Up-Regulation of Endothelin Type A Receptor in Human and Rat Radiation Proctitis: Preclinical Therapeutic Approach With Endothelin Receptor Blockade

An Oligomeric Sulfated Hyaluronan and Silk-Elastinlike Polymer Combination Protects against Murine Radiation Induced Proctitis

Semisynthetic glycosaminoglycan ethers (SAGEs) are short, sulfated hyaluronans which combine the natural properties of hyaluronan with chemical sulfation. In a murine model, SAGEs provide protection against radiation induced proctitis (RIP), a side effect of lower abdominal radiotherapy for cancer. The anti-inflammatory effects of SAGE have been studied in inflammatory diseases at mucosal barrier sites; however, few mechanisms have been uncovered necessitating high throughput methods. SAGEs were combined with silk-elastinlike polymers (SELPs) to enhance rectal accumulation in mice. After high radiation exposure to the lower abdominal area, mice were followed for 3 days or until they met humane endpoints, before evaluation of behavioral pain responses and histological assessment of rectal inflammation. RNA sequencing was conducted on tissues from the 3-day cohort to determine molecular mechanisms of SAGE–SELP. After 3 days, mice receiving the SAGE–SELP combination yielded significantly lowered pain responses and amelioration of radiation-induced rectal inflammation. Mice receiving the drug–polymer combination survived 60% longer than other irradiated mice, with a fraction exhibiting long term survival. Sequencing reveals varied regulation of toll like receptors, antioxidant activities, T-cell signaling, and pathways associated with pain. This investigation elucidates several molecular mechanisms of SAGEs and exhibits promising measures for prevention of RIP.

Silk-elastinlike copolymers enhance bioaccumulation of semisynthetic glycosaminoglycan ethers for prevention of radiation induced proctitis

Radiation-induced proctitis (RIP) is a debilitating adverse event that occurs commonly during lower abdominal radiotherapy. The lack of prophylactic treatment strategies leads to diminished patient quality of life, disruption of radiotherapy schedules, and limitation of radiotherapy efficacy due to dose-limiting toxicities. Semisynthetic glycosaminoglycan ethers (SAGE) demonstrate protective effects from RIP. However, low residence time in the rectal tissue limits their utility. We investigated controlled delivery of GM-0111, a SAGE analogue with demonstrated efficacy against RIP, using a series of temperature-responsive polymers to compare how distinct phase change behaviors, mechanical properties and release kinetics influence rectal bioaccumulation. Poly(lactic acid)-co-(glycolic acid)-block-poly(ethylene glycol)-block-poly(lactic acid)-co-(glycolic acid) copolymers underwent macroscopic phase separation, expelling >50% of drug during gelation. Poloxamer compositions released GM-0111 cargo within 1 h, while silk-elastinlike copolymers (SELPs) enabled controlled release over a period of 12 h. Bioaccumulation was evaluated using fluorescence imaging and confocal microscopy. SELP-415K, a SELP analogue with 4 silk units, 15 elastin units, and one elastin unit with lysine residues in the monomer repeats, resulted in the highest rectal bioaccumulation. SELP-415K GM-0111 compositions were then used to provide localized protection from radiation induced tissue damage in a murine model of RIP. Rectal delivery of SAGE using SELP-415K significantly reduced behavioral pain responses, and reduced animal mass loss compared to irradiated controls or treatment with traditional delivery approaches. Histological scoring showed RIP injury was ameliorated for animals treated with GM-0111 delivered by SELP-415K. The enhanced bioaccumulation provided by thermoresponsive SELPs via a liquid to semisolid transition improved rectal delivery of GM-0111 to mice and radioprotection in a RIP model.

Quantitative MRI in murine radiation-induced rectocolitis: comparison with histopathological inflammation score

Murine radiation-induced rectocolitis is considered to be a relevant animal model of gastrointestinal inflammation. The purpose of our study was to compare quantitative MRI and histopathological features in this gastrointestinal inflammation model. Radiation rectocolitis was induced by localized single-dose radiation (27 Gy) in Sprague-Dawley rats. T₂ -weighted, T₁ -weighted and diffusion-weighted MRI was performed at 7 T in 16 rats between 2 and 4 weeks after irradiation and in 10 control rats. Rats were sacrificed and the histopathological inflammation score of the colorectal samples was assessed. The irradiated rats showed significant increase in colorectal wall thickness (2.1 ± 0.3 mm versus 0.8 ± 0.3 mm in control rats, P < 0.0001), normalized T₂ signal intensity (4 ± 0.8 versus 2 ± 0.4 AU, P < 0.0001), normalized T₁ signal intensity (1.4 ± 0.1 versus 1.1 ± 0.2 AU, P = 0.0009) and apparent and pure diffusion coefficients (ADC and D) (2.06 × 10^-3 ± 0.34 versus 1.51 × 10^-3 ± 0.23 mm² /s, P = 0.0004, and 1.97 × 10^-3 ± 0.43 mm² /s versus 1.48 × 10^-3 ± 0.29 mm² /s, P = 0.008, respectively). Colorectal wall thickness (r = 0.84, P < 0.0001), normalized T₂ signal intensity (r = 0.85, P < 0.0001) and ADC (r = 0.80, P < 0.0001) were strongly correlated with the histopathological inflammation score, whereas normalized T₁ signal intensity and D were moderately correlated (r = 0.64, P = 0.0006, and r = 0.65, P = 0.0003, respectively). High-field MRI features of single-dose radiation-induced rectocolitis in rats differ significantly from those of control rats. Quantitative MRI characteristics, especially wall thickness, normalized T₂ signal intensity, ADC and D, are potential markers of the histopathological inflammation score.

Monocytes/Macrophages Mobilization Orchestrate Neovascularization after Localized Colorectal Irradiation

In patients undergoing radiotherapy for cancer, radiation dose to healthy tissue can occur, causing microvascular damage. Monocytes that have been shown to promote tissue revascularization comprise the subsets: CD11b⁺Ly6G^-7/4^hi/monocytes^hi and CD11b⁺Ly6G^-7/4^lo/monocytes^lo. We hypothesized that monocytes were implicated in postirradiation blood vessel formation. C57Bl6 mice underwent localized colorectal irradiation and were sacrificed at different times after exposure. Bone marrow, spleen, blood and colon were collected. Fourteen days postirradiation, colons expressed proangiogenic actors and adhesion molecules. Monocytes^hi, which were the main subset of infiltrating monocytes, mobilized to the blood from spleen and bone marrow, peaking at day 14 postirradiation, and were associated with lymphocyte Th1 polarization. At day 28 postirradiation, angiographic score and capillary density increased by ∼1.8-fold, and then returned to nonirradiated levels at day 60. Clodronate-mediated depletion of circulating monocytes prior to irradiation resulted in a ∼1.4-fold decrease in angiographic score and capillary density compared to the nontreated control. Histological analysis of the colon in clodronate-treated mice revealed a massive decrease of macrophage and lymphocyte infiltration as well as reduced collagen deposition in crypt area at day 21. However, late depletion of monocytes from day 25 postirradiation had no effect on fibrotic process. These findings demonstrate a central role for monocyte/macrophage activation in the orchestration of a neovascularization mechanism after localized colorectal irradiation.

Osteopontin knockout does not influence the severity of rectal damage in a preclinical model of radiation proctitis in mice

BACKGROUND

Radiation damage to the normal gut is a dose-limiting factor in the application of radiation therapy to treat abdominal and pelvic cancers. All tissue cell types react in concert to orchestrate an acute inflammatory reaction followed by a delayed chronic scarring process. Osteopontin (OPN) is a matricellular protein known to be involved in various physiological but also pathological processes such as tissue inflammation and fibrosis.

AIMS

The aim of our study was to determine whether OPN knockout influences the severity of radiation proctitis and to investigate the role of OPN in the development of radiation-induced gut damage.

RESULTS

Here we show that human radiation proctitis is associated with increased immunostaining of the intracellular and extracellular/matrix-linked isoforms of OPN. Moreover, endothelial cells in vitro and rectal tissue in a preclinical model of radiation proctitis in mice both respond to radiation exposure by a sustained increase in OPN mRNA and protein levels. Genetic deficiency of OPN did not influence radiation-induced rectal damage and was associated with significantly decreased animal survival. The acute and late radiation injury scores were similar in OPN-null mice compared with their control littermates.

CONCLUSION

This study shows that in our model and given the pleiotropic actions of OPN in tissue inflammation and fibrosis, further studies are necessary to understand the precise roles of OPN in radiation-induced proctitis and to determine whether OPN is a useful therapeutic tool in prevention of radiation-induced intestinal tissue injury.

Mesenchymal stem cell therapy induces glucocorticoid synthesis in colonic mucosa and suppresses radiation-activated T cells: new insights into MSC immunomodulation

Non-neoplastic tissues around an abdomino-pelvic tumor can be damaged by the radiotherapy protocol, leading to chronic gastrointestinal complications that affect the quality of life with substantial mortality. Stem cell-based approaches using immunosuppressive bone marrow mesenchymal stem cells (MSCs) are promising cell therapy tools. In a rat model of radiation proctitis, we evidenced that a single MSC injection reduces colonic mucosa damages induced by ionizing radiation with improvement of the re-epithelization process for up to 21 days. Immune cell infiltrate and inflammatory molecule expressions in the colonic mucosa were investigated. We report that MSC therapy specifically reduces T-cell infiltration and proliferation, and increases apoptosis of radiation-activated T cells. We assessed the underlying molecular mechanisms and found that interleukin-10 and regulatory T lymphocytes are not involved in the immunosuppressive process in this model. However, an increased level of corticosterone secretion and HSD11b1 (11β-hydroxysteroid dehydrogenase type 1)-steroidogenic enzyme expression was detected in colonic mucosa 21 days after MSC treatment. Moreover, blocking the glucocorticoid (GC) receptor using the RU486 molecule statistically enhances the allogenic lymphocyte proliferation inhibited by MSCs in vitro and abrogates the mucosal protection induced by MSC treatment in vivo. Using the irradiation model, we found evidence for a new MSC immunosuppressive mechanism involving GCs.

Mesenchymal stem cell therapy stimulates endogenous host progenitor cells to improve colonic epithelial regeneration

Patients who undergo pelvic radiotherapy may develop severe and chronic complications resulting from gastrointestinal alterations. The lack of curative treatment highlights the importance of novel and effective therapeutic strategies. We thus tested the therapeutic benefit of mesenchymal stem cells (MSC) treatment and proposed molecular mechanisms of action. MSC efficacy was tested in an experimental model of radiation-induced severe colonic ulceration histologically similar to that observed in patients. In this model, MSC from bone marrow were administered intravenously, immediately or three weeks (established lesions) after irradiation. MSC therapy reduces radiation-induced colonic ulceration and increases animal survival. MSC treatment induces therapeutic efficacy whatever the time of cell infusion. Infused-MSC engraft in the colon but also increase endogenous MSC mobilization in blood that have lasting benefits over time. In vitro analysis demonstrates that the MSC effect is mediated by paracrine mechanisms through the non-canonical WNT (Wingless integration site) pathway. In irradiated rat colons, MSC treatment increases the expression of the non-canonical WNT4 ligand by epithelial cells. The epithelial regenerative process is improved after MSC injection by stimulation of colonic epithelial cells positive for SOX9 (SRY-box containing gene 9) progenitor/stem cell markers. This study demonstrates that MSC treatment induces stimulation of endogenous host progenitor cells to improve the regenerative process and constitutes an initial approach to arguing in favor of the use of MSC to limit/reduce colorectal damage induced by radiation.

Gene expression analysis in chronic postradiation proctopathy

PURPOSE

Radiotherapy is one of the important treatment modalities for tumors of pelvic organs. The fixed location of the rectum and its anatomic relationship with other pelvic organs makes it prone to radiation injury resulting in chronic radiation proctopathy in 5% to 20% of patients. Endothelial dysfunction has been associated with a number of pathophysiological processes. Endothelial cells synthesize and release various factors that regulate angiogenesis, inflammatory responses, hemostasis, as well as vascular tone and permeability.

METHODS

Rectum tissue samples from 20 patients with established chronic radiation proctopathy were analysed for the expression of genes related to oxidative stress, tissue hypoxia, angiogenesis, and inflammation [endoglin (ENG), activin receptor-like kinase 1 (ALK1), platelet endothelial cell adhesion molecule 1 (PECAM), vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), hypoxia-inducible factor 1 (HIF-1), and interleukin-1 beta (IL-1β)].

RESULTS

Overexpression of HIF-1, VEGF, FGF2, and IL-1β was detected in affected tissue. For the first time, a significant suppression of activin receptor-like kinase 1 and ENG could be revealed.

CONCLUSION

The data provided here allow further insight into the pathogenesis of radiation-induced rectum injury. Radiation-induced damage is not confined to a single event but involves complex signaling between different pathways, enhancing and maintaining the processes that lead to mucosal damage. The results indicate that postradiation tissue hypoxia is critical for fibrosis, which involves changes in the expression of profibrotic and angiogenic factors in rectal tissue.

Mast cells are an essential component of human radiation proctitis and contribute to experimental colorectal damage in mice

Radiation proctitis is characterized by mucosal inflammation followed by adverse chronic tissue remodeling and is associated with substantial morbidity and mortality. Mast cell hyperplasia has been associated with diseases characterized by pathological tissue remodeling and fibrosis. Rectal tissue from patients treated with radiotherapy shows mast cell hyperplasia and activation, suggesting that these cells play a role in the development of radiation-induced sequelae. To investigate the role of mast cells in radiation damage, experimental radiation proctitis was induced in a mast cell-deficient (W(sh)/W(sh)) mouse model. The colon and rectum of W(sh)/W(sh) and wild-type mice were exposed to 27-Gy single-dose irradiation and studied after 2 and 14 weeks. Irradiated rodent rectum showed mast cell hyperplasia. W(sh)/W(sh) mice developed less acute and chronic rectal radiation damage than their control littermates. Tissue protection was associated with increased tissue neutrophil influx and expression of several inflammatory mediators immediately after radiation exposure. It was further demonstrated that mast cell chymase, tryptase, and histamine could change human muscularis propria smooth muscle cells into a migrating/proliferating and proinflammatory phenotype. These data show that mast cells have deleterious effects on both acute and chronic radiation proctitis, possibly by limiting acute tissue neutrophil influx and by favoring phenotypic orientation of smooth muscle cells, thus making them active participants in the radiation-induced inflammatory process and dystrophy of the rectal wall.

Potential targets for intervention in radiation-induced heart disease

Radiotherapy of thoracic and chest wall tumors, if all or part of the heart was included in the radiation field, can lead to radiation-induced heart disease (RIHD), a late and potentially severe side effect. RIHD presents clinically several years after irradiation and manifestations include accelerated atherosclerosis, pericardial and myocardial fibrosis, conduction abnormalities, and injury to cardiac valves. The pathogenesis of RIHD is largely unknown, and a treatment is not available. Hence, ongoing pre-clinical studies aim to elucidate molecular and cellular mechanisms of RIHD. Here, an overview of recent pre-clinical studies is given, and based on the results of these studies, potential targets for intervention in RIHD are discussed.

Preclinical research into basic mechanisms of radiation-induced heart disease

Radiation-induced heart disease (RIHD) is a potentially severe side effect of radiotherapy of thoracic and chest wall tumors if all or part of the heart was included in the radiation field. RIHD presents clinically several years after irradiation and manifestations include accelerated atherosclerosis, pericardial and myocardial fibrosis, conduction abnormalities, and injury to cardiac valves. There is no method to prevent or reverse these injuries when the heart is exposed to ionizing radiation. This paper presents an overview of recent studies that address the role of microvascular injury, endothelial dysfunction, mast cells, and the renin angiotensin system in animal models of cardiac radiation injury. These insights into the basic mechanisms of RIHD may lead to the identification of targets for intervention in this late radiotherapy side effect.

Pathogenetic mechanisms in radiation fibrosis

Deregulation of normal regenerative responses to physical, chemical and biological toxins in susceptible individuals leads to abnormal remodelling of extracellular matrix with pathological fibrosis. Processes deregulated after radiotherapy have much in common with processes associated with fibrotic diseases affecting the heart, skin, lungs, kidneys, gastro-intestinal tract and liver. Among the secreted factors driving fibrosis, transforming growth factor beta 1 (TGFβ1) produced by a wide range of inflammatory, mesenchymal and epithelial cells converts fibroblasts and other cell types into matrix-producing myofibroblasts. Even if required for the initiation of fibrosis, inflammation and the continued stimulus of TGFβ1 may not be needed to maintain it. After myofibroblast activation, collagen production can be perpetuated independently of TGFβ1 by autocrine induction of a cytokine called connective tissue growth factor. The role of inflammation, the origins and activation of myofibroblasts as biosynthetic cells and the downstream pathways of extracellular matrix synthesis in common fibrotic states are reviewed. Oxidative stress, hypoxia and microvascular damage are also considered, before examining the same processes in the context of radiotherapy. One of the main uncertainties is the relevance of very early events, including inflammatory responses in blood vessels, to fibrosis. Despite the power of animal models, including genetic systems, the potential contribution of research based on human tissue samples has never been greater. A closer interaction between scientists researching fibrosis and radiation oncologists holds enormous promise for therapeutic advances.