Analysis of potential drivers of tungsten-enhanced breast cancer metastasis: A longitudinal study of bone marrow adipocytes

Tungsten (W) is classified as an emerging environmental toxicant due to increased human exposure and lack of knowledge of the health risks. Epidemiological and in vivo studies reveal exposure to W contributes to the carcinogenic process, but molecular mechanisms are poorly defined. Due to a cohort of breast cancer patients accidentally exposed to W during intraoperative radiotherapy, our lab is investigating the effects of W on breast cancer progression and metastasis. W is known to store in the bone, causing long-term exposure and toxicity. Previous research in our lab has shown in multiple triple-negative breast cancer orthotopic models, W enhances breast cancer metastasis to the bone niche. Bone marrow adipocytes (BMA) play an important role in metastasis through secretion of adipokines/cytokines that drive tumor cells homing, colonization, and growth by changing the microenvironment. Understanding changes throughout metastasis is crucial to uncover adipokines/cytokines that could drive colonization and proliferation of tumor cells in the bone niche after W exposure. 6-8 week old female BALB/c or C57BL/6 mice were exposed to 15ppm W in drinking water or tap water for 4 weeks. After 4 weeks, mice had orthotopic injections of 4T1 (BALB/c) or E0771-Luc (C57BL/6) cells into the mammary fat pad. Longitudinal time points were taken to track changes with no tumor cell injection (0 week; 0W), 2 week post injection (2 week; 2W), and 3 week post injection (3 week; 3W). At the end, femurs were used for immunohistochemistry staining of Perilipin-1+ (Plin1+) adipocytes in bone marrow. Bone marrow from tibiae was cultured to select for mesenchymal stromal cells (MSC), which were then differentiated into BMA. Cell supernatant and RNA were collected from both MSCs and BMA to profile changes in adipokines/cytokines. Both models had increased metastasis to the bone after W exposure, 4T1 induced greater systemic inflammation compared to E0771-Luc. Adiponectin levels remained unchanged in E0771-Luc, but increased after W exposure at 2W and 3W in 4T1. CXCL2 expression was increased after W exposure at 0W and 2W and trending at 3W in 4T1 and increased at 3W in E0771-Luc. Plin-1+ staining revealed E0771-Luc has more adipocytes compared to 4T1, regardless of exposure. Some analytes did not change with W exposure or weekly, suggesting that those may not be not the main drivers of metastasis. Analytes like Adiponectin showed changes after W exposure, but were dependent upon the model. This suggests that there are differences between models and W might do slightly different things in each one, including systemic inflammation that we observed more in the 4T1 compared to the E0771-Luc. CXCL2 was increased in both models, suggesting a common key player in enhanced metastasis to the bone. This study provides insights into adipokine/cytokines that might be crucial players in W enhanced breast cancer metastasis to the bone.