Fig. 9

The influence of oxygen on colony- and sphere-forming abilities. a Representative images of colonies were formed in semi-soft agar in normoxic and hypoxic cultures. The number of viable ACHN colonies in normoxia was significantly bigger than in hypoxia, while there were no differences in HKCSC. b Representative images of cells grown in sphere-promoting conditions at the fifth day of culture in normoxia and hypoxia. The ACHN cell line showed reduced colonies and spheres in hypoxia, which is a reflection of similar hypoxic inhibition in monolayer culture. Caki-2 was not able to create colonies; nevertheless, its number of spheres was greater in hypoxia, as was hypoxia-promoted Caki-2 monolayer proliferation. Alternatively, HKCSC created colonies but not spheres