Abstract High-Linear Energy Transfer (LET) ion radiation, such as 28Si ions, is densely ionizing and poses a significant risk to astronauts during long-duration space missions. We previously showed that mice exposed to high-LET ionizing radiation (IR) exhibit greater accumulation of senescent cells in the intestine than those exposed to equivalent doses of low-LET γ-rays. However, the mechanisms driving this persistent senescence remain unclear. Given the role of Natural killer (NK) cells in senescent cell clearance, we investigated the impact of IR on intestinal NK cell function. At 60 days post-irradiation, intestinal tissues from 28Si-exposed mice showed a significant reduction in NKp46⁺ NK cells and decreased expression of molecules associated with NK activation and epithelial interactions. NK cell subtype analysis further revealed a decline in functionally mature populations involved in recognizing stressed cells. In parallel, intestinal epithelial cells (IECs) displayed altered expression of NK cell regulatory ligands, including reduced activating signals and increased inhibitory signaling associated with Qa-1b (non-classical MHC class Ib). Mechanistically, these changes were linked to activation of p38 Mitogen-Activated Protein Kinase (MAPK) signaling. Using irradiated intestinal organoids, we observed that pharmacological inhibition of the p38 MAPK pathway decreased Qa-1b expression and enhanced NK cell cytotoxic activity. Causality experiments further demonstrated that Qa-1b directly regulates NK cell–mediated cytotoxicity against senescent IECs. Collectively, these findings indicate that high-LET IR compromises intestinal immune surveillance by impairing NK cell function through a p38 MAPK–Qa-1b signaling axis, providing mechanistic insight into radiation-induced immune dysregulation.

Exposure to high-linear energy transfer (LET) heavy ions (Z > 2) present in galactic cosmic radiation (GCR) is predicted to pose a significant but uncertain risk of gastric (stomach) cancer among astronauts. Uncertainties in current risk estimate models are primarily attributed to the lack of in vivo radiobiological data on dose- and LET-responses of high-LET heavy-ions. To address this gap, we investigated dose- and LET-dependent gastric tumorigenesis in male Apc1638N/+ mice following exposure to γ rays and 28Si ions (69 keV/μm) at doses of 5, 10, and 50 cGy. Additionally, a separate cohort of mice were exposed to 10 cGy of 4He (1.6 keV/μm), 56Fe (148 keV/μm), and 50 cGy of sequentially delivered 4-ions (60 % 1H, 20 % 4He, 10 % 16O, and 10 % 28Si ions) GCR simulation (GCRsim). Animals were euthanized at 5 months post-exposure and formalin-fixed hematoxylin and eosin-stained gastric tissues sections were used for tumor counting as well as for carcinoma identification. Both γ and 28Si induced a dose-dependent increase in tumor burden, with 28Si producing a more pronounced tumorigenic and carcinogenic response. Additionally, the relative risk of carcinoma in the 50 cGy GCRsim group was 12.25, that far exceed the relative risk of 3.5 noted after 50 cGy γ radiation. Further we demonstrate exposure to 69 keV/μm 28Si-ion radiation as a more potent driver of gastric tumorigenesis exceeding those of both γ (∼0.2 keV/μm) and 148 keV/μm 56Fe-ion radiation, suggesting a non-linear response. These findings underscore the potentially disproportionate biological impact of intermediate high-LET ions, such as 28Si, within the complex GCR environment.

Following the publication of the above paper, it was drawn to the Editor's attention by a concerned reader that the statistical analysis in this study may not have employed the most appropriate statistical tests; namely, the paired Student's t‑test was used for comparisons between independent groups, which the reader considered may have inflated the statistical significance. Neither may the paired Student's t‑test have been the most appropriate test to have been selected for various of the migration and invasion assay experiments, wherein at least three groups were being compared. Owing to the fact that the Editorial Office has been made aware of the possibility of inappropriate statistics handling in this paper, we are issuing an Expression of Concern to notify readers of this potential problem while the Editorial Office continues to investigate this matter further. [Molecular Medicine Reports 1: 641‑646, 2008; DOI: 10.3892/mmr_00000005].

Long-duration space missions expose astronauts to galactic cosmic radiation (GCR), a complex spectrum of high-charge, high-energy (HZE) ions that pose significant risks of chronic tissue injury. To model these effects, we examined intestinal outcomes in wild-type mice 5 months after low-dose (50 cGy) 33-ion mixed-field GCR simulation (GCRsim). GCRsim induced sustained DNA double-strand breaks (DSBs) and oxidative stress, as shown by elevated γH2AX foci and 4-HNE staining. Intestinal epithelial cells (IECs) exhibited pronounced senescence, marked by increased SA-β-gal activity, p16 upregulation, LaminB1 loss, and induction of senescence-associated secretory phenotype (SASP) cytokines (Cxcl10, IL-6, IL-1β, Icam1). GCRsim also elevated circulating LINE-1 DNA and reduced expression of DNA-degrading nucleases (DNase2, TREX1), indicating impaired extracellular DNA clearance. Targeted molecular study revealed persistent activation of the cGAS–STING pathway, with elevated cGAS, STING, pTBK1, pIKKα/β, and nuclear pIRF3, pIRF7, and p65, consistent with chronic innate immune signaling. Functionally, GCRsim altered nutrient absorption gene expression—upregulating glucose transporters (Slc2a2, Slc2a5, Slc5a1) and gut hormones (Cck, Gip), while downregulating cholesterol/fat transporters (Npc1, Npc1l1). Biochemical markers supported intestinal injury, with decreased serum citrulline and increased intestinal fatty acid-binding protein (I-FABP), indicating barrier compromise. Collectively, these findings demonstrate that GCRsim drives sustained intestinal dysfunction, highlighting the need for countermeasures to protect GI health during deep-space missions.

Exposure to high-linear energy transfer (LET) heavy ions, such as 28Si, poses a significant cancer risk for astronauts. While previous studies have linked high-LET radiation exposure to persistent oxidative stress and dysregulated stress responses in intestinal crypt cells with an increased risk of tumorigenesis, the relationship between IR-induced oxidative DNA damage and intestinal cancer risk remains incompletely understood. Here, we investigated the time-dependent effects of 28Si-ion radiation on intestinal tumorigenesis and oxidative DNA damage in Apc1638N/+ mice, a model for human intestinal cancer predisposition. Male Apc1638N/+ mice were exposed to 10 cGy of either γ-rays (low-LET) or 28Si-ions (high-LET), and intestinal tumor burden was assessed at 60 and 150 days post-irradiation. While both radiation groups showed modest, non-significant tumor increases at 60 days, 28Si-irradiated mice exhibited an approximately 2.5-fold increase in tumor incidence by 150 days, with a higher incidence of invasive carcinomas compared to γ and sham groups. Serum 8-OxodG levels, a marker of systemic oxidative stress, were significantly elevated in the 28Si-ion group, correlating with increased intestinal 8-OxodG staining. Additionally, assessment of the proliferation marker Cyclin D1 and metaplasia marker Guanylyl Cyclase C (GUCY2C) also revealed significant crypt cell hyperproliferation accompanied by increased metaplasia in 28Si-exposed mouse intestines. Positive correlations between serum 8-OxodG and tumor-associated endpoints provide compelling evidence that exposure to 28Si-ions induces progressive intestinal tumorigenesis through sustained oxidative DNA damage, crypt cell hyperproliferation, and metaplastic transformation. This study provides evidence in support of the radiation quality-dependent progressive increase in systemic and intestinal levels of 8-OxodG during intestinal carcinogenesis. Moreover, the progressive increase in oxidative DNA damage and simultaneous increase in oncogenic events after 28Si exposure also suggest that non-targeted effects might be a significant player in space radiation-induced intestinal cancer development. The correlation between serum 8-OxodG and oncogenic endpoints supports its potential utility as a predictive biomarker of high-LET IR-induced intestinal carcinogenesis, with implications for astronaut health risk monitoring during long-duration space missions.

Exposure to ionizing radiation (IR), both low-LET (e.g., X-rays, γ rays) and high-LET (e.g., heavy ions), increases the risk of gastrointestinal (GI) cancer. Previous studies have linked IR-induced GI cancer to cellular senescence associated secretory phenotype (SASP) signaling. This study explores the potential of senolytic therapy to mitigate IR-induced GI carcinogenesis. Male Apc1638N/+ mice were exposed to γ and 28Si-ions (69 keV/μm) IR. Two months later, they were treated with the senolytic agent ABT-263 orally for 5 days/week until euthanasia, followed by tumor counting and biospecimen collection at five months post-exposure. Tumors were classified as adenoma or carcinoma by a pathologist. Serum cytokine levels were measured, and the markers of senescence (p16), SASP (IL6), and oncogenic β-catenin signaling were assessed using in-situ immunostaining of intestinal tissue. Both low- and high-LET radiation exposure led to an increased frequency of adenoma and carcinoma in Apc1638N/+ mice, accompanied by increased cellular senescence, acquisition of SASP, and overexpression of BCL-XL protein in a subset of these cells. Furthermore, administration of ABT-263 resulted in the elimination of senescent/SASP cells, a decrease in pro-inflammatory cytokines (TNFRSF1B, CCL20, CXCL4, P-selectin, CCL27, and CXCL16) at the systemic level, and downregulation of β-catenin signaling that coincided with decreased GI cancer development. This study suggests a link between IR-induced senescent/SASP cell accumulation and GI cancer development. It also shows that the senolytic agent ABT-263 can regulate IR-induced inflammatory cytokines and carcinogenic mediators both systemically and in intestinal tissue. These findings support the potential of senolytic intervention to reduce IR-induced GI cancer risk.

Heavy ion radiation, prevalent in outer space and relevant for radiotherapy, is densely ionizing and poses a risk to intestinal stem cells (ISCs), which are vital for maintaining intestinal homeostasis. Earlier studies have shown that heavy-ion radiation can cause chronic oxidative stress, persistent DNA damage, cellular senescence, and the development of a senescence-associated secretory phenotype (SASP) in mouse intestinal mucosa. However, the specific impact on different cell types, particularly Lgr5+ intestinal stem cells (ISCs), which are crucial for maintaining cellular homeostasis, GI function, and tumor initiation under genomic stress, remains understudied. Using an ISCs-relevant mouse model (Lgr5+ mice) and its GI tumor surrogate (Lgr5+Apc1638N/+ mice), we investigated ISCs-specific molecular alterations after high-LET radiation exposure. Tissue sections were assessed for senescence and SASP signaling at 2, 5 and 12 months post-exposure. Lgr5+ cells exhibited significantly greater oxidative stress following 28Si irradiation compared to γ-ray or controls. Both Lgr5+ cells and Paneth cells showed signs of senescence and developed a senescence-associated secretory phenotype (SASP) after 28Si exposure. Moreover, gene expression of pro-inflammatory and pro-growth SASP factors remained persistently elevated for up to a year post-28Si irradiation. Additionally, p38 MAPK and NF-κB signaling pathways, which are critical for stress responses and inflammation, were also upregulated after 28Si radiation. Transcripts involved in nutrient absorption and barrier function were also altered following irradiation. In Lgr5+Apc1638N/+ mice, tumor incidence was significantly higher in those exposed to 28Si radiation compared to the spontaneous tumorigenesis observed in control mice. Our results indicate that high-LET 28Si exposure induces persistent DNA damage, oxidative stress, senescence, and SASP in Lgr5+ ISCs, potentially predisposing astronauts to altered nutrient absorption, barrier function, and GI carcinogenesis during and after a long-duration outer space mission.

e16544 Background: Nivolumab with cabozantinib is an accepted treatment option for metastatic RCC (mRCC). Generic TKI access has improved, although nivolumab at currently licensed doses remains unaffordable in India. Immunotherapy is not reimbursable through national health insurance schemes, therefore patients pay out-of-pocket. We evaluated the practice patterns and clinical outcomes with low dose nivolumab combined with TKI in a tertiary academic hospital in India. Methods: We reviewed and abstracted clinical records of mRCC patients treated with nivolumab and TKIs between December 2019 and January 2022. Due to variations in nivolumab dosing frequencies, a metric of dose/Kg/28 days was used for comparative analysis. Patients also had treatment de-escalation in the form of decrease in dose or frequency of nivolumab. Those treated with such de-escalation strategies were noted along with reasons for de-escalation. PFS, OS were calculated as per standard definitions and adverse events graded as per CTCAE4.1. Results: We identified 53 patients who received nivolumab and TKI with 33(62.2%) IMDC intermediate and 12(22.6%) poor prognoses. The mean age was 54.9±8.5 years, predominantly male (83%), non-clear cell histology in 12(22.6%) and clear cell in the remaining. Site of metastases were: pulmonary 43 (81%), CNS 6 (11.3%), liver 16(30%), non-regional nodes 24(45%) and bone 18 (33.9%). Forty-three (81.1%) received no prior systemic therapy. The TKIs used were Lenvatinib (47.2%), cabozantinib(34%) and Axitinib (2%). Fourteen (26.4%) had a flat starting nivolumab dose of 40mg and the median dose of the cohort was 140mg (IQR, 40-240) every 21 days (IQR, 21-28) resulting in a median adjusted weight-based dosing of 2.2mg/kg/28days (IQR, 1.1- 4). Treatment de-escalation was undertaken in 36 (67.9%) due to financial toxicity 24(45.3%) or drug toxicity 10 (18.9%). Interval nephrectomy was performed in 9 (17%). At the median dose (2.2mg/kg/28days) 26 patients with low dose (LD) and 27 high dose (HD) nivolumab were compared. The median PFS of LD and HD groups were 17 (95% CI,10.8-23.1) months and 21 (95% CI,5.7-36.2) months respectively (P=0.75). The median OS of the LD and HD was NR and 21 (4.9-37) months respectively (P=0.017). The grade 3&4 adverse events were palmoplantar dysesthesia 7 (13.2%), hypertension 7(13.2%), arthritis in 3 (5.7%). One patient had Fournier’s gangrene and another had a pulmonary embolism. Primary hypothyroidism 28(52.8%) was the commonest grade 2 adverse event. Cost of 28 days of treatment was ₹ 87,280 ($1055.11 USD). Conclusions: Using LD nivolumab with TKI did not result in inferior survival and is less expensive than the currently approved dose. Treatment de-escalation due to financial toxicity was common and reflects reality in LMICs. Low dose strategies in mRCC warrant evaluation in prospective clinical trials.

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.

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.

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 Apc1638N/+ 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

Background Cancer stem cells (CSCs) play crucial role in tumor progression, drug resistance and relapse in various cancers. CSC niche is comprised of various stromal cell types including Tumor-associated macrophages (TAMs). Extrinsic ques derived from these cells help in maintenance of CSC phenotype. TAMs have versatile roles in tumor progression however their function in enrichment of CSC is poorly explored. Methods Mouse macrophages (RAW264.7) cells were activated by interaction with conditioned media (CM) of murine breast cancer cells (4T1) into TAMs and the effect of activated macrophage (TAM) derived factors was examined on enrichment of cancer stem cells (CSCs) and tumor growth using in vitro and in vivo models. Results In this study, we report that macrophages upon interaction with breast cancer cells activate tumor promoting function and exhibit differential expression of various proteins as shown by secretome analysis using proteomics studies. Based on secretome data, we found that Interleukin-6 (IL-6) is one of the up-regulated genes expressed in activated macrophages. Further, we confirm that TAMs produce high levels of IL-6 and breast cancer cell derived factors induce IL-6 production in activated macrophages via p38-MAPK pathway. Furthermore, we demonstrate that tumor activated macrophages induce enrichment of CSCs and expression of CSC specific transcription factors such as Sox-2, Oct-3/4 and Nanog in breast cancer cells. We further prove that TAM derived IL-6 plays a key role in TAM mediated CSC enrichment through activation of Signal transducer and activator of transcription 3 (STAT-3) signaling. TAM derived IL-6 influences breast cancer cell migration and angiogenesis. Moreover, our in vivo findings indicated that TAM derived IL-6 induces CSC population and resulting tumor growth in breast cancer. Conclusion These finding provide evidence that TAM derived IL-6 plays a major role in CSC enrichment and tumor progression in breast cancer and IL-6 and its regulated signalling network may act as potential therapeutic target for management of breast cancer.

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.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.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.

Context Patients with seminoma present with advanced disease. End-of-treatment (EOT) positron emission tomography-computed tomography (PET-CT) is done to assess response and direct management of post-chemotherapy residual masses. Purpose This article assesses the utility of EOT PET-CT in the management of post-chemotherapy residual lymph nodal masses seminoma. Materials and Methods We analyzed all patients with seminoma who underwent an EOT PET-CT from January 2015 to January 2020 at our center and calculated the positive predictive value (PPV) and negative predictive value (NPV) of EOT PET-CT in the entire cohort of patients and among subgroups. Results A total of 34 male patients underwent EOT PET-CT. Fourteen (41.2%) were stratified as good risk and 20 (58.8%) as intermediate risk. The median follow-up was 23 months (interquartile range: 9.75–53 months). In 23 patients there were residual masses of size more than 3 cm at the EOT PET scan. EOT PET was positive as per the SEMPET criteria in 18 (78%) out of 23 patients. None underwent retroperitoneal lymph node dissection. All four who underwent image-guided biopsy, showed only necrosis on pathology. One patient with positive mediastinal node (standardized uptake value 13.6) had granulomatous inflammation. There was no relapse or progression during this period of follow-up. The NPV for EOT PET-CT for the entire cohort, > 3 cm, and > 6 weeks cutoff were 100%, respectively. The PPV for EOT PET-CT for the entire cohort, > 3 cm residual mass, and > 6 weeks cutoff were 8.7, 11.11, and 6.67%, respectively. Conclusion EOT PET-CT has a low PPV and high NPV in predicting viable tumor in post-chemotherapy residual masses among patients with seminomatous germ cell tumors. If required, EOT PET positivity can be confirmed by a biopsy or reassessed with a repeat PET-CT imaging to document persistent disease prior to further intervention.

One of the hallmarks of a cancer cell is the ability for indefinite proliferation leading to the immortalization of the cell. Activation of several signaling pathways leads to the immortalization of cancer cells via the reactivation of enzyme telomerase (hTERT). hTERT is active in germ cells, stem cells and also cancer cells. An earlier report from our lab suggests that SMAR1, a tumor suppressor protein, is significantly downregulated in the higher grades of colorectal cancers. Our study identifies SMAR1 as a transcriptional repressor of hTERT. We find that SMAR1 interacts with HDAC1/mSin3a co-repressor complex at the hTERT promoter and brings about HDAC1-mediated transcriptional repression of the promoter. Most solid tumors including colorectal cancer reactivate hTERT expression as it confers several advantages to the cancer cells like increased proliferation and angiogenesis. One of these non-canonical functions of hTERT is inducing the pool of cancer stem cell population. We find that in the CD133HighCD44High cancer stem cells population, SMAR1 expression is highly diminished leading to elevated hTERT expression. We also find that knockdown of SMAR1 promotes total CD133+CD44+ population and impart enhanced sphere-forming ability to the colorectal cancer cells. SMAR1 also inhibits invasion and metastasis in colorectal cancer cell lines via repression of hTERT. Our study provides evidence that downregulation of SMAR1 causes activation of hTERT leading to an increase in the cancer stem cell phenotype in colorectal cancer cells.

Abstract 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.

Context-dependent reciprocal crosstalk between cancer and surrounding stromal cells in the tumor microenvironment is imperative for the regulation of various hallmarks of cancer. A myriad of growth factors, chemokines, and their receptors aids in the interaction between cancer cells and tumor microenvironmental components. Osteopontin is a chemokine-like protein, overexpressed in different types of cancers. Osteopontin plays a crucial role in orchestrating dialogue between cancer and stromal cells. Osteopontin, in tumor microenvironment, is produced in tumor as well as stromal cells. Tumor-derived osteopontin regulates proliferation, migration, activation, and differentiation of different types of stromal cells. Osteopontin secreted from tumor cells regulates the generation of cancer-associated fibroblasts from resident fibroblasts and mesenchymal stem cells. Osteopontin also shapes immunosuppressive tumor microenvironment by controlling regulatory T cells and tumor-associated macrophages. Moreover, secretion of osteopontin from tumor stroma has been highly documented. Stromal cell-derived osteopontin induces epithelial-to-mesenchymal transition, angiogenesis, metastasis, and cancer stem cell enrichment. Tumor- or stroma-derived osteopontin mainly functions through binding with cell surface receptors, integrins and CD44, and activates downstream signaling events like PI-3 kinase/Akt and MAPK pathways. Presumably, disrupting the communication between the tumor cells and surrounding microenvironment by targeting osteopontin-regulated signaling using specific antibodies, small-molecule inhibitors, and chemotherapeutic agents is a novel therapeutic strategy for clinical management of cancer.

Tumor-stroma interactions are important determinants for the disease course in cancer. While stromal influence has been known to often play a tumor-promoting role, incomplete mechanistic insight into this phenomenon has prevented its therapeutic targeting. Stromal fibroblasts can be activated by tumor cells to differentiate into cancer-associated fibroblasts (CAFs), that exhibit the traits of myofibroblasts, and in turn, they increase cancer aggressiveness. Here, we report the crosstalk between the cancer cells and stromal fibroblasts that leads to tumor progression. The process is initiated by secretion of a chemokine like protein, osteopontin (OPN) from the cancer cells that differentiates the fibroblasts to myofibroblasts. Tumor-derived OPN achieves this transition by engaging CD44 and αvβ3 integrins on the fibroblast surface, which mediates signaling via Akt and ERK to induce Twist1-dependent gene expression. The OPN-driven CAFs then secrete CXCL12, which in turn triggers epithelial to mesenchymal transition (EMT) in the tumor cells. OPN, produced by the cancer cells, and CXCL12, secreted by activated fibroblasts, are necessary and sufficient to perpetuate the crosstalk. Knocking out OPN in carcinogen-induced mammary tumors or knocking down OPN in cancer cells and fibroblast co-implanted xenografts abrogates myofibroblast differentiation, Twist1, and CXCL12 expression. OPN expression is correlated with CAF-specific gene signature as shown by breast tumor tissue microarray consisting of 100 patient specimens. Bioinformatics analyses have confirmed that the expression of OPN is significantly correlated with the expression of myofibroblast-specific markers as demonstrated in human breast carcinoma dataset of 2509 patients. Our findings describe OPN and CXCL12 act as compelling targets to curb the tumor-promoting features of the stromal components and further suggested that OPN-regulated CXCL12 network might act as potential therapeutic target for the management of CAF-mediated breast cancer progression.

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 Apc1638N/+, 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 Apc1638N/+ mice.

The metabolic shift induced by hypoxia in cancer cells has not been explored at volatilomic level so far. The volatile organic metabolites (VOMs) constitute an important part of the metabolome and their investigation could provide us crucial aspects of hypoxia driven metabolic reconfiguration in cancer cells. To identify the altered volatilomic response induced by hypoxia in metastatic/aggressive breast cancer (BC) cells. BC cells were cultured under normoxic and hypoxic conditions and VOMs were extracted using HS-SPME approach and profiled by standard GC–MS system. Univariate and multivariate statistical approaches (p < 0.05, Log2 FC ≥ 0.58/≤ − 0.58, PC1 > 0.13/< − 0.13) were applied to select the VOMs differentially altered after hypoxic treatment. Metabolic pathway analysis was also carried out in order to identify altered metabolic pathways induced by the hypoxia in the selected BC cells. Overall, 20 VOMs were found to be significantly altered (p < 0.05, PC1 > 0.13/< − 0.13) upon hypoxic exposure to BC cells. Further, cell line specific volatilomic alterations were extracted by comparative metabolic analysis of aggressive (MDA-MB-231) vs. non-aggressive (MCF-7) cells incubated under hypoxia and normoxia. In this case, 15 and 12 VOMs each were found to be significantly altered in aggressive cells when exposed to hypoxic and normoxic condition respectively. Out of these, 9 VOMs were found to be uniquely associated with hypoxia, 6 were specific to normoxia and 6 were found common to both the conditions. Formic acid was identified as the most prominent molecule with higher abundance levels in aggressive as compared to non-aggressive cells in both conditions. Furthermore, metabolic pathway analyses revealed that fatty acid biosynthesis and nicotinate and nicotinamide metabolism were significantly altered in aggressive as compared to non-aggressive cells in normoxia and hypoxia respectively. Higher formate overflow was observed in aggressive cells compared to non-aggressive cells incubated under both the conditions, reinforcing its correlation with aggressive and invasive cancer type. Moreover, under hypoxia, aggressive cells preferred to be bioenergetically more efficient whereas, under normoxia, fatty acid biosynthesis was favoured when compared to non-aggressive cells.