Abstract 426: In-field head and neck irradiation radiosensitivity of FancD2-/- mice and bystander effect reduction of distant bone marrow hematopoietic progenitor cells.
Authors: Berhane Hebist , Goff Julie , Kalash Ronny , Epperly Michael W. , Dixon Tracy , Shields Donna , Franicola Darcy , Greenberger Joel S. 
Published: August 2014

Background: Irradiation induced normal tissue toxicity limits effective radiotherapy of individuals with DNA repair defects including Fanconi anemia. We quantitated in-field head and neck tissue response in irradiated Fanconi anemia knockout mice, FancD2-/-, compared to wild type, FancD2+/+ & heterozygous FancD2+/- mice. We also assessed bystander effect of head and neck irradiation on distant bone marrow hematopoietic progenitor cell numbers.

Method: Adult 10-12wk old FevB background FancD2+/+, +/- and -/- mice were irradiated to the head & neck to 24Gy, 26Gy, 28Gy or 30Gy (n=3) shielding all tissue below the cervical spine. On day 2 or 5 post irradiation, mice were sacrificed and tongue tissue and one femur excised for histopathology. Bone marrow of the contralateral femur was plated for colony assay. Colony forming unit-granulocyte macrophage (CFU-GM), burst forming unit erythroid (BFU-E), and colony forming unit-granulocyte-erythroid-megakaryocyte-monocyte (CFU-GEMM) numbers were counted & each genotype compared to its unirradiated control. H&E stained tongue sections were scored for oral mucositis.

Results: Both FancD2-/- & FancD2+/- mice were radiosensitive to lower doses compared to FancD2+/+ mice measured as percent ulceration of the squamous layer of tongue epithelium 5 days post irradiation. Both FancD2+/- and FancD2-/- mice had significantly higher ulceration after 26Gy (52.8±6.5%, p=0.0014 and and 59.4±3.4%, p=0.0001, respectively) compared to wild type FancD2+/+ (21.7±4.7%). At the lower dose of 24Gy, FancD2+/- and -/- had higher percent ulceration (p=0.0001 and p=0.0003) than FancD2+/+ mice irradiated to even higher doses of 26Gy and 28Gy. FancD2+/+ mice had high levels of ulceration after 28Gy (p=0.2355). While there was no difference in distant bone marrow cellularity between irradiated groups, both FancD2-/- & FancD2+/- showed bystander reduction in colony forming cells. CFU-GM were significantly reduced at 2 days after 26Gy in FancD2+/- mice compared to unirradiated controls (p=0.007). FancD2 -/- mice had decreased BFU-E after 24Gy (p=0.009) & CFU-GEMM after 26Gy (p=0.048) and reduced BFU-E numbers after 26Gy (p=0.031). FancD2-/- mice had significantly less CFU-GM after either 26Gy or 28Gy (p=0.017 and p=0.028, respectively). FancD2-/- & +/- mice, at 5 days after 26Gy, had less CFU-GM (p=0.001 and 0.012, respectively) and CFU-GEMM (p=0.014 and p=0.004, respectively) compared to unirradiated controls. There was no reduction in CFU-GM, BFU-E or CFU-GEMM in wild type FancD2+/+mice after 28 or 30Gy.

Conclusion: Biallelic or monoallelic loss of the FA gene renders mice radiosensitive to in-field head and neck irradiation compared to wild type mice, and is accompanied by a distant femur marrow bystander effect including reduction of colony forming unit.

Supported by NIAID U19-A 1068021 and FA Research Foundation

Citation Format: Hebist Berhane, Julie Goff, Ronny Kalash, Michael W. Epperly, Tracy Dixon, Donna Shields, Darcy Franicola, Joel S. Greenberger. In-field head and neck irradiation radiosensitivity of FancD2-/- mice and bystander effect reduction of distant bone marrow hematopoietic progenitor cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 426. doi:10.1158/1538-7445.AM2013-426