RESUMO
Breast cancer in young patients is known to exhibit more aggressive biological behavior and is associated with a less favorable prognosis than the same disease in older patients, owing in part to an increased incidence of brain metastases. The mechanistic explanations behind these findings remain poorly understood. We recently reported that young mice, in comparison to older mice, developed significantly greater brain metastases in four mouse models of triple-negative and luminal B breast cancer. Here we have performed a quantitative mass spectrometry-based proteomic analysis to identify proteins potentially contributing to age-related disparities in the development of breast cancer brain metastases. Using a mouse hematogenous model of brain-tropic triple-negative breast cancer (MDA-MB-231BR), we harvested subpopulations of tumor metastases, the tumor-adjacent metastatic microenvironment, and uninvolved brain tissues via laser microdissection followed by quantitative proteomic analysis using high resolution mass spectrometry to characterize differentially abundant proteins potentially contributing to age-dependent rates of brain metastasis. Pathway analysis revealed significant alterations in signaling pathways, particularly in the metastatic microenvironment, modulating tumorigenesis, metabolic processes, inflammation, and neuronal signaling. Tenascin C (TNC) was significantly elevated in all laser microdissection (LMD) enriched compartments harvested from young mice relative to older hosts, which was validated and confirmed by immunoblot analysis of whole brain lysates. Additional in vitro studies including migration and wound-healing assays demonstrated TNC as a positive regulator of tumor cell migration. These results provide important new insights regarding microenvironmental factors, including TNC, as mechanisms contributing to the increased brain cancer metastatic phenotype observed in young breast cancer patients.
RESUMO
PURPOSE: Breast cancer diagnosed in young patients is often aggressive. Because primary breast tumors from young and older patients have similar mutational patterns, we hypothesized that the young host microenvironment promotes more aggressive metastatic disease. EXPERIMENTAL DESIGN: Triple-negative or luminal B breast cancer cell lines were injected into young and older mice side-by-side to quantify lung, liver, and brain metastases. Young and older mouse brains, metastatic and naïve, were analyzed by flow cytometry. Immune populations were depleted using antibodies or a colony-stimulating factor-1 receptor (CSF-1R) inhibitor, and brain metastasis assays were conducted. Effects on myeloid populations, astrogliosis, and the neuroinflammatory response were determined. RESULTS: Brain metastases were 2- to 4-fold higher in young as compared with older mouse hosts in four models of triple-negative or luminal B breast cancer; no age effect was observed on liver or lung metastases. Aged brains, naïve or metastatic, contained fewer resident CNS myeloid cells. Use of a CSF-1R inhibitor to deplete myeloid cells, including both microglia and infiltrating macrophages, preferentially reduced brain metastasis burden in young mice. Downstream effects of CSF-1R inhibition in young mice resembled that of an aged brain in terms of myeloid numbers, induction of astrogliosis, and Semaphorin 3A secretion within the neuroinflammatory response. CONCLUSIONS: Host microenvironmental factors contribute to the aggressiveness of triple-negative and luminal B breast cancer brain metastasis. CSF-1R inhibitors may hold promise for young brain metastasis patients.