Influence of LET and oxygen status on cell survival and adhesion molecule expression

Hypoxia is one of the most common causes for tumor radio-resistance and metastasis. High LET irradiation is expected to reduce these problems. To measure the oxygen enhancement ratio (OER), the relative biological effectiveness (RBE) and the adhesion molecule expression, experiments with different LET, ions (carbon, nitrogen, oxygen and lithium) at different oxygen concentrations have been done. 1)To simulate different tumor conditions, CHO-K1 (Chinese Hamster Ovary) cell survival, has been measured after x-ray or carbon (100 keV/μm) irradiation under normoxic (air), hypoxic (0.5% oxygen) and anoxic (0% oxygen) conditions. The carbon irradiation gave an OER value of 1.8±0.1 in anoxia, while for photon irradiation it results in a value of 2.4±0.1. In hypoxia, the OER values decrease to 1.29±0.07 and to 1.5±0.1 for carbon and photon irradiation respectively. 2)To measure the influence of LET and atomic number on the OER, survival curves and measurement of RBE and OER with carbon ion at different LET, nitrogen and oxygen have been done. •The results showed that even if there were almost no differences in RBE in this LET range under oxic conditions, in anoxia RBE increases with increasing LET. The range of values found was from 3.1±0.2 for carbon 100 keV/μm to 4.4±0.2 for nitrogen 160 keV/μm (anoxia) and from 2.6±0.2 to 2.4±0.2 (normoxia). OER values decrease with increasing LET. Using different ions with different LET, the values found were from 1.8±0.1 for carbon 100 keV/μm to 1.30±0.04 for nitrogen 160 keV/μm. A clear influence of atomic number could not be seen in this atomic number range. 3)To measure a possible influence of the atomic numbers on the RBE for normal tissue and tumor tissue, experiments with irradiation of extended volume have been performed with nitrogen and oxygen and compared with carbon measurements. •Measurements resulting in a comparable survival on the entrance channel and exhibit the highest efficiency in the tumor for nitrogen ion. Mono-energetic lithium experiments showed RBE values close to 1 in the first centimetres of the plateau and an increase in RBE inside the Bragg peak. Results were compared to different model calculations. iv 4)As a model to better resemble the conditions in a human tumor and to study the E-cadherin expression after X-ray and carbon ion exposure, the PC3 cell line (Human prostate cancer cells) has been used. Survival curves experiment with normoxic and re-oxygenated chronic hypoxic cells have been performed. •After 72 hours in hypoxia/re-oxygenation the cells showed a decrease in radio-resistance when irradiated with X-rays but not when irradiated with carbon ions. Cell cycle synchronization due to an insufficient oxygenation could be the explanation for this. 5)To study the adhesion molecules and to understand the underlying mechanisms that give to the cells the invasive phenotype measurements of E-cadherin protein and gene expression have been performed. No difference after 24 hours anoxia in the protein expression was discovered compared to the normal oxic condition. Irradiation with X-rays produces a slight increase of E-cadherin after hypoxic treatment compared to normoxic cells. A low dose of carbon ion irradiation resulted in an over-expression of E-cadherin. For X-rays, this effect was not found. X-ray irradiation with low doses seems to reduce E-cadherin expression compared to unirradiated cells or irradiation with high doses