Preferential uptake of antibody targeted calcium phosphosilicate nanoparticles by metastatic triple negative breast cancer cells in co-cultures of human metastatic breast cancer cells plus bone osteoblasts

1055 Background: The outcome for patients with triple negative (TN) cancers is poor at least in part because of a lack of targeted therapies. Although 50% of TN breast cancers over-express EGFR, the use of EGFR inhibitors as single agents in patients with unselected and TN metastatic breast cancers has produced disappointing results. Likewise, mTOR inhibitors have modest activity as single agents in metastatic breast cancer. mTOR inhibitors have been demonstrated to activate the Akt pathway by a possible feedback mechanism, which could potentially sensitize TN breast cancer cells to upstream inhibitors. We have previously demonstrated that EGFR inhibitors in combination with rapamycin (RAPA) decrease cell survival, increase apoptosis, and are synergistic in TN breast cancer cells, compared to any of the agents alone (AACR 2008). We, therefore, evaluated the combination of mTOR and EGFR inhibition in vivo. Methods: Athymic mice were inoculated with TN (MDA-MB-231) breast cancer cells. One week after cell inoculation, mice were treated with vehicle, lapatinib 75mg/kg by mouth daily, RAPA 3mg/kg IP biweekly, or the combination. After 4 weeks of treatment, mice were sacrificed and tumors were assessed for target proteins by Western blotting and immunohistochemistry Results: The combination of RAPA and lapatinib resulted in a significant decrease in TN breast tumor volume (76 mm3), compared to rapamycin alone (133 mm3, p = 0.01), lapatinib alone (183 mm3, p < 0.0001) or control (188 mm3, p = 0.005). Neither lapatinib nor RAPA alone inhibited tumor growth significantly compared to control (p > 0.05). Interestingly, in contrast to our findings in vitro, the increase in pAkt noted in RAPA treated tumors was not decreased by lapatinib, despite the significant decrease in tumor size in tumors treated with the combination. Conclusions: These studies demonstrate that the combination of mTOR inhibition and lapatinib significantly inhibit TN breast cancer growth, compared with either agent alone. Given the lack of targeted therapies in TN breast cancers, these data support the possibility that mTOR inhibition can sensitize TN breast cancers to EGFR inhibitors. A clinical trial evaluating the combination of lapatinib and RAD001 as second-line therapy for TN metastatic breast cancer is planned. [Table: see text]

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BSCI-15. Osteopontin plays a crucial role in invasiveness of triple negative breast cancer cells in the context of human microglia

Neuro-Oncology Advances ◽

10.1093/noajnl/vdab071.014 ◽

2021 ◽

Vol 3 (Supplement_3) ◽

pp. iii4-iii4

Author(s):

Kamil Wojnicki ◽

Agata Kochalska ◽

Katarzyna Poleszak ◽

Adria-Jaume Roura ◽

Ewa Matyja ◽

...

Keyword(s):

Breast Cancer ◽

Cancer Cells ◽

Triple Negative Breast Cancer ◽

Breast Cancer Cells ◽

Triple Negative ◽

Metastatic Breast ◽

Breast Cancer Cell Lines ◽

Breast Cancers ◽

Human Microglia

Abstract The triple-negative breast cancer (TNBC) is the most malignant among breast cancers and has the high risk of developing metastasis into the brain. Metastases of breast cancers are increasing and pose a clinical challenge as the current treatments are not effective due to the unique brain microenvironment for metastatic breast cancer cells. While the contribution of brain macrophages to the formation of the metastatic niche is established, factors responsible for the crosstalk between cells remain elusive. SPP1 encoding a secreted phosphoprotein 1 (ostepontin) is highly overexpressed in malignant breast cancers. We evaluated the role of SPP1 in invasion and metastasis of human breast cancer cells. We found the increased invasion of triple-negative MDA-MB-231 (MDA-231) cells in the presence of human microglial HMSV40 cells. Using Western blot analysis demonstrated the elevated levels of focal adhesion kinase (FAK) and signal transducer and activator of transcription 3 (STAT3) in MDA-231 cells in co-cultures. Moreover, blocking SPP1 and integrin interactions with the synthetic RGD peptide, efficiently diminished both basic and microglia-induced invasion of MDA-231. To assess the role of SPP1 in cell invasion, we established the MDA-231 cells with knocked-down SPP1 expression using shRNA (shSPP1). Interestingly, the shSPP1 cells were unresponsive towards HMSV40 microglia. We have previously found that an antibiotic minocycline reduces SPP1 expression in glioma cells. We performed cell toxicity studies on 4 breast cancer cell lines and various non-malignant cells. All tested malignant cancer cells were more sensitize to minocycline than non-cancerous cells and breast cancer cells derived from TNBC were the most susceptible. Altogether, we demonstrate that microglia support invasion of breast cancer cells via SPP1/osteopontin triggering the integrin signalling, and minocycline by downregulating SPP1 expression may reduce both basic and microglia-induced cancer invasion. Therefore, we purpose that minocycline could be a new therapeutics targeting metastatic brain cancers.

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