Characterization of sphere-forming cells with stem-like properties from the small cell lung cancer cell line H446

A relatively novel paradigm in tumor biology hypothesizes that cancer growth is driven by tumor cells with stem-like properties. However, direct proof of a population of stem cells in small cell lung cancer (SCLC) remains elusive. In this study, we enriched for stem-like cells from the SCLC cell line H446 by growing them as spheres in a defined serum-free medium. Sphere-derived cells have increased in vitro clonogenic and in vivo tumorigenic potentials as well as drug-resistant properties. After enrichment for stem-like cells, we used multiple candidate stem cell markers to examine the expression profile and found that the sphere-derived cells contained a higher proportion of cells expressing the stem cell surface markers uPAR and CD133 when compared with parental cells. To identify a selectable marker for the sphere-forming cells, we evaluated the sphere-forming abilities of uPAR(+) and uPAR(-) cells as well as the sphere-forming abilities of CD133(+) and CD133(-) cells. Both CD133(+) and CD133(-) cell fractions were capable of forming spheres, and no statistically significant difference was observed in the sphere-forming efficiency between these two populations. In contrast, cells derived from the uPAR(+) fraction were capable of forming spheres, whereas cells derived from the uPAR(-) fraction remained as single cells. Moreover, uPAR(+) cells efficiently formed transplantable tumors, whereas uPAR(-) cells were unable to initiate tumors when transplanted at equivalent cell numbers. In addition, uPAR(+) cells could differentiate into CD56(+) cells. CK+ cells, and uPAR(-) cells. These data support the existence of a population of tumor sphere-forming cells with stem cell properties in the H446 SCLC cell line. Furthermore, the stem cell population may be enriched in cells expressing the uPAR cell surface marker. (c) 2012 Elsevier Ireland Ltd. All rights reserved.