Abstract B69: Macrophages along with pathogens in the microenvironment enhance the aggressive behavior of triple-negative breast cancer (TNBC) in an in vitro model.

Background: Macrophages in breast cancer microenvironment have been associated with earlier relapse and decreased overall survival especially in patients with TNBC (Campbell et al. 2011). Infectious agents have been linked to approximately 20% of all cancers but the role of pathogens in TNBC has not been fully explored. We sought to investigate in an in vitro model the effect of macrophages along with pathogens in the tumor microenvironment on enhancing the aggressive behavior of TNBC. Methods: Expression patterns of Toll-like receptors were examined in 4 breast cancer cell lines and THP-1 cell line. THP-1 cell line was differentiated into macrophages using phorbol 12-myristate 13-acetate (PMA). Calcein®-labeled MDA-MB-231 TNBC cell line was seeded in trans-wells in the presence and absence of macrophages grown in multi-well cell culture plates. Pattern of invasion of the MDA-MB-231 breast cancer cell line in the presence of virus infected serum free condition media (CM) was assessed using a modified Boyden Chamber concept in the absence and presence of macrophages. Lipopolysaccharide (LPS) and Polyinosine-polycitidylic acid (poly I:C) were used as toll-like receptor ligands simulating pathogen infection. Results: Data showed an increased invasion of MDA-MB-231 in the presence of macrophages and macrophage condition media (percent invasion 17.7% media only, 37.8 % with macrophages, and 36.1% with condition media from macrophages, p<0.0001). Invasion is enhanced by the addition of mouse mammary tumor virus infected condition media (MMTV-CM) (invasion increased from 17.7% to 52.8%, p<0.001). With the addition of macrophages and macrophage CM, percent invasion increased from 52.8% to 62.5% (p<0.01) and to 61.0% (p<0.05) respectively. While there was no effect when poly I:C and LPS were used alone in serum free media , poly I:C increased the percent invasion in the presence of macrophages and CM from macrophages to 47.7% (p<0.0001)and 35.2% (p<0.0001), respectively. LPS increased invasion with macrophage CM to 30.2% (p<0.01). Quantitative real-time PCR showed that toll-like receptors TLR3 and TLR4 mRNA levels in macrophages increased about 3 folds in the presence of MMTV. Conclusion: In this in vitro model, the presence of macrophages potentiates the aggressive behavior of MDA-MB-231 breast cancer cell line. Additionally, this effect is enhanced by the presence of MMTV in the microenvironment, potentially through activation of toll-like receptors in macrophages. Further studies will examine the role of inflammation induced by pathogens in the identification of a high-risk subgroup of patients with breast cancer that can benefit from novel therapies to target inflammation in the tumor microenvironment and improve clinical outcomes. Citation Format: Elias I. Obeid, Bifeng Zhang, Olufunmilayo I. Olopade. Macrophages along with pathogens in the microenvironment enhance the aggressive behavior of triple-negative breast cancer (TNBC) in an in vitro model. [abstract]. In: Proceedings of the Fifth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2012 Oct 27-30; San Diego, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(10 Suppl):Abstract nr B69.