Abstract P1-06-05: Expansion of tumor initiating cells is mediated by tumor microenvironment in breast cancer metastasis

Background: Breast cancer metastasis which ultimately results in breast cancer death, is an event believed to be initiated by the migration of tumor initiating cells (TIC) from the primary tumor to niches for micrometastatic disease. Recent data suggests the tumor microenvironment promotes TIC. The clinical relevance of secreted factors from the microenvironment on TIC surrogate, mammosphere (MS) formation and MS sensitivity to drug therapy was investigated using breast cancer patient fluids inherently conditioned by the tumor microenvironment: post-operative seromas and malignant pleural effusions.

Methods: Fluids from 48 patients with breast cancer (15 seromas and 33 pleural effusions) and mesenchymal stem cells (MSC) from healthy donors were collected on IRB approved protocols. Cellular components were eliminated from patient-derived fluids using density-gradient centrifugation. MSC conditioned media (MSC-CM) was collected from 3D cultures of primary MSC. Luminex multiplex array platform was used to characterize 79 cytokine and growth factor components of all fluids. In addition, MSC-CM and patient-derived fluids were added to cultures of breast cancer cell lines: MCF-7, an estrogen receptor (ER)-positive cell line; SUM149, a triple-negative inflammatory breast cancer cell line; and SUM159, a triple-negative metaplastic breast cancer cell line and MS forming efficiency was examined.

Results: Our results show that pleural effusions and seromas are enriched for factors also secreted by MSC such as MCP-1, GRO, IL-6, and VEGF-A. We found remarkable similarities regarding the cytokines and growth factors profile in pleural effusions and seromas. Both patient-derived fluids have comparable amount of Angiopoetin-2, Leptin, TNF-beta, VEGF, IL-2, IL-3, IL-4 and IL-10. EGF, TNF-alpha, IL-1, IL-6, IL-8 and IL-16 were significantly different between pleural effusions and seromas. Seroma fluid from bilateral drains in a patient with an invasive cancer and a contralateral benign mastectomy had very similar cytokine concentrations. Moreover, MSC-CM and pleural fluids from ER-positive and ER-negative patients increased the MS formation efficiency of both triple-negative cell lines while seroma fluids from ER-positive and ER-negative patients increased the MS formation efficiency of ER-positive cell line MCF-7. Finally, we evaluated the impact of a panel of drugs (simvastatin, pravastatin and erlotinib) on cell cultures grown with MSC-CM and patient-derived fluids. We found that the effect of chemotherapies on MS formation can be attenuated by patient-derived fluids.

Conclusions: Seroma and pleural effusion fluids from breast cancer patients have similar cytokine profiles, change MS formation efficiency of standard breast cancer cell models, and mediate sensitivity to therapy. Here we demonstrate that host and microenvironmental factors are critical for determining resistance to therapy and may be independent of obvious tumor related factors. Future studies will investigate the prognostic implications of factors that promote TIC survival in the fluid tumor microenvironment.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-06-05.

P2-01-13: Impact of Erlotinib on MSC-Mediated TIC Expansion and EMT

Background: Recently, we have demonstrated that mesenchymal stem cells (MSC) and MSC secreted factors (MSC-CM) have a profound effect on tumor initiating cells (TIC) enriched mammosphere formation and latency of tumor xenografts formation from breast cancer cell lines. Furthermore these interactions increased the expression of epithelial mesenchymal transition (EMT)-associated proteins which are associated with tumor cell invasion and metastasis as well as the TIC phenotype. (Klopp, A. H. et al., 2010, PLoS One. 5, e12180). Our data suggest that the presence of MSC in the tumor microenvironment may increase metastases by conferring stem progenitor cell biology on more differentiated non-metastatic cells. In addition, preliminary data suggested MSC-CM upregulated EGFR signaling in breast cancer cells. Therefore, we hypothesized that inhibiting EGFR signaling with erlotinib (tyrosin kinase inhibitor) can suppress MSC-mediated TIC expansion and EMT.

Methods & Results: In order to demonstrate that erlotinib inhibits MSC-CM promoted expansion of TIC, we cultured breast cancer cells lines (SUM149, SUM159, SUM190, MDA-IBC3 and MCF-7) in anchorage independent conditions with MSC-CM and treated them with increasing concentrations of erlotinib. The efficiency of mammosphere formation was examined after 5 days. We found that erlotinib inhibited MSC mediated increase in mammosphere formation in triple negative cell lines SUM149 and SUM159, and HER2−positive cell lines SUM190 and MDA-IBC3, but not in ER-positive, erlotinib resistant MCF-7 cells. Furthermore, we evaluated the impact of erlotinib on cell cultures grown with breast cancer patient-derived fluids, such as seroma and malignant pleural effusions. We observed that the effect of erlotinib on mammospheres formation was attenuated by both types of patient fluids.

Discussion: Patients with triple negative breast cancer have the highest rates of metastases and no available targeted therapies for treatment. EGFR is expressed in a significant proportion of triple negative breast cancers, and recent clinical and preclinical studies suggest that EGFR may contribute to the metastasis or aggressiveness of triple negative breast cancer. Here we demonstrate that host and environmentally-derived factors are critical for determining resistance to erlotinib. In vivo studies regarding the ability of erlotininb to prevent MSC-enhanced TIC survival and metastases are underway.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-01-13.