Margret Schmidt

Effect of selective inhibitors of inflammation on oral mucositis: Preclinical studies

OBJECTIVE Oral mucositis is a severe, dose-limiting side effect of radio(chemo)therapy for head and neck tumors. The epithelial radiation response (ulceration) is accompanied by inflammatory changes. Their interaction with the epithelial processes remains unclear. The present study was initiated to determine the effect of inhibition of TNF-alpha or COX-2 on the epithelial radiation response in the mouse tongue model. METHODS Daily fractionated irradiation was given with 5 x 3 Gy/week over one (days 0-4) or two weeks (days 0-4, 7-11). Each protocol was terminated by graded test doses (5 dose groups, 10 animals each) to a defined area of the lower tongue surface to generate full dose-effect curves for mucosal ulceration. A TNF-alpha inhibiting antibody (Infliximab) or a COX-2 inhibitor (Celecoxib) was administered. RESULTS No effect of Infliximab or Celecoxib was found in any of the protocols. Isoeffective doses for ulcer induction were unchanged. Also, the time course of the response was largely unaffected. CONCLUSIONS Inhibition of TNF-alpha or COX-2, two dominating inflammatory pathways, did not result in modulation of the response of oral epithelium during fractionated irradiation. This suggests that the inflammatory changes mediated through TNF-alpha or COX-2 are not relevant for the epithelial radiation response of oral mucosa.

Modulation of radiation-induced oral mucositis (mouse) by selective inhibition of β1 integrin

INTRODUCTION Oral mucositis is a severe side effect of radio(chemo)therapy for head and neck tumors, for which β1 integrins have been proposed as potential therapeutic targets. The present study was initiated to determine the effect of selective inhibition of β1 integrin on the oral epithelial radiation response. MATERIALS AND METHODS Daily fractionated irradiation was given with 5 × 3 Gy/week over 1 or 2 weeks with/without the β1 integrin-inhibiting monoclonal antibody AIIB2 or an IgG control. Each protocol was terminated by graded test doses to generate full dose-effect curves for mucosal ulceration. The same technique was used for single dose irradiation. RESULTS Combined single dose irradiation plus AIIB2 resulted in a significant decrease of the ED50 compared to irradiation alone or control IgG. No effect of AIIB2 was found with fractionated irradiation over 1 week. With 2 weeks of fractionation, AIIB2 induced a significant increase in the ED50 for the terminating test irradiation when administered in week 2. The time course of the response was largely unaffected by β1 integrin inhibition. CONCLUSIONS A reduction of mucosal reactions by β1 integrin inhibition later in a course of fractionation was observed, i.e. when epithelial repopulation processes were active. Further mechanistic studies are required.

Local hypoxia in oral mucosa (mouse) during daily fractionated irradiation – Effect of pentoxifylline

PURPOSE A significant reduction of radiation-induced oral mucositis by systemic application of pentoxifylline has been demonstrated in a mouse tongue model. However, the underlying mechanisms remain unclear. The present study focuses on the development of local hypoxia in mouse tongue during daily fractionated irradiation and a potential modulation by pentoxifylline. MATERIALS AND METHODS Daily fractionated irradiation with 5×3Gy/week (days 0-4, 7-11) was given to the snouts of mice. Groups of 3 animals per day were sacrificed between day 0 and 14. Pentoxifylline (15mg/kg, s.c.) was administered daily from day -5 to the day before the mice were sacrificed. The expression of intrinsic hypoxia markers HIF-1α and GLUT1 in the epithelium of the lower tongue surface was analysed by immunohistochemistry in 3 animals per day; the percentage of positive epithelial cells and the staining intensity were analysed as endpoints. RESULTS Compared to untreated control tissue, fractionated irradiation resulted in a progressive increase in the expression of both hypoxia markers. This effect was significantly reduced by pentoxifylline. CONCLUSION An early onset of local hypoxia occurs during fractionated irradiation in mouse tongue epithelium. The effect is markedly reduced by the mucoprotective agent pentoxifylline, suggesting a mucositis-promoting role of hypoxia; this, however, deserves further investigation.

Nebenwirkung als Zeichen von Wirkung

ZusammenfassungBei einer kurativen Strahlentherapie müssen immer Normalgewebsanteile in das Bestrahlungsfeld eingeschlossen werden. Eine gewisse, akzeptierte Häufigkeit an Komplikationen ist daher als Zeichen einer effektiven Therapie und nicht a priori als Fehlbehandlung anzusehen.