Cellular kinetics of murine lung: model system to determine basis for radioprotection with keratinocyte growth factor

Keratinocyte growth factor-2 is protective in lipopolysaccharide-induced acute lung injury in rats

Keratinocyte growth factor-2 (KGF-2) plays a key role in lung development, but its role in acute lung injury has not been well characterized. Lipopolysaccharide instillation caused acute lung injury, which significantly elevated lung wet-to-dry weight ratio, protein and neutrophils in bronchoalveolar lavage fluid (BALF), inhibited surfactant protein A and C expression in lung tissue, and increased pathological injury. Pretreatment with KGF-2 improved the above lung injury parameters, partially restored surfactant protein A and C expression, and KGF-2 given 2-3 days before LPS challenge showed maximum lung injury improvement. Pretreatment with KGF-2 also markedly reduced the levels of TNF-α, MIP-2, IL-1β and IL-6 in BALF and the levels of IL-1β and IL-6 in lung tissue. Histological analysis showed there was increased proliferation of alveolar type II epithelial cells in lung parenchyma, which reached maximal 2 days after KGF-2 instillation. Intratracheal administration of KGF-2 attenuates lung injury induced by LPS, suggesting KGF-2 may be potent in the intervention of acute lung injury.

Mesenchymal stromal cell turnover in the normal adult lung revisited

We have employed a simple and robust noninvasive method of continuous in vivo long-term bromodeoxyuridine (BrdU) labeling to analyze lung mesenchymal stromal cell turnover in adult mice in the steady state. Mathematical modeling of BrdU uptake in flow cytometrically sorted CD45negCD31negSca-1poslung cells following long-term feeding of BrdU to mice in their drinking water reveals that lung mesenchymal stromal cells cycle continuously throughout life. Analysis of BrdU incorporation during long-term feeding and during chasing (delabeling) following replacement of BrdU-water with normal water shows that the CD45negCD31negSca-1poslung mesenchymal stromal cell compartment turns over at a rate of ∼2.26% per day with a time to half-cycled of 44 days, an estimated cell proliferation rate of 0.004/day, and a cell death rate of 0.018/day.

Proliferation of human lung cancer in an orthotopic transplantation mouse model

The objective of this study was to clarify the growth and proliferation style of human lung cancer grown in an orthotopic transplantation model. The human lung squamous cell carcinoma SQ5 and adenocarcinoma A549 cell lines were used. Tumor cells suspended in serum-free medium were directly injected into the main bronchi of anesthetized female Balb/c athymic nude mice with simultaneous administration of 0.01 M ethylenediaminetetraacetic acid. Bromodeoxyuridine was injected into mice 20 min before sacrifice. Lung tissue with tumor nodules and subcutaneous tumors were fixed and confirmed by histological examinations. Bromodeoxyuridine-labeled cells in the tumor area were counted, and the proliferation index was calculated. Lung tumor colonies of various sizes were obtained in the SQ5- and A549-cell orthotopically transplanted mice. Orthotopic SQ5 tumors whose minor diameter was 40-700 μm and major diameter was 80-830 μm showed no definite necrosis. Orthotopic SQ5 tumors whose minor diameter was 540-5,200 μm and major diameter was 600-6,100 μm showed definite necrosis in the tumor center. Similar results were also found in the orthotopic A549 tumors. The proliferation index was 7.38 (3.03)/10.63 (3.10) in the orthotopic SQ5 tumors with/without necrosis and 6.99 (2.10) in the subcutaneous SQ5 tumors with necrosis, respectively. The proliferation index was 2.70 (0.88)/3.53 (1.70) in the orthotopic A549 tumors with/without necrosis and 3.91 (0.63) in the subcutaneous A549 tumors with necrosis, respectively. The data suggest that this orthotopic transplantation model may provide the proper organ microenvironment for lung cancer growth and may be suitable for the target therapy research of human lung cancer.

Keratinocyte growth factor prevents radiation damage to salivary glands by expansion of the stem/progenitor pool

Irradiation of salivary glands during radiotherapy treatment of patients with head and neck cancer evokes persistent hyposalivation. This results from depletion of stem cells, which renders the gland incapable of replenishing saliva to produce acinar cells. The aim of this study was to investigate whether it is possible to expand the salivary gland stem/progenitor cell population, thereby preventing acinar cell depletion and subsequent gland dysfunction after irradiation. To induce cell proliferation, keratinocyte growth factor (DeltaN23-KGF, palifermin) was administered to C57BL/6 mice for 4 days before and/or after local irradiation of salivary glands. Salivary gland vitality was quantified by in vivo saliva flow rates, morphological measurements, and a newly developed in vitro salisphere progenitor/stem cell assay. Irradiation of salivary glands led to a pronounced reduction in the stem cells of the tissues, resulting in severe hyposalivation and a reduced number of acinar cells. DeltaN23-KGF treatment for 4 days before irradiation indeed induced salivary gland stem/progenitor cell proliferation, increasing the stem and progenitor cell pool. This did not change the relative radiation sensitivity of the stem/progenitor cells, but, as a consequence, an absolute higher number of stem/progenitor cells and acinar cells survived after radiation. Postirradiation treatment with DeltaN23-KGF also improved gland function, and this effect was much more pronounced in DeltaN23-KGF pretreated animals. Post-treatment with DeltaN23-KGF seemed to act through accelerated expansion of the pool of progenitor/stem cells that survived the irradiation treatment. Overall, our data indicate that DeltaN23-KGF is a promising drug to enhance the number of salivary gland progenitor/stem cells and consequently prevent radiation-induced hyposalivation. Disclosure of potential conflicts of interest is found at the end of this article.

Successful Mitigation of Delayed Intestinal Radiation Injury Using Pravastatin is not Associated with Acute Injury Improvement or Tumor Protection

PURPOSE

To investigate whether pravastatin mitigates delayed radiation-induced enteropathy in rats, by focusing on the effects of pravastatin on acute cell death and fibrosis according to connective tissue growth factor (CTGF) expression and collagen inhibition.

METHODS AND MATERIALS

Mitigation of delayed radiation-induced enteropathy was investigated in rats using pravastatin administered in drinking water (30 mg/kg/day) 3 days before and 14 days after irradiation. The ileum was irradiated locally after surgical exteriorization (X-rays, 19 Gy). Acute apoptosis, acute and late histologic alterations, and late CTGF and collagen deposition were monitored by semiquantitative immunohistochemistry and colorimetric staining (6 h, 3 days, 14 days, 15 weeks, and 26 weeks after irradiation). Pravastatin antitumor action was studied in HT-29, HeLa, and PC-3 cells by clonogenic cell survival assays and tumor growth delay experiments.

RESULTS

Pravastatin improved delayed radiation enteropathy in rats, whereas its benefit in acute and subacute injury remained limited (6 h, 3 days, and 14 days after irradiation). Delayed structural improvement was associated with decreased CTGF and collagen deposition but seemed unrelated to acute damage. Indeed, the early apoptotic index increased, and severe subacute structural damage occurred. Pravastatin elicited a differential effect, protecting normal intestine but not tumors from radiation injury.

CONCLUSION

Pravastatin provides effective protection against delayed radiation enteropathy without interfering with the primary antitumor action of radiotherapy, suggesting that clinical transfer is feasible.

Maintenance of radiation-induced intestinal fibrosis: cellular and molecular features

Recent advances in cell and molecular radiobiology clearly showed that tissue response to radiation injury cannot be restricted to a simple cell-killing process, but depends upon continuous and integrated pathogenic processes, involving cell differentiation and crosstalk between the various cellular components of the tissue within the extracellular matrix. Thus, the prior concept of primary cell target in which a single-cell type (whatever it's epithelial or endothelial cells) dictates the whole tissue response to radiation injury has to be replaced by the occurrence of coordinated multicellular response that may either lead to tissue recovery or to sequel development. In this context, the present review will focus on the maintenance of the radiation-induced wound healing and fibrogenic signals triggered by and through the microenvironment toward the mesenchymal cell compartment, and will highlight how sequential and sustained modifications in cell phenotypes will in cascade modify cell-to-cell interactions and tissue composition.

Radiation pneumonitis and fibrosis: Mechanisms underlying its pathogenesis and implications for future research

Radiation pneumonitis and subsequent radiation pulmonary fibrosis are the two main dose-limiting factors when irradiating the thorax that can have severe implications for patients' quality of life. In this article, the current concepts about the pathogenetic mechanisms underlying radiation pneumonitis and fibrosis are presented. The clinical course of fibrosis, a postulated acute inflammatory stage, and a late fibrotic and irreversible stage are discussed. The interplay of cells and the wide variety of molecules orchestrating the immunologic response to radiation, their interactions with specific receptors, and the cascade of events they trigger are elucidated. Finally, the implications of this knowledge with respect to the therapeutic interventions are critically presented.

Palifermin: a keratinocyte growth factor that reduces oral mucositis after stem cell transplant for haematological malignancies

Mucositis occurs in < or = 98% of patients undergoing stem cell transplant for haematological malignancies and is associated with significant morbidity and mortality. Patients with severe mucositis have more pain, more difficulty with daily activities such as talking and eating, and are more likely to have bacteraemia. Palifermin is a keratinocyte growth factor that has been shown to decrease severity and duration of mucositis with a concurrent decrease in patient-reported symptoms and use of narcotics and total parenteral nutrition. Research is ongoing into palifermin's potential ability to decrease graft-versus-host disease and improve reconstitution of functional T lymphocytes after allogeneic stem cell transplant, to hasten wound healing and to reduce mucositis following external beam radiation therapy in solid tumour patients.

Development of an orthotopic transplantation model in nude mice that simulates the clinical features of human lung cancer

The objective of the present study was to establish an orthotopic tumor transplantation model in nude mice that closely resembles the clinical features of human lung cancer. The human lung adenocarcinoma A549 cell line and the squamous cell carcinoma SQ5 cell line were used. Tumor cells suspended in serum-free medium were injected directly into the main bronchi of anesthetized female Balb/c athymic nude mice (7-9 weeks old) with or without simultaneous administration of 0.01 M ethylenediaminetetracetic acid (EDTA). In some experiments, lung carcinoma cells harvested from tumors transplanted subcutaneously were recultured and used for intratracheal implantation. Tumor nodules that formed in the lung were counted and confirmed by histological examination. Administration of A549 cells with EDTA resulted in a 70% engraftment rate (n = 10). Recultured A549 cells without and with EDTA resulted in 20% (n = 5) and 80% (n = 5) engraftment rates, respectively. Administration of SQ5 cells without or with EDTA formed 50% (n = 4) and 67% (n = 6) engraftment rates, respectively. Recultured SQ5 cells with EDTA further increased the engraftment rate to 100% (n = 6). Multiple tumors formed mainly in the left lung and the upper lobe of the right lung. Simultaneous administration of EDTA resulted in greater numbers of tumor nodules in the lung. Histological findings revealed that A549 tumor nodules were distributed primarily in alveoli. The SQ5 solid tumors invaded bronchioles and occupied the alveoli. This reproducible orthotopic transplantation model produced tumor growth that simulated the clinical features of human lung cancer.

Preclinical evaluation of erythropoietin administration in a model of radiation-induced kidney dysfunction

PURPOSE

To test whether the clinically available growth factor erythropoietin (EPO) influences radiation-induced normal-tissue damage in a model of kidney dysfunction.

METHODS

Animal experiments were conducted to test the role of EPO administration in a C3H mouse model of unilateral kidney irradiation with 6, 8, and 10 Gy and to assess the effects of 2 different dose levels of EPO. The kidney function was assessed before radiotherapy, as well as 19, 25, 31, and 37 weeks thereafter by means of (99m)Tc-dimercaptosuccinat scans (static scintigraphy).

RESULTS

Concomitant EPO administration significantly increased the degree of radiation-induced kidney dysfunction. A dose of 2,000 IU/kg body weight per injection tended to cause more damage than the lower dose of 500 IU/kg.

CONCLUSION

Administration of growth factors concomitant to radiotherapy might modify the development of kidney dysfunction. Although insulin-like growth factor-1 has previously been shown to protect the kidney, such an effect could not be demonstrated for EPO. The latter agent even increased the development of nephropathy.

Human fibroblast growth factor 20 (FGF-20; CG53135-05): a novel cytoprotectant with radioprotective potential

The aim was to evaluate the radioprotective properties of recombinant human fibroblast growth factor 20 (FGF-20; CG53135-05) in vitro and in vivo and to examine its effects on known cellular pathways of radioprotection. Relative transcript levels of the cyclooxygenase 2 (COX2), Mn-super oxide dismutase (SOD), CuZn-SOD, extracellular (EC)-SOD, nuclear respiratory factor 2 (Nrf2), glutathione peroxidase 1 (GPX1) and intestinal trefoil factor 3 (ITF3) genes, which are involved in radiation response pathways, were assessed by reverse transcriptase-polymerase chain reaction (RT-PCR) in NIH/3T3, IEC18, CCD-18Co, CCD-1070sk and human umbilical vein endothelial cells (HUVEC) cells exposed to FGF-20. Activation of the radioprotective signal transduction pathways initiating with the serine/threonine Akt kinase and the extracellular regulated kinase (ERK) were analysed. Levels of intracellular hydrogen peroxide and cytosolic redox potential were also measured in irradiated and unirradiated cells in the presence or absence of FGF-20. The effects of FGF-20 on cell survival in vitro following ionizing radiation were evaluated using clonogenic assays. To test the potential activity of FGF-20 as a radioprotectant in vivo, mice were administered a single dose of FGF-20 (4 mg kg(-1), intraperitoneally (i.p.) 1 day before lethal total-body irradiation and evaluated for survival. In vitro exposure to FGF-20 increased expression of the Nrf2 transcription factor and oxygen radical scavenging enzymes such as MnSOD, activated signal transduction pathways (ERK and Akt) and resulted in increased survival of irradiated cells in vitro. FGF-20 treatment also resulted in a concomitant reduction in intracellular levels of injurious reactive oxygen species (ROS) following acute ionizing irradiation. Finally, prophylactic administration of FGF-20 to mice before potentially lethal, whole-body X-irradiation led to significant increases in overall survival. FGF-20 reduced the lethal effects of acute ionizing radiation exposure in cells by up-regulating important signalling and free radical scavenging pathways. Survival-sparing effects of FGF-20 prophylaxis in acutely irradiated mice presumably are elicited by comparable mechanisms. These results indicate that FGF-20, has significant radioprotective attributes with potential applications in clinical and non-clinical exposure settings.

Models for Evaluating Agents Intended for the Prophylaxis, Mitigation and Treatment of Radiation Injuries Report of an NCI Workshop, December 3–4, 2003

To develop approaches to prophylaxis/protection, mitigation and treatment of radiation injuries, appropriate models are needed that integrate the complex events that occur in the radiation-exposed organism. While the spectrum of agents in clinical use or preclinical development is limited, new research findings promise improvements in survival after whole-body irradiation and reductions in the risk of adverse effects of radiotherapy. Approaches include agents that act on the initial radiochemical events, agents that prevent or reduce progression of radiation damage, and agents that facilitate recovery from radiation injuries. While the mechanisms of action for most of the agents with known efficacy are yet to be fully determined, many seem to be operating at the tissue, organ or whole animal level as well as the cellular level. Thus research on prophylaxis/protection, mitigation and treatment of radiation injuries will require studies in whole animal models. Discovery, development and delivery of effective radiation modulators will also require collaboration among researchers in diverse fields such as radiation biology, inflammation, physiology, toxicology, immunology, tissue injury, drug development and radiation oncology. Additional investment in training more scientists in radiation biology and in the research portfolio addressing radiological and nuclear terrorism would benefit the general population in case of a radiological terrorism event or a large-scale accidental event as well as benefit patients treated with radiation.

Modulation of rodent spinal cord radiation tolerance by administration of platelet-derived growth factor

PURPOSE

To examine the role of platelet-derived growth factor (PDGF) for ameliorating radiation myelopathy of the cervical spinal cord in a rodent model.

METHODS AND MATERIALS

After developing the technique for cannulation of the basal cistern, initial animal experiments were conducted to test the feasibility of intrathecal continuous infusion of PDGF in a model of cervical spinal cord irradiation in adult Fisher F-344 rats and to determine the most effective dose level of PDGF. Subsequently, the dose-modification factor was determined in a larger group of rats. Irradiation was given in 2 fractions (16 Gy followed by 14-24 Gy) and animals were examined for the development of paresis.

RESULTS

The initial dose-finding experiment revealed significant differences in the incidence of radiation myelopathy (100% in saline-treated control rats, 25% with the most effective dose of PDGF, up to 100% with less effective doses). The most effective dose of PDGF was 0.014 mug per day. Subsequent experiments revealed a median effective dose (ED(50)) of 35.6 Gy (95% confidence interval, 34.7-36.5 Gy) for animals receiving this dose of PDGF in contrast to 33.8 Gy (33.4-34.3 Gy) for the control group (p = 0.003). The dose-modification factor obtained with this dose of PDGF was 1.05.

CONCLUSIONS

Intrathecal administration of PDGF concomitant to irradiation of the cervical spinal cord in rats was feasible. Treatment with PDGF significantly increased the tolerance of the spinal cord. The PDGF experiments should be viewed as a proof of principle that brief therapeutic intervention in the earliest phase of damage induction can reduce late effects in the spinal cord. They form the basis for further studies of growth factor administration in this particular model.