Antibody – VX35 OncologyC35, a protein encoded by a novel gene (C17orf37) that is broadly upregulated in breast cancer (REF 1), is an antigenic target for antibody mediated, cancer-specific immunotherapy. The C35 gene is located on chromosome 17q12, only 505 nucleotides from the 3’ end of the ERBB2 oncogene, the antigenic target for trastuzumab (Herceptin™) therapy. As part of the HER2 amplicon (REF 2), C35 is co-amplified with ERBB2 and almost all HER2+ breast tumors co-express C35. C35 overexpression is, however, not dependent on amplification and approximately 50% of C35+ breast tumors do not overexpress Her2/neu. Immunohistochemical analysis detects high levels and uniform expression of C35 protein in approximately 32% of Grade I and 66% of Grades 2 and 3 infiltrating ductal carcinomas of the breast (in contrast to 20% over-expressing Her2/neu) and 38% of infiltrating lobular carcinoma (typically Her2/neu negative). In addition to breast carcinoma, C35 overexpression has been identified in tumors arising in other tissues, including prostate adenocarcinoma (REF 3), ovarian cancer (REF 4), colorectal metastases to liver and hepatocellular carcinoma . C35 protein was not detected in 38 different normal human tissues, except for the Leydig cells of testes and low levels in normal breast and prostate tissue samples. Progress has been made in defining the significance and function of C35 in cancer. C35 has been implicated in oncogenesis, epithelial to mesenchymal transition, cell proliferation (REF 4), and cell migration and invasion. C35 has been shown to modulate NF-kB activity through AKT activation, which in turn, regulates expression of factors such as uPA, MMP9 and VEGF, suggesting that C35 may play a role in invasion and migration (REF 3). Although C35 resides predominantly in the cytoplasm, we have demonstrated exposure of C35 on the tumor cell surface during apoptosis induced as a result of treatment with chemotherapy or antibody therapeutics. The prevalence of C35 overexpression in breast and other cancers, the relative lack of expression in normal tissues, and the role of C35 in oncogenesis and metastatic progression suggest that C35 is an important new target for the development of antibody therapeutics for cancer. We have selected a high affinity human IgG1 antibody that binds specifically to C35. We have used a C35+/HER2+ mouse xenograft tumor model to demonstrate an additive impact on tumor growth inhibition when anti-C35 antibody is administered in combination with HER2 targeted therapies. This additive effect is more effective than either drug alone. VX35/Anti-C35 antibody is currently in the final stages of preclinical testing. 
Figure 1. C35 expression in Breast Cancer. Immunohistochemistry of intraductal carcinoma of breast. Sections of formalin fixed paraffin-embedded tissue were stained with polyclonal rabbit anti-C35, anti-c-erb-B2 or isotype control antibodies. The top panel is example of a C35+/ERBB2+ tumor (scores of 4+C35 and 3+Her2), and the bottom panel is an example of a C35+/ERBB2- tumor (scores 2+C35 & 0 Her2; faint cytoplasmic stain is negative according to HercepTest™ guidelines). 40X magnification. 
Figure 2. C35 is expressed in a wide range of primary tumors. Immunohistochemistry of various tumor types using a multi-cancer array obtained from the National Disease Research Interchange (NDRI). The table illustrates the frequency of C35 and HER2 expression in multiple tumor types. For both C35 or Her2 markers, sections with a score of 2+ or greater were considered positive. 
Figure 3. In vivo Tumor Growth Inhibition. An anti-C35 antibody was tested for the ability to inhibit the growth of C35+/HER2+ BT474 breast cancer xenografts in athymic nu/nu mice. Tumor bearing mice were divided into groups of 9 mice each, and treated twice weekly with a suboptimal dose of Herceptin (0.5 mg/kg) plus 40 mg/kg of anti-C35 Mab or an irrelevant mouse antibody. The data demonstrate that treatment with Herceptin + Anti-C35 MAb inhibited the growth of these xenograft tumors to a greater extent than Herceptin alone.
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