(A–D) Effect of genetic FTO inhibition on radiation response of UM-SCC-22B (22B) HNSCC cells in vivo. 22B doxycycline inducible control (shScr) or FTO knockdown (shFTO) cells were injected s.c. into male immunodeficient mice. When tumors reached ~200–300 mm³, mice treated with (1 μg/mL doxycycline in the drinking water) for 2 days before sham or 10 Gy irradiation. (A and B) Treatment schedule (A) and tumor growth curve (B) for the inducible control and FTO knockdown 22B tumor studies (n = 5–7 mice per group). Day 0 is the first day of tumor measurements. (C and D) Xenograft weights and representative xenograft images at the endpoint. (E–G) Effect of pharmacologic FTO inhibition on radiation response of 22B HNSCC cells in vivo. 22B cells were injected s.c. into male immunodeficient mice. When tumors reached approximately 100–200 mm³ mice treated with vehicle or the FTO inhibitor FB23-2 (4.6 mg/kg, i.p.) for 2 days before sham or 10 Gy irradiation. (E) Treatment schedule for the treatments in the 22B tumor studies. Day 0 is the first day of tumor measurements. (F) Tumor growth curves are shown (n = 7–8 mice per group). (G) Xenograft weights and representative xenograft images at the endpoint are shown. Arrows show the 14- and 18-day endpoints for the different comparison groups; the vertical dashed red line shows the time of irradiation; the orange box shows the scheme of doxycycline treatment; the blue box shows the timing of vehicle and FB23-2 treatment. Scale bar: 1 cm. *P < 0.05 as determined by 2-tailed t tests of the adjusted means from the generalized linear regression model. Data are presented as mean ± SEM.