Therapeutic implications of a human neutralizing antibody to the macrophage-stimulating protein receptor tyrosine kinase (RON), a c-MET family member.

RON is a member of the c-MET receptor tyrosine kinase family. Like c-MET, RON is expressed by a variety of epithelial-derived tumors and cancer cell lines and it is thought to play a functional role in tumorigenesis. To date, antagonists of RON activity have not been tested in vivo to validate RON as a potential cancer target. In this report, we used an antibody phage display library to generate IMC-41A10, a human immunoglobulin G1 (IgG1) antibody that binds with high affinity (ED50 = 0.15 nmol/L) to RON and effectively blocks interaction with its ligand, macrophage-stimulating protein (MSP; IC50 = 2 nmol/L). We found IMC-41A10 to be a potent inhibitor of receptor and downstream signaling, cell migration, and tumorigenesis. It antagonized MSP-induced phosphorylation of RON, mitogen-activated protein kinase (MAPK), and AKT in several cancer cell lines. In HT-29 colon, NCI-H292 lung, and BXPC-3 pancreatic cancer xenograft tumor models, IMC-41A10 inhibited tumor growth by 50% to 60% as a single agent, and in BXPC-3 xenografts, it led to tumor regressions when combined with Erbitux. Western blot analyses of HT-29 and NCI-H292 xenograft tumors treated with IMC-41A10 revealed a decrease in MAPK phosphorylation compared with control IgG-treated tumors, suggesting that inhibition of MAPK activity may be required for the antitumor activity of IMC-41A10. To our knowledge, this is the first demonstration that a RON antagonist and specifically an inhibitory antibody of RON negatively affects tumorigenesis. Another major contribution of this report is an extensive analysis of RON expression in approximately 100 cancer cell lines and approximately 300 patient tumor samples representing 10 major cancer types. Taken together, our results highlight the potential therapeutic usefulness of RON activity inhibition in human cancers.

DEGA/AMIGO-2, a leucine-rich repeat family member, differentially expressed in human gastric adenocarcinoma: effects on ploidy, chromosomal stability, cell adhesion/migration and tumorigenicity.

We have discovered DEGA, a novel cDNA differentially expressed in human gastric adenocarcinomas. The DEGA gene product contains a signal peptide, five leucine-rich repeat motifs and a single IgG, and transmembrane domain, suggesting its residence on the plasma membrane. Transfection of 293 cells with a DEGA-GFP fusion construct confirmed its cell surface localization. Although the cytosolic portion of the DEGA gene product does not contain known protein domains, approximately one-fifth of these residues are either a serine or a threonine, suggesting that DEGA may play a role in signal transduction. BLAST searches revealed DEGA to be an exact match to AMIGO-2, a recently identified, but functionally uncharacterized protein related to AMIGO, a leucine-rich repeat containing cell adhesion molecule implicated in axon tract development. In this report, we show that DEGA/AMIGO-2 mRNA is differentially expressed in approximately 45% of tumor versus normal tissue from gastric adenocarcinoma patients. Stable expression of a DEGA/AMIGO-2 antisense construct in the gastric adenocarcinoma cell line, AGS, led to altered morphology, increased ploidy, chromosomal instability, decreased cell adhesion/migration, and a nearly complete abrogation of tumorigenicity in nude mice. These findings suggest a potential etiologic role for DEGA/AMIGO-2 in gastric adenocarcinoma.

Mutation of the protein tyrosine kinase consensus site in the herpes simplex virus 1 alpha22 gene alters ICP22 posttranslational modification.

We previously reported that at least eight HSV-1 and five HSV-2 proteins were tyrosine phosphorylated in infected human and mouse cells and the first phosphotyrosine-modified gene product identified was the ICP22 regulatory protein (Blaho, J. A., Zong, C. S., and Mortimer, K. A., 1997, J. Virol. 71, 9828-9832). All electrophoretic forms of ICP22 are tyrosine phosphorylated with the exception of the fastest migrating (unmodified) isoform. We now report the following. (i) ICP22 that reacted with a specific anti-phosphotyrosine antibody contained a significant amount of phosphotyrosine based on phospho-amino acid analysis. These results validate the discovery of ICP22 tyrosine phosphorylation. (ii) Wild-type ICP22 extracted from infected HEp-2 cells migrated as at least seven isoforms, termed ICP22a-g, in denaturing gels. (iii) The primary structure of ICP22 possesses a sequence that is homologous to protein tyrosine kinase recognition sites. A virus, termed RF141, was generated in which ICP22 tyrosine(193) in the kinase target site was mutated to an alanine. (iv) Biochemical analyses of infected HEp-2 and primary HFF cells indicated that the distributions of ICP22 isoforms differed between RF141 and control HSV-1(F). (v) The accumulations of representative viral polypeptides in RF141-infected HEp-2 cells appeared similar to wild-type virus. (vi) RF141 had reduced efficiencies of plating in HFF cells compared to control Vero cells. These differences increased as the multiplicity of infection decreased. Based on these results, we conclude (vii) that ICP22 tyrosine(193) is required for optimal posttranslational modification of the protein in HSV-1 infected human epithelial HEp-2 and primary human fibroblast cells.