Radiation-induced Gastrointestinal Toxicity Research Articles

Discordance in acute gastrointestinal toxicity between synchrotron-based proton and linac-based electron ultra-high dose rate irradiation.

Proton FLASH has been investigated using cyclotron and synchrocyclotron beamlines but not synchrotron beamlines. We evaluated the impact of dose rate (ultra-high [UHDR] vs. conventional [CONV]) and beam configuration (shoot-through [ST] vs. spread-out-Bragg-peak [SOBP]) on acute radiation-induced gastrointestinal toxicity (RIGIT) in mice. We also compared RIGIT between synchrotron-based protons and linac-based electrons with matched mean dose rates. We administered abdominal irradiation (12-14 Gy single fraction) to female C57BL/6J mice with an 87 MeV synchrotron-based proton beamline (2 cm diameter field size as a lateral beam). Dose rates were 0.2 Gy/s (S-T pCONV), 0.3 Gy/s (SOBP pCONV), 150 Gy/s (S-T pFLASH), and 230 Gy/s (SOBP pFLASH). RIGIT was assessed by the jejunal regenerating crypt assay and survival. We also compared responses to proton [pFLASH and pCONV] with responses to electron CONV (eCONV, 0.4 Gy/s) and electron FLASH (eFLASH, 188-205 Gy/s). The number of regenerating jejunal crypts at each matched dose was lowest for pFLASH (similar between S-T and SOBP), greater and similar between pCONV (S-T and SOBP) and eCONV, and greatest for eFLASH. Correspondingly, mice that received pFLASH SOBP had the lowest survival rates (50% at 50 days), followed by pFLASH S-T (80%), and pCONV SOBP (90%), but 100% of mice receiving pCONV S-T survived (log-rank P = 0.047 for the four groups). Our findings are consistent with an increase in RIGIT after synchrotron-based pFLASH versus pCONV. This negative proton-specific FLASH effect versus linac-based electron irradiation underscores the importance of understanding the physical and biological factors that will allow safe and effective clinical translation.

Redefining FLASH Radiation Therapy: The Impact of Mean Dose Rate and Dose Per Pulse in the Gastrointestinal Tract

The understanding of how varying radiation beam parameter settings affect the induction and magnitude of the FLASH effect remains limited. We sought to systematically evaluate how the magnitude of radiation-induced gastrointestinal toxicity depends on the interplay between mean dose rate (MDR) and dose per pulse (DPP). C57BL/6J mice received total abdominal irradiation (TAI, 11-14 Gy single fraction) through either conventional (CONV) irradiation (low-DPP and low MDR, CONV) or through various combinations of DPP and MDR up to ultra-high-dose-rate beam conditions. DPPs ranging from 1 to 6 Gy were evaluated, while the total dose and MDR (>100 Gy/s) were kept constant; the effects of MDR were evaluated for the range of 0.3 to 1440 Gy/s, while the total dose and DPP were kept constant. Radiation-induced gastrointestinal toxicity was quantified in nontumor-bearing mice through the regenerating crypt assay and survival assessment. Tumor response was evaluated through tumor growth delay. Within each tested total dose using a constant MDR (>100 Gy/s), increasing DPP led to an increase in sparing (an increase in the number of regenerating crypts), with a more prominent effect seen at 12- and 14-Gy TAI. Interestingly, at DPPs of >4 Gy, a similar level of crypt sparing was demonstrated irrespective of the MDR used (from 0.3 to 1440 Gy/s). At a fixed high-DPP of 4.7 Gy, survival was equivalently improved relative to CONV irrespective of MDR. However, at a lower DPP of 0.93 Gy, an MDR of 104 Gy/s produced a greater survival effect compared with 0.3 Gy/s. We also confirmed that high-DPP, regardless of MDR, produced the same magnitude of tumor growth delay relative to CONV using a clinically relevant melanoma mouse model. This study demonstrates the strong influence that the beam parameter settings have on the magnitude of the FLASH effect. Both high-DPP and ultra-high-dose-rate appeared independently sufficient to produce FLASH sparing of gastrointestinal toxicity while isoeffective tumor response was maintained across all conditions.

Discordance in acute gastrointestinal toxicity between synchrotron-based proton and linac-based electron ultra-high dose rate irradiation.

Proton FLASH has been investigated using cyclotron and synchrocyclotron beamlines but not synchrotron beamlines. We evaluated the impact of dose rate (ultra-high [UHDR] vs. conventional [CONV]) and beam configuration (shoot-through [ST] vs. spread-out-Bragg-peak [SOBP]) on acute radiation-induced gastrointestinal toxicity (RIGIT) in mice. We also compared RIGIT between synchrotron-based protons and linac-based electrons with matched mean dose rates. We administered abdominal irradiation (12-14 Gy single fraction) to female C57BL/6J mice with an 87 MeV synchrotron-based proton beamline (2 cm diameter field size as a lateral beam). Dose rates were 0.2 Gy/s (S-T pCONV), 0.3 Gy/s (SOBP pCONV), 150 Gy/s (S-T pFLASH), and 230 Gy/s (SOBP pFLASH). RIGIT was assessed by the jejunal regenerating crypt assay and survival. We also compared responses to proton [pFLASH and pCONV] with responses to electron CONV (eCONV, 0.4 Gy/s) and electron FLASH (eFLASH, 188-205 Gy/s). The number of regenerating jejunal crypts at each matched dose was lowest for pFLASH (similar between S-T and SOBP), greater and similar between pCONV (S-T and SOBP) and eCONV, and greatest for eFLASH. Correspondingly, mice that received pFLASH SOBP had the lowest survival rates (50% at 50 days), followed by pFLASH S-T (80%), and pCONV SOBP (90%), but 100% of mice receiving pCONV S-T survived (log-rank P = 0.047 for the four groups). Our findings are consistent with an increase in RIGIT after synchrotron-based pFLASH versus pCONV. This negative proton-specific FLASH effect versus linac-based electron irradiation underscores the importance of understanding the physical and biological factors that will allow safe and effective clinical translation.

P53 suppresses MHC class II presentation by intestinal epithelium to protect against radiation-induced gastrointestinal syndrome

Radiation-induced gastrointestinal syndrome is a major complication and limiting factor for radiotherapy. Tumor suppressor p53 has a protective role in radiation-induced gastrointestinal toxicity. However, its underlying mechanism remains unclear. Here we report that regulating the IL12-p40/MHC class II signaling pathway is a critical mechanism by which p53 protects against radiation-induced gastrointestinal syndrome. p53 inhibits the expression of inflammatory cytokine IL12-p40, which in turn suppresses the expression of MHC class II on intestinal epithelial cells to suppress T cell activation and inflammation post-irradiation that causes intestinal stem cell damage. Anti-IL12-p40 neutralizing antibody inhibits inflammation and rescues the defects in intestinal epithelial regeneration post-irradiation in p53-deficient mice and prolongs mouse survival. These results uncover that the IL12-p40/MHC class II signaling mediates the essential role of p53 in ensuring intestinal stem cell function and proper immune reaction in response to radiation to protect mucosal epithelium, and suggest a potential therapeutic strategy to protect against radiation-induced gastrointestinal syndrome.

Mitigative and anti-inflammatory effects of Trichostatin A against radiation-induced gastrointestinal toxicity and gut microbiota alteration in mice

Purpose Radiation-induced gastrointestinal injury (RIGI) is a serious side effect of abdominal and pelvic radiotherapy, which often limits the treatment of gastrointestinal and gynaecological cancers. RIGI is also observed during accidental radiological or nuclear scenarios with no approved agents available till date to prevent or mitigate RIGI in humans. Trichostatin A (TSA), an epigenetic modulator, has been currently in clinical trials for cancer treatment and is also well known for its antibiotic and antifungal properties. Methods In this study, partial body (abdominal) irradiation mice model was used to investigate the mitigative effect of TSA against gastrointestinal toxicity caused by gamma radiation. Mice were checked for alterations in mean body weight, diarrheal incidence, disease activity index and survival against 15 Gy radiation. Structural abnormalities in intestine and changes in microbiota composition were studied by histopathology and 16S rRNA sequencing of fecal samples respectively. Immunoblotting and biochemical assays were performed to check protein nitrosylation, expression of inflammatory mediators, infiltration of inflammatory cells and changes in pro-inflammatory cytokine. Results TSA administration to C57Bl/6 mice improved radiation induced mean body weight loss, maintained better health score, reduced disease activity index and promoted survival. The 16S rRNA sequencing of fecal DNA demonstrated that TSA influenced the fecal microbiota dynamics with significant alterations in the Firmicutes/Bacteriodetes ratio. TSA effectively mitigated intestinal injury, down-regulated NF-κB, Cox-2, iNOS expression, inhibited PGE2 and protein nitrosylation levels in irradiated intestine. The upregulation of NLRP3-inflammasome complex and infiltrations of inflammatory cells in the inflamed intestine were also prevented by TSA. Subsequently, the myeloperoxidase activity in intestine alongwith serum IL-18 levels was found reduced. Conclusion These findings provide evidence that TSA inhibits inflammatory mediators, alleviates gut dysbiosis, and promotes structural restoration of the irradiated intestine. TSA, therefore, can be considered as a potential agent for mitigation of RIGI in humans.

Biomodified Extracellular Vesicles Remodel the Intestinal Microenvironment to Overcome Radiation Enteritis.

Ionizing radiation (IR) is associated with the occurrence of enteritis, and protecting the whole intestine from radiation-induced gut injury remains an unmet clinical need. Circulating extracellular vesicles (EVs) are proven to be vital factors in the establishment of tissue and cell microenvironments. In this study, we aimed to investigate a radioprotective strategy mediated by small EVs (exosomes) in the context of irradiation-induced intestinal injury. We found that exosomes derived from donor mice exposed to total body irradiation (TBI) could protect recipient mice against TBI-induced lethality and alleviate radiation-induced gastrointestinal (GI) tract toxicity. To enhance the protective effect of EVs, profilings of mouse and human exosomal microRNAs (miRNAs) were performed to identify the functional molecule in exosomes. We found that miRNA-142-5p was highly expressed in exosomes from both donor mice exposed to TBI and patients after radiotherapy (RT). Moreover, miR-142 protected intestinal epithelial cells from irradiation-induced apoptosis and death and mediated EV protection against radiation enteritis by ameliorating the intestinal microenvironment. Then, biomodification of EVs was accomplished via enhancing miR-142 expression and intestinal specificity of exosomes, and thus improved EV-mediated protection from radiation enteritis. Our findings provide an effective approach for protecting against GI syndrome in people exposed to irradiation.

Utility of Long-Term Follow-Up to Determine Safety in Radiotherapy-Specific Trials for Localized Prostate Cancer: Meta-Analysis of 29 Randomized Trials

Guideline and clinical adoption of new radiotherapeutic approaches commonly requires 5-10 years of follow-up in randomized trials to ensure long-term safety. This is resource intensive and slows the pace of advancement. We hypothesized that the relative risk (RR) of radiation-induced gastrointestinal (GI) or genitourinary (GU) toxicity would remain similar or decrease overtime with long-term follow-up.PubMed and Embase were systematically searched for randomized trials evaluating changes in radiotherapy (RT; hypofractionation, dose escalation, change in field size) for localized prostate cancer published between 1970 and 2020. Yearly toxicity estimates were digitally extracted for GI and GU toxicity. Short- and long-term toxicity were defined as toxicity arising in years 1-3 and 5-10 post-RT, respectively. RR differences of toxicity between trial arms were calculated, and differences between short- and long-term relative risk measures of toxicity were compared using paired sample Wilcoxon signed-rank tests weighted by trial size.Median follow-up was 6 years (range 3-16) of the included 29 trials (n = 18,069 men). Of trials that reported risk group (67%), 90% of patients had intermediate and high-risk disease, and 57% of patients received ADT. There was no evidence of an increase in the RR of any grade of GI or GU toxicity with follow-up beyond 3 years. The mean RR point estimate of short- vs long-term GI and GU toxicity consistently decreased over time, which was represented by negative values for all grades. Mean differences (late RR - early RR) for grade 1, 2+ and 3+ GI toxicity were (-0.12, P < 0.01), (-0.12, P = 0.02), and (-0.08, P = 1.0), respectively. There were no significant differences in the mean relative risk difference (late RR - early RR) over time for late grade 1 (-0.05, P = 0.3), 2+ (-0.04, P = 0.5), or 3+ (-0.03, P = 0.8) GU toxicity.While toxicity events may continue to occur over time, the relative difference at later time points is similar or lower compared to early time points. Thus, our data does not support concerns for very late relative increases in radiation-induced toxicity. Physician reported toxicity assessed up to 3 years post-treatment is likely sufficient to establish safety following alternative radiotherapy dose/fractionation schedules and target volumes in prostate cancer.

Low-Intensity Exercise Modulates Gut Microbiota to Fight Against Radiation-Induced Gut Toxicity in Mouse Models.

Radiation-induced gastrointestinal (GI) tract toxicity halts radiotherapy and degrades the prognosis of cancer patients. Physical activity defined as “any bodily movement produced by skeletal muscle that requires energy expenditure” is a beneficial lifestyle modification for health. Here, we investigate whether walking, a low-intensity form of exercise, could alleviate intestinal radiation injury. Short-term (15 days) walking protected against radiation-induced GI tract toxicity in both male and female mice, as judged by longer colons, denser intestinal villi, more goblet cells, and lower expression of inflammation-related genes in the small intestines. High-throughput sequencing and untargeted metabolomics analysis showed that walking restructured the gut microbiota configuration, such as elevated Akkermansia muciniphila, and reprogramed the gut metabolome of irradiated mice. Deletion of gut flora erased the radioprotection of walking, and the abdomen local irradiated recipients who received fecal microbiome from donors with walking treatment exhibited milder intestinal toxicity. Oral gavage of A. muciniphila mitigated the radiation-induced GI tract injury. Importantly, walking did not change the tumor growth after radiotherapy. Together, our findings provide novel insights into walking and underpin that walking is a safe and effective form to protect against GI syndrome of patients with radiotherapy without financial burden in a preclinical setting.

Development of an Objective Scoring System for Endoscopic Assessment of Radiation-Induced Upper Gastrointestinal Toxicity.

Simple SummaryHigh-dose radiation therapy techniques have gained increasing interest in pancreatic cancer treatment, but toxicity to the upper gastrointestinal (GI) organs remains a major concern. We aimed to develop an objective toxicity scoring system to be used during endoscopic evaluation that allows for direct assessment of the stomach and duodenum before and after radiation treatment. Our toxicity scoring takes into account the pathological categories of erythema, edema, ulceration, and stricture to determine radiation-related GI toxicity. We assessed and validated the upper GI toxicity of 19 locally advanced pancreatic cancer trial patients undergoing stereotactic body radiation therapy (SBRT). With future usage, we hope this scoring system will provide objective and reliable assessments of changes in GI toxicity during the radiation treatment of pancreatic cancer and for GI toxicity assessment during radiation therapy research trials.We developed and implemented an objective toxicity scoring system to be used during endoscopic evaluation of the upper gastrointestinal (GI) tract in order to directly assess changes in toxicity during the radiation treatment of pancreatic cancer. We assessed and validated the upper GI toxicity of 19 locally advanced pancreatic cancer trial patients undergoing stereotactic body radiation therapy (SBRT). Wilcoxon-signed rank tests were used to compare pre- and post-SBRT scores. Comparison of the toxicity scores measured before and after SBRT revealed a mild increase in toxicity in the stomach and duodenum (p < 0.005), with no cases of severe toxicity observed. Kappa and AC1 statistics analysis were used to evaluate interobserver agreement. Our toxicity scoring system was reliable in determining GI toxicity with a good overall interobserver agreement for pre-treatment scores (stomach, κ = 0.71, p < 0.005; duodenum, κ = 0.88, p < 0.005) and post-treatment scores (stomach, κ = 0.71, p < 0.005; duodenum, κ = 0.76, p < 0.005). The AC1 statistics yielded similar results. With future usage, we hope this scoring system will be a useful tool for objectively and reliably assessing changes in GI toxicity during the treatment of pancreatic cancer and for GI toxicity assessments and comparisons during radiation therapy research trials.

Abdominal FLASH irradiation reduces radiation-induced gastrointestinal toxicity for the treatment of ovarian cancer in mice

Radiation therapy is the most effective cytotoxic therapy for localized tumors. However, normal tissue toxicity limits the radiation dose and the curative potential of radiation therapy when treating larger target volumes. In particular, the highly radiosensitive intestine limits the use of radiation for patients with intra-abdominal tumors. In metastatic ovarian cancer, total abdominal irradiation (TAI) was used as an effective postsurgical adjuvant therapy in the management of abdominal metastases. However, TAI fell out of favor due to high toxicity of the intestine. Here we utilized an innovative preclinical irradiation platform to compare the safety and efficacy of TAI ultra-high dose rate FLASH irradiation to conventional dose rate (CONV) irradiation in mice. We demonstrate that single high dose TAI-FLASH produced less mortality from gastrointestinal syndrome, spared gut function and epithelial integrity, and spared cell death in crypt base columnar cells compared to TAI-CONV irradiation. Importantly, TAI-FLASH and TAI-CONV irradiation had similar efficacy in reducing tumor burden while improving intestinal function in a preclinical model of ovarian cancer metastasis. These findings suggest that FLASH irradiation may be an effective strategy to enhance the therapeutic index of abdominal radiotherapy, with potential application to metastatic ovarian cancer.

Prophylactic Faecalibacterium prausnitzii treatment prevents the acute breakdown of colonic epithelial barrier in a preclinical model of pelvic radiation disease

ABSTRACT Every year, millions of people around the world benefit from radiation therapy to treat cancers localized in the pelvic area. Damage to healthy tissue in the radiation field can cause undesirable toxic effects leading to gastrointestinal complications called pelvic radiation disease. A change in the composition and/or function of the microbiota could contribute to radiation-induced gastrointestinal toxicity. In this study, we tested the prophylactic effect of a new generation of probiotic like Faecalibacterium prausnitzii (F. prausnitzii) on acute radiation-induced colonic lesions. Experiments were carried out in a preclinical model of pelvic radiation disease. Rats were locally irradiated at 29 Gray in the colon resulting in colonic epithelial barrier rupture. Three days before the irradiation and up to 3 d after the irradiation, the F. prausnitzii A2-165 strain was administered daily (intragastrically) to test its putative protective effects. Results showed that prophylactic F. prausnitzii treatment limits radiation-induced para-cellular hyperpermeability, as well as the infiltration of neutrophils (MPO+ cells) in the colonic mucosa. Moreover, F. prausnitzii treatment reduced the severity of the morphological change of crypts, but also preserved the pool of Sox-9+ stem/progenitor cells, the proliferating epithelial PCNA+ crypt cells and the Dclk1+/IL-25+ differentiated epithelial tuft cells. The benefit of F. prausnitzii was associated with increased production of IL-18 by colonic crypt epithelial cells. Thus, F. prausnitzii treatment protected the epithelial colonic barrier from colorectal irradiation. New-generation probiotics may be promising prophylactic treatments to reduce acute side effects in patients treated with radiation therapy and may improve their quality of life.

Extracellular vesicles derived from mesenchymal stromal cells mitigate intestinal toxicity in a mouse model of acute radiation syndrome

BackgroundHuman exposure to high doses of radiation resulting in acute radiation syndrome and death can rapidly escalate to a mass casualty catastrophe in the event of nuclear accidents or terrorism. The primary reason is that there is presently no effective treatment option, especially for radiation-induced gastrointestinal syndrome. This syndrome results from disruption of mucosal barrier integrity leading to severe dehydration, blood loss, and sepsis. In this study, we tested whether extracellular vesicles derived from mesenchymal stromal cells (MSC) could reduce radiation-related mucosal barrier damage and reduce radiation-induced animal mortality.MethodsHuman MSC-derived extracellular vesicles were intravenously administered to NUDE mice, 3, 24, and 48 h after lethal whole-body irradiation (10 Gy). Integrity of the small intestine epithelial barrier was assessed by morphologic analysis, immunostaining for tight junction protein (claudin-3), and in vivo permeability to 4 kDa FITC-labeled dextran. Renewal of the small intestinal epithelium was determined by quantifying epithelial cell apoptosis (TUNEL staining) and proliferation (Ki67 immunostaining). Statistical analyses were performed using one-way ANOVA followed by a Tukey test. Statistical analyses of mouse survival were performed using Kaplan-Meier and Cox methods.ResultsWe demonstrated that MSC-derived extracellular vesicle treatment reduced by 85% the instantaneous mortality risk in mice subjected to 10 Gy whole-body irradiation and so increased their survival time. This effect could be attributed to the efficacy of MSC-derived extracellular vesicles in reducing mucosal barrier disruption. We showed that the MSC-derived extracellular vesicles improved the renewal of the small intestinal epithelium by stimulating proliferation and inhibiting apoptosis of the epithelial crypt cells. The MSC-derived extracellular vesicles also reduced radiation-induced mucosal permeability as evidenced by the preservation of claudin-3 immunostaining at the tight junctions of the epithelium.ConclusionsMSC-derived extracellular vesicles promote epithelial repair and regeneration and preserve structural integrity of the intestinal epithelium in mice exposed to radiation-induced gastrointestinal toxicity. Our results suggest that the administration of MSC-derived extracellular vesicles could be an effective therapy for limiting acute radiation syndrome.

Ultra high dose rate (35\u2009Gy/sec) radiation does not spare the normal tissue in cardiac and splenic models of lymphopenia and gastrointestinal syndrome

Recent reports have shown that very high dose rate radiation (35–100 Gy/second) referred to as FLASH tends to spare the normal tissues while retaining the therapeutic effect on tumor. We undertook a series of experiments to assess if ultra-high dose rate of 35 Gy/second can spare the immune system in models of radiation induced lymphopenia. We compared the tumoricidal potency of ultra-high dose rate and conventional dose rate radiation using a classical clonogenic assay in murine pancreatic cancer cell lines. We also assessed the lymphocyte sparing potential in cardiac and splenic irradiation models of lymphopenia and assessed the severity of radiation-induced gastrointestinal toxicity triggered by the two dose rate regimes in vivo. Ultra-high dose rate irradiation more potently induces clonogenic cell death than conventional dose rate irradiation with a dose enhancement factor at 10% survival (DEF10) of 1.310 and 1.365 for KPC and Panc02 cell lines, respectively. Ultra-high dose rate was equally potent in depleting CD3, CD4, CD8, and CD19 lymphocyte populations in both cardiac and splenic irradiation models of lymphopenia. Radiation-induced gastrointestinal toxicity was more pronounced and mouse survival (7 days vs. 15 days, p = 0.0001) was inferior in the ultra-high dose rate arm compared to conventional dose rate arm. These results suggest that, contrary to published data in other models of radiation-induced acute and chronic toxicity, dose rates of 35 Gy/s do not protect mice from the detrimental side effects of irradiation in our models of cardiac and splenic radiation-induced lymphopenia or gastrointestinal mucosal injury.

Rectal Wall vs. Whole Rectum Dose: Which Volume Better Predicts Gastrointestinal Toxicity from Prostate External Beam Radiotherapy?

Radiation-induced gastrointestinal (GI) toxicity is an important complication of prostate cancer (PCa) radiotherapy (RT) that radiation oncologists seek to minimize by respecting dose constraints for the rectum. It remains unclear whether dose to the rectal wall or whole rectum better predicts GI toxicity. This study used prospectively collected toxicity data from a registered phase III randomized trial to address this question. Dose-volume histogram (DVH) data was extracted from patients enrolled in PCS V, a multi-institutional phase III trial that compared conventionally fractionated (76 Gy in 38 fractions) to hypofractionated RT (68 Gy in 25 fractions) in PCa patients. Acute and late GI toxicity was assessed at 0-6 months and 6-24 months, respectively, using the Common Terminology Criteria for Adverse Events (CTCAE v.4). Rectal wall and whole volumes were collected prospectively. Dosimetric values evaluated were the whole rectum and rectal wall V50, V60, V60, V65, V70, V75, Dmax, and Dmean. Spearman’s rho (ρ) was used to correlate each DVH point of both rectum contours to acute and late GI toxicity. A Fisher’s z-transformation was then performed to test the significance of the difference between the rectal wall and whole rectum ρ’s for individual DVH points. Wilcoxon signed rank test was used to determine whether paired differences of the GI toxicity grade associated with rectal wall vs. whole rectum were significant. In total, DVH data was obtained from 155 patients, with 83 patients having been treated conventionally and 72 with hypofractionation. Spearman’s ρ correlation test revealed a strong association between the whole rectum DVH points and acute GI toxicity, namely for V60 (p=0.04), V65 (p=0.01), V70 (p=0.01) and Dmax (p=0.04). When the same analysis was conducted for late toxicity, only the V50 and Dmean points yielded a marginally significant correlation (p=0.049 and 0.042, respectively). These findings were not observed in the hypofractionated arm. There was no significant association between the rectal wall’s DVH points with either acute nor late GI toxicity in both arms. While the Fisher’s z-transformation analysis did not reveal any significant differences between the correlations of individual DVH points obtained from the rectal wall and whole rectum with acute or late GI toxicity, the distribution of Spearman’s ρ was significantly higher for the whole rectum, compared to its wall for acute toxicity (p=0.047) in the conventional arm. Our data suggests that the whole rectum DVH profile better correlates with acute GI toxicity than that of the rectal wall. Furthermore, the whole rectum’s DVH distribution rather than individual DVH points correlated more reliably with acute GI toxicity. Set-up protocols aiming to minimize rectal wall inter- and intra-fractional movement to improve the accuracy of rectal wall dosimetric values to predict toxicity are thus worthy of future study.

Transient enhancement of p53 activity protects from radiation-induced gastrointestinal toxicity

Gastrointestinal (GI) syndrome is a serious side effect and dose-limiting toxicity observed in patients undergoing lower-abdominal radiotherapy. Previous mouse studies show that p53 gene dosage determines susceptibility to GI syndrome development. However, the translational relevance of p53 activity has not been addressed. Here, we used a knock-in mouse in which the p53-Mdm2 negative feedback loop is genetically disrupted. These mice retain biallelic p53 and thus, normal basal p53 levels and activity. However, due to the lack of p53-mediated Mdm2 transcription, irradiated Mdm2P2/P2 mice exhibit enhanced acute p53 activity, which protects them from GI failure. Intestinal crypt cells residing in the +4 and higher positions exhibit decreased apoptosis, increased p21 expression, and hyperproliferation to reinstate intestinal integrity. Correspondingly, pharmacological augmentation of p53 activity in wild-type mice with an Mdm2 inhibitor protects against GI toxicity without affecting therapeutic outcome. Our results suggest that transient disruption of the p53-Mdm2 interaction to enhance p53 activity could be a viable prophylactic strategy for alleviating GI syndrome in patients undergoing radiotherapy.

Abstract 3745: Mechanisms of HIF2-mediated small intestine radioprotection

Abstract Pancreatic cancer is the fourth-leading cause of cancer-related deaths in the United States, and it is projected to become the second by 2030. The 5-year overall survival rate for locally advanced pancreatic cancer (LAPC) remains &amp;lt; 5%. Chemotherapy regimens often fail due to poor drug delivery and penetration into the tumor. Because surgery is not feasible by definition in LAPC, radiation therapy (RT) is the only option to achieve local control. However, irradiating the pancreas is challenging because potentially curative doses are limited by the neighboring small intestine, which can only tolerate a maximum of 50Gy. A selective radioprotector of the intestinal tract could allow pancreatic cancer patients to receive a higher, and potentially definitive, dose of radiation by increasing the duodenum’s tolerance to survive radiation injury. The EGLN prolyl hydroxylases are cellular oxygen sensors that regulate cell survival and metabolism through the degradation of hypoxia-inducible factors (HIFs) in the presence of oxygen. Our group has shown that HIF2 stabilization through genetic or pharmacologic inhibition of the EGLN family prevents death from radiation-induced gastrointestinal toxicity in mice without protecting the primary tumor. To understand the mechanism by which HIF2 mediates this protection, we generated intestinal organoids from mice with a Cre-inducible allele that expresses a non-degradable form of human HIF1 or HIF2. Whole transcriptomic analysis revealed HIF1 and HIF2 have distinct gene responses in the small intestinal crypt. HIF2 induced the expression of known radiation modulators and genes involved in oxidative damage response, tissue healing, and intestinal homeostasis such as the non-canonical Wnt5a. We validated HIF2 drives Wnt5a expression in multiple organoid model systems. We then generated knockouts (KO) of Wnt5a or Ror2, its cognate receptor, using the Cre/lox system to test if Wnt5a is necessary and sufficient for radioprotection. By using the spheroid formation assay, a modified clonogenic assay, we found Wnt5a KO organoids had decreased crypt regeneration following RT. Our preliminary data suggest Wnt5a protects the duodenum from RT by increasing intestinal stem cell survival. Citation Format: Carolina J. Garcia Garcia, Suman Govindaraju, Marimar de la Cruz Bonilla, Cullen M. Taniguchi. Mechanisms of HIF2-mediated small intestine radioprotection [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 3745.

Neutropenic Enterocolitis in Critically Ill Patients: Spectrum of the Disease and Risk of Invasive Fungal Disease.

Neutropenic enterocolitis occurs in about 5.3% of patients hospitalized for hematologic malignancies receiving chemotherapy. Data from critically ill patients with neutropenic enterocolitis are scarce. Our objectives were to describe the population of patients with neutropenic enterocolitis admitted to an ICU and to investigate the risk factors of invasive fungal disease. A multicentric retrospective cohort study between January 2010 and August 2017. Six French ICUs members of the Groupe de Recherche Respiratoire en Onco-Hématologie research network. Adult neutropenic patients hospitalized in the ICU with a diagnosis of enteritis and/or colitis. Patients with differential diagnosis (Clostridium difficile colitis, viral colitis, inflammatory enterocolitis, mesenteric ischemia, radiation-induced gastrointestinal toxicity, and Graft vs Host Disease) were excluded. None. We included 134 patients (median Sequential Organ Failure Assessment 10 [8-12]), with 38.8% hospital mortality and 32.1% ICU mortality rates. The main underlying malignancies were acute leukemia (n = 65, 48.5%), lymphoma (n = 49, 36.6%), solid tumor (n = 14, 10.4%), and myeloma (n = 4, 3.0%). Patients were neutropenic during a median of 14 days (9-22 d). Infection was documented in 81 patients (60.4%), including an isolated bacterial infection in 64 patients (47.8%), an isolated fungal infection in nine patients (6.7%), and a coinfection with both pathogens in eight patients (5.0%). Radiologically assessed enteritis (odds ratio, 2.60; 95% CI, 1.32-7.56; p = 0.015) and HIV infection (odds ratio, 2.03; 95% CI, 1.21-3.31; p = 0.016) were independently associated with invasive fungal disease. The rate of invasive fungal disease reaches 20% in patients with neutropenic enterocolitis when enteritis is considered. To avoid treatment delay, antifungal therapy might be systematically discussed in ICU patients admitted for neutropenic enterocolitis with radiologically assessed enteritis.

The protective role of jervine against radiation-induced gastrointestinal toxicity

In this study, we investigated whether jervine (J) could prevent gastrointestinal (GI) side effects of abdominopelvic radiotherapy (RT) in Wistar-Albino female rats. Rats were divided into five groups: control (C), J only (J), J administered at 5 mg/kg/days for 7 days, RT only (RT), J before RT (J + RT), J administered for seven days before RT, J both before and after RT (J + RT + J), and J administered for 7 days before RT and after RT for 3 days. The weights of rats were measured on the 1st, 7th, and 10th days of the study. Rats were sacrificed to obtain tissues from the liver and intestine, which was followed by taking blood samples intracardially. In addition, the tissues were stained with pyruvate dehydrogenase (PDH) immunohistochemically. In our study, J supplementation markedly reduced weight loss, and histopathological, immunohistochemical, biochemical results suggest that J had a protective effect on GI toxicity following RT.

Abstract 979: EGLN inhibition reduces gastrointestinal radiation toxicity and improves survival in a murine model of locally advanced pancreatic cancer

Abstract Rationale: Pancreatic cancer is almost always fatal since chemotherapy is only modestly effective and surgery is often not possible. Radiation therapy (RT) can be a definitive treatment in localized pancreatic cancer, but gastrointestinal toxicity to the nearby duodenum limits its efficacy. There are no known medications that can prevent or treat this gastrointestinal radiotoxicity, but we find that FG-4592, a small molecule inhibitor of EGLN proteins, reduces radiation damage to the intestines by selectively enhancing HIF expression within normal intestines but not within tumors. Methods: We developed a murine model of spontaneous pancreatic cancer (KrasLSL/+; Trp53FL/+; Ptf1aCre/+) that behaves similarly to locally advanced disease. KPC mice were screened for tumors by weekly ultrasounds and upon diagnosis were sequentially assigned to receive one of four possible treatments: Vehicle only (VEH), FG-4592 (FG), RT concurrent with vehicle (RT+VEH), or RT concurrent with FG-4592 (RT+FG). Mice were enrolled on a rolling basis and the total time from diagnosis to treatment end was approximately three weeks. Radiation treatments were planned to administer a total of 75Gy in 15 daily fractions. Results: A total of 70 KPC mice were evaluated. The administration of high-dose radiation therapy of &amp;gt;65Gy (high-dose) with or without radioprotection improved survival compared to all animals that received ≤65Gy (low-dose) of treatment or no RT (37 days [95% CI 33-41] vs. 15 days [10-21] vs. 15 days [10-20], respectively; p=0.005). KPC animals that received dose-escalated radiation lived significantly longer compared to unirradiated controls that received vehicle or FG-4592 alone. The median overall survival was compared amongst the treatment groups and was highest (p&amp;lt;.001) for mice that received RT with FG-4592 for radioprotection (43 days, [95% CI 39-47]) versus RT with vehicle (36 days, [95% CI 10-62]), FG alone (29 days, [95% CI 21-37]), or vehicle alone (9 days, [95% CI 5-13]). High-dose RT reduced death from local progression as determined by reduced jaundice and obstruction on necropsy which was present in 64% (25/39) of mice who did not receive RT versus 0% (0/29) who received RT with or without radioprotection (p=0.02). The addition of FG-4592 to RT further improved survival compared to RT + vehicle controls by eliminating radiation-induced gastrointestinal toxicity. Approximately 56% (5/9) of animals that received high-dose RT without radioprotection died from fatal GI bleeding, whereas no bleeding was seen in animals who received high dose RT+ FG-4592 (P&amp;lt;.0001). Thus, these experiments demonstrate a proof of concept that selective radioprotection of the intestinal tract by EGLN inhibition enables higher, and potentially curative, doses of cytotoxic therapy without any tumor protection. Citation Format: Cullen M. Taniguchi, Tara N. Fujimoto, Lauren E. Colbert, Jessica M. Moilkentine, Amit Deorukhkar, Laura J. Baseler, Ramesh Tailor, Gabriel O. Sawakuchi. EGLN inhibition reduces gastrointestinal radiation toxicity and improves survival in a murine model of locally advanced pancreatic cancer [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 979.

Pancreas-Based Multisystem Dysfunction in Radiation-Induced Gastrointestinal Toxicity

Pancreas-Based Multisystem Dysfunction in Radiation-Induced Gastrointestinal Toxicity