Fanconi anemia (FA) is an inherited disorder characterized by defective DNA 
repair and cellular sensitivity to DNA crosslinking agents. Clinically, FA is 
associated with high risk for marrow failure, leukemia and head and neck 
squamous cell carcinoma (HNSCC). Radiosensitivity in FA patients compromises the 
use of total-body irradiation for hematopoietic stem cell transplantation and 
radiation therapy for HNSCC. A radioprotector for the surrounding tissue would 
therefore be very valuable during radiotherapy for HNSCC. Clonogenic radiation 
survival curves were determined for pre- or postirradiation treatment with the 
parent nitroxide Tempol or JP4-039 in cells of four FA patient-derived cell 
lines and two transgene-corrected subclonal lines. FancG(-/-) (PD326) and 
FancD2(-/-) (PD20F) patient lines were more sensitive to the DNA crosslinking 
agent mitomycin C (MMC) than their transgene-restored subclonal cell lines (both 
P < 0.0001). FancD2(-/-) cells were more radiosensitive than the transgene 
restored subclonal cell line (ñ = 2.0 ± 0.7 and 4.7 ± 2.2, respectively, P = 
0.03). In contrast, FancG(-/-) cells were radioresistant relative to the 
transgene-restored subclonal cell line (ñ = 9.4 ± 1.5 and 2.2 ± 05, 
respectively, P = 0.001). DNA strand breaks measured by the comet assay 
correlated with radiosensitivity. Cell lines from a Fanc-C and Fanc-A patients 
showed radiosensitivity similar to that of Fanc-D2(-/-) cells. A 
fluorophore-tagged JP4-039 (BODIPY-FL) analog targeted the mitochondria of the 
cell lines. Preirradiation or postirradiation treatment with JP4-039 at a lower 
concentration than Tempol significantly increased the radioresistance and 
stabilized the antioxidant stores of all cell lines. Tempol increased the 
toxicity of MMC in FancD2(-/-) cells. These data provide support for the 
potential clinical use of JP4-039 for normal tissue radioprotection during 
chemoradiotherapy in FA patients.