Identification of mammary tumor susceptibility genes and effects of Doxorubicin treatment on juvenile mice
Gebuijs, Ine Gerdine Elisabeth
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Breast cancer is the second largest cause of cancer deaths in women in the United States. The mortality is around 23 women per 100,000 cases. Studies have identified numerous risk factors, which are amongst others: age, a family history of breast cancer and the presence of certain genetic changes. Determination of individual risk allows treatment of individuals with cancer proportionally to their risk. Genome wide association (GWA) studies have been used to identify polymorphisms underlying breast cancer and other forms of cancer. In the first project described, a comparison is performed between breast and colorectal cancer GWA studies. Goals were to list which SNPs were found in the studies over the last years, how many cases and controls took part in the study and the number of SNPs genotyped. With these data, it was determined how many people were needed to find one SNP and a trend was made visible for both cancer type studies. It was shown that in time, less people were necessary to identify one significantly associated SNP. The platforms that were used in the studies were larger, increasing chances of identification and also detection methods became more precise. To detect sporadic cancer genes unidentified by GWA studies, mouse models have been found to be very useful. Finding mammary tumor susceptibility genes in mice can lead to identification of their human homologues, to eventually be able to target the individuals with the highest risk for preventive measures. Recombinant congenic (RC) mouse strains are a powerful tool to detect linkage between genotype and expressed phenotype because their genetic heterogeneity is low. RC mice carry 12,5% of donor alleles and 87,5% of background alleles, so any variation between the mice can be addressed to a small genetic region. In the second project, mice of the CcS/Dem (CcS) RC strains were used, each carrying a different random set of 12.5% STS donor strain and 87.5% BALB/c- neu background strain alleles, where neu is the mouse homologue of the human ErbB2 (HER2) oncogene causing breast cancer. The mice were injected with N-ethyl-N-nitrosourea (ENU) and palpated weekly for the presence of tumors, which were measured weekly. After 50 days of tumor appearance, mice were sacrificed and their tumor and lungs were taken out for analysis. A large difference of almost 8 months was seen for the day of tumor appearance. Also the presence of lung metastases varied substantially between the mice, from very early onset to late onset or no presence at all. With the known genotype of these ErbB2 + recombinant congenic mice, the genes that might be involved in the process causing these differences could be identified by linkage analysis. Breast cancer patients are often treated with chemotherapeutics, but also a range of cancers in children and young adults are treated with anthracyclines like Doxorubicin (DOX), a potent antitumor agent also known for its cardiotoxicity. Especially children are sensitive to DOX-induced cardiotoxicity, leading to hypotension, tachycardia, and arrhythmia. It is also observed that the drug decreases the trabecular bone volume in proximal rat tail vertebrae, and negative effects of DOX on trabecular bone volume and cortical bone thickness have been observed in growing rabbits, all together suggesting an inhibitory effect of DOX on bone formation. By use of several strains of RC mice, it was investigated what the effects of DOX were on the heart weight, the tibia length and the bodyweight. Juvenile mice of two weeks old were injected with 5 mg/kg of DOX weekly for 5 or 6 weeks and their bodyweight was measured twice a week. After the injections series, the animals were sacrificed and the heart and tibia were taken out for measurements and further histological investigation. Preliminary results show a significant variation in the effect of DOX on bodyweight (p<0.0001), differing between the strains. For heart weight and tibia length, these effects are still under investigation, but the first impression is that some strains seem to be more affected on their heart, while others have more bone growth inhibition. By genotyping these mice, it might become clear which genes or gene combinations are responsible for these three different phenotypes expressed by the DOX-injected mice.