[Show abstract][Hide abstract] ABSTRACT: CD44 is a major cellular receptor for hyaluronic acids. The stem structure of CD44 encoded by ten normal exons can be enlarged by ten variant exons (v1-v10) by alternative splicing. We have succeeded in preparing MV5 fully human IgM and its class-switched GV5 IgG monoclonal antibody (mAb) recognizing the extracellular domain of a CD44R1 isoform that contains the inserted region coded by variant (v8, v9 and v10) exons and is expressed on the surface of various human epithelial cancer cells.
We demonstrated the growth inhibition of human cancer xenografts by a GV5 IgG mAb reshaped from an MV5 IgM. The epitope recognized by MV5 and GV5 was identified to a v8-coding region by the analysis of mAb binding to various recombinant CD44 proteins by enzyme-linked immunosorbent assay. GV5 showed preferential reactivity against various malignant human cells versus normal human cells assessed by flow cytometry and immunohistological analysis. When ME180 human uterine cervix carcinoma cells were subcutaneously inoculated to athymic mice with GV5, significant inhibition of tumor formation was observed. Furthermore, intraperitoneal injections of GV5markedly inhibited the growth of visible established tumors from HSC-3 human larynx carcinoma cells that had been subcutaneously transplanted one week before the first treatment with GV5. From in vitro experiments, antibody-dependent cellular cytotoxicity and internalization of CD44R1 seemed to be possible mechanisms for in vivo anti-tumor activity by GV5.
CD44R1 is an excellent molecular target for mAb therapy of cancer, possibly superior to molecules targeted by existing therapeutic mAb, such as Trastuzumab and Cetuximab recognizing human epidermal growth factor receptor family.
[Show abstract][Hide abstract] ABSTRACT: (Cancer Sci 2010; 101: 673–678)
Similar to normal tissue stem cells, cancer stem cells (CSCs) are thought to be quiescent or slow-cycling and, thereby, insensitive to chemo- and radiotherapies. CD44, a cell surface component that interacts with the extracellular matrix, has been found to be highly expressed in CSCs of several solid tumors. However, the relevancy between CD44+ cells and slow-cycling cells and the underlying mechanisms for the emergence of CD44+ CSCs during tumorigenesis have not been elucidated. Here we show that a gastric gland residing at the squamo-columnar junction (SCJ) in normal mouse stomach contains CD44+ stem cell-like slow-cycling cells and that this characteristic CD44+ gland was expanded by prostaglandin E2 (PGE2) and Wnt signaling in K19-Wnt1/C2mE mouse, a genetic mouse model for gastric tumorigenesis. The analysis of three transgenic mouse lines, K19-Wnt1, K19-C2mE and K19-Wnt1/C2mE, revealed that the expansion of CD44+ SCJ cells is triggered by PGE2-mediated signaling and is prominently enhanced by the addition of Wnt activation. Furthermore, each expanded CD44+ gland in gastric tumor of K19-Wnt1/C2mE mouse contains a few BrdU label-retaining quiescent or slow-cycling cells, suggesting that the CD44+ SCJ cells in normal mouse are candidates for the cell-of-origin of gastric CSCs. These observations suggest that PGE2-mediated inflammatory signaling and Wnt signaling cooperatively trigger the expansion of CD44+ slow-cycling stem-like cells in SCJ, leading to development of lethal gastric tumors in mice.