Epitope recognized by AOM1 on human OPN was determined using a series of overlapping synthetic peptides corresponding to the region 143-172 of human OPN. AOM1 binds to SVVYGLRSKS motif which is a binding site
for AZD2281 in vitro integrins α4β1, α4β7, α9β1, and α9β4R (Figure 1). The epitope is immediately CHIR-99021 adjacent to the RGD sequence which is the binding site for another family of integrins (αvβ3, αvβ1, αvβ5, αvβ5, α5β1 and α8β1). In addition, the AOM1 binding epitope spans over the main thrombin cleavage site on OPN. The ability of AOM1 to inhibit OPN binding to integrin αvβ3 which is considered to be the major receptor by which OPN regulates cancer cell migration and proliferation, and to prevent thrombin-mediated cleavage of OPN was characterized in an ELISA-based and western blot assays, respectively. In both cases www.selleckchem.com/products/AZD8931.html AOM1 demonstrated high inhibitory activity (Figure 1B&C). Therefore, this unique binding epitope allows AOM1 to inhibit multiple functional activities of OPN by preventing signaling through integrins as well as blocking cleavage of OPN by thrombin which has been shown to produce functionally more active OPN fragments than the full length molecule. Of note, AOM1 has high selectivity for OPN and does not recognize other RGD containing proteins
which is consistent with its binding epitope. Figure 1 Development of anti-OPN antibody. A Amino acid sequence of OPNa (full length OPN). Truncated isoforms OPNb and OPNc are highlighted with blue and yellow, respectively. Binding sites for integrins are highlighted with green (RGD binding integrins) and orange (LDV binding integrins). Thrombin cleavage site is marked by a red arrow. B Characterization of AOM1 including its cross-reactivity, binding epitope, dissociation constant (KD) for the Fab and its ability to inhibit binding of recombinant OPNa to immobilized integrin αvβ3 have been determined. C Selectivity of AOM1 for human OPN over other RGD-motif containing proteins was assessed by ELISA as detailed in Materials and Methods. RGD containing
proteins were immobilized on an immunosorbent plate and binding of AOM1 assessed at 0.1, 1, 10 and 1000 nM concentrations. With the exception of 1000 nM AOM1 vs. ColA1, there was no binding observed at any concentration of AOM1 up to 1000 nM versus thrombospondin, RNA Synthesis inhibitor vitronectin, ColA1 and fibronectin whilst saturated binding was observed vs. OPN at antibody concentrations as low as 0.1 nM AOM1. Each bar represents mean OD450 nm value of triplicate measurements with standard error bars. OPN acts as a chemotactic agent for human tumor cells and monocytes To identify a potential therapeutic indication for AOM1 we first screened a series of human and mouse cancer cells to identify cell lines that express OPN receptors in particular αvβ3 and CD44v6. As illustrated in Figure 2A-C, FACS analysis identified at least three cell lines expressing OPN receptors including JHH4, MDA-MB435, and MSTO-211H.