Belinda Rivera

Experimentelle Daten zum Einsatz von Insulin-Like Growth Factor-1 (IGF-1) und Basic Fibroblast Growth Factor (bFGF) zur Prävention einer Strahlenmyelopathie

Hintergrund: Aktuelle Modelle zur Pathogenese der Strahlenmyelopathie lassen den präventiven Einsatz von Wachstumsfaktoren sinnvoll erscheinen. Daher sollte überprüft werden, ob Insulin-Like Growth Factor-1 (IGF-1) und Basic Fibroblast Growth Factor (bFGF) als Einzelsubstanzen oder in Kombination die Strahlentoleranz des zervikalen Rückenmarks von Ratten beeinflussen. Material und Methoden: Das Zervikalmark von 68 erwachsenen Fisher-F344-Ratten wurde mit zwei Einzelfraktionen bis insgesamt 30–36 Gy bestrahlt (16 Gy plus 14–20 Gy). Begleitend wurde eine kontinuierliche intrathekale Infusion von bFGF (44 Ratten) oder NaCl (24 Ratten) in die Cisterna magna gegeben. In einem weiteren Experiment erhielten 14 Ratten IGF-1 subkutan, begleitend zur Bestrahlung mit 34 Gy bzw. 36 Gy. 20 Ratten wurden der Kombinationstherapie unterzogen, d.h. intrathekale Infusion von bFGF plus subkutane Injektion von IGF-1, beginnend 24 Stunden vor der ersten Fraktion für 4 Tage (33 Gy bzw. 36 Gy). Die Tiere wurden bis zur Entwicklung einer Myelopathie oder maximal 12 Monate nachbeobachtet. Post mortem erfolgten histopathologische Untersuchungen. Ergebnisse: In der bFGF- und der IGF-1-Gruppe wurde eine signifikante Verlängerung der medianen Latenzzeit beobachtet. In der Kombinationsgruppe galt dies für die mit 36 Gy bestrahlten Tiere. Mit 33 Gy bestrahlte Ratten zeigten dagegen auch ein signifikant reduziertes Myelopathierisiko (p = 0,0015). Schlussfolgerung: Die Kombination aus IGF-1 und bFGF war wirksamer als die Einzelsubstanzen. Wir beobachteten eine signifikant geringere Myelopathierate nach einer mittleren Bestrahlungsdosis, wohingegen bei einer hohen Dosis nur eine Verzögerung der Myelopathie zu konstatieren war. Diese Ergebnisse weisen darauf hin, dass kurze Interventionen die strahleninduzierte Neurotoxizität reduzieren können. Weitere Studien zur Optimierung dieser Strategie sind vorgesehen.Background: Current models of radiation myelopathy provide a rationale for growth factor-based prevention strategies. Thus, we tested whether insulin-like growth factor-1 (IGF-1) and basic fibroblast growth factor (bFGF) alone or in combination modulate radiation tolerance of the rat cervical spinal cord. Materials and Methods: The cervical spinal cord of 68 adult Fisher F344 rats received a total dose of 30–36 Gy, given as a single fraction of 16 Gy followed by a second radiation dose of 14–20 Gy. Continuous intrathecal infusion of bFGF (44 rats) or saline (24 rats) into the cisterna magna was given concomitantly. A further experiment included 14 additional rats which were treated with subcutaneous injection of IGF-1 parallel to irradiation with a total dose of 34 Gy or 36 Gy. 20 rats received combined treatment, i.e. intrathecal infusion of bFGF plus subcutaneous injection of IGF-1, starting 24 hours before irradiation (total dose 33 Gy or 36 Gy) for a total of 4 days. Animals were followed until myelopathy developed or for a maximum of 12 months. Histopathologic examinations were performed post mortem. Results: Treatment with bFGF alone or IGF-1 alone increased the median time to myelopathy significantly. In the 36-Gy group, after combination treatment a comparable prolongation of latency was seen. Moreover, rats treated with 33 Gy and combined bFGF plus IGF-1 showed a significantly reduced risk of myelopathy, too (p = 0.0015, Figures 1 and 2). Conclusion: Combination of IGF-1 and bFGF was more potent than single agent treatment. We observed a significantly reduced myelopathy rate at an intermediate radiation dose level and a longer time to myelopathy at a high-dose level. This finding strengthens the evidence that brief therapeutic intervention can decrease radiation-induced neurotoxicity. Further studies will be undertaken to optimize this strategy.

Effects of insulin-like growth factor-1 (IGF-1) and amifostine in spinal cord reirradiation

Purpose:To test whether insulin-like growth factor-1 (IGF-1) and amifostine modulate the reirradiation tolerance of rat cervical spinal cord. Initial experiments by the authors’ group suggested that administration of each agent alone significantly increased the median latent time to radiation myelopathy (RM) in previously unirradiated animals but did not change the dose-response relationship. Because of different modes of action, a follow-up study was undertaken to test the combined treatment.Material and Methods:The cervical spinal cord of 51 adult Fisher F-344 rats received a single fraction of 16 Gy, which corresponds to approximately 75% of the median paresis dose (ED50), followed 5 months later by a second radiation dose, which ranged from 17 to 21 Gy. The study animals received a single intrathecal injection of 0.3 mg amifostine into the cisterna magna 30-60 min before reirradiation plus three subcutaneous doses of IGF-1 (700 µg) starting from 24 h before to 24 h after reirradiation. Control animals received saline injections via the same routes. Animals were followed until RM developed or until 12 months from reirradiation. Histopathologic examinations were performed post mortem.Results:No animals showed any neurologic abnormalities before reirradiation. RM occurred in controls versus treated rats after a mean latency of 218 versus 314 days (19 Gy; p = 0.11) and 104 versus 186 days (21 Gy; p = 0.002) from second dose (Figure 1). ED50 was 18.2 versus 19.4 Gy (p = 0.15; Figure 2). Treatment with IGF-1 and amifostine did not significantly influence the rates of tumor induction or intercurrent death.Conclusion:IGF-1 and amifostine significantly reduced RM rates after 21 Gy. The shift of the dose-response curve suggests an increase of the ED50 for single-dose treatment by approximately 7%. Thus, brief therapeutic intervention might slightly decrease radiation-induced neurotoxicity in a retreatment situation.Ziel:Untersuchung der Fähigkeit von insulin-like growth factor-1 (IGF-1) und Amifostin, die Zweitbestrahlungstoleranz des Rückenmarks von Ratten zu beeinflussen. Erste eigene Experimente ergaben, dass die Applikation jeder Einzelsubstanz bei noch nicht vorbestrahlten Tieren die mediane Latenzzeit bis zum Auftreten einer Strahlenmyelopathie signifikant verlängerte, ohne jedoch die Dosis-Wirkungs-Beziehung zu verändern. Da die Substanzen unterschiedliche Wirkmechanismen aufweisen, wurde die Kombination der beiden Behandlungen in einem Folgeexperiment getestet.Material und Methodik:Das zervikale Rückenmark von 51 erwachsenen Fisher-F-344-Ratten erhielt eine Einzeitdosis von 16 Gy, die ca. 75% der medianen Toleranzdosis (ED50) entspricht. Nach 5 Monaten wurde eine zweite Bestrahlungsdosis von 17-21 Gy gegeben. Ein Teil der Tiere erhielt 30-60 min vor der Zweitbestrahlung eine intrathekale Injektion von 0,3 mg Amifostin in die Cisterna magna. Zusätzlich wurden drei subkutane Injektionen von IGF-1 (jeweils 700 µg) gegeben, die erste 24 h vor, die letzte 24 h nach der Zweitbestrahlung. Die Kontrolltiere erhielten Kochsalzinjektionen über die gleichen Zugangswege. Alle Tiere wurden bis zur Entwicklung einer Strahlenmyelopathie oder für maximal 12 Monate nach der Zweitbestrahlung nachbeobachtet. Post mortem erfolgten histopathologische Untersuchungen.Ergebnisse:Keines der Tiere entwickelte neurologische Auffälligkeiten vor der Zweitbestrahlung. Eine Strahlenmyelopathie trat nach einer mittleren Latenzzeit von 218 versus 314 Tagen (Kontrollen vs. IGF-1/Amifostin, 19 Gy; p = 0,11) und 104 versus 186 Tagen (21 Gy; p = 0,002) nach der Zweitbestrahlung auf (Abbildung 1). Die ED50 betrug 18,2 versus 19,4 Gy (p = 0,15; Abbildung 2). Die Gabe von IGF-1 und Amifostin hatte keinen signifikanten Einfluss auf die Entstehung strahleninduzierter Tumoren bzw. die Rate interkurrenter Todesfälle.Schlussfolgerung:IGF-1 und Amifostin führten zu einer signifikanten Reduktion der Strahlenmyelopathie-Rate nach 21 Gy. Die Verschiebung der Dosis-Effekt-Kurve spricht für einen Anstieg der ED50 für Einzeitbestrahlungen um ca. 7%. Somit kann eine kurze Therapie die aus einer Zweitbestrahlung resultierende Neurotoxizität offensichtlich etwas reduzieren.

Lung imaging of laboratory rodents in-vivo

We have been acquiring respiratory-gated micro-CT images of live mice and rats for over a year with our General Electric (formerly Enhanced Vision Systems) hybrid scanner. This technique is especially well suited for the lung due to the inherent high tissue contrast. Our current studies focus on the assessment of lung tumors and their response to experimental agents, and the assessment of lung damage due to chemotherapy agents. We have recently installed a custom-built dual flat-panel cone-beam CT scanner with the ability to scan laboratory animals that vary in size from mice to large dogs. A breath-hold technique is used in place of respiratory gating on this scanner. The objective of this pilot study was to converge on scan acquisition parameters and optimize the visualization of lung damage in a mouse model of fibrosis. Example images from both the micro-CT scanner and the flat-panel CT scanner will be presented, as well as preliminary data describing spatial resolution, low contrast resolution, and radiation dose parameters.

Evaluation of insulin-like growth factor-1 for prevention of radiation-induced spinal cord damage

Aim: To test whether insulin-like growth factor-1 (IGF-1) ameliorates radiation-induced spinal cord myelopathy and to establish the dose-effect relationship for this growth factor which has not been administered in conjunction with spinal cord irradiation to date. Methods: Animal experiments were conducted to test the feasibility of IGF-1 injection in a model of cervical spinal cord irradiation in adult Fisher F-344 rats and to determine the most effective dose level of IGF-1. Irradiation was given in two fractions (16 Gy followed by 18 Gy) and animals were examined for the development of paresis (follow-up 12 months). Results: The dose-finding experiment revealed significant differences in the incidence of radiation myelopathy (RM). The most effective dose of IGF-1 was 50 μg per day. Conclusions: IGF-1 showed promising activity as a radioprotective agent in a model of high-dose spinal cord irradiation. Further studies are needed to examine the results with multiple small doses of radiation as widely applied in clinical protocols.

SU‐FF‐I‐60: Image Quality Improvement Using a Custom Ventilator for Respiratory‐Gated Micro‐CT

Purpose: Acquiring Micro‐CT images of murine lungsin vivo requires respiratory gating to achieve optimal tissuecontrast at full inspiration. The use of a custom small‐animal ventilator and a specific acquisition technique has resulted in a dramatic improvement in image quality. Method and Materials: A commercially available small animal ventilator was customized for use with our commercially available micro‐CT scanner. The modified ventilator can hold the pressure in rodent lungs at a constant level (essentially perform a series of short breath‐holds at full inspiration), and can be programmed to trigger the scanner acquisition phase. The ventilator is set to cyclicly achieve a pre‐set pressure level of the anesthetic gas mixture (inspiration), trigger the x‐ray on phase of the scanner, acquire a single frame during the stable pressure phase, close the x‐ray shutter, and finally release the pressure of the anesthetic gas mixture (expiration) while the scanner rotates to the next view position, at which point the cycle repeats. Images can be reconstructed with either 90 or 45 micron isotropic voxels. Example images of several mice with lungtumors will be presented. Radiation dose is estimated to be about 0.26 Gy per scan session using this methodology. Results: This implementation has produced images with improved visibility of the tissue components, including airways and pulmonary blood vessels. The margins of individual lung lobes can be identified, which is very helpful when determining the location of a pathologic structure (lesion) for research purposes or subsequent necropsy. The improved image quality is also very helpful in the detection of small (0.3–0.5 mm diameter) lung lesions. Conclusion:Lungcancer research can benefit from extensive use of mouse models to investigate potential new treatment approaches. The use of improved non‐invasive imaging has positively impacted our lungcancer research program.