β1 integrin inhibitory antibody induces apoptosis of breast cancer cells, inhibits growth, and distinguishes malignant from normal phenotype in three dimensional cultures and in vivo

Current therapeutic approaches to cancer are designed to target molecules that contribute to malignant behavior but leave normal tissues intact. 01 integrin is a candidate target well known for mediating cell-extracellular matrix (ECM) interactions that influence diverse cellular functions; its aberrant expression has been implicated in breast cancer progression and resistance to cytotoxic therapy. The addition of beta(1) integrin inhibitory agents to breast cancer cells at a single-cell stage in a laminin-rich ECM (three-dimensional 1rECM) culture was shown to down-modulate beta(1), integrin signaling, resulting in malignant reversion. To investigate beta(1) integrin as a therapeutic target, we modified the three-dimensional IrECM protocol to approximate the clinical situation: before treatment, we allowed nonmalignant cells to form organized acinar structures and malignant cells to form tumor-like colonies. We then tested the ability of beta(1) integrin inhibitory antibody, AII beta 2, to inhibit tumor cell growth in several breast cancer cell lines (T4-2, MDA-MB-231, BT474, SKBR3, and MCF-7) and one nonmalignant cell line (S-1). We show that % integrin inhibition resulted in a significant loss of cancer cells, associated with a decrease in proliferation and increase in apoptosis, and a global change in the composition of residual colonies. In contrast, nonmalignant cells that formed tissue-like structures remained resistant. Moreover, these cancer cell-specific antiproliferative and proapoptotic effects were confirmed in vivo with no discernible toxicity to animals. Our findings indicate that, integrin is a promising therapeutic target, and that the three-dimensional IrECM culture assay can be used to effectively distinguish malignant and normal tissue response to therapy.