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Most cancer patients with brain metastases are treated with radiation therapy, yet this modality has not yet been meaningfully incorporated into preclinical experimental brain metastasis models. We applied two forms of whole brain radiation therapy (WBRT) to the brain-tropic 231-BR experimental brain metastasis model of triple-negative breast cancer. When compared to sham controls, WBRT as 3 Gy × 10 fractions (3 × 10) reduced the number of micrometastases and large metastases by 87.7 and 54.5 %, respectively (both p < 0.01); whereas a single radiation dose of 15 Gy × 1 (15 × 1) was less effective, reducing metastases by 58.4 % (p < 0.01) and 47.1 % (p = 0.41), respectively. Neuroinflammation in the adjacent brain parenchyma was due solely to a reaction from metastases, and not radiotherapy, while adult neurogenesis in brains was adversely affected following both radiation regimens. The nature of radiation resistance was investigated by ex vivo culture of tumor cells that survived initial WBRT (“Surviving” cultures). The Surviving cultures surprisingly demonstrated increased radiosensitivity ex vivo. In contrast, re-injection of Surviving cultures and re-treatment with a 3 × 10 WBRT regimen significantly reduced the number of large and micrometastases that developed in vivo, suggesting a role for the microenvironment. Micrometastases derived from tumor cells surviving initial 3 × 10 WBRT demonstrated a trend toward radioresistance upon repeat treatment (p = 0.09). The data confirm the potency of a fractionated 3 × 10 WBRT regimen and identify the brain microenvironment as a potential determinant of radiation efficacy. The data also nominate the Surviving cultures as a potential new translational model for radiotherapy.

Purpose: Brain metastases of breast cancer cause neurocognitive damage and are incurable. We evaluated a role for temozolomide in the prevention of brain metastases of breast cancer in experimental brain metastasis models. Experimental Design: Temozolomide was administered in mice following earlier injection of brain-tropic HER2–positive JIMT-1-BR3 and triple-negative 231-BR-EGFP sublines, the latter with and without expression of O6-methylguanine-DNA methyltransferase (MGMT). In addition, the percentage of MGMT-positive tumor cells in 62 patient-matched sets of breast cancer primary tumors and resected brain metastases was determined immunohistochemically. Results: Temozolomide, when dosed at 50, 25, 10, or 5 mg/kg, 5 days per week, beginning 3 days after inoculation, completely prevented the formation of experimental brain metastases from MGMT-negative 231-BR-EGFP cells. At a 1 mg/kg dose, temozolomide prevented 68% of large brain metastases, and was ineffective at a dose of 0.5 mg/kg. When the 50 mg/kg dose was administered beginning on days 18 or 24, temozolomide efficacy was reduced or absent. Temozolomide was ineffective at preventing brain metastases in MGMT-transduced 231-BR-EGFP and MGMT-expressing JIMT-1-BR3 sublines. In 62 patient-matched sets of primary breast tumors and resected brain metastases, 43.5% of the specimens had concordant low MGMT expression, whereas in another 14.5% of sets high MGMT staining in the primary tumor corresponded with low staining in the brain metastasis. Conclusions: Temozolomide profoundly prevented the outgrowth of experimental brain metastases of breast cancer in an MGMT-dependent manner. These data provide compelling rationale for investigating the preventive efficacy of temozolomide in a clinical setting. Clin Cancer Res; 20(10); 2727–39. ©2014 AACR.

Purpose: Brain metastases of breast cancer cause neurocognitive damage and are incurable. We evaluated in experimental brain metastasis model a role of temozolomide, an oral brain permeable alkylating agent characterized by significant uptake in the central nervous system, in the prevention of brain metastases of breast cancer. Material and methods: To assess preventive role of temozolomide, mice were inoculated with 175,000 triple-negative 231-BR-EGFP cells in 0.1 mL PBS in the left ventricle of the heart. Three days after tumor cell inoculation, mice were randomized to temozolomide at the dose of 50 mg/kg delivered by oral gavage in saline, 5 days a week for 4 weeks, or vehicle. Subsequent experiments used temozolomide doses of 25, 10, 5, 1 and 0.5 mg/kg. To evaluate the efficacy of temozolomide in treating established BM, mice received temozolomide (50 mg/kg) beginning on either day 18 or day 24 post-injection of 231-BR-EGFR cells, 5 days a week for two and one week, respectively. To investigate the impact of temozolomide on survival, mice injected with 231-BR-EGFP cells were randomized to vehicle, temozolomide on days 3-14, or temozolomide on days 17-28 post-injection, per the schedule described above. To determine the functional contribution of MGMT expression in the BM preventive model, similar experiments were performed using 231-BR-EGFP cells with induced MGMT expression, and MGMT-positive Jimt-1 cells. Metastases were counted in step sections of one hemisphere of each brain. Additionally, the percentage of MGMT-positive tumor cells in 62 patient-matched sets of breast cancer primary tumors and resected brain metastases was determined immunohistochemically. Results: Temozolomide, when dosed at 50, 25, 10 or 5 mg/kg, 5 days/week, beginning 3 days after inoculation, completely prevented the formation of experimental brain metastases from MGMT-negative 231-BR-EGFP cell line. At a 1 mg/kg dose, temozolomide prevented 68% of large brain metastases, and was ineffective at a dose of 0.5 mg/kg. When the 50 mg/kg dose was administered beginning on days 18 or 24, temozolomide efficacy was reduced or absent. Both schedules of temozolomide (days 3-14 and days 17-28) significantly increased survival (P = .0003 by long-rank test). Earlier administration of temozolomide resulted in long term survival of 6 and 2 out of 10 mice, respectively; a significant difference compared to vehicle (P < .0001 and .0003, respectively).Temozolomide was ineffective at preventing brain metastases in the MGMT-positive 231-BR-EGFP and Jimt-BR3 sublines. In 62 patient-matched sets of primary breast tumors and resected brain metastases 43.5% of the specimens had concordant low MGMT expression, while in another 14.5% sets high MGMT staining in the primary tumor corresponded with low staining in the brain metastasis. Conclusions: Temozolomide profoundly prevents the outgrowth of experimental brain metastases of breast cancer in a MGMT-dependent manner. The majority of patients had low MGMT expressing brain metastases. These data provide a compelling rationale for investigating preventive efficacy of temozolomide in high-risk advanced breast cancer patients. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-11-04.

Brain metastases are a significant cause of morbidity and mortality for patients with cancer, yet preventative and therapeutic options remain an unmet need. The cytokine pigment epithelium–derived factor (PEDF) is downregulated in resected human brain metastases of breast cancer compared with primary breast tumors, suggesting that restoring its expression might limit metastatic spread. Here, we show that outgrowth of large experimental brain metastases from human 231-BR or murine 4T1-BR breast cancer cells was suppressed by PEDF expression, as supported by in vitro analyses as well as direct intracranial implantation. Notably, the suppressive effects of PEDF were not only rapid but independent of the effects of this factor on angiogenesis. Paralleling its cytotoxic effects on breast cancer cells, PEDF also exerted a prosurvival effect on neurons that shielded the brain from tumor-induced damage, as indicated by a relative 3.5-fold reduction in the number of dying neurons adjacent to tumors expressing PEDF. Our findings establish PEDF as both a metastatic suppressor and a neuroprotectant in the brain, highlighting its role as a double agent in limiting brain metastasis and its local consequences. Cancer Res; 72(1); 144–53. ©2012 AACR.

Lapatinib, a small molecule EGFR/HER2 inhibitor, partially inhibits the outgrowth of HER2+ brain metastases in preclinical models and in a subset of CNS lesions in clinical trials of HER2+ breast cancer. We investigated the ability of lapatinib to reach therapeutic concentrations in the CNS following 14C-lapatinib administration (100 mg/kg p.o. or 10 mg/kg, i.v.) to mice with MDA-MD-231-BR-HER2 brain metastases of breast cancer. Drug concentrations were determined at differing times after administration by quantitative autoradiography and chromatography. 14C-Lapatinib concentration varied among brain metastases and correlated with altered blood-tumor barrier permeability. On average, brain metastasis concentration was 7–9-fold greater than surrounding brain tissue at 2 and 12 h after oral administration. However, average lapatinib concentration in brain metastases was still only 10–20% of those in peripheral metastases. Only in a subset of brain lesions (17%) did lapatinib concentration approach that of systemic metastases. No evidence was found of lapatinib resistance in tumor cells cultured ex vivo from treated brains. Results show that lapatinib distribution to brain metastases of breast cancer is partially restricted and blood-tumor barrier permeability is a key component of lapatinib therapeutic efficacy which varies between tumors.

Brain metastasis from breast cancer is an increasingly important clinical problem. Here we assessed the role of CD44hi/CD24lo cells and pathways that regulate them, in an experimental model of brain metastasis. Notch signaling (mediated by γ-secretase) has been shown to contribute to maintenance of the cancer stem cell (CSC) phenotype. Cells sorted for a reduced stem-like phenotype had a reduced ability to form brain metastases compared with unsorted or CD44hi/CD24lo cells (P < 0.05; Kruskal–Wallis). To assess the effect of γ-secretase inhibition, cells were cultured with DAPT and the CD44/CD24 phenotypes quantified. 231-BR cells with a CD44hi/CD24lo phenotype was reduced by about 15% in cells treated with DAPT compared with DMSO-treated or untreated cells (P = 0.001, ANOVA). In vivo, mice treated with DAPT developed significantly fewer micro- and macrometastases compared with vehicle treated or untreated mice (P = 0.011, Kruskal–Wallis). Notch1 knockdown reduced the expression of CD44hi/CD24lo phenotype by about 20%. In vitro, Notch1 shRNA resulted in a reduction in cellular growth at 24, 48, and 72 hours time points (P = 0.033, P = 0.002, and P = 0.009, ANOVA) and about 60% reduction in Matrigel invasion was observed (P < 0.001, ANOVA). Cells transfected with shNotch1 formed significantly fewer macrometastases and micrometastases compared with scrambled shRNA or untransfected cells (P < 0.001; Kruskal–Wallis). These data suggest that the CSC phenotype contributes to the development of brain metastases from breast cancer, and this may arise in part from increased Notch activity. Mol Cancer Res; 9(7); 834–44. ©2011 AACR.

Purpose: As chemotherapy and molecular therapy improve the systemic survival of breast cancer patients, the incidence of brain metastases increases. Few therapeutic strategies exist for the treatment of brain metastases because the blood-brain barrier severely limits drug access. We report the pharmacokinetic, efficacy, and mechanism of action studies for the histone deactylase inhibitor vorinostat (suberoylanilide hydroxamic acid) in a preclinical model of brain metastasis of triple-negative breast cancer. Experimental Design: The 231-BR brain trophic subline of the MDA-MB-231 human breast cancer cell line was injected into immunocompromised mice for pharmacokinetic and metastasis studies. Pharmacodynamic studies compared histone acetylation, apoptosis, proliferation, and DNA damage in vitro and in vivo. Results: Following systemic administration, uptake of [14C]vorinostat was significant into normal rodent brain and accumulation was up to 3-fold higher in a proportion of metastases formed by 231-BR cells. Vorinostat prevented the development of 231-BR micrometastases by 28% (P = 0.017) and large metastases by 62% (P < 0.0001) compared with vehicle-treated mice when treatment was initiated on day 3 post-injection. The inhibitory activity of vorinostat as a single agent was linked to a novel function in vivo: induction of DNA double-strand breaks associated with the down-regulation of the DNA repair gene Rad52. Conclusions: We report the first preclinical data for the prevention of brain metastasis of triple-negative breast cancer. Vorinostat is brain permeable and can prevent the formation of brain metastases by 62%. Its mechanism of action involves the induction of DNA double-strand breaks, suggesting rational combinations with DNA active drugs or radiation. (Clin Cancer Res 2009;15(19):6148–57)

Brain metastases of breast cancer seem to be increasingin incidence as systemic therapy improves. Metastatic disease in the brain is associated with high morbidity and mortality. We present the first gene expression analysis of laser-captured epithelial cells from resected human brain metastases of breast cancer compared with unlinked primary breast tumors. The tumors were matched for histology, tumor-node-metastasis stage, and hormone receptor status. Most differentially expressed genes were down-regulated in the brain metastases, which included, surprisingly, many genes associated with metastasis. Quantitative real-time PCR analysis confirmed statistically significant differences or strong trends in the expression of six genes: BMP1, PEDF, LAMγ3, SIAH, STHMN3, and TSPD2. Hexokinase 2 (HK2) was also of interest because of its increased expression in brain metastases. HK2 is important in glucose metabolism and apoptosis. In agreement with our microarray results, HK2 levels (both mRNA and protein) were elevated in a brain metastatic derivative (231-BR) of the human breast carcinoma cell line MDA-MB-231 relative to the parental cell line (231-P) in vitro. Knockdown of HK2 expression in 231-BR cells using short hairpin RNA reduced cell proliferation when cultures were maintained in glucose-limiting conditions. Finally, HK2 expression was analyzed in a cohort of 123 resected brain metastases of breast cancer. High HK2 expression was significantly associated with poor patient survival after craniotomy (P = 0.028). The data suggest that HK2 overexpression is associated with metastasis to the brain in breast cancer and it may be a therapeutic target. (Mol Cancer Res 2009;7(9):1438–45)

The brain is increasingly being recognized as a sanctuary site for metastatic tumor cells in women with HER2-overexpressing breast cancer who receive trastuzumab therapy. There are no approved or widely accepted treatments for brain metastases other than steroids, cranial radiotherapy, and surgical resection. We examined the efficacy of lapatinib, an inhibitor of the epidermal growth factor receptor (EGFR) and HER2 kinases, for preventing the outgrowth of breast cancer cells in the brain in a mouse xenograft model of brain metastasis.EGFR-overexpressing MDA-MB-231-BR (231-BR) brain-seeking breast cancer cells were transfected with an expression vector that contained or lacked the HER2 cDNA and used to examine the effect of lapatinib on the activation (ie, phosphorylation) of cell signaling proteins by immunoblotting, on cell growth by the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, and on cell migration using a Boyden chamber assay. The outgrowth of large (ie,50 microm(2)) and micrometastases was counted in brain sections from nude mice that had been injected into the left cardiac ventricle with 231-BR cells and, beginning 5 days later, treated by oral gavage with lapatinib or vehicle (n = 22-26 mice per treatment group). All statistical tests were two-sided.In vitro, lapatinib inhibited the phosphorylation of EGFR, HER2, and downstream signaling proteins; cell proliferation; and migration in 231-BR cells (both with and without HER2). Among mice injected with 231-BR-vector cells, those treated with 100 mg lapatinib/kg body weight had 54% fewer large metastases 24 days after starting treatment than those treated with vehicle (mean number of large metastases per brain section: 1.56 vs 3.36, difference = 1.80, 95% confidence interval [CI] = 0.92 to 2.68, P.001), whereas treatment with 30 mg lapatinib/kg body weight had no effect. Among mice injected with 231-BR-HER2 cells, those treated with either dose of lapatinib had 50%-53% fewer large metastases than those treated with vehicle (mean number of large metastases per brain section, 30 mg/kg vs vehicle: 3.21 vs 6.83, difference = 3.62, 95% CI = 2.30 to 4.94, P.001; 100 mg/kg vs vehicle: 3.44 vs 6.83, difference = 3.39, 95% CI = 2.08 to 4.70, P.001). Immunohistochemical analysis revealed reduced phosphorylation of HER2 in 231-BR-HER2 cell-derived brain metastases from mice treated with the higher dose of lapatinib compared with 231-BR-HER2 cell-derived brain metastases from vehicle-treated mice (P.001).Lapatinib is the first HER2-directed drug to be validated in a preclinical model for activity against brain metastases of breast cancer.

Retrospective studies of breast cancer patients suggest that primary tumor Her-2 overexpression or trastuzumab therapy is associated with a devastating complication: the development of central nervous system (brain) metastases. Herein, we present Her-2 expression trends from resected human brain metastases and data from an experimental brain metastasis assay, both indicative of a functional contribution of Her-2 to brain metastatic colonization. Of 124 archival resected brain metastases from breast cancer patients, 36.2% overexpressed Her-2, indicating an enrichment in the frequency of tumor Her-2 overexpression at this metastatic site. Using quantitative real-time PCR of laser capture microdissected epithelial cells, Her-2 and epidermal growth factor receptor (EGFR) mRNA levels in a cohort of 12 frozen brain metastases were increased up to 5- and 9-fold, respectively, over those of Her-2–amplified primary tumors. Co-overexpression of Her-2 and EGFR was also observed in a subset of brain metastases. We then tested the hypothesis that overexpression of Her-2 increases the colonization of breast cancer cells in the brain in vivo. A subclone of MDA-MB-231 human breast carcinoma cells that selectively metastasizes to brain (231-BR) overexpressed EGFR; 231-BR cells were transfected with low (4- to 8-fold) or high (22- to 28-fold) levels of Her-2. In vivo, in a model of brain metastasis, low or high Her-2–overexpressing 231-BR clones produced comparable numbers of micrometastases in the brain as control transfectants; however, the Her-2 transfectants yielded 3-fold greater large metastases (>50 μm2; P < 0.001). Our data indicate that Her-2 overexpression increases the outgrowth of metastatic tumor cells in the brain in this model system. [Cancer Res 2007;67(9):4190–8]

Purpose: The blood–brain barrier (BBB) is modified to a blood–tumor barrier (BTB) as a brain metastasis develops from breast or other cancers. We (i) quantified the permeability of experimental brain metastases, (ii) determined the composition of the BTB, and (iii) identified which elements of the BTB distinguished metastases of lower permeability from those with higher permeability. Experimental Design: A SUM190-BR3 experimental inflammatory breast cancer brain metastasis subline was established. Experimental brain metastases from this model system and two previously reported models (triple-negative MDA-231-BR6, HER2+ JIMT-1-BR3) were serially sectioned; low- and high-permeability lesions were identified with systemic 3-kDa Texas Red dextran dye. Adjoining sections were used for quantitative immunofluorescence to known BBB and neuroinflammatory components. One-sample comparisons against a hypothesized value of one were performed with the Wilcoxon signed-rank test. Results: When uninvolved brain was compared with any brain metastasis, alterations in endothelial, pericytic, astrocytic, and microglial components were observed. When metastases with relatively low and high permeability were compared, increased expression of a desmin+ subpopulation of pericytes was associated with higher permeability (231-BR6 P = 0.0002; JIMT-1-BR3 P = 0.004; SUM190-BR3 P = 0.008); desmin+ pericytes were also identified in human craniotomy specimens. Trends of reduced CD13+ pericytes (231-BR6 P = 0.014; JIMT-1-BR3 P = 0.002, SUM190-BR3, NS) and laminin α2 (231-BR6 P = 0.001; JIMT-1-BR3 P = 0.049; SUM190-BR3 P = 0.023) were also observed with increased permeability. Conclusions: We provide the first account of the composition of the BTB in experimental brain metastasis. Desmin+ pericytes and laminin α2 are potential targets for the development of novel approaches to increase chemotherapeutic efficacy. Clin Cancer Res; 22(21); 5287–99. ©2016 AACR.

Cancer metastasis is a significant contributor to breast cancer patient morbidity and mortality. In order to develop new anti-metastatic therapies, we need to understand the biological and biochemical mechanisms of metastasis. Toward these efforts, we and others have studied metastasis suppressor genes, which halt metastasis in vivo without affecting primary tumor growth. The first metastasis suppressor gene identified was nm23, also known as NDP kinase. Nm23 represents the most widely validated metastasis suppressor gene, based on transfection and knock-out mouse strategies. The biochemical mechanism of metastasis suppression via Nm23 is unknown and likely complex. Two potential mechanisms include binding proteins and a histidine kinase activity. Elevation of Nm23 expression in micrometastatic tumor cells may constitute a translational strategy for the limitation of metastatic colonization in high risk cancer patients. To date, medroxyprogesterone acetate (MPA) has been identified as a candidate compound for clinical testing.

Although knowledge of molecular biology and cellular physiology has advanced at a rapid pace, much remains to be learned about delivering chemotherapy and antibodies across the blood–brain barrier (BBB) for the diagnosis and treatment of central nervous system (CNS) disease. A meeting, partially funded by an NIH R13 grant, was convened to discuss the state of the science, current knowledge gaps, and future directions in the delivery of drugs and proteins to the CNS, for the treatment of primary and metastatic brain tumors. Meeting topics included CNS metastases and the BBB, and chemoprotection and chemoenhancement in CNS disorders. The discussions regarding CNS metastases generated possibilities of chemoprotection as a means not only to decrease treatment-related toxicity but also to increase chemotherapy dose intensity. The increasing incidence of sanctuary brain metastasis from breast cancer, in part due to the difficulty of monoclonal antibodies (mAbs) such as herceptin to cross the BBB, was one of the most salient “take home” messages of the meeting.

Background: Reestablishment of metastasis suppressor gene expression may constitute a therapeutic strategy for high-risk breast cancer patients. We previously showed that medroxyprogesterone acetate (MPA), a progestin that has been tested as treatment for advanced breast cancer, elevates expression of the Nm23-H1 metastasis suppressor gene in hormone receptor–negative metastatic human breast carcinoma cell lines in vitro via a glucocorticoid receptor–based mechanism. Here, we tested whether MPA treatment inhibits metastatic colonization of a hormone receptor–negative breast cancer cell line in vivo. Methods: We tested the soft-agar colony-forming efficiency of untransfected MDA-MB-231T human breast carcinoma cells and MDA-MB-231T cells transfected with antisense Nm23-H1 in the presence and absence of MPA. Pharmacokinetic studies were used to establish dose and injection schedules that led to MPA serum levels in mice similar to those achievable in humans. For in vivo studies, nude mice were injected intravenously with MDA-MB-231T cells. After 4 weeks, mice were randomized to control or MPA arms. Endpoints included incidence, number, and size of gross pulmonary metastases; Nm23-H1 protein expression in gross metastases; and side effects. All statistical tests were two-sided. Results: MPA reduced colony formation of MDA-MB-231T cells by 40%–50% but had no effect on colony formation of Nm23-H1 antisense transfectants. Metastases developed in 100% (95% confidence interval [CI] = 78% to 100% and 77% to 100%, respectively) of control mice injected with MDA-MB-231T cells. In two independent experiments, only 73% (95% CI = 45% to 92%) and 64% (95% CI = 35% to 87%) of mice injected with 2 mg of MPA developed metastases. Mice injected with 2 mg of MPA showed reductions in the mean numbers, per mouse, of all metastases and of large (>3 mm) metastases ( P = .04 and .013, respectively). Nm23-H1 was expressed at high levels in 43% of pulmonary metastases in MPA-treated mice but only 13% of metastases in untreated mice. Mice receiving at least 1-mg doses of MPA gained more weight than control-treated mice but exhibited no bone density alterations or abnormal mammary fat pad histology. Conclusion: Our preclinical results show that MPA appears to elevate Nm23-H1 metastasis suppressor gene expression, thereby reducing metastatic colonization. The data suggest a new use for an old agent in a molecularly defined subset of breast cancer patients.

Metastatic disease remains a significant contributor to morbidity and mortality in patients with breast cancer. An improved molecular and biochemical understanding of the metastatic process is expected to fuel the development of new therapeutic approaches. The suppression of tumor metastasis, despite tumor cell expression of oncogenes and metastasis-promoting events, has become a diverse and fruitful field of investigation. Although many genetic events promote metastasis, several genes show relatively reduced expression levels in metastatic tumor cells in mouse model systems and in aggressive human tumors. Re-expression of a metastasis-suppressor gene in a metastatic tumor cell line results in a significant reduction in metastatic behavior in vivo with no effect on tumorigenicity. The known metastasis-suppressor gene products nm23, KAI1, mitogen-activated protein kinase kinase 4, breast cancer metastasis suppressor-1, KiSS1, RHOGDI2, CRSP3, and vitamin D3-upregulated protein/thioredoxin interacting protein exhibit unexpected biochemical functions that have shed new light on signaling events that are important in metastasis. Most metastasis suppressors function at the translationally important stage of outgrowth of micrometastatic tumor cells at a distant site. We hypothesize that elevation of metastasis suppressor gene expression in micrometastatic tumor cells in the adjuvant high-risk population of patients with breast cancer will halt metastatic colonization and have a clinical benefit. DNA methylation inhibitors have shown limited promise in increasing metastasis-suppressor gene expression, and ligands of the nuclear hormone receptor family are currently under investigation in vitro and in vivo. Clinical testing of agents that increase metastasis-suppressor gene expression is expected to require tailored trial designs.

Breast cancer brain metastases remain incurable. The blood-brain barrier (BBB) is a multicellular dynamic structure regulating exchanges between the blood and the central nervous system. As cancer cells colonize the brain, the BBB evolves into a blood-tumor barrier (BTB). The BTB limits compound penetration and therefore contributes to poor efficacy of chemotherapy. While the BBB has been well characterized in developmental and neurodegenerative disease studies, the BTB composition remains unknown. We have characterized the BTB in three model systems of brain metastasis of breast cancer developed in the laboratory: a triple negative (231-BR6), and two HER2 overexpressing (SUM190-BR3, JIMT-1-BR3) subtypes. Using Texas Red dextran (TRD) as a marker of permeability and quantitative immunofluorescence staining, we analyzed the cellular and molecular composition of: 1) unaltered BBB vs. BTB, and 2) BTB in highly permeable metastases vs. BTB in poorly permeable metastases. The BTB developed from the BBB in a series of alterations, including a neuroinflammatory reaction with astrogliosis, endothelial cell dilation, increased VEGF, reduced astrocyte endfoot polarity, and decrease in PDGFR+ pericytes. Only 10% of the metastatic lesions harbored a profound TRD exudation, which correlated with paclitaxel efficacy. We hypothesized that specific cellular and molecular changes account for the heterogeneity and increase in TRD diffusion. When metastases with relatively low- and high-TRD diffusion were compared, highly permeable metastases correlated with an increased expression of desmin+ pericytes in three models (231-BR6 p=0.0002; JIMT-1-BR3 p=0.004; SUM190-BR3 p=0.008) and a decrease in CD13+ pericytes in two model systems (231-BR6 p=0.014; JIMT-1-BR3 p=0.002). Decreased expression of laminin α2 in the parenchymal basement membrane (231-BR6 p=0.001; JIMT-1-BR3 p=0.049; SUM190-BR3 p=0.023) were associated with higher permeability. Desmin+ pericytes have been associated with pathological conditions such as fibrosis and spinal cord injury. Seven over nine human craniotomy specimens were positive for Desmin staining, validating clinically the relevance of our findings. We subsequently hypothesized that the desmin+ pericyte subpopulation functionally contributes to increased permeability. Desmin+ pericytes were produced in vitro by co-culturing primary mouse pericytes with astrocytes. When desmin+ or CD13+ pericytes were added to in vitro transendothelial electrical resistance (TEER) models of the BBB, the desmin+ pericytes exhibited less resistance, indicative of higher permeability. The data suggest that desmin+ pericytes may facilitate the permeability of the BTB. These studies show that the BTB in brain metastasis model systems involves consistent molecular changes. These data may identify new strategies to selectively permeabilize the BTB and enhance chemotherapeutic efficacy. Citation Format: Brunilde Gril, L. Tiffany Lyle, Paul R. Lockman, Chris E. Adkins, Afroz Shareef Mohammad, Emily Sechrest, Emily Hua, Diane Palmieri, David J. Liewehr, Seth M. Steinberg, Wojciech Kloc, Ewa Izycka-Swieszewska, Renata Duchnowska, Nayyar Naema, Priscilla K. Brastianos, Patricia S. Steeg. Desmin+pericyte subpopulations correlated with blood-tumor barrier permeability in brain metastases of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4933. doi:10.1158/1538-7445.AM2017-4933

Breast cancer frequently metastasizes to the brain, colonizing a neuro-inflammatory microenvironment. The molecular pathways facilitating this colonization remain poorly understood.Expression profiling of 23 matched sets of human resected brain metastases and primary breast tumors by two-sided paired t test was performed to identify brain metastasis-specific genes. The implicated DNA repair genes BARD1 and RAD51 were modulated in human (MDA-MB-231-BR) and murine (4T1-BR) brain-tropic breast cancer cell lines by lentiviral transduction of cDNA or short hairpin RNA (shRNA) coding sequences. Their functional contribution to brain metastasis development was evaluated in mouse xenograft models (n = 10 mice per group).Human brain metastases overexpressed BARD1 and RAD51 compared with either matched primary tumors (1.74-fold, P.001; 1.46-fold, P.001, respectively) or unlinked systemic metastases (1.49-fold, P = .01; 1.44-fold, P = .008, respectively). Overexpression of either gene in MDA-MB-231-BR cells increased brain metastases by threefold to fourfold after intracardiac injections, but not lung metastases upon tail-vein injections. In 4T1-BR cells, shRNA-mediated RAD51 knockdown reduced brain metastases by 2.5-fold without affecting lung metastasis development. In vitro, BARD1- and RAD51-overexpressing cells showed reduced genomic instability but only exhibited growth and colonization phenotypes upon DNA damage induction. Reactive oxygen species were present in tumor cells and elevated in the metastatic neuro-inflammatory microenvironment and could provide an endogenous source of genotoxic stress. Tempol, a brain-permeable oxygen radical scavenger suppressed brain metastasis promotion induced by BARD1 and RAD51 overexpression.BARD1 and RAD51 are frequently overexpressed in brain metastases from breast cancer and may constitute a mechanism to overcome reactive oxygen species-mediated genotoxic stress in the metastatic brain.

Despite major therapeutic advances in the management of patients with breast cancer, central nervous system (CNS) metastases remain an intractable problem, particularly in patients with metastatic HER2-positive and triple-negative breast cancer. As systemic therapies to treat extracranial disease improve, some patients are surviving longer, and the frequency of CNS involvement seems to be increasing. Furthermore, in the early-stage setting, the CNS remains a potential sanctuary site for relapse. This review highlights advances in the development of biologically relevant preclinical models, including the development of brain-tropic cell lines for testing of agents to prevent and treat brain metastases, and summarizes our current understanding of the biology of CNS relapse. From a clinical perspective, a variety of therapeutic approaches are discussed, including methods to improve drug delivery, novel cytotoxic agents, and targeted therapies. Challenges in current trial design and endpoints are reviewed. Finally, we discuss promising new directions, including novel trial designs, correlative imaging techniques, and enhanced translational opportunities. Clin Cancer Res; 19(23); 6404–18. ©2013 AACR.

Brain (central nervous system; CNS) metastases pose a life-threatening problem for women with advanced metastatic breast cancer. It has recently been shown that the vasculature within preclinical brain metastasis model markedly restricts paclitaxel delivery in approximately 90% of CNS lesions. Therefore to improve efficacy, we have developed an ultra-small hyaluronic acid (HA) paclitaxel nanoconjugate (∼5 kDa) that can passively diffuse across the leaky blood–tumor barrier and then be taken up into cancer cells (MDA–MB–231Br) via CD44 receptor–mediated endocytocis. Using CD44 receptor–mediated endocytosis as an uptake mechanism, HA-paclitaxel was able to bypass p-glycoprotein–mediated efflux on the surface of the cancer cells. In vitro cytoxicity of the conjugate and free paclitaxel were similar in that they (i) both caused cell-cycle arrest in the G2–M phase, (ii) showed similar degrees of apoptosis induction (cleaved caspase), and (iii) had similar IC50 values when compared with paclitaxel in MTT assay. A preclinical model of brain metastases of breast cancer using intracardiac injections of Luc-2 transfected MDA–MB–231Br cells was used to evaluate in vivo efficacy of the nanoconjugate. The animals administered with HA–paclitaxel nanoconjugate had significantly longer overall survival compared with the control and the paclitaxel-treated group (P < 0.05). This study suggests that the small molecular weight HA–paclitaxel nanoconjugates can improve standard chemotherapeutic drug efficacy in a preclinical model of brain metastases of breast cancer. Mol Cancer Ther; 12(11); 2389–99. ©2013 AACR.

Background Brain metastasis is an increasingly common complication for breast cancer patients; approximately 15– 30% of breast cancer patients develop brain metastasis. However, relatively little is known about how these metastases form, and what phenotypes are characteristic of cells with brain metastasizing potential. In this study, we show that the targeted knockdown of MMP-1 in breast cancer cells with enhanced brain metastatic ability not only reduced primary tumor growth, but also significantly inhibited brain metastasis. Methods Two variants of the MDA-MB-231 human breast cancer cell line selected for enhanced ability to form brain metastases in nude mice (231-BR and 231-BR3 cells) were found to express high levels of matrix metalloproteinase-1 (MMP-1). Short hairpin RNA-mediated stable knockdown of MMP-1 in 231-BR and 231-BR3 cells were established to analyze tumorigenic ability and metastatic ability. Results Short hairpin RNA-mediated stable knockdown of MMP-1 inhibited the invasive ability of MDA-MB 231 variant cells in vitro, and inhibited breast cancer growth when the cells were injected into the mammary fat pad of nude mice. Reduction of MMP-1 expression significantly attenuated brain metastasis and lung metastasis formation following injection of cells into the left ventricle of the heart and tail vein, respectively. There were significantly fewer proliferating cells in brain metastases of cells with reduced MMP-1 expression. Furthermore, reduced MMP-1 expression was associated with decreased TGFα release and phospho-EGFR expression in 231-BR and BR3 cells. Conclusions Our results show that elevated expression of MMP-1 can promote the local growth and the formation of brain metastases by breast cancer cells.

INTRODUCTION: The overall goal of this study was to assess the utility of three-dimensional magnetic resonance imaging (MRI) for monitoring the temporal and spatial development of experimental brain metastasis in mice. MATERIALS AND METHODS: Brain metastatic human breast cancer cells (231-BR or 231-BR-HER2) were injected intracardially in nude mice for delivery to the brain. Mouse brains were imaged in vivo at different time points using a balanced steady-state-free precession (bSSFP) pulse sequence at 1.5 T. Brains were categorized into four regions: cortex, central brain, olfactory, and posterior. The number of metastases and their volumes were quantified for both cell lines. RESULTS: There was no difference in the mean number of metastases for either cell line. The volumes of metastases in mice injected with 231-BR-HER2 cells were significantly larger than those for mice injected with 231-BR cells. The growth rate for 231-BR-HER2 metastases was 67.5% compared with 54.4% for the 231-BR metastases. More than 50% of metastases were located in the cortex and 25% to 30% of metastases were identified in the central brain for each time point and for mice injected with either cell line. The volumes of metastases were significantly larger in mice with fewer metastases at end point. SIGNIFICANT CONCLUSIONS: MRI provided a comprehensive accounting of the number and size of experimental brain metastases in the whole mouse brain at multiple time points. This approach has provided new information about the temporal and spatial development of metastases in the brain not possible by other histopathologic or imaging methods.

The incidence of brain metastasis is increasing. In fact, the incidence of brain metastasis outnumbers that of primary brain tumors by a factor of ten and is by far the most common neurologic complication of cancer. The reasons underlying the increasing incidence of brain metastasis are unclear, but may be associated with increased patient survival, improved imaging techniques, and greater awareness of the disease. With the increasing incidence, however, it is apparent that our understanding of the biology and epidemiology of brain metastasis is limited. Although most solid primary tumors can develop metastatic disease in the brain, approximately 80% of all brain metastases arise from adenocarcinomas of lung (50–60%) and breast (15–20%) and from malignant melanoma (5–10%). Brain metastases can develop from renal or colon cancers and other solid tumors but do so less frequently than metastases from the lung or breast. Within the brain, metastatic cancer cells can seed and grow in the brain parenchyma and the leptomeninges. Risk factors associated with the development of brain metastasis may vary according to origin of the primary cancer, which also often dictates the clinical experience and prognosis for a patient with a brain metastasis. Recently, a Graded Prognostic Assessment tool was developed to aid in treatment decisions and brain metastasis specific clinical trial strategies. Historically, patients with brain metastases have been excluded from clinical trials that enrolled metastatic cancer patients. Regardless of the origin of the primary cancer, prognosis is poor for patients who develop brain metastases, with median overall survival ranging from 4.8 to 13.8 months across all primary tumor histologies.

Few therapeutic strategies exist for the treatment of metastatic tumor cells in the brain because the blood–brain barrier (BBB) limits drug access. Thus the identification of molecular targets and accompanying BBB permeable drugs will significantly benefit brain metastasis patients. Polo-like kinase 1 (Plk1) is an attractive molecular target because it is only expressed in dividing cells and its expression is upregulated in many tumors. Analysis of a publicly available database of human breast cancer metastases revealed Plk1 mRNA expression was significantly increased in brain metastases compared to systemic metastases (P = 0.0018). The selective Plk1 inhibitor, GSK461364A, showed substantial uptake in normal rodent brain. Using a breast cancer brain metastatic xenograft model (231-BR), we tested the efficacy of GSK461364A to prevent brain metastatic colonization. When treatment was started 3 days post-injection, GSK461364A at 50 mg/kg inhibited the development of large brain metastases 62% (P = 0.0001) and prolonged survival by 17%. GSK461364A sensitized tumor cells to radiation induced cell death in vitro. Previously, it was reported that mutations in p53 might render tumor cells more sensitive to Plk1 inhibition; however, p53 mutations are uncommon in breast cancer. In a cohort of 41 primary breast tumors and matched brain metastases, p53 immunostaining was increased in 61% of metastases; 44% of which were associated with primary tumors with low p53. The data suggest that p53 overexpression occurs frequently in brain metastases and may facilitate sensitivity to Plk1 inhibition. These data indicate Plk1 may be a new druggable target for the prevention of breast cancer brain metastases.

Purpose: Brain metastases of breast cancer contribute significantly to patient morbidity and mortality. We have tested pazopanib, a recently approved antiangiogenic drug that targets VEGFR1, VEGFR2, VEGFR3, PDGFRβ, PDGFRα, and c-kit, for prevention of experimental brain metastases and mechanism of action. Experimental Design: In vitro assays included B-Raf enzymatic assays, Western blots, and angiogenesis assays. For in vivo assays, HER2 transfectants of the brain seeking sublines of MDA-MB-231 cells (231-BR-HER2) and MCF7 cells (MCF7-HER2-BR3, derived herein) were injected into the left cardiac ventricle of mice and treated with vehicle or pazopanib beginning on day 3 postinjection. Brain metastases were counted histologically, imaged, and immunostained. Results: Treatment with 100 mg/kg of pazopanib resulted in a 73% decline in large 231-BR-HER2 metastases (P < 0.0001) and a 39% decline in micrometastases (P = 0.004). In vitro, pazopanib was directly antiproliferative to 231-BR-HER2 breast cancer cells and inhibited MEK and ERK activation in vitro despite B-Raf and Ras mutations. Enzymatic assays demonstrated that pazopanib directly inhibited the wild type and exon 11 oncogenic mutant, but not the V600E mutant forms of B-Raf. Activation of the B-Raf targets pERK1/2 and pMEK1/2 was decreased in pazopanib-treated brain metastases whereas blood vessel density was unaltered. In the MCF7-HER2-BR3 experimental brain metastasis model, pazopanib reduced overall brain metastasis volume upon magnetic resonance imaging (MRI) by 55% (P = 0.067), without affecting brain metastasis vascular density. Conclusions: The data identify a new activity for pazopanib directly on tumor cells as a pan-Raf inhibitor and suggest its potential for prevention of brain metastatic colonization of HER2+ breast cancer. Clin Cancer Res; 17(1); 142–53. ©2010 AACR.

Purpose: Brain metastases of breast cancer appear to be increasing in incidence, confer significant morbidity, and threaten to compromise gains made in systemic chemotherapy. The blood–tumor barrier (BTB) is compromised in many brain metastases; however, the extent to which this influences chemotherapeutic delivery and efficacy is unknown. Herein, we answer this question by measuring BTB passive integrity, chemotherapeutic drug uptake, and anticancer efficacy in vivo in two breast cancer models that metastasize preferentially to brain. Experimental Design:Experimental brain metastasis drug uptake and BTB permeability were simultaneously measured using novel fluorescent and phosphorescent imaging techniques in immune-compromised mice. Drug-induced apoptosis and vascular characteristics were assessed using immunofluorescent microscopy. Results: Analysis of over 2,000 brain metastases from two models (human 231-BR-Her2 and murine 4T1-BR5) showed partial BTB permeability compromise in greater than 89% of lesions, varying in magnitude within and between metastases. Brain metastasis uptake of 14C-paclitaxel and 14C-doxorubicin was generally greater than normal brain but less than 15% of that of other tissues or peripheral metastases, and only reached cytotoxic concentrations in a small subset (∼10%) of the most permeable metastases. Neither drug significantly decreased the experimental brain metastatic ability of 231-BR-Her2 tumor cells. BTB permeability was associated with vascular remodeling and correlated with overexpression of the pericyte protein desmin. Conclusions: This work shows that the BTB remains a significant impediment to standard chemotherapeutic delivery and efficacy in experimental brain metastases of breast cancer. New brain permeable drugs will be needed. Evidence is presented for vascular remodeling in BTB permeability alterations. Clin Cancer Res; 16(23); 5664–78. ©2010 AACR.

Interactions between tumor cells and the microenvironment are crucial to tumor formation and metastasis. The central nervous system serves as a "sanctuary" site for metastasis, resulting in poor prognosis in diagnosed patients. The incidence of brain metastasis is increasing; however, little is known about interactions between the brain and metastatic cells. Brain pathology was examined in an experimental model system of brain metastasis, using a subline of MDA-MB-231 human breast cancer cells. The results were compared with an analysis of sixteen resected human brain metastases of breast cancer. Experimental metastases formed preferentially in specific brain regions, with a distribution similar to clinical cases. In both the 231-BR model, and in human specimens, Ki67 expression indicated that metastases were highly proliferative (approximately 50%). Little apoptosis was observed in either set of tumors. In the model system, metastases elicited a brain inflammatory response, with extensive reactive gliosis surrounding metastases. Similarly, large numbers of glial cells were found within the inner tumor mass of human brain metastases. In vitro co-cultures demonstrated that glia induced a approximately 5-fold increase in metastatic cell proliferation (P0.001), suggesting that brain tissue secretes factors conducive to tumor cell growth. Molecules used to signal between tumor cells and the surrounding glia could provide a new avenue of therapeutic targets for brain metastases.

Plasminogen activator inhibitor-1 (PAI-1) is a physiological inhibitor of urokinase (uPA), a serine protease known to promote cell migration and invasion. Intuitively, increased levels of PAI-1 should be beneficial in down-regulating uPA activity, particularly in cancer. By contrast, in vivo, increased levels of PAI-1 are associated with a poor prognosis in breast cancer. This phenomenon is termed the “PAI-1 paradox”. Many factors are responsible for the upregulation of PAI-1 in the tumor micro-environment. We hypothesize that there is a breast cancer predisposition to a more aggressive stage when PAI-1 is upregulated as a consequence of Metabolic Syndrome (MetS). MetS exerts a detrimental effect on the breast tumor microenvironment that supports cancer invasion. People with MetS have an increased risk of coronary heart disease, stroke, peripheral vascular disease and hyper-insulinemia. Recently, MetS has also been identified as a risk factor for breast cancer. We hypothesize the existence of the “PAI-1 cycle”. Sustained by MetS, adipocytokines alter PAI-1 expression to promote angio-genesis, tumor-cell migration and procoagulant micro-particle formation from endothelial cells, which generates thrombin and further propagates PAI-1 synthesis. All of these factors culminate in a chemotherapy-resistant breast tumor microenvironment. The PAI-1 cycle may partly explain the PAI-1 paradox. In this hypothesis paper, we will discuss further how MetS upregulates PAI-1 and how an increased level of PAI-1 can be linked to a poor prognosis.

Central nervous system or brain metastases traditionally occur in 10-16% of metastatic breast cancer patients and are associated with a dismal prognosis. The development of brain metastases has been associated with young age, and tumors that are estrogen receptor negative, Her-2+ or of the basal phenotype. Treatment typically includes whole brain irradiation, or either stereotactic radiosurgery or surgery with whole brain radiation, resulting in an approximately 20% one year survival. The blood-brain barrier is a formidable obstacle to the delivery of chemotherapeutics to the brain. Mouse experimental metastasis model systems have been developed for brain metastasis using selected sublines of human MDA-MB-231 breast carcinoma cells. Using micron sized iron particles and MRI imaging, the fate of MDA-MB-231BR cells has been mapped: Approximately 2% of injected cells form larger macroscopic metastases, while 5% of cells remain as dormant cells in the brain. New therapies with permeability for the blood-brain barrier are needed to counteract both types of tumor cells.

Background and Objectives Evaluation of the ductal epithelium of the breast at increased risk for breast cancer is needed to define the carcinogenic pathway, for risk assessment, and to improve selection of women for chemoprevention therapy. We studied the feasibility of combining breast ductal endoscopy with ductal lavage in the high-risk contralateral breast of women with ipsilateral breast cancer for the evaluation of high-risk ducts and acquisition of ductal epithelial cells for analysis. Methods Breast ducts were studied by ductal lavage and ductal endoscopy, and epithelial cell content studied cytologically and quantitatively. Results Twenty-five subjects and 44 ducts, including 22 (50.0%) which did not produce nipple aspirate fluid (NAF), were studied. Cellular atypia was present in five subjects. Ductal endoscopy was performed on 1 or more ducts in 24 subjects. Structural changes were noted in 63.6% of the ducts, most commonly fibrous stranding or bridging. Ductal sampling with endoscopic brush and coil sampling devices provided additional cellular samples of relatively pure ductal epithelial content (≥91% purity) in 8/11 subjects. Conclusions Breast ductal endoscopy combined with ductal lavage represents a feasible approach for characterizing the ducts and ductal epithelium of the high-risk breast, especially in a research setting. J. Surg. Oncol. 2006;94:555–564. © 2006 Wiley-Liss, Inc.

Clinically symptomatic metastases to the central nervous system (CNS) occur in approximately 10 to 15% of patients with metastatic beast cancer. CNS metastases are traditionally viewed as a late complication of systemic disease, for which few effective treatment options exist. Recently, patients with Her-2-positive breast tumors who were treated with trastuzumab have been reported to develop CNS metastases at higher rates, often while responding favorably to treatment. The blood:brain barrier and the unique brain microenvironment are hypothesized to promote distinct molecular features in CNS metastases that may require tailored therapeutic approaches. New research approaches using cell lines that reliably and preferentially metastasize in vivo to the brain have been reported. Using such model systems, as well as in vitro analogs of blood-brain barrier penetration and tissue-based studies, new molecular leads into this disease are unfolding.

Brain metastases occur in approximately 35% of metastatic breast cancer patients whose tumors overexpress HER2. Brain colonization of cancer cells occurs in a unique environment, containing microglia, oligodendrocytes, astrocytes and neurons. While a neuroinflammatory response has been documented in brain metastasis, its contribution to cancer progression and therapy remains poorly understood. Using a model system to study experimental brain metastasis of breast cancer, we intensively characterized the brain metastatic microenvironment of a brain tropic, HER2-transfected MDA-MB-231 human breast carcinoma subline (231-BR-HER2). The 231-BR-HER2 cell line was injected into the left cardiac ventricle of immunocompromised mice; mice were treated with vehicle, 30mg/kg or 100mg/kg pazopanib twice a day beginning on day 3 post-injection, for 4 weeks. Pazopanib, a multispecific tyrosine kinase inhibitor targeting VEGFR-1, -2, and -3, PDGFR-α and β, and c-kit, directly targeted tumor cells through the disruption of B-Raf pathway, prevents the outgrowth of 231-BR-HER2 large brain metastases by 73% (p Citation Format: Brunilde M. Gril, Diane Palmieri, Yong Qian, David J. Liewehr, Seth M. Steinberg, Talha Anwar, Zoraida Andreu, Daniel Masana, Patricia S. Steeg, Fernando Vidal-Vanaclocha. PDGFRβ activation defines a subset of astrocytes in the neuroinflammatory microenvironment of breast cancer brain metastasis, inhibitable by pazopanib. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1442. doi:10.1158/1538-7445.AM2013-1442

The DNA double-strand break (DSB) repair gene RAD51 was found to be overexpressed (1.5-fold, p=0.001) at the mRNA level in resected brain metastases compared to primary breast tumors from the same patients. RAD51 was also overexpressed (1.4-fold, p=0.008) specifically in brain metastases from breast cancer compared to systemic (bone/lung) metastases. We therefore hypothesize that RAD51 promotes brain metastasis development in breast cancer patients and investigated RAD51 as functional driver of brain metastases, independent of its recognized role in resistance to DNA-damaging chemotherapy. RAD51 was overexpressed at physiologically relevant levels in brain-metastatic variants of human MDA-MB-231 breast carcinoma cells (231-BR) and 4T1 murine mammary carcinoma cells (4T1-BR). In vitro, RAD51 overexpression results in a 35-40% (p In intracardiac-injected mice, overexpression of RAD51 increased formation of large brain metastases, the equivalent of clinically detectable lesions, (3.3-fold, p=0.005; 3.3-fold, p=0.02) and micro-metastases (3.1-fold, p=0.01; 2.0-fold, p=0.04), compared to vector controls in 231-BR and 4T1-BR models, respectively. ShRNA-mediated RAD51 knockdown in 4T1-BR cells had the opposite effect, reducing large brain metastases (2.5-fold, p=0.001) and micro-metastases (2.5-fold, p=0.01). RAD51 modulation had no effect on lung metastasis development in tail-vein injected mouse models of 231-BR or 4T1-BR cells. To distinguish between roles for RAD51 in initiation vs. outgrowth of brain metastasis, we quantified iron-labeled 231-BR cells in the brain microenvironment at 3, 7 and 12 days post-injection. On day 12, we observed significantly more RAD51-overexpressing single cells compared to vector controls, with a clear trend discernable by day 7 (fold-changes over vector: 1.1-fold, p=0.8; 2.4-fold, p=0.07 and 2.8-fold, p=0.001 for days 3, 7 and 12, respectively). Together these data suggest that RAD51 drives initiation of brain metastases from breast cancer. Citation Format: Stephan Woditschka, Diane Palmieri, Renata Duchnowska, Jacek Jassem, Sunil Badve, George W. Sledge, Patricia S. Steeg. Overexpression of RAD51 promotes brain metastases from breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4589. doi:10.1158/1538-7445.AM2013-4589

505 Background: Brain metastases (BM) of breast cancer constitute an important part of therapeutic failures and are associated with severe morbidity and mortality. The risk of BM is particularly high in HER2+ advanced breast cancer pts. We earlier developed in this group a 13-gene signature strongly predicting for rapid development of BM (J Clin Oncol 2008; 26: 45s). Now, we validated these results in an independent group of pts and on culture model system. Methods: Discovery group included 87 samples analyzed using cDNA synthesis, annealing, selection, extension, ligation and array hybridization (DASL). Independent validation group included 75 samples analyzed using quantitative reverse-transcriptase PCR. 3D culture validation model system used immortal, non-tumorigenic human MCF10A breast epithelial cells with and without ectopic expression of HER-2 and RAD51, a DNA double strand break repair gene (one of the three genes of this group overexpressed in 13-gene signature). The number and morphology of breast acini were scored using indirect immunoflourescence and confocal microscopy. Results: Median brain metastasis-free survival (BMFS) in the discovery group for ‘high’ vs. ‘low’ expression signature tumors was 36 months and 66 months, respectively (P=0.0068), and in the validation group 54 and 86 months, respectively (P=0.032). Short BMFS was also associated with ER-negativity; BMFS in the cohort of ‘high’ 13-gene signature and ER- tumors vs. other 3 groups was 31 months and 66 months in discovery group, and 41 and 77 months in validation group (P

Overexpression of the DNA double-strand break (DSB) repair gene RAD51 was identified as part of a 13-gene signature predictive of rapid brain metastasis development (≤3 years vs. >3 years after diagnosis, HR=3.03, p=0.0008) in primary tumors of chemotherapy-naïve HER2+ metastatic breast cancer patients. We also found RAD51 mRNA overexpressed (1.5-fold, p=0.001) in resected brain metastases compared to primary breast tumors from the same patients. In addition, RAD51 expression was significantly higher (1.4-fold, p=0.008,) in brain metastases compared to systemic (bone/lung) metastases. We therefore hypothesize that RAD51 promotes brain metastasis development in breast cancer patients. Given the known role of RAD51 in homologous recombination, important for the repair of DNA DSBs, it was unknown whether RAD51 would promote brain metastasis of breast cancer only in the presence of DNA-damaging chemotherapy or, alternatively, have endogenous biological functions in tumor cells. To functionally evaluate whether RAD51 promotes brain metastases, RAD51 was overexpressed at physiologically relevant levels in a brain-metastatic variants of triple-negative MDA-MB-231 breast carcinoma (231-BR) cells. In vitro, this resulted in a ∼30% increase in clonogenic colony formation (p=0.004), without affecting cell proliferation rates. RAD51 overexpression also conferred chemoresistance to DNA DSB inducing agents such as 25uM carboplatin (p=0.03) and 25nM doxorubicin (p=0.02), but not to agents that do not cause DNA DSBs, such as 2.5nM paclitaxel. In vivo, overexpression of RAD51 in 231-BR cells increased formation of large brain metastases, the equivalent of clinically detectable lesions, (4.0 and 3.3-fold, p=0.01 and p=0.005) and micro-metastases (3.1 and 3.5-fold, p=0.01 and p=0.001) in two independent xenograft experiments. Importantly, this brain-metastasis promoting effect occurred without drugs to induce DSB. This effect was recapitulated in a second animal model based on a brain-metastatic subline of 4T1 murine mammary carcinoma cells (4T1-BR). In this model, RAD51 overexpression increased large brain metastases (3.3-fold, p=0.02) and micro-metastases (2.0-fold, p=0.04) compared to vector control. ShRNA-mediated RAD51 knockdown in 4T1-BR cells resulted in the opposite effect, reducing large brain metastases (1.8-fold, p=0.1) and micro-metastases (2.5-fold, p=0.04). Together these data suggest a driving role for RAD51 in the development of brain metastases from breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5306. doi:1538-7445.AM2012-5306

634 Background: BM is a common occurrence in HER2-positive breast cancer pts. If the pts most likely to develop BM could be identified, prophylactic strategies might prevent or delay occurrence of this failure. Our previous work focusing on clinical and pathological factors coupled with gene expression analysis identified a 13 gene signature that together could predict the likelihood brain metastases within the first 3 years (early vs. late occurrence) after diagnosis (J Clin Oncol 2008; 26: 45s). More specifically, it suggested that a number of proteins involved in DNA double strand break repair are overexpressed in untreated primary breast tumors from patients who developed BM within 3 years of diagnosis. Methods: To determine the impact of DNA repair genes in early breast tumorigenesis, a 3D culture model system of immortal, nontumorigenic human MCF10A breast cells was used, with and without ectopic expression of HER2 and the DNA repair genes BARD1 and RAD51 from the signature. The number and morpholog...

e21138 Background: Brain metastases of breast cancer occurs in approximately one-third of metastatic triple negative and HER2+ breast cancer patients and contributes to patient morbidity and mortality. The identification and validation of molecular pathways underlying brain metastases of breast cancer may lead to the development of effective therapeutics. Methods: We have identified 23 sets of matched primary breast tumors and resected brain metastases, and determined their gene expression profiles using the DASL platform on formalin-fixed, paraffin embedded tumor sections. Multiple independent shRNAs to L1CAM or a control shRNA were transfected into a brain metastatic derivative (231-BR) of human MDA-MB-231 breast carcinoma cells. Brain metastases were quantified one month after intracardiac injection. Results: Patient characteristics: mean age at diagnosis of brain metastases: 48 years (range 29-68 years); 10 HER2+(3+)/ER- (43.5%), 1 HER2(2+)/ER- (4.4%), 2 HER2(2+)/ER+ (8.7%), 3 HER2-/ER+ (13%), 2 HER2(...

To investigate the molecular mechanisms responsible for breast cancer metastasis to the brain, a gene expression analysis was performed using formalin-fixed, paraffin embedded sections of matched primary breast tumors and resected brain metastases. The neuronal cell adhesion molecule L1CAM was upregulated by approximately 1.57 fold in the brain metastases relative to the primary tumors (p=0.037). This trend was most apparent in Her-2+ tumors (p=0.044) and did not extend to ER+ patients (p=0.42). L1CAM has been correlated to decreased patient survival in breast cancer. MDA-MB-231 breast cancer cells selected to grow in the brain (231-BR) expressed 6.4 fold greater L1CAM on western blots than the parental cell line (231-P). Using three shRNA constructs, L1CAM expression was decreased by 1.76, 3.82, and 63.3 fold in the 231-BR cell line. Decreased L1CAM expression inhibited the clonogenic formation of 231-BR cells by 40-50% (p Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2667. doi:10.1158/1538-7445.AM2011-2667

Brain metastases occur in 10-20% of metastatic breast cancer patients. The one year survival rate is approximately 20%. Brain metastasis is typically diagnosed late in breast cancer progression; however, studies suggest that the incidence of brain metastasis may be increasing under current chemotherapeutic regimens. We have investigated changes in gene expression associated with the acquisition of brain metastatic potential by breast cancer. A DNA microarray analysis comparing human brain metastases and a cohort of unlinked primary breast carcinomas identified Pigment Epithelium-Derived Factor (PEDF) as down-regulated in the brain metastases relative to the primary tumors (mean ∼14X lower by QPCR validation). The data suggest the hypothesis that PEDF may have a negative impact on brain metastatic progression. PEDF, a secreted factor, has been shown to act as a tumor suppressor, has strong anti-angiogenic activity, but supports the proliferation/viability/ differentiation of neural tissue. We hypothesize that the multiple roles of PEDF make it a potent agent which targets not only tumor cells, but also the microenvironment of the brain. In vitro experiments demonstrated that PEDF can promote death of breast cancer cells. Conversely, PEDF promoted neuronal survival, in vitro. In a xenograft model system (231BR, a brain-tropic derivative of human MDA-MB-231 breast cancer cells) PEDF overexpression inhibited formation of large brain metastases (∼2-fold, p=0.001) and reduced proliferation of PEDF-expressing breast cancer cells in mouse brain metastases (11% Ki67-positive, PEDF-positive vs. >56% Ki67-positive, PEDF-negative). In an intracranial implantation model, expression of PEDF by breast cancer cells lead to a rapid reduction in brain metastatic tumor volume. Histological examination suggests that PEDF reduces gliosis and protects neurons concomitant to suppression of metastatic growth. The data suggest the intriguing possibility that PEDF overexpression may concurrently inhibit brain metastasis of breast cancer cells but preserve neuronal function. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2846. doi:10.1158/1538-7445.AM2011-2846

The DNA double-strand break repair genes BARD1 and RAD51 were identified as part of a 13-gene signature predictive of early brain metastasis development (≤3 years vs. >3 years, HR=3.03, p=0.0008) in primary tumor sections from patients with HER2+ metastatic breast cancer. These data suggested that BARD1 and RAD51 overexpression would act early in breast cancer progression. In a gene expression analysis, these two genes were overexperessed (1.5 fold, p=0.0008 and 1.5 fold, p=0.001, respectively) in brain metastases compared to primary breast tumors from the same women. Their expression was also significantly higher (1.5 fold, p=0.01 and 1.4 fold, p=0.008, respectively) in brain metastases compared to systemic (bone/lung) metastases. These observations led us to hypothesize that BARD1 and RAD51 may be drivers of brain metastasis development in breast cancer patients. To evaluate the role of BARD1 and RAD51 on primary tumorigenesis, each gene was overexpressed in non-tumorigenic immortal human breast epithelial MCF10A cells. Three-dimensional MCF10A morphology was categorized as: single acinus, multi-acinar, invasive or solid acinus. Overexpression of BARD1 and RAD51 significantly increased the number of multi-acinar structures (2.1 fold, p=0.02 and 1.9 fold, p=0.05, respectively), as well as the number of invasive structures (3.1 fold, p=0.03 and 6.1 fold, p=0.005, respectively). To evaluate the functional significance of BARD1 and RAD51 on promoting brain metastasis development, the two genes were overexpressed in brain-metastatic triple-negative breast carcinoma MDA-MB-231 BR cells. This resulted in a 30% increase in multiplicity of clonogenic colonies (BARD1 p=0.001, RAD51 p=0.004), without affecting cell proliferation rates. Importantly, BARD1 and RAD51 overexpression conferred significant chemoresistance to DNA double-strand break inducing agents such as 25µM carboplatin (BARD1 p=0.005, RAD51 p=0.03) and 25nM doxorubicin (BARD1 p=0.03, RAD51 p=0.02), but not to agents that do not cause DNA double-strand breaks, such as 2.5nM paclitaxel. We are currently investigating whether overexpression of BARD1 and/or RAD51 can increase brain metastasis formation in vivo and whether this depends on the presence of chemotherapy-induced DNA double-strand breaks. High expression of BARD1 and RAD51 in primary breast tumors was predictive of early brain metastasis development in a 13-gene signature and is a clinical feature of brain metastases from breast cancer. Their overexpression is associated with an aggressive tumorigenic phenotype and chemoresistance to DNA double-strand break inducing agents, both of which could drive primary tumor spread and brain metastases development. BARD1 and RAD51 overexpression are brain metastases-specific molecular attributes, and represent potential novel targets for brain metastasis prevention and treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1478. doi:10.1158/1538-7445.AM2011-1478

Introduction: High vascular density of brain metastases of breast cancer has been correlated with both poor patient prognosis and with potential chemotherapeutic success. Inversely a low vascular density implies there would be decreased distribution of anti-cancer chemotherapeutics, and over time reduced efficacy of tumor kill. Given that there is heterogeneity in response to chemotherapeutics in human brain metastases and metastases are different than primary tumors; we used a novel brain metastases of breast cancer model to characterize vascular density, and corresponding changes in tumor permeability, hypoxia and survival. Methods: Brain seeking metastatic tumor lines MDA-MB-231-Br and 4T1-Br5 were injected via the left cardiac ventricle in separate experiments and brain metastases developed for ∼28 days and ∼15 days respectively. After development, both 14C-AIB and indocyanine green (ICG) were injected and allowed to circulate for 10 and 1 min respectively. Near infrared imaging was used to identify ICG filled vessels to quantify vascular density of lesions compared to normal brain. To determine permeability, concentrations of 14C-AIB in blood and brain tissue were calculated using autoradiography. Immunofluorescent analysis was performed using anti-HIF-1α and anti Ki67 antibodies and co-stained with DAPI. Results: A significant amount of metastatic lesions were observed to have developed in each model. Lesions varied in size from 0.028 to 2.3mm2. Vascular density was significantly decreased (MDA 176 ± 96 and 4T1 201 ± 76) compared to control brain (429 ± 25) and to an RG2 implanted glioma used as a positive control (736 ± 168). Based on accumulation of 14C-AIB, metastases (range: 22 nCi/g to 1682 nCi/g) were considered to be either permeable (3 fold or greater uptake compared to adjacent control tissue) or non-permeable. There was no strong correlation between lesion size and permeability (r2=0.23) or vascular density (r2 = 0.06). HIF-1α was expressed in both permeable and non-permeable lesions. Lastly, no significant difference was seen in the percentage of Ki67 positive cells in the MDA (permeable 41 ± 2.9, n=7; and non-permeable 40.8 ± 2.7, n=14) and 4T1 model (permeable 52.0 ± 4.6, n=6; and non-permeable 45.0 ± 2.8, n=6). Discussion: This data provides a correlation of permeability to vascular density, HIF-1α and Ki67 in a brain metastases model. While, both brain model systems exhibited a high degree of heterogeneous permeability, in neither model did permeability strongly correlate with vascular density, lesion size, HIF-1α expression and positivity for Ki67. Based upon the data, this experimental model may reflect the heterogeneity seen in human brain metastases of breast cancer and suggests there are other biological factors besides vascular density which correlate with drug distribution and or tumor/survival growth. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2373.

1005 Background: The prevalence of brain metastasis from breast cancer (BCA) is increasing. We have identified several potential therapeutic targets through gene expression profiling of human BCA brain metastases. One potential target, hexokinase II (HK-2), is up-regulated in brain metastases as compared to unlinked primary tumors. HK-2 plays a vital role in the generation of many components required for cell growth and inhibits apoptosis through mitochondrial binding. We hypothesized that HK-2 promotes metastatic cell proliferation in the brain and that its increased expression would negatively impact patient survival post-resection. Methods: The gene expression profile of surgically resected human BCA brain metastases was compared to that of non-related unlinked primary invasive ductal carcinomas using cDNA microarray analysis. In a separate retrospective study, we generated survival curves dividing a cohort of 113 patients based on HK-2 immunoreactivity in resected brain metastases. To evaluate the fun...