Inhibiting the Cytosolic Phospholipase A2-Arachidonic Acid Pathway With Arachidonyl Trifluoromethyl Ketone Attenuates Radiation-Induced Lung Fibrosis.

PURPOSE: Radiation-induced lung fibrosis (RILF) is a serious late complication of thoracic radiation therapy. Inflammation is crucial in fibroblast activation and RILF, and arachidonic acid (AA) is an important inflammatory mediator released by cytosolic phospholipase A2 (cPLA2) and reduced by arachidonyl trifluoromethyl ketone (ATK)-targeting of cPLA2. Here, we aimed to investigate the roles of the cPLA2/AA pathway in RILF and assess the potential of targeting cPLA2 to prevent RILF. METHODS AND MATERIALS: A computed tomography scan was used to obtain the mean lung density, and hematoxylin-eosin, Masson's trichrome, and Sirius Red staining were used to assess the histopathologic conditions in mouse models. AA levels in mouse serum and cell supernatants were tested by enzyme-linked immunosorbent assay. Fibroblast phenotype alterations were examined by a Cell Counting Kit-8, manual cell counting, and a Transwell system. The protein levels were evaluated via Western blotting, immunofluorescence, and immunohistochemistry. RESULTS: AA protected fibroblasts against radiation-induced growth inhibition and promoted fibroblast activation, which was characterized by enhanced α-smooth muscle actin expression and migration capacity. Radiation could activate fibroblasts by upregulating cPLA2 expression and AA production, which could be reversed by ATK. Moreover, inhibiting cPLA2 with ATK significantly attenuated collagen deposition and radiation-induced pulmonary fibrosis in mouse models. We further identified extracellular-signal regulated protein kinase (ERK) as the downstream target of the radiation-AA regulatory axis. Radiation-induced AA increased phosphorylated-ERK levels, promoting cyclinD1, cyclin-dependent kinase 6, and α-smooth muscle actin expression and contributing to fibroblast activation. Inhibiting P-ERK impaired radiation- and AA-induced fibroblast activation. The related molecular mechanisms were verified using specimens from animal models. CONCLUSIONS: Our findings uncover the role of the cPLA2/AA-ERK regulatory axis in response to radiation in pulmonary fibroblast activation and recognize cPLA2 as the key regulatory molecule during RILF for the first time. Targeting cPLA2 may be a promising protective strategy against RILF.

Docosahexaenoic Acid Attenuates Radiation-Induced Myocardial Fibrosis by Inhibiting the p38/ET-1 Pathway in Cardiomyocytes.

PURPOSE: Radiation-induced myocardial fibrosis (RIMF) is a severe delayed complication of thoracic irradiation (IR). Endothelin-1 (ET-1) is critical in cardiac fibroblast activation, and docosahexaenoic acid (DHA) is protective against various cardiac diseases. This study aimed to explore the roles of ET-1 in RIMF and the potential of DHA in preventing RIMF. METHODS AND MATERIALS: Hematoxylin and eosin, sirius red, and Masson trichrome staining were carried out to evaluate the histopathologic conditions in mouse models. Enzyme-linked immunosorbent assays were used to detect the concentration of ET-1 in serum and cell supernatants. Western blotting, immunofluorescence, and immunohistochemistry were used to assess the protein levels. The phenotypic alterations of cardiac fibroblasts were evaluated by cell proliferation/migration assays and α-smooth muscle actin (α-SMA) detection. RESULTS: Radiation increased ET-1 expression and secretion by increasing p38 phosphorylation in cardiomyocytes, and ET-1 markedly promoted the activation of cardiac fibroblasts, which were characterized by enhanced fibroblast proliferation, migration, and α-SMA expression. Cardiomyocyte-derived ET-1 mediated radiation-induced fibroblast activation by targeting the PI3K-AKT and MEK-ERK pathways in fibroblasts. DHA suppressed ET-1 levels by blocking p38 signaling in cardiomyocytes and significantly attenuated the activation of cardiac fibroblasts induced by the IR/ET-1 axis. Importantly, DHA decreased collagen deposition and α-SMA expression, alleviating cardiac fibrosis caused by radiation in mouse models. CONCLUSIONS: Our findings demonstrate that radiation facilitates cardiac fibroblast activation by enhancing p38/ET-1 signaling in cardiomyocytes, revealing the IR/p38/ET-1 regulatory axis in RIMF for the first time. DHA effectively inhibits fibroblast activation by targeting p38/ET-1 and can be recognized as a promising protective agent against RIMF.

CD155 promotes radioresistance and malignancy of esophageal cancer by regulating Hippo-YAP pathway.

The expression of CD155 has been observed to increase in various human cancers, but its role in the development of esophageal cancer (EC) is unclear. Radiotherapy is one of the primary therapeutic options for EC. However, radioresistance is still a severe issue in EC treatment. In this study, Oncomine database mining, immunohistochemistry, and survival analysis showed that higher expression of CD155 in patients with EC than in healthy controls. In vitro and in vivo, we found for the first time that irradiation increased the expression of CD155 in EC cells. CD155 knockdown inhibited cell proliferation and migration and tumor formation, and significantly increased radiosensitivity in EC. The in vivo model with high CD155 expression significantly promoted the proliferation and migration of EC cells. Furthermore, increased CD155 expression was associated with poor prognosis in patients with EC. CD155 regulated the Hippo-Yap pathway, influencing cell proliferation and migration. Therefore, CD155 is essential for the proliferation, migration, and radioresistance of EC. CD155 inhibition may be a viable strategy for improving radiation treatment efficacy in individuals with EC.

SPP1 promotes radiation resistance through JAK2/STAT3 pathway in esophageal carcinoma.

BACKGROUND: Therapeutic resistance to radiotherapy is one of the major obstacles in clinical practice that significantly affect the therapeutic efficiency and prognosis of human esophageal carcinoma (ESCA). Thus, it is critical to understand the molecular mechanisms of radiation resistance in ESCA. Secreted phosphoprotein 1 (SPP1) plays an essential role in various human cancers, but its role in radiation resistance remains unclear. METHOD: Cell culture and transfection; Cell Counting Kit-8 (CCK-8) assays; EdU incorporation assays; Patient sample collection and medical records review; Transwell assays; Colony formation assays; Wound healing assays; Western blot; Immunofluorescence; Immunohistochemistry; Irradiation; Flow cytometry; Animal studies; Human Apoptosis Array Kit; Bioinformatics. RESULT: In the current study, we reported the novel phenomenon that radiation-treated human ESCA cells upregulated SPP1 expression, which in turn contributed to the ESCA resistance to radiotherapy. We also reported the tumor-promoting effect of SPP1 in ESCA systematically and comprehensively. Furthermore, subsequent studies by knocking down or overexpressing SPP1 in human ESCA cells showed that SPP1 could facilitate the repair of DNA damage and the survival of tumor cells post-radiation in ESCA, which might contribute to the development of radiation resistance during the radiotherapy process. More detailed investigations on the downstream molecular pathway suggested that radiation could increase the phosphorylation level of JAK2 and STAT3 by increasing SPP1 expression. Further in vivo validation using a mouse ESCA xenograft model showed that SPP1 overexpression significantly increased tumor volume while either SPP1 knockdown or pharmacological inhibition of the JAK2-STAT3 pathway reduced tumor volume in a synergistic manner with radiotherapy. CONCLUSION: Collectively, these findings suggested that the SPP1/JAK2/STAT3 axis is a critical player in ESCA progression and radiation resistance, which is a potential therapeutic target for combined therapy with the standard radiotherapy regimen to improve curative effect and increase patients' survival with ESCA.

The role of exosomes in tumour immunity under radiotherapy: eliciting abscopal effects?

As a curative treatment of localized tumours or as palliative control, radiotherapy (RT) has long been known to kill tumour cells and trigger the release of proinflammatory factors and immune cells to elicit an immunological response to cancer. As a crucial part of the tumour microenvironment (TME), exosomes, which are double-layered nanometre-sized vesicles, can convey molecules, present antigens, and mediate cell signalling to regulate tumour immunity via their contents. Different contents result in different effects of exosomes. The abscopal effect is a systemic antitumour effect that occurs outside of the irradiated field and is associated with tumour regression. This effect is mediated through the immune system, mainly via cell-mediated immunity, and results from a combination of inflammatory cytokine cascades and immune effector cell activation. Although the abscopal effect has been observed in various malignancies for many years, it is still a rarely identified clinical event. Researchers have indicated that exosomes can potentiate abscopal effects to enhance the effects of radiation, but the specific mechanisms are still unclear. In addition, radiation can affect exosome release and composition, and irradiated cells release exosomes with specific contents that change the cellular immune status. Hence, fully understanding how radiation affects tumour immunity and the interaction between specific exosomal contents and radiation may be a potential strategy to maximize the efficacy of cancer therapy. The optimal application of exosomes as novel immune stimulators is under active investigation and is described in this review.