Antitumor effects of novel mAbs against cationic amino acid transporter 1 (CAT1) on human CRC with amplified CAT1 gene.

Copy number alterations detected by comparative genomic hybridization (CGH) can lead to the identification of novel cancer-related genes. We analyzed chromosomal aberrations in a set of 100 human primary colorectal cancers (CRCs) using CGH and found a solute carrier (SLC) 7A1 gene, which encodes cationic amino acid transporter 1 (CAT1) with 14 putative transmembrane domains, in a chromosome region (13q12.3) with a high frequency of gene amplifications. SLC7A1/CAT1 is a transporter responsible for the uptake of cationic amino acids (arginine, lysine, and ornithine) essential for cellular growth. Microarray and PCR analyses have revealed that mRNA transcribed from CAT1 is overexpressed in more than 70% of human CRC samples, and RNA interference-mediated knockdown of CAT1 inhibited the cell growth of CRCs. Rats were immunized with rat hepatoma cells expressing CAT1 tagged with green fluorescent protein (GFP), and rat splenocytes were fused with mouse myeloma cells. Five rat monoclonal antibodies (mAbs) (CA1 ~ CA5) reacting with HEK293 cells expressing CAT1-GFP in a GFP expression-dependent manner were selected from established hybridoma clones. Novel anti-CAT1 mAbs selectively reacted with human CRC tumor tissues compared with adjacent normal tissues according to immuno-histochemical staining and bound strongly to numerous human cancer cell lines by flow cytometry. Anti-CAT1 mAbs exhibited internalization activity, antibody-dependent cellular cytotoxicity, and migration inhibition activity against CRC cell lines. Furthermore, CA2 inhibited the in vivo growth of human HT29 and SW-C4 CRC tumors in nude mice. This study suggested CAT1 to be a promising target for mAb therapy against CRCs.

Transient depletion of p53 followed by transduction of c-Myc and K-Ras converts ovarian stem-like cells into tumor-initiating cells.

Although the existence of tumor-initiating cells (T-ICs) in several types of human cancer has been documented, the contribution of somatic stem cells to the development of T-ICs has remained unclear. Here, we show that normal mouse ovary contains epithelial cell adhesion molecule (EpCAM)-expressing stem-like cells that possess the ability to differentiate into cytokeratin 8 (CK8)-expressing epithelial progeny cells. Furthermore, RNA interference-mediated transient depletion of the tumor suppressor p53 followed by retrovirus-mediated transfer of c-Myc and K-Ras oncogenes in EpCAM-expressing ovarian stem-like cells resulted in the generation of ovarian T-ICs. The established ovarian T-ICs gave rise to hierarchically organized lethal tumors in vivo and were able to undergo peritoneal metastasis. Finally, subsequent RNA interference-mediated knockdown of p53 in tumor cells triggered the expansion of EpCAM-expressing stem-like tumor cells and induced further tumor growth. These data reveal a role for p53 in the development and expansion of ovarian stem-like tumor cells and subsequent malignant progression.