced oxidative stress in mouse intestinal and colonic cells. When considered along with higher lipid peroxidation after carbon irradiation relative to γ-rays, our data have implications for functional changes in intestine and carcinogenesis in colon after carbon radiotherapy as well as space travel.

Abstract 4158: Differential intestinal tumorigenesis and DNA repair response in APCMin/+ mice after acute and fractionated proton radiation

Ionizing radiation (IR) exposure is a risk factor for colorectal cancer (CRC) development. With increasing interest in exploring outer space, astronauts on prolonged space missions such as a mission to Mars are expected to receive IR doses that could heighten the risk of CRC. It is estimated that about 90% of the IR in outer space is energetic protons, and the radiation dose during solar particle events (SPEs) could reach up to 2 Gy behind shielding. However, the risk of CRC after energetic proton radiation is not yet fully defined due to lack of human or animal model data. The purpose of the current study was to quantitatively and qualitatively compare and characterize differences in intestinal tumorigenesis between acute and fractionated proton irradiation in APCMin/+ mice, a well-established mouse model for human CRC. Mice were exposed to 1.88 Gy of proton radiation delivered in a single fraction or in 4 equal daily fractions (0.47 Gy x 4). Since proton dose to astronauts are variable based on space environment, in this initial study we chose a high single dose and a lower daily dose pattern to assess intestinal tumorigenesis. Intestinal tumor frequency and grade were noted, and tumor samples were collected from irradiated and control mice euthanized 100 to 110 days after radiation exposure. Molecular analysis was focused on DNA damage and repair, and cellular proliferative signaling pathways relevant to CRC using immunoblots, immunohistochemistry, and qPCR. Relative to control and fractionated-protons, there was significantly higher intestinal tumor frequency and grade after acute (single dose) proton irradiation. Decreased cellular differentiation and increased oxidative damage to DNA was observed after acute proton radiation. At the molecular level, our data showed increased DNA double strand breaks associated with decreased levels of DNA repair proteins, and upregulation of proliferative β-catenin and Akt signaling after acute proton exposure. Since increased DNA damage was not associated with concomitant increased apoptosis, our data suggest continued proliferation of cells bearing sub-lethal damage to promote tumorigenesis. In the fractionated proton group, tumor frequency and grade as well as molecular changes were comparable to sham-irradiated control group. When considered along with decreased tumor frequency and upregulation of DNA repair pathways after fractionation, our data are suggestive of marked differences in carcinogenic effects of acute vs. fractionated proton radiation. In summary, our data suggest that acute exposure to proton radiation is associated with higher risk of intestinal tumorigenesis in APCMin/+ mice with implications for gastrointestinal cancer risk in astronauts undertaking long duration space missions and in patients undergoing proton radiotherapy.

Citation Format: Kamal Datta, Shubhankar Suman, Santosh Kumar, Albert J. Fornace. Differential intestinal tumorigenesis and DNA repair response in APCMin/+ mice after acute and fractionated proton radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4158.

Abstract 4163: Space radiation-induced persistent DNA damage and alterations in cytoskeletal remodeling pathways affect intestinal epithelial cell migration in mice

Lombardi Comprehensive Cancer Center, and Department of Biochemistry and Molecular & Cellular Biology Georgetown University, Washington, DC 20057, USA.

Heavy ion space radiation is considered as a risk factor of gastrointestinal (GI) cancer and perturbed intestinal epithelial cell (IEC) migration has been implicated in GI carcinogenesis. The purpose of the current study was to assess rate of IEC migration as well as dissect key IEC migration signaling events after exposure to heavy ion 56Fe irradiation and compare the results to sham- and γ-irradiation. Male C57BL/6J mice were exposed to 0.5 Gy of either γ or 56Fe radiation and control mice were sham irradiated. IEC migration distance was measured 7 and 60 d after exposure using BrdU pulse labeling. We also analyzed cell polarity, microtubule dynamics, and adhesion dynamics using immunoblots and immunofluorescence. Measure of IEC migration rate showed a greater decrease after 56Fe relative to γ radiation at both the time points. At the molecular level, compared to sham and γ radiation, 56Fe radiation exhibited significantly greater impairment of cell adhesion dynamics evidenced by altered integrins and Rock1 as well as cytoskeletal dynamics evidenced by altered MLCK expression. Similarly, perturbed cell polarity, tight junction, and microtubule dynamics was revealed by the deregulation of Par3, Claudin1, Scribble, Occludin, ZO-1, phospho-Tau and MAP1B. Also, the Wnt/β-catenin and EphB/EphrinB pathways critical for IEC migration consistently showed greater deregulation at both the time points tested after 56Fe radiation relative to γ -rays. Taken together, our molecular findings correlate with the BrdU pulse labeling data, and demonstrate greater effects of heavy ion 56Fe on IEC migration relative to γ -rays. In summary, our results have demonstrated for the first time that radiation can disrupt cell migration dynamics through alteration of signaling molecules involved in crucial cellular processes and these results have implications for heavy ion space radiation-induced gastrointestinal homeostatic deregulation and carcinogenesis.

Citation Format: Santosh Kumar, Shubhankar Suman, Albert Fornace, Kamal Datta. Space radiation-induced persistent DNA damage and alterations in cytoskeletal remodeling pathways affect intestinal epithelial cell migration in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4163.

Abstract 5057: Exposure to highly energetic charged (hze) particle radiation is associated with higher colitis and colorectal cancer incidence in IL10-/- mice

Epidemiological data from atom-bomb survivors and from radiotherapy patients have highlight an underlying risk of colitis and colorectal cancer (CRC) after ionizing radiation-exposure. In contrast, astronauts planning to undertake deep space exploration such as mission to Mars have risk of radiation exposure from highly energetic charged (HZE) particles present in galactic cosmic radiation (GCR) and risk of colitis and CRC after HZE-exposure is yet to be determined. Therefore, animal studies are warranted to address existing uncertainties in colitis and CRC risk prediction after exposure to HZE radiation. Here we report IL10-/- mice as a suitable mouse model for assessment of colitis and CRC risk after exposure to space radiation.

Male mice (n=12 mice/group) were whole-body exposed to sham-radiation, γ-rays and 28Si-ion (300 MeV/n; 70 keV/μm; 1.4 Gy). Mice were sacrificed three months after irradiation, and colon swiss-rolls sections were analyzed for colitis and CRC grade was noted in hematoxylin and eosin stained sections. Immunohistochemistry (β-catenin, Cyclin-D1, phospho-H3, iNOS, phoshoNfKβ-p65, and Cox2) was also performed to assess HZE-induced proliferative and inflammatory signaling. Further, inflammation-associated gene-expression analysis was also conducted in both radiation-induced tumor and adjoining normal tissue area.

Here we report that relative to controls and γ-ray, colitis score, colon tumor incidence, size and grade was significantly higher after space (28Si-ion) radiation exposure. Higher number of phospho-H3 positive cells in 28Si-ion exposed mouse colon demonstrated increased proliferative index and in increased colon tumors of higher grade, could be due to greater activation of β-catenin and its downstream effector cyclin D1. In addition, higher accumulation of iNOS, phoshoNfKβ-p65, and Cox2 in stromal and epithelial cells after space radiation exposure clearly indicates upregulation of both immune and epithelial inflammation as drivers of colitis and CRC development. Inflammation associated protein markers and gene expression signatures were more pronounced after 28Si-ion exposure. Significant up-regulation of GATA4, ICAM1, ITGA2 and EGFR were exclusive to 28Si-ion exposed mouse colon, however PTGES and TGFβ1 were upregulated in both γ and 28Si-ion exposed mice.

Overall, this study suggests that IL10-/- mouse are a suitable model to assess IR-induced colitis and CRC risk, and that space radiation carries higher risk of colitis and CRC incidence, relative to γ-rays at comparable doses. This study has implications for risk prediction in astronauts planning for deep space mission and also for cancer patients planning to undergo particle radiotherapy.

Citation Format: Shubhankar Suman, Bo-Hyun Moon, Albert J. Fornace, Kamal Datta. Exposure to highly energetic charged (hze) particle radiation is associated with higher colitis and colorectal cancer incidence in IL10-/- mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5057.

Abstract A49: Using IL10-/- mouse model to assess heavy-ion radiation exposure-associated colitis and colorectal cancer incidence

Underlying risk of γ-ray-induced colitis and colorectal cancer incidence is emphasized by the studies on atom bomb survivors and also in patients undergoing radiotherapy. However, uncertainties in colitis and CRC risk prediction after exposure to high-LET space (particle) radiation exposure has not been realized due to lack of reliable in vivo data. Here we report IL10-/- mice as a suitable mouse model for assessment of colitis and CRC risk after exposure to space radiation.

Male mice (n=12 mice/group) were whole-body exposed to sham-radiation, γ-rays (137Cs-source, 2.0 Gy), and 28Si-ion (300 MeV/n; 70 keV/μm; 1.4 Gy). We used γ-ray equitoxic doses using relative biologic effectiveness (RBE) values determined earlier. Mice were sacrificed 90 days after irradiation, and colon swiss rolls were prepared and histopathologic assessment of colitis score and CRC grade was noted. Further, inflammation-associated gene-expression analysis was conducted in both radiation-induced tumor and adjoining normal tissue area. Immunohistochemistry (β-catenin, Cyclin-D1, and phospho-histone H3) was also performed to assess HZE-induced proliferative signaling.

Relative to controls and γ-ray, colitis score, colon tumor incidence, size, and grade were significantly higher after space (28Si-ion) radiation exposure. Additionally, tumor incidence per unit of radiation (per cGy) was also higher after 28Si-ion radiation relative to γ radiation. Higher number of phospho-histone H3-positive cells in 28Si-ion exposed mouse colon demonstrated increased proliferative index resulting in increased intestinal tumors of larger size and grade was due to greater activation of β-catenin and its downstream effector cyclin D1. Inflammatory gene signature was more pronounced after 28Si-ion exposure. Significant upregulation of GATA4, ICAM1, ITGA2, and EGFR was exclusive to 28Si-ion exposed mouse colon; however, PTGES and TGFβ1 were upregulated in both γ and 28Si-ion exposed mice.

Overall, our findings suggest that IL10-/- mice are a suitable model to assess IR-induced colitis and CRC risk and space radiation carries higher risk of colitis and CRC incidence, relative to γ-rays at comparable doses. This study has implications for risk prediction in astronauts planning for deep-space missions and also for cancer patients planning to undergo particle radiotherapy.

Citation Format: Shubhankar Suman, Bo-Hyun Moon, Albert J. Fornace, Jr., Kamal Datta. Using IL10-/- mouse model to assess heavy-ion radiation exposure-associated colitis and colorectal cancer incidence [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A49.

Abstract A25: Intestinal tumorigenesis in APCMin/+ mice was higher after acute relative to fractionated proton radiation: Implications for space radiation-induced colorectal carcinogenesis

Ionizing radiation (IR) is a risk factor for colorectal cancer (CRC) based on epidemiologic studies. With increasing interest in exploring outer space, astronauts on prolonged space missions such as a mission to Mars will be exposed to IR doses that are expected to heighten the risk of CRC. Sources of space radiation beyond Earth's magnetosphere are galactic cosmic radiation (GCR) and solar particle event (SPE) and about 90% of the IR in outer space is energetic protons, which are more damaging than photon radiations such as γ-rays. While astronauts on deep-space missions are estimated to receive ~250 μGy/day of proton, radiation dose during SPE could reach up to ~2 Gy behind shielding. However, the risk of CRC after energetic proton radiation is not yet fully defined due to lack of human or animal model data. Limitations in obtaining adequate human data mandate that in vivo mechanistic data for CRC risk estimates be obtained using animal models and surrogate biologic and molecular end points relevant to human disease process. The purpose of the current study was to quantitatively and qualitatively compare and characterize differences in intestinal tumorigenesis between acute and fractionated proton irradiation in APCMin/+ mice, a well-established mouse model for human CRC. Mice were exposed to 1.88 Gy of proton radiation delivered in a single fraction or in 4 equal daily fractions (0.47 Gy x 4). Since proton dose to astronauts is variable based on space environment, in this initial study we chose a high single dose and a low daily dose pattern to assess intestinal tumorigenesis. Intestinal tumor frequency and grade were noted, and tumor and normal tissue samples were collected from irradiated and control mice euthanized 100 to 110 days after radiation exposure. Molecular analysis was focused on DNA damage, genomic instability, specific epigenetic changes and mutation analysis, and cellular proliferative signaling pathways relevant to CRC using immunoblots, immunohistochemistry, and PCR. Relative to control and fractionated protons, there was significantly higher intestinal tumor frequency and grade after acute proton irradiation. At the molecular level our data showed increased DNA damage and DNA double-strand breaks, decreased genomic stability, and upregulation of proliferative β-catenin and Akt signaling after acute proton exposure. Since increased DNA damage was not associated with concomitant increased apoptosis and there was increased microsatellite instability, our data are suggestive of continued proliferation of cells bearing sublethal damages. Mutational analysis showed significantly more tumors had higher overall mutation frequency and increased p53 hot spot mutations after acute relative to fractionated proton exposure. In fractionated proton groups, tumor frequency and grade as well as molecular changes were statistically comparable to control groups. When considered along with higher mutational frequency and altered promoter methylation of key CRC-related genes in tumor adjacent normal tissues, our data are suggestive of marked differences in carcinogenesis of acute vs. fractionated proton radiation with higher tumorigenic effects associated with acute exposures.

Citation Format: Shubhankar Suman, Bo-Hyun Moon, Albert J. Fornace, Jr., Kamal Datta. Intestinal tumorigenesis in APCMin/+ mice was higher after acute relative to fractionated proton radiation: Implications for space radiation-induced colorectal carcinogenesis [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A25.

Metabolomics based predictive classifier for early detection of pancreatic ductal adenocarcinoma

The availability of robust classification algorithms for the identification of high risk individuals with resectable disease is critical to improving early detection strategies and ultimately increasing survival rates in PC. We leveraged high quality biospecimens with extensive clinical annotations from patients that received treatment at the Medstar-Georgetown University hospital. We used a high resolution mass spectrometry based global tissue profiling approach in conjunction with multivariate analysis for developing a classification algorithm that would predict early stage PC with high accuracy. The candidate biomarkers were annotated using tandem mass spectrometry. We delineated a six metabolite panel that could discriminate early stage PDAC from benign pancreatic disease with >95% accuracy of classification (Specificity = 0.85, Sensitivity = 0.9). Subsequently, we used multiple reaction monitoring mass spectrometry for evaluation of this panel in plasma samples obtained from the same patients. The pattern of expression of these metabolites in plasma was found to be discordant as compared to that in tissue. Taken together, our results show the value of using a metabolomics approach for developing highly predictive panels for classification of early stage PDAC. Future investigations will likely lead to the development of validated biomarker panels with potential for clinical translation in conjunction with CA-19-9 and/or other biomarkers.

Alcohol withdrawal upregulates mRNA encoding for CaV2.1-α1 subunit in the rat inferior colliculus

We previously reported increased current density through P-type voltage-gated Ca²⁺ channels in inferior colliculus (IC) neurons during alcohol withdrawal. However, the molecular correlate of this increased P-type channel current is currently unknown. Here, we probe changes in mRNA and protein expression of the pore-forming Ca_V2.1-α1 (P/Q-type) subunits in IC neurons during the course of alcohol withdrawal-induced seizures (AWSs). Rats received three daily doses of ethanol or the vehicle every 8 h for 4 consecutive days. The IC was dissected at various time intervals following alcohol withdrawal, and the mRNA and protein levels of the Ca_V2.1-α1 subunits were measured. In separate experiments, rats were tested for acoustically evoked seizure susceptibility 3, 24, and 48 h after alcohol withdrawal. AWSs were observed 24 h after withdrawal; no seizures were observed at 3 or 48 h or in the control-treated rats. Compared to control-treated rats, the mRNA levels of the Ca_V2.1-α1 subunit were increased 1.9-fold and 2.1-fold at 3 and 24 h, respectively; change in mRNA expression was nonsignificant at 48 h following alcohol withdrawal. Western blot analyses revealed that protein levels of the Ca_V2.1-α1 subunits were not altered in IC neurons following alcohol withdrawal. We conclude that expression of the Cacna1a mRNA increased before the onset of AWS susceptibility, suggesting that altered Ca_V2.1 channel expression may play a role in AWS pathogenesis.

Radioresistant Sf9 insect cells readily undergo an intrinsic mode of apoptosis in response to histone deacetylase (HDAC) inhibition

Insect cell lines have been utilized as an important higher eukaryotic model system to decipher stress responses and cell death mechanisms. Lepidopteran Sf9 cells (derived from the ovaries of Spodoptera frugiperda) display nearly 100 times higher resistance to ionizing radiation in contrast to mammalian cells, which is partly contributed by an unusually high HDAC activity. However, their response to HDAC inhibition remains to be evaluated. In the present study, the effects of HDAC inhibitor (NaBt) on Sf9 cellular/nuclear morphology, cell cycle progression, DNA damage/repair, redox status, and mitochondrial perturbations were evaluated. NaBt-induced apoptosis was evident at 18 h in Sf9 cells at 2 mM concentration, primarily through mitochondrial induction of oxidative stress and subsequent DNA damage. Cell cycle analysis revealed appearance of sub-G1 DNA content at 12 h onwards and DNA fragmentation by 18 h. Initial few hours of treatment caused significant loss in MMP through oxidation of mitochondrial inner membrane protein, i.e., cardiolipin. HDAC inhibition-mediated apoptosis was associated with increased Bax/Bcl2 ratio, mitochondrial cytochrome-c release, and caspase-3 activation. The study thus infers that Sf9 cells, which can withstand very high radiation doses, are quite sensitive to the increase in the chromatin acetylation levels. In addition, HDAC inhibition also sensitized Sf9 cells to radiation-induced DNA damage, further corroborating our recent finding that chromatin compactness contributes significantly to their radioresistance. Therefore, the study demonstrates prominence of prevailing DNA/chromatin protective mechanisms in Lepidopteran insect cells.

Increased Transgenerational Intestinal Tumorigenesis in Offspring of Ionizing Radiation Exposed Parent APC1638N/+ Mice

The purpose of the study was to assess transgenerational intestinal tumorigenic effects of low dose ionizing radiation employing a well-characterized mouse model of human colorectal cancer. Mice (6 to 8 weeks old APC^1638N/+ mice; n=20 per study group) were exposed to whole-body 25 cGy x-rays and mated 2 days post-irradiation. Intestinal tumorigenesis in male and female F1 mice from No Parents Irradiated (NPI), Both Parents Irradiated (BPI), and Male Parent Irradiated (MPI) groups were compared 210 days after birth. Male and female Direct Parent Irradiated (DPI) groups were additional controls for male and female F1 groups respectively. Data showed higher intestinal tumor frequency (± standard error of the mean) in male and female F1 from BPI (male: 7.81 ± 0.91; female: 5.45 ± 0.36) as well as from MPI (male: 6.30 ± 0.33; female: 4.45 ± 0.33) mice relative to F1 from NPI mice (male: 4.2 ± 0.48; female: 3.35 ± 0.37). Compared to male and female DPI (male: 5.55 ± 0.40; female: 3.60 ± 0.22), tumor frequency in F1 mice of BPI and MPI, though higher, was not statistically significant except for DPI vs. BPI in male mice. Additionally, both BPI and MPI showed increased frequency of larger tumors relative to NPI. In summary, our observations demonstrated that the APC^1638N/+ mice due to its low spontaneous tumor frequency could serve as an effective model to study risk of transgenerational carcinogenesis in gastrointestinal tissues after exposure to clinically relevant low doses of ionizing radiation.

Abstract 5469: Low dose ionizing radiation induces persistent activation of NADPH oxidase pathway in mouse colon

Exposure to ionizing radiation has been linked to persistent oxidative stress. The purpose of the current study was to characterize the role of NADPH oxidase pathway in radiation-induced increased oxidant production in colon epithelial cells. Mice (C57BL/6J; 6-8 weeks, male) were exposed to either sham or 0.5 Gy γ radiation, and NADPH oxidase pathway and oxidative stress markers were assessed in colon samples 60 d after exposure. Radiation exposure led to higher elevation of 4-HNE and 8-oxo-dG staining relative to unirradiated control. We also observed increased staining for the proliferative marker phospho-histone H3 in colon sections of irradiated mice. PCR analysis showed increased expression of two NADPH oxidase isoforms, Nox1 and Nox3, in irradiated samples. Additionally, expression of NoxA1 and Noxo1 along with Hif1α were also increased after radiation. Immunoblot analysis confirmed the PCR results, and ChIP assay revealed greater binding of stress response factor GATA6 and Hif1α to Nox1 and Nox3, and Nox3 promoters respectively after radiation exposure relative to control. Co-immunoprecipitation experiments show enhanced binding of Rac1, an activator of NADPH oxidase, to Nox1 and Nox3. In summary, we demonstrated that exposure to a low dose of γ radiation caused long-term upregulation of NADPH oxidase isoforms as well as its regulators and activators such as NoxA1, Noxo1, Hif1α, TLR4, GATA6, Doux1, and Doux2. When considered along with our results on oxidative stress and proliferative markers, our observations on NADPH oxidase pathway provides new insight into molecular events contributing to radiation-induced persistent oxidative stress and cell proliferation in colon, and have implications for colorectal carcinogenesis.

Note: This abstract was not presented at the meeting.

Citation Format: Santosh Kumar, Shubhankar Suman, Bo-Hyun Moon, Albert J. Fornace, Kamal Datta. Low dose ionizing radiation induces persistent activation of NADPH oxidase pathway in mouse colon [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5469. doi:10.1158/1538-7445.AM2017-5469

Abstract 5465: Persistent oxidative stress in mouse intestinal and colonic epithelial cells after exposure to 12C-ion radiation

Purpose: 12C-ion radiotherapy is demonstrating favorable results compared to photon radiotherapy for select cancers. While normal tissue exposure is lower with 12C-ions relative to γ-rays, it cannot be completely eliminated and therefore, late tissue toxicity, inflammation and secondary carcinogenesis cannot be ruled out. The goal of this study was to assess the extent of persistent oxidative stress (POS) after 12C radiation exposure and compare the results to that after γ radiation exposure.

Methods and Materials: Mice (C57BL/6J; 6 to 8 weeks; male) were irradiated with 0.5 or 1.3 Gy of γ or 12C-ion, and intestinal (IEC), colonic (CEC) epithelial cells and tissues were collected 2 months after radiation exposure. In epithelial cells, intracellular ROS, mitochondrial superoxide, mitochondrial membrane potential (MMP), and cardiolipin oxidation were studied by flow-cytometry. Superoxide dismutase (SOD), catalase, and NADPH oxidase activity along with lipid oxidation were also assessed in epithelial cells using biochemical assays.

Results: Our results clearly showed radiation quality and dose-dependent induction of POS. Both intestine and colon showed a higher elevation of intracellular ROS, mitochondrial superoxide, NADPH oxidase activity, and mitochondrial cardiolipin oxidation after 12C relative to γ radiation. Moreover, antioxidant enzyme activity in intestine and colon was also significantly reduced in 12C-irradiated mice. Compared to γ radiation, membrane lipid damage was remarkably higher in both intestine and colon of 12C-ion irradiated mice. At 0.5 Gy, persistent oxidative damage indicated by 4-hydroxynonenal was 3-fold in colon and 1.6 fold in intestine after 12C relative γ radiation.

Conclusions: Mitochondrial deregulation, increased NADPH oxidase activity and loss of SOD and catalase activities were the major contributory events in 12C-ion-induced POS in mouse GI-tissues. Compared to intestine, colon was more susceptible to POS induction that might be due to progressive cell turnover in intestine resulting in faster elimination of initial damage signal in a given time than colon. Taken together, our data suggest that normal tissue exposure to 12C radiation carries higher long-term risk relative to γ-rays at comparable doses and further detail evaluation is warranted.

Citation Format: Shubhankar Suman, Santosh Kumar, Albert J. Fornace, Kamal Datta. Persistent oxidative stress in mouse intestinal and colonic epithelial cells after exposure to 12C-ion radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5465. doi:10.1158/1538-7445.AM2017-5465

Low and high dose rate heavy ion radiation-induced intestinal and colonic tumorigenesis in APC1638N/+ mice

Ionizing radiation (IR) is a recognized risk factor for colorectal cancer (CRC) and astronauts undertaking long duration space missions are expected to receive IR doses in excess of permissible limits with implications for colorectal carcinogenesis. Exposure to IR in outer space occurs at low doses and dose rates, and energetic heavy ions due to their high linear energy transfer (high-LET) characteristics remain a major concern for CRC risk in astronauts. Previously, we have demonstrated that intestinal tumorigenesis in a mouse model (APC^1638N/+) of human colorectal cancer was significantly higher after exposure to high dose rate energetic heavy ions relative to low-LET γ radiation. The purpose of the current study was to compare intestinal tumorigenesis in APC^1638N/+ mice after exposure to energetic heavy ions at high (50cGy/min) and relatively low (0.33cGy/min) dose rate. Male and female mice (6-8 weeks old) were exposed to either 10 or 50cGy of ²⁸Si (energy: 300MeV/n; LET: 70keV/μm) or ⁵⁶Fe (energy: 1000MeV/n; LET: 148keV/μm) ions at NASA Space Radiation Laboratory in Brookhaven National Laboratory. Mice (n=20 mice/group) were euthanized and intestinal and colon tumor frequency and size were counted 150days after radiation exposure. Intestinal tumorigenesis in male mice exposed to ⁵⁶Fe was similar for high and low dose rate exposures. Although male mice showed a decreasing trend at low dose rate relative to high dose rate exposures, the differences in tumor frequency between the two types of exposures were not statistically significant after ²⁸Si radiation. In female mice, intestinal tumor frequency was similar for both radiation type and dose rates tested. In both male and female mice intestinal tumor size was not different after high and low dose rate radiation exposures. Colon tumor frequency in male and female mice after high and low dose rate energetic heavy ions was also not significantly different. In conclusion, intestinal and colonic tumor frequency and size was similar irrespective of energetic heavy ion radiation dose rate suggesting that carcinogenic potential of energetic heavy ions is independent of dose rate.