We and others have reported that cancer side population (SP) cells have self-renewal and multidrug resistance capabilities. These phenotypes are similar to those of cancer stem cells (CSCs), cancer stem-like cells and tumor-initiating cells (TICs). It has also been reported that upregulation
of the epidermal growth factor receptor (EGFR) significantly increases the number of cancer SP cells, conversely, molecular targeting of EGFR tyrosine kinases using specific kinase inhibitors downregulates CSCs. Thus, we used flow cytometric analysis and cell sorting to examine cancer SP cells
in the SCA9.cl-15, WR21 and A253 cell lines that originate from a salivary gland tumor (SGT). We successfully isolated cancer SP cells from all of these cell lines. SP cells were detected following treatment of these cell lines with the receptor tyrosine kinase inhibitors (RTKIs) lapatinib,
erlotinib and vandetanib. Several studies reported that RTKIs mostly reduced the SP population in cancer cells. We did not observe any detectable morphological differences between SP cells and non-SP cells. We found that the EGF RTKI lapatinib decreased the number of cancer SP cells in all
cell lines investigated; however, the EGF RTKI erlotinib did not cause significant differences in the frequency of cancer SP cells in these cell lines. Addition of vandetanib significantly increased the number of cancer SP cells and upregulated the phosphorylated Akt. As far as we know, this
is the first report to show that one of the RTKIs, vandetanib, can activate Akt and increase the number of cancer SP cells. It has been reported that RTKIs could competitively inhibit ABC transporters and subsequently reduced the number of SP cells. However, our observation indicated that
signaling changes induced by RTKIs could even activate Akt and induce the SP population. Investigation of the SP phenotype of SGTs is important for the establishment of optimal cancer therapy.
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Document Type: Research Article
Oral Health Science Center HRC7, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba City 261-8502, Japan
Department of Biochemistry, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba City 261-8502, Japan
Publication date: January 1, 2012
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The International Journal of Oncology provides an international forum for the publication of the latest, cutting-edge research in the broad area of oncology and cancer treatment. The journal accepts original high quality works and reviews on all aspects of oncology research including carcinogenesis, metastasis, epidemiology, chemotherapy and viral oncology. Through fair and efficient peer review, the journal is dedicated to publishing top tier research in the field, offering authors rapid publication as well as high standards of copy-editing and production. The International Journal of Oncology is published on a monthly basis in both print and early online.
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