Preview

PDF, German Download (1MB) | Terms of use

Abstract

Background: It has been proven that the sporadic forms of CRC often develop from colonadenomas. Various mutations then contribute to the degeneration. These include changes in the tumour suppressor genes APC and TP53 as well as in the oncogene KRAS. An established mouse model was further modified. The basis for the control of the APC, KRAS and TP53 mutations is the floxing of the corresponding DNA sections and cutting out by the Cre recombinase. Subsequently, the mutation becomes effective. In the existing model, tumor induction is achieved by adding Cre recombinase via adenovirus. Objective: The aim of this work is to switch tumor induction in the existing mouse model adenovirus to tumor induction by the selective estrogen receptor modulator tamoxifen due to the human pathogenic properties of the adenovirus. Methods: This requires a model containing both the floxed genes and a local mutation control. Local control is achieved by the use of the gut-specific promoter villin. Since the most effective dose of tamoxifen is unknown, we have used reporter animals. After recombination, blue-colored intestinal sections can be found in the histological preparation of these animals so that conclusions can be drawn about the appropriate dose by quantitative determination. The determined tamoxifen dose is then applied to the tumor-forming animals. All animals are operated for this and the tumor induction medium (virus/ Tamoxifen) is applied into a pinched colon segment. Results: After application of 500 µM Tamoxifen the animals developed colon tumors. However, no tumors of the small intestine could be excluded at lower or higher concentrations. In addition, even without the addition of tamoxifen, tumour development in older animals could be delayed. Conclusions: It was shown that tumor induction by tamoxifen is not as reliable as induction by adenovirus. This is partly due to the fact that the Cre recombinase is pre-existent in the experimental animals in the new model and leads to tumour development through its own activity even without the application of tamoxifen. On the other hand, the promoter villin cannot achieve sufficient colon specificity, since villin is expressed both in the colon and in the small intestine, so that tumours also develop there. Therefore, it is currently not possible to switch the model to tumor induction by tamoxifen.