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1058 Poster scattered ions in the Bragg peak with cell nuclei. The model has been DNa-PK-dependency for the sensitivity to different types of applied to experimental data for c~ particles [oublished by Barendsen. Using DNA damage the model, various aspects have been studied, e.g. relative number of ions M.R. Edaren. L.M. Persson, B.K. Lind contributing to the dose in different parts of the Bragg peak, probability of Karolinska Instituter, Medical Radiation .Physics, Stockholm, Sweden cell inactivation as a function of the number of hits of cell nucleus etc. In this

way, changes in the value of inactivation probability in different parts of the Different types of DNA damaging agents (i.e. ionising radiation, UVC radia- Bragg peak can be described and understood. tion, cisplatin) were used for investigating the role of DNA-dependent pro- tein kinase (DNA-PK) in vitro. The human glioma cell lines (M059J and 1061 Poster M059K) were used in clonogenic survival experiments. M059J is deficient The role of DNA-PK in the process of aberration formation in in DNA-PKCS (PRKDC), which is required for the non-homologous end- irradiated human glioblastoma cell lines j(~ining (NHEJ) pathway of DNA double-strand breaks (DSBs) repair. Irradi- H. Schmidberoer 1, M. Rave-Frank 1, H. Hofman-Hf3ther 1, C.F. Hess 1, ations were performed with a series of doses of low LET (Co60 photons) P. Virsik-KOpp 2 during aerobic and hypoxic (pure nitrogen) conditions, as welt as with high- LET (accelerated nitrogen ions at 140 eV/nm). The cell cultures were incu- 1University GOttingen, Radiotherapy and Radiation Oncology, GOttin. bated with different concentrations of cisplatin, hydrogen peroxide and gen, Germany exposed to UVC. 2University GOttingen, Clinical Radiation Biology and Physics, GOttin- The SF2 values were 0.51 (low LET), 0.02 (high LET) and 0.74 (nitrogen) gen, Germany and the OER 1.8 (at 50% survival) for the M059K cells. The RBE was 3.5- 4.1 depending on cell survival model used in the calculations. For M059J Purpose: DNA-PK plays a crucial role in NHEJ, the non-homologous end- cells the SF2 values were 0.02 (low LET), 0.03 (high LET) and 0.13 (nitro- joining, an important mechanism of DNA double-strand break repair. It is gen) given an RBE of inity and an OER of 1.8 (at 50% survival). M059K widely accepted that a double-strand break is the DNA-lesion causing the cells were more sensitive to exposure to UVC and cisplatin in comparison formation of structural chromosome aberrations, which can arise either from to M059J cells. Hydrogen peroxide was more cytotoxic for the DNA-PKCS unrepaired or from mlsrepaired dsb's. The role of the various DNA repair deficient cells, mechanisms in the formation of different aberration types, and particularly Both cell lines are sensitive to all agents tested in comparison to other cell of the DNA-PK-dependent NHEJ is not yet fully understood. We investigat- types. They are both defective in repairing DNA lesions, to which extent ed the role of this special protein kinase in a tumour cell line model: the varies with type of DNA damage induced. DNA-PK proficient M059-K line and the DNA-PK deficient (both alleles

deleted) M059-J line. The formation of radiation-induced aberrations in 1059 Poster these cell lines was analysed and the effect of the DNA-PK inhibitor Wort- Ta rge t ing cell surface sialic acid; results in t w o cy tos ta t i c mannin upon the aberration formation was studied. resistant ovarian cancer cel l - l ines Material and methods: Aberrations were analysed in confluent tumour cells B. Frankenda/1, M. Marquez 2, S. Ni/sson 2, L. Lennartsson 2, L. Zhaoxu 2, irradiated with 200 kV X-rays. FISH and standard Giemsa-staining were J. Hi/tunen 3, A. Ho/mberg 2 applied. In experiments with Wortmannin, 50 microM were added to M059-

K cells 1 hour before irradiation. 1Karo/inska Hospital, Radiumhemmet, Stockholm, Sweden Results: DNA-PK deficient cells showed a manifold higher yield of simple 2Karo/inska/nstitute, CCK, R8/3, App/. Chemistry, Stockholm, Sweden stable and unstable and of complex aberrations in comparison with DNA-

PK proficient cells. The largest differences were observed for excess acen- 3Map Medical Technologies, He/sinki, Finland tric fragments and for complex aberrations. DNA-PK inhibition by Wortman-

nin in M059-K cells resulted in a manifold increase in aberration yield, Background; Numerous previou s studies have shown that cell surface sia- however the formation of dicentrics was less affected than the other aber- lylation on malignant cells is strongly increased compared to normal tissue, ration types. At the same radiation dose, yields of acantric fragments were This study investigates the effect on tumor cell growth when the sialic acid of the same quantity in DNA-PK deficient M059-J cells and in Wortmannin- residues are blocked by electrostatic interaction with a cationic carbohy- treated M059-K cells.

drate polymer. Conclusion: Our results confirm a crucial role for NHEJ in the aberration for- Methods; Cationic dextran conjugates (CatDex) were prepared by periodate marion process; however, different aberration types are unevenly affected. oxidation and subsequent coupling of ligands through reductive amination. Since all analysed aberration types can be formed in the absence of DNA- A fluorimetric cytotoxicity assay (FMCA) was used for the cell survival PK as well, the DNA-PK-dependent form of NHEJ is not the sole mecha- assay. Two chemotherapy resistant ovarian cancer cell-lines OVCAR-3 and nism for the formation of a specific type of aberration in the studied tumour SK-OV-3 were seeded into 96 well microtiter plates. CatDex and Carbo- cells. platin were added at different concentrations (3 - 12,uM) and incubated for

72h. 1062 Poster Additionally, CatDex was fluorescence labelled (FITC) and interaction with the tumor cells was studied using fluorescence microscopy. Double strand breaks induced by Carbon Ion Irradiation in Results; Carboplatin (3-12pM) did not have any effect on the cell growth, prostate cancer cells CatDex showed a growth inhibitory effect that was concentration dependent H. Nishimura 1, R. Sasaki 1, Y. Ejima 1, K. Ando 2, Y. Furusawa 2, T. Soeji- ( i.e. the number of cationic side groups/dextran molecule and the molarity ma 1, E. Yoden 1, Y. Demizu 1, T. Kawabe 1, K. Sugimura 1 used). If the substitution was < 20% the growth inhibitory effect was small 1Kobe University Graduate School of Medicine, Division of Radiology, Ko- and difficult to reproduce. When it was 20-22%, about half of the cells died. Higher substitution resulted in complete cell death. The results correlated be, Japan with the fluorescent images i.e. strong cell killing effect showed intensive 2National Institute of Radiological ScienCes, Heavy-Ion Radiobiology cell membrane interaction. Research Group, Chiba, Japan Conclusion; Blocking of cell surface sialic acid causes cell death in two chemotherapy resistant ovarian cancer cell lines. Targeting and blocking of Purpose: A phase I / II clinical trials on carbon ion radiotherapy against eialic acid may indicate a new method for intraperitoneal treatment of prostate cancers were carried out in National Institute of Radiological Sci- advanced ovarian cancer. Clinical studies to explore this concept are ences (NIRS, Chiba, Japan). 3 year local control rate is about 94-98%. approaching. Therefore, carbon ion irradiation could be a promising treatment strategy

against prostate cancer. However, biological and molecular mechanisms of 1060 Poster carbon ion irradiation have not been clarified. Carbon ion irradiation is high Bragg peak and relative biological efficiency of different ions LET irradiation, and its biological feature is direct effect on DNA that

induces high frequent double strand breaks (DSBs). In this study, we M. L:okaiicek I L. Judas 1,2 P. Kundrat 1 focused on the mechanisms after carbon ion irradiation in human prostate 1Institute of Physics, Prague 8, Czech Republic cancer cells, especially assessing DSBs, DNA repair proteins and their 2Faculty Hospital, Department of Oncology, Prague 2, Czech Republic nuclear foci formation.

Method and Materials: Human androgen refractory prostate cancer cell line A model of radiobiological mechanism in Bragg peak is proposed that DU-145 was investigated. Carbon ions were accelerated with Heavy Ion enables to describe quantitatively the dependence of RBE on linear energy Medical Accelerator in Chiba (HIMAC) at NIRS. Cell-killing effect of X-ray transfer. The model is based on analysis of the interaction of slowly moving and carbon ion irradiation was assessed using a colony-formation assay.

The amount of double strand breaks and repair rate was assessed by