Identification of a distinct population of CD133+CXCR4+ cancer stem cells in ovarian cancer

CD133 and CXCR4 were evaluated in the NCI-60 cell lines to identify cancer stem cell rich populations. Screening revealed that, ovarian OVCAR-3, -4 and -5 and colon cancer HT-29, HCT-116 and SW620 over expressed both proteins. We aimed to isolate cells with stem cell features sorting the cells expressing CXCR4+CD133+ within ovarian cancer cell lines. The sorted population CD133+CXCR4+ demonstrated the highest efficiency in sphere formation in OVCAR-(3), OVCAR-(4) and OVCAR-(5) cells. Moreover OCT4, SOX2, KLF4 and NANOG were highly expressed in CD133+CXCR4+ sorted OVCAR-(5) cells. Most strikingly CXCR4+CD133+ sorted OVCAR-(5) and -(4) cells formed the highest number of tumors when inoculated in nude mice compared to CD133-CXCR4-, CD133+CXCR4-, CD133-CXCR4+ cells. CXCR4+CD133+ OVCAR-(5) cells were resistant to cisplatin, overexpressed the ABCG(2) surface drug transporter and migrated toward the CXCR4 ligand, CXCL12. Moreover, when human ovarian cancer cells were isolated from 37 primary ovarian cancer, an extremely variable level of CXCR4 and CD133 expression was detected. Thus, in human ovarian cancer cells CXCR4 and CD133 expression identified a discrete population with stem cell properties that regulated tumor development and chemo resistance. This cell population represents a potential therapeutic target.