Peptide ligands that specifically target tumor cells represent useful tools for cancer therapy. They can be used for the transport and specific delivery of cell death‐inducing sequences or chemotoxic drugs to tumor cells. Here we describe a peptide from a conserved region of Bag‐1 (Bcl‐2 associated athanogene‐1) proteins that induces cell death without the need for a pro‐drug conjugate or fusion with a death‐inducing sequence. Stable expression of the Bag‐1 peptide in 22Rv.1 prostate tumor cells interferes with tumor cell growth and survival in vivo and in vitro and elevates the level of apoptosis in tumor cells treated with the topoisomerase inhibitor II etoposide. Structural analysis using NMR and circular dichronism (CD) show that this peptide is completely unstructured. Nevertheless it interacts with specific sequences of the glucose regulated proteins GRP75 and GRP78. Domain mapping studies identified the ATPase domain of GRP78 and the substrate‐binding domain of GRP75 as interaction sites of the Bag1‐peptide. Both GRP75 and GRP78 belong to the heat shock protein family and act as protective chaperones in the unfolded protein response. In addition both proteins are over expressed in many human tumors and are found exclusively on the surface of tumor cells. In particular, the GRP78 protein that is present on the surface of tumor cells is glycosylated. Using deglycosylation and GST‐pull down analysis, we can show that the Bag1‐peptide also binds to the glycosylated form of GRP78 indicating its ability to target tumor cells by binding to the cell surface. Thus we have identified a candidate peptide for a broad‐based tumor therapy that function by interfering with the action of GRP75 and GRP78.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B85.