Upregulation and spatial shift in the localization of the mannose 6-phosphate/insulin-like growth factor II receptor during radiation enteropathy development in the rat

Pharmacological induction of transforming growth factor-beta1 in rat models enhances radiation injury in the intestine and the heart

Radiation therapy in the treatment of cancer is dose limited by radiation injury in normal tissues such as the intestine and the heart. To identify the mechanistic involvement of transforming growth factor-beta 1 (TGF-β1) in intestinal and cardiac radiation injury, we studied the influence of pharmacological induction of TGF-β1 with xaliproden (SR 57746A) in rat models of radiation enteropathy and radiation-induced heart disease (RIHD). Because it was uncertain to what extent TGF-β induction may enhance radiation injury in heart and intestine, animals were exposed to irradiation schedules that cause mild to moderate (acute) radiation injury. In the radiation enteropathy model, male Sprague-Dawley rats received local irradiation of a 4-cm loop of rat ileum with 7 once-daily fractions of 5.6 Gy, and intestinal injury was assessed at 2 weeks and 12 weeks after irradiation. In the RIHD model, male Sprague-Dawley rats received local heart irradiation with a single dose of 18 Gy and were followed for 6 months after irradiation. Rats were treated orally with xaliproden starting 3 days before irradiation until the end of the experiments. Treatment with xaliproden increased circulating TGF-β1 levels by 300% and significantly induced expression of TGF-β1 and TGF-β1 target genes in the irradiated intestine and heart. Various radiation-induced structural changes in the intestine at 2 and 12 weeks were significantly enhanced with TGF-β1 induction. Similarly, in the RIHD model induction of TGF-β1 augmented radiation-induced changes in cardiac function and myocardial fibrosis. These results lend further support for the direct involvement of TGF-β1 in biological mechanisms of radiation-induced adverse remodeling in the intestine and the heart.

Single nucleotide polymorphisms of DNA repair genes as predictors of radioresponse

Radiation therapy is a key modality in the treatment of cancer. Substantial progress has been made in unraveling the molecular events which underpin the responses of malignant and surrounding normal tissues to ionizing radiation. An understanding of the genes involved in processes such as DNA double-strand break repair, DNA damage response, cell-cycle control, apoptosis, cellular antioxidant defenses, and cytokine production, has evolved toward examination of how genetic variants, most often, single nucleotide polymorphisms (SNPs), may influence interindividual radioresponse. Experimental approaches, such as candidate SNP-association studies, genome-wide association studies, and massively parallel sequencing are being proposed to address these questions. We present a focused review of the evidence supporting an association between SNPs in DNA repair genes and radioresponse in normal tissues and tumors. Although preliminary results indicate possible associations, there are methodological weaknesses in many of the studies, and independent validation of SNPs as biomarkers of radioresponse in much larger cohorts will likely require research cooperation through international consortia.

Radiation-induced posttranscriptional control of M6P/IGF2r expression in breast cancer cell lines

The mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2r), a member of the IGF axis of growth factors, is a negative regulator of cell growth and a putative tumor suppressor gene. Regulation of M6P/IGF2r levels is critical in breast physiology; low expression is associated with various aspects of breast cancer. We have found that ionizing radiation induces the rapid expression of M6P/IGF2r in a dose-dependent manner in MCF7 human breast cancer cells. We show that this increase is mediated, at least in part, by a stabilization of M6P/IGF2r transcripts by radiation in both ER positive (MCF7 and T47D) and ER negative (MDA-MB-231) breast cancer cell lines. It is probable, therefore, that posttranscriptional dysregulation of M6P/IGF2r is a contributing mechanism in breast cancer development and breast cancer response to therapy. This is a novel find that underscores the importance of posttranscriptional control of radiation-induced gene expression-a phenomenon that has often been paradigmatically attributed to transcriptional control.

A Dose-Dependent Decrease in the Fraction of Cases Harboring M6P/IGF2R Mutations in Hepatocellular Carcinomas from the Atomic Bomb Survivors

The risk for hepatocellular carcinoma (HCC) development is significantly heightened in the atomic bomb survivors, but the mechanism is unclear. We have previously reported finding a radiation dose-dependent increase in HCCs with TP53 mutations from the survivors. We now show that, in the same HCC samples, the frequency of 3'-untranslated region (3'UTR) mutations in M6P/IGF2R, a candidate HCC tumor suppressor gene, decreases with dose (P = 0.0091), implying a radiation dose-dependent negative selection of cells harboring such mutations. The fact that they were in the 3'UTR implicates changes in transcript stability rather than in protein function as the mechanism. Moreover, these M6P/IGF2R 3'UTR mutations and the TP53 mutations detected previously were mutually exclusive in most of the tumors, suggesting two independent pathways to HCC development, with the TP53 pathway being more favored with increasing radiation dose than the M6P/IGF2R pathway. These results suggest that tumors attributable to radiation may be genotypically different from tumors of other etiologies and hence may provide a way of distinguishing radiation-induced cancers from "background" cancers--a shift from the current paradigm.

Current concepts in radiation enteritis and implications for future clinical trials

BACKGROUND

Radiation enteritis is one of the most feared complications of abdominal and pelvic radiation. Once its occurs, the process is relentless and may result in the patient's death. Available treatment is only supportive. Recent progress in molecular biology has shed some light on the pathogenesis of radiation enteritis and other diseases that are characterized by excessive fibrosis. New treatment modalities may be devised to improve the outcome of patients who are affected with this complication.

METHODS

A literature search was used to identify the common denominator between many radiation-induced fibrotic conditions and other sclerotic diseases. Factors that affect the disease process and possible therapeutic interventions were evaluated.

RESULTS

The hyperstimulation of transforming growth factor beta1 (TGF-beta1) leads to increased fibrosis and, ultimately, organ failure. Interferon gamma (IFN-gamma) inhibits the effects of TGF-beta1 in the nucleus. The fibrotic process may be reverted by IFN-gamma in various pathologic conditions.

CONCLUSIONS

Radiation enteritis and other radiation-induced, long-term complications are characterized by excessive stimulation of TGF-beta1. Preliminary studies suggest that IFN-gamma may be effective in the treatment of patients with radiation-induced cutaneous fibrosis. IFN-gamma should be considered in Phase I-II studies to assess its toxicity and efficacy in the treatment of patients with radiation enteritis.

Cytokines in coagulation and thrombosis: a preclinical and clinical review

The cytokine network is a complex and dynamic system, involved in numerous biological responses in the human body. This review of the current literature describes the role of cytokines and their interaction with the coagulation system, specifically in the maintenance of the thrombo-hemorrhagic balance in vivo in human subjects and in animals. In general, cytokines are thrombogenic, but they are amenable to therapeutic manipulations and hence are a potentially attractive tool in the clinician's armamentarium. Studies of the effects of cytokines in vivo are difficult because cytokines act in a very finite microenvironment and, although their actions are significant, they are transient. Most of the available clinical data related to interactions between cytokines and the coagulation system focuses on the role of tumor necrosis factor-alpha and interleukin-1 in septicemia and septic shock. However, several other cytokines and related proteins, such as platelet activating factor and plasminogen activator inhibitor, are also known to influence coagulation and thrombosis. These factors interact closely with cytokines, and have been included in this review for a better understanding of their interactions with traditional cytokines. Studies that utilize cell culture systems do not accurately model the in vivo status of this complex system and, hence, this review has excluded such studies. The role of the cytokine network in coronary artery disease, angiogenesis, or neoplasia has been addressed elsewhere by other workers and is not discussed here. By emphasizing important in vivo interactions, the intention of this review is to serve as an impetus to further translational research, both clinical and in the laboratory.

Effects of radiation damage on intestinal morphology

The current flow of papers on intestinal structure, radiation science, and intestinal radiation response is reflected in the contents of this review. Multiparameter findings and changes in compartments, cells, or subcellular structure all contribute to the overall profile of the response. The well-recognized changes in proliferation, vessels, and fibrogenesis are accompanied by alterations in other compartments, such as neuroendocrine or immune components of the intestinal wall. The responses at the molecular level, such as in levels of hormones, cytokines, or neurotransmitters, are of fundamental importance. The intestine responds to localized radiation, or to changes in other organs that influence its structure or function: some structural parameters respond differently to different radiation schedules. Apart from radiation conditions, factors affecting the outcome include the pathophysiology of the irradiated subject and accompanying treatment or intervention. More progress in understanding the overall responses is expected in the next few years.

Recombinant soluble transforming growth factor beta type II receptor ameliorates radiation enteropathy in mice

BACKGROUND & AIMS

Transforming growth factor (TGF)-beta has been implicated in many fibrotic conditions. However, its mechanistic role in radiation toxicity is equivocal despite compelling correlative evidence. This study assessed whether in vivo administration of a soluble TGF-beta type II receptor (TbetaR-II) protein ameliorates intestinal radiation injury (radiation enteropathy).

METHODS

A recombinant fusion protein, consisting of the extracellular portion of mouse TbetaR-II and the Fc portion of mouse immunoglobulin (Ig) G, was produced. A 5-cm segment of mouse ileum was exposed to 19 Gy x-radiation. TbetaR-II:Fc fusion protein (1 mg/kg every other day) or mouse IgG was administered from 2 days before to 6 weeks after irradiation. Radiation injury was assessed at 6 weeks using quantitative histology, morphometry, and immunohistochemistry. Collagen was measured colorimetrically, and TGF-beta1 messenger RNA was assessed with fluorogenic probe reverse-transcription polymerase chain reaction.

RESULTS

Compared with IgG controls, TbetaR-II:Fc-treated mice exhibited less structural injury, preservation of mucosal surface area, and less intestinal wall fibrosis. Intestinal TGF-beta1 messenger RNA increased in TbetaR-II:Fc-treated mice, whereas TGF-beta immunoreactivity decreased. TbetaR-II:Fc treatment increased crypt cell proliferation but otherwise did not affect unirradiated intestine.

CONCLUSIONS

Long-term modulation of TGF-beta with a TbetaR-II:Fc fusion protein is feasible and ameliorates radiation enteropathy. These data confirm the putative role of TGF-beta in intestinal radiation fibrosis.