ESTRO 36 Abstract Book

S56 ESTRO 36 _______________________________________________________________________________________________

OC-0117 Cisplatin sensitizes radioresistant mesenchymal stem cells A. Rühle 1 , R. Lopez Perez 1 , K.J. Weber 2 , J. Debus 1,2 , P.E. Huber 1,2 , N.H. Nicolay 1,2 1 German Cancer Research Center, Radiation Oncology, Heidelberg, Germany 2 University Hospital, Radiation Oncology, Heidelberg, Germany Purpose or Objective Mesenchymal stem cells (MSCs) have been shown to aid the regeneration of tissue damage induced by ionizing radiation or cisplatin. While these stem cells are relatively resistant to photon irradiation and cisplatin treatment alone, the influence of clinically relevant cisplatin-based chemo-radiation regimes on the survival and functional abilities of MSCs is unknown. Material and Methods The survival of human bone marrow-derived MSCs was assessed after pre-treatment with different doses of cisplatin, and the influence of cisplatin chemo-radiation on cellular morphology, adhesion and migratory abilities and differentiation potential was analyzed. Cell cycle distribution and apoptosis levels of MSCs were measured using flow cytometry, and DNA double strand break repair capacities were evaluated by immunofluorescence. Results Cisplatin pre-treatment resulted in a dose-dependent radiosensitization with sensitizer enhancement ratio values ranging between 1.07 and 1.30 depending on the cisplatin treatment dose. Cellular morphology, adhesion and migratory abilities were not significantly influenced by cisplatin chemo-radiation. MSC differentiation capability along the adipogenic and chondrogenic lineages was preserved after chemo-radiation, and the defining stem cell surface markers were stably expressed irrespective of treatment. Cisplatin pre-treatment resulted in an accumulation of MSCs in the radiosensitive G2/M phase of the cell cycle. Immunofluorescence analyses showed an increase in both initial and residual radiation-induced DNA double strand breaks following pre- treatment with cisplatin. Conclusion We could demonstrate for the first time that pre- treatment with cisplatin resulted in a dose-dependent sensitization of radioresistant MSCs, whereas the defining stem cell characteristics of the stem cells were largely preserved. A cisplatin-mediated G2/M phase arrest and an increase in residual radiation-induced DNA double strand breaks may at least be partly responsible for the radiosensitizing effect of cisplatin in MSCs. OC-0118 Mesenchymal stem cells are resistant to ionizing radiation irrespective of their tissue of origin N.H. Nicolay 1,2 , A. Rühle 2 , O. Xia 2 , R. Lopez Perez 2 , J. Debus 1,2 , P.E. Huber 1,2 1 University Hospital, Radiation Oncology, Heidelberg, Germany 2 German Cancer Research Center, Radiation Oncology, Heidelberg, Germany Purpose or Objective Mesenchymal stem cell-based therapies may provide a novel approach to treat radiation-induced organ damage. While mesenchymal stem cells (MSCs) required for those potential treatments can be harvested from various different tissues, the influence of ionizing radiation on the stem cells from diverse original tissues themselves is largely unknown. Material and Methods The radiation response of MSCs isolated from human bone marrow, adipose tissue and umbilical cord was investigated. Cellular survival, cell cycle effects and apoptosis were measured and compared to that of differentiated fibroblasts. The influence of irradiation on

the defining stem cell properties was assessed, and the radiation effects on MSC morphology, surface marker expression, adhesion and migration capabilities and the differentiation potential were measured. Immunocytochemical analyses of DNA damage and repair foci were carried out to quantify the MSCs' ability for DNA double strand break repair. Results MSCs from different tissues were found to exhibit a relative radiation resistance comparable to that of differentiated fibroblasts. Irradiated MSCs demonstrated a prolonged arrest in G2 phase of the cell cycle, but were able to avoid induction of apoptosis even after treatment with high radiation doses. Surface marker expression, stem cell adhesion and migration capability were not generally reduced by irradiation, and MSCs also maintained their potential for adipogenic, osteogenic and chondrogenic differentiation. Analysis of DNA damage/repair foci demonstrated a swift and efficient repair of radiation-induced DNA double strand breaks in MSCs, providing an explanation for the observed radiation resistance of these stem cells. Conclusion These data demonstrate for the first time that MSCs from diverse human tissues exhibit comparable resistance to ionizing radiation and also largely maintain their defining stem cell characteristics independent of their original tissue. The observed radiation resistance of MSCs from different tissues will help to establish diverse stem cell sources for future MSC-based therapies against radiation- induced organ damage. OC-0119 Dermatan sulfate mitigates radiation-induced oral mucositis (mouse) – biological mechanisms S. Gruber 1 , E. Bozsaky 1 , M. Arnold 1 , S. Pfaffinger 1 , S. Hetzendorfer 1 , V. Gernedl 1 , A. Rohorzka 1 , L. Kowald 1 , S. Morava 1 , J. Mayer 1 , P. Kuess 1 , W. Dörr 1 1 Medizinische Universität Wien Medical University of Vienna, Univ.Klinik f. Strahlentherapie, Vienna, Austria Purpose or Objective Oral mucositis is the most frequent, dose limiting early adverse event of head-and-neck cancer radio(chemo)therapy. The present study quantified the mucoprotective effect of dermatan sulfate (DS) and characterised the underlying biological mechanisms. Irradiation- and DS-mediated changes of epithelial proliferation, cell junction formation, inflammation and hypoxia were investigated. Material and Methods The study comprises functional and mechanistic investigations. For the functional assessment of mucosal ulcer incidence and time course, mice were irradiated with 5x3 Gy/week over one (days 0-4) or two weeks (days 0-4, 7-11). Each protocol was concluded by graded top-up doses (day 7/14) to generate complete dose-effect curves. Daily doses of DS (4 mg/kg subcutaneously) were applied over varying time intervals during either the first or the second week of fractionation alone, or during both weeks, respectively. In the mechanistic analyses, groups of five mice per experimental arm were sacrificed every second day during the two week fractionated irradiation, the tongues were excised and subjected to histological / immunohistochemical processing. Results DS significantly increased the isoeffective doses for the induction of oral mucositis in almost all protocols. DS furthermore prolonged the latency to epithelial ulceration and reduced ulcer duration. Proliferation measurements did not show any substantial or systematical effect of DS. In contrast, the radiation-induced increase in the expression of the adherens junction proteins e-cadherin and β-catenin as well as the tight junction proteins claudin and occludin occurred significantly earlier and more pronounced with additional DS treatment. The expression of IL-1β and NF-κB as markers of inflammation was