The sphere formation ability <i>in vitro</i> and tumorigenicity <i>in vivo</i>.

<p>(A) The spheroid formation assay. A total of 1×10⁴ cells were plated on low attachment dishes on day 10 and cultured with serum-free medium for 10 days. In the O-, K- and OSK-SW480 cultures, the number of spheroids was significantly increased compared to that of the M-SW480 cells. The error bars indicate the SD (n = 3). Scale bars: 100 µm. (B) The tumorigenicity of the cells after implantation in the subcutaneous regions of immunodeficient nude mice. A total of 1×10⁶ cells (left panel) or 3×10⁵ cells (right panel) were subcutaneously injected into both flanks of immunodeficient nude mice on day 10. The volume of the tumors derived from the K- and OSK-SW480 cells were obviously higher than those of the Wt-, M-, O- and S-SW480 cells for both numbers of injected cells. The red bars indicate the median tumor volume. **P<0.01, N.S.: not significant, Dunnett's test (except of †: U-test).