FOXM1 and osteosarcoma: C3-Luc2.3-FoxO1 cells are a derivative of U2OS osteosarcoma cells with a doxycycline-inducible FoxM1-GFP fusion protein [25], a tamoxifen-inducible constitutively active FoxO1(AAA)-ER fusion protein and a FoxM1/FoxO1-dependent firefly luciferase.