Expression of stem cell marker genes in canine prostate cancer cell lines as basis for the development of molecular therapeutic tools Canines Prostata Karzinom CSC Suspension System. Prostate carcinoma is the most frequent cancer affecting men worldwide. Because aggressive carcinomas characterized by metastasis and recurrence are difficult to treat and eventually lead to death new strategies for curative therapies are sought. The dog is the only animal that spontaneously develops prostate cancer a fact that has drawn more and more attention to the possible use of this canine disease as a naturally occurring animal model for human prostate cancer. Moreover the canine tumor resembles very much the aggressive metastatic prostate carcinoma in man in the sense that both are castration resistant tend to metastasize early and predominantly to the skeleton and are thought to be derived from the basal layers of the prostatic epithelium. Like in various other cancer types cancer stem cells or tumor initiating cells respectively are thought to play a pivotal role in tumor initiation progression metastasis and therapy resistance. For prostate carcinoma their existence has been proven for man but hitherto not in the dog. In the presented thesis several cell lines derived from benign as well as malignant canine prostate neoplasias were investigated with regard to possible stem cell like properties such as expression of certain surface antigens and genes thought to be potential markers of CSC. The cell lines investigated were: CT1258 established from a canine prostate adenocarcinoma two derivatives of this line stably transfected with either an expression vector encoding for EGFP or EGFP HMGA2 fusion protein DT08 40 from a transitional cell carcinoma of the prostate and DT08 46 from a prostate cyst. Markers analysed by flow cytometry PCR and qPCR respectively were CD34 CD44 CD133 C KIT ITGA6 C MYC NANOG DDX5 KLF4 SOX2 MELK and OCT4. Moreover cultivated CT1258 cells were transferred to serum free culture conditions in order to enrich cells able to grow in spherical form a typical property of CSCs. Spheroid cells were then analyzed for gene expression profiles and surface antigens mentioned above in comparison to the parental adherent cells. Whereas CD44 was strongly expressed in all cell lines analyzed only weak expression of CD133 could be demonstrated in the two transfected cell lines but neither in the parental line CT1258 nor in the two other lines. Weak expression of ITGA6 MELK and DDX5 was found in almost all cell lines with the exception of the transfected lines where expression was very weak. This was also the case for OCT4 in all lines. Comparison of adherent and spheroid cells revealed a tendency to lower expression of all markers in the spheroidal cells with the exception of ITGA6 which was distinctly higher in the spheroids. In conclusion a characteristic marker expression profile was found for each analyzed cell line. Also spheres could successfully be generated from the prostate carcinoma cell line CT1258. Comparison of the markers between adherent and spheroidal cells showed different expression of ITGA6 and C MYC. The description of the analyzed genes shows a characteristic pattern for each cell line and also the presence of a specifically enriched cell population in the spheroidal cells which might be indicative of the presence of cancer stem cells.