Changes of breast cancer growth and metastasis in murine models modulated by an aromatase inhibitor, a low calcium diet or a high fat diet

Breast cancer (BC) is the most commonly diagnosed cancer in women, the leading cause of cancer death in females worldwide, and the second in American women (after lung cancer) according to CDC. In the most advanced stage of BC, stage IV, cancer cells metastasize from the original site to distant organs, such as bone, lung and liver. Tumor metastasis is responsible for nearly all of the morbidity and mortality associated with BC. Treatments of BC fail in the advanced stage, when metastases have already occurred. To mimic late stage BC in female patients, a mouse model was utilized to create a micro-metastatic lesion by implanting a small number of metastatic murine mammary tumor cells into the marrow cavity of tibia. Subsequent lung metastasis was evaluated. Previously our group reported that estrogens and phytoestrogens stimulated BC primary tumor growth in mice. Estradiol stimulated ER negative BC metastasis in mice. Based on foregoing studies, the hypothesis of this study is that the aromatase inhibitor letrozole may inhibit BC metastases to lungs by suppressing estrogen synthesis. BC growth on the bone micro-metastatic site and lung metastases were monitored in live animals via Bioluminescence Imaging (BLI). Effects of ovariectomy and letrozole on body estradiol levels were examined. Tumor nodules on lungs stained with India ink were counted. Furthermore, tumor grown in lungs was analyzed via H&E staining and proliferative cell percentage in lung tumors was calculated via Ki-67 staining. Our results showed that ovariectomy lowered body estrogen level and increased bone tumor area and density as indicated by BLI, while letrozole inhibited BC lung metastases in mice inoculated with murine 4T1 cancer cells. In a following project, the effects of a Low Calcium Diet (LCD) on BC metastases from bone to lungs, and its effects on the bone microenvironment in mice inoculated with murine 4T1 cells were studied. Bioluminescence imaging and India ink staining were used to evaluate tumor metastasis to the lungs. India ink stained lungs showed that LCD increased tumor numbers on the surface of lungs compared with control diet. LCD also induced negative impacts on the bone microenvironment where the primary tumor grows. In the third project, the effects of a high fat diet (HFD) on BC growth and metastasis in mice inoculated with murine 4T1 or 4T1.2 BC cells were studied. HFDs have been associated with BC progression and metastasis, indicated to increase BC risk by raising estradiol level. In BALB/c mice, dietary fat was found to increase mammary tumor growth and metastasis, and increase mortality. In this study, effects of HFD on mammary ductal tumor growth and BC metastasis in mice were evaluated. Metastases from bone to visceral tissues were monitored by BLI. It is found in this project that HFD increased BC metastasis to lung and liver in mice injected with 4T1.2 cells as shown by H&E staining. Mice injected with 4T1.2 cells developed more aggressive metastasis than mice with 4T1 cells, and also had higher liver weight and more liver lipid accumulation