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The EphA2 receptor tyrosine kinase has emerged as a promising new therapeutic target in cancer due to its high expression in tumors. EphA2-specific antibodies have been used to deliver drugs and toxins to tumor cells, leading to inhibition of tumor growth and metastatic dissemination. We previously identified two related peptides, YSA and SWL, that selectively bind to the ligandbinding domain of EphA2 but not other Eph receptors, and could therefore be useful as selective targeting agents. Here we characterize the two peptides and a series of derivatives. Based on systematic amino acid replacements, only 5 YSA residues appear to be critical for high affinity receptor binding. Furthermore, a peptide comprising only the first 5 residues of YSA retains selectivity for EphA2. Similar to ephrin-A1, the physiological ligand for EphA2, both YSA and SWL activate EphA2 and inhibit downstream oncogenic signaling pathways in PC3 cancer cells. The two peptides and derivatives are quite stable in conditioned cell culture medium and show promise for delivering drugs and imaging agents to EphA2-expressing tumors.The EphA2 receptor tyrosine kinase, a member of the large Eph receptor family, is a promising therapeutic target in cancer because it is widely overexpressed in many cancer types, including breast, ovarian, prostate, pancreatic and lung cancer (1-3). EphA2 is present not only in the tumor cells but also in the tumor vasculature, while it is undetectable in normal quiescent vasculature (4,5). Furthermore, high EphA2 levels have been associated with a poor clinical prognosis (1-3) and with the more malignant, basal type of breast and prostate cancers (6,7). EphA2 overexpression has indeed been shown to induce oncogenic transformation and invasiveness of cultured mammary epithelial cells (8), and EphA2 downregulation with siRNA or anti-sense oligonucleotides has a negative impact on tumor growth and metastasis in mouse cancer models (9,10). Interestingly, EphA2 is tyrosine phosphorylated (activated) at low to undetectable levels in most tumors, suggesting an oncogenic role that is independent of ligand-mediated activation (11-13).Five glycosylphosphatidylinositol (GPI)-linked ligands (ephrin-A1 to -A5) can induce EphA2 tyrosine phosphorylation and activation in mammalian cells (14). A number of † This work was supported by NIH grant CA82713 (to EBP), a grant from MedImmune (to EBP), and Department of Defense Breast Cancer Research Program grant W81XWH-07-1-0462 (to ZH and EBP), Prostate Cancer Research Program grant W81XWH-06-1-0077 (to EBP) and Postdoctoral Fellowship DAAMD17-01-1-0168 (to MK). (11,13,15). Therefore, EphA2 functions as a tumor suppressor when its signaling ability is activated by ephrin ligands, whereas its tumor promoting effects may be ligand-independent (3,12,13,16).A number of EphA2-targeting agents have been developed. Several agonistic monoclonal antibodies and ephrin-A1 Fc, a soluble form of ephrin-A1, have been shown to decrease tumor growth and metastasis in mouse models (17)(18)(19)(20...

SUMMARY ARTS (Apoptosis-Related protein in the TGF-β Signaling pathway) is a mitochondrial protein that binds XIAP (X-linked Inhibitor of Apoptosis Protein) upon entering the cytosol, thus promoting cell death. Expression of ARTS is lost in some malignancies. Here we show that ARTS binds to XIAP at BIR1, a domain distinct from the caspase-binding sites. Furthermore, ARTS interacts with the E3 ligase Siah-1 (seven in absentia homolog 1) to induce ubiquitination and degradation of XIAP. Cells lacking either Siah or ARTS contain higher steady-state levels of XIAP. Thus, ARTS serves as an adapter to bridge Siah-1 to XIAP, targeting it for destruction.

Overactivation or overexpression of β-catenin in the Wnt (wingless) signaling pathway plays an important role in tumorigenesis. Interaction of β-catenin with T-cell factor (Tcf) DNA binding proteins is a key step in the activation of the proliferative genes in response to upstream signals of this Wnt/β-catenin pathway. Recently, we identified a new small molecule inhibitor, named BC21 (C(32)H(36)Cl(2)Cu(2)N(2)O(2)), which effectively inhibits the binding of β-catenin with Tcf4-derived peptide and suppresses β-catenin/Tcf4 driven reporter gene activity. This inhibitor decreases the viability of β-catenin overexpressing HCT116 colon cancer cells that harbor the β-catenin mutation, and more significantly, it inhibits the clonogenic activity of these cells. Down-regulation of c-Myc and cyclin D1 expression, the two important effectors of the Wnt/β-catenin signaling, is confirmed by treating HCT116 cells with BC21. This compound represents a new and modifiable potential anticancer candidate that targets β-catenin/Tcf-4 interaction.

The chemokine receptor CXCR4 is one of two principal coreceptors for HIV-1 entry into target cells. CXCR4 is known to form homodimers. We previously demonstrated that the amino (N)-terminus of viral macrophage protein (vMIP)-II is the major determinant for CXCR4 recognition, and that V1 peptide derived from the N-terminus of vMIP-II (1-21 residues) showed significant CXCR4 binding. Interestingly, an all-D-amino acid analog of V1 peptide, DV1 peptide, displayed even higher binding affinity and strong antiviral activity in inhibiting the replication of CXCR4-dependent HIV-1 strains. In the present study, we synthetically linked two DV1 peptides with the formation of a disulfide bond between the two cysteine residues present in the peptide sequence to generate a dimeric molecule potentially capable of interacting with two CXCR4 receptors. DV1 dimer showed enhanced binding affinity and antiviral activity compared with DV1 monomer. Ligand binding site mapping experiments showed that DV1 dimer overlaps with HIV-1 gp120 on CXCR4 binding sites, including several transmembrane (TM) residues located close to the extracellular side and the N-terminus of CXCR4. This finding was supported by the molecular modeling of CXCR4 dimer–DV1 dimer interaction based on the crystal structure of CXCR4, which showed that DV1 dimer is capable of interacting with the CXCR4 dimeric structure by allowing the N-terminus of each DV1 monomer to reach into the binding pocket of CXCR4 monomer. The development of this bivalent ligand provides a tool to further probe the functions of CXCR4 dimerization and to study CXCR4 heterodimerization with other receptors.