Abstract P1-05-08: Targeting integrin signaling suppresses invasive recurrence in a three-dimensional model of radiation treated ductal carcinoma in situ

Abstract

Abstract Background: DCIS (ductal carcinoma in situ) is comprised of cancerous cells that are contained within the milk duct and separated from the stroma by a basement membrane. Akt activation is implicated in breast cancer progression and also upregulated in ∼30% of DCIS lesions. We have previously shown that β1-integrin inhibition enhanced the efficacy of ionizing radiation (IR) in invasive breast cancer, via an Akt-mediated effect. Radiation therapy (RT) is commonly used to treat DCIS, resulting in a decrease in recurrence risk by ∼50%. However, DCIS still recurs in a substantial number of patients, and as invasive disease half of the time. This study aimed to identify the effects of IR on Akt-driven DCIS, and possible mechanisms underlying invasive progression in surviving cells. Materials and Methods: To model DCIS, we took advantage of the ability of non-invasive mammary epithelial cells, MCF10A that form duct-like structures in 3-dimensional laminin-rich extracellular matrix (3D lrECM), and overexpressed an activated myristoylated form of the serine/threonine kinase, Akt. The 3D lrECM cultured MCF10A-Akt cells show filled lumen and retained basal polarity, characteristic of DCIS lesions in vivo. After DCIS structures formed in 3D lrECM, cultures were exposed to 8 Gy IR. Confocal microscopy analysis, western blot analysis, matrigel chemoinvasion assay and matix degradation assay were performed to characterize the IR effect on luminal or basal cells of the DCIS like structures. Results: MCF10A-Akt structures post-8 Gy IR shows a significant increase in apoptosis measured by cleaved caspase-3 (n = 3, P < 0.05). When we propagated cells post-IR in 3D lrECM, an invasive phenotype emerged in a sub-population of survivors (n = 3, P < 0.01). We also confirmed that inhibitory antibodies to β1-integrin suppressed the invasive phenotype that was induced by 8 Gy IR. In addition to this, invasion activity emerged by 8 Gy IR was inhibited by nuclear factor-kappaB (NF-κB) inhibitor JSH-23 (n = 3, P < 0.01). Finally, inhibition of β1-integrins or NF-κB translocation completely suppresses the formation of invasive colonies. Discussion: In present study, we found that inhibition of β1-integrins abrogates the emergence of an invasive phenotype among surviving clones. Our current data suggest that regulation of β1-integrin signaling via NF-κB plays an important role in the emergence of invasive disease after radiation, and may be an important clinical target. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-08.