Blocking internalization of pBP1, a secreted homeoprotein, kills breast cancer cells but not normal breast epithelial cells.

Abstract

Abstract Abstract #3068 Background: BP1 is a member of the homeobox gene family, a highly conserved family of transcription factor genes. pBP1 is a homeotic protein that is upregulated in 80% of invasive ductal breast tumors. We have previously shown that the percentage of pBP1 positive breast cancer cases increases with the extent of cellular proliferation and carcinogenesis. BP1 expression is associated with aggressive tumors: 100% of ER negative tumors were BP1 positive, compared with 73% of ER positive tumors. pBP1 is secreted by MCF-7 cells, T47D cells, and MDA-MB-231 breast cancer cells, but not by MCF10A or H16N2 normal breast epithelial cells. In all cell lines tested, secreted pBP1 is internalized, resulting in stimulation of growth. Moreover, incubation of MCF-7 or MCF10A cells in recombinant pBP1 results in stimulation of several oncogenes, including bcl-2, Twist, and Met. These results led us to ask whether we could abrogate mitogenic stimulation by addition of anti-pBP1 antibody.
 Materials and Methods. Cells were incubated in 10 µg/ml anti-BP1 Ab (Novus) or 10 µg/ml IgG for three days. Growth was measured using MTT assays and apoptosis was assessed by flow cytometry after staining with Annexin V (Trevigen).
 Results. Addition of anti-BP1 Ab to the growth medium of MCF-7 cells, T47D cells, and MDA-MB-231 cells caused significant growth inhibition and apoptosis. In contrast, addition of anti-BP1 Ab to the growth medium of MCF10A and H16N2 cells did not lead to significant growth inhibition or apoptosis.
 Discussion. Our novel finding that pBP1 is secreted by breast cancer cells but not normal breast epithelial cells was the impetus to test the effect of adding anti-BP1 Ab to the growth media of both types of cells. Remarkably, anti-BP1 Ab kills only the breast cancer cells, suggesting they may be BP1-dependent. Our data indicate it may be possible to specifically target BP1 positive breast cancer cells in the 80% of women with BP1 positive tumors. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3068.