a5b1 integrin mediates survival of breast cancer cells in 3-dimensional culture that can be specifically targeted for therapy.

Abstract

#4126 Background: β1 integrin signaling has been implicated in breast cancer progression and has been shown to facilitate resistance to radiation that could be abrogated using β1 integrin inhibitory antibody, AIIB2. In the present study, we investigated whether a specific alpha heterodimer of β1 integrin was preferentially mediating a pro-survival signal in human breast cancer cells, and if it could specifically be targeted for therapy.
 Materials and Methods: We used three-dimensional (3D) laminin-rich extracellular matrix (lrECM) culture to compare the relative levels of alpha heterodimer expression in malignant HMT3522-T4-2 and nonmalignant cell line HMT3522-S-1. Total cell lysates were probed by western blot to detect several possible alpha integrins. In addition, to investigate whether α5β1 mediated an important pro-survival signal, we treated 3D lrECM cultures with a small peptide inhibitor of α5β1 integrin and fibronectin interaction, Ac-PHSCN-NH2 (ATN-161) and measured apoptotic response using TUNEL (terminal deoxynucleotidyl transferase (TdT)-mediated nick end labeling) assay.
 Results: We found that expression of α5β1 was upregulated in HMT3522-T4-2 malignant breast cell line compared to nonmalignant cell line HMT3522-S-1. Inhibition using ATN-161 resulted in a significant dose-dependent increase in TUNEL positive cells.
 Discussion: We have previously shown that inhibitory antibody to β1 integrin, AIIB2, leads to selective apoptosis and decreased proliferation in human breast cancer cells in 3DlrECM culture and in vivo. In addition, combining β1 integrin inhibition with IR allowed for reduction of IR dose necessary to achieve growth inhibition in vivo. Here, we show that in HMT3522-T4-2 breast cancer cell line, inhibition of α5 integrin and fibronectin interaction using ATN-161 significantly enhanced apoptosis in 3D lrECM. These data indicate that fibronectin and its receptor, α5β1 are important for survival signaling in breast cancer and may be an important target to enhance radiotherapy efficacy. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4126.