Amifostine Therapeutic Enhancement of Vascularity In An Irradiated Model of Mandibular Fracture Repair Model

Purpose: Radiation-induced pathologic fractures (Fx) of the mandible can have devastating effects on a patient's quality of life. Delayed Fx healing is related to the damage of blood supply and/or the impairment in the proliferation of bone cellular constituents. We have previously demonstrated the cyto-protective effect of the antioxidative drug Amifostine (AMF) on bone osteoprogenitor cells. Utilizing micro-computed tomography (µCT) after vessel perfusion, the purpose of our study is to ascertain whether AMF can also preserve the vascularity of the highly cortical murine mandible after exposure to human equivalent dose of radiation (HEDR) in a mandibular model of pathologic fracture repair.

Methods: Twenty-four male Sprague Dawley rats were randomized into 3 groups. Group 1, Fx (n=9), Group 2, XRT/Fx (n=5) and Group 3 AMF/XRT/Fx (n=7). Group 2 and 3 underwent a 5-day fractionated HEDR over the left hemimandibles. Group 3 received AMF prior to XRT. After 14 days of recovery, all groups underwent a unilateral left mandibular osteotomy with bilateral external fixation. Four to eight hours post-operatively, all animals were distracted to a maximal 2.1mm fracture gap. Consolidation and healing were allowed for 40 days prior to left ventricular catheterization and perfusion with Microfil, a silicone rubber radiopaque contrast. Vascular radiomorphometrics were quantified with µCT imaging and analyzed via One-way Anova and post Hoc Tukey with statistical significance at p<0.05.

Results: All radiated animals demonstrated clinical signs of radiation-induced mucositis and alopecia, but were less apparent in the AMF pre-treated group. We observed a 84% rate of bony union in the Fx group compared to 67% in the AMF/XRT/FX group and 25% in the XRT/Fx group. Further analysis revealed a substantial increase in Vessel Number (123%, p<0.05) and a corresponding decrease in Vessel Separation (55.5%, p<0.05) between AMF and non-AMF irradiated fractured mandibles.

Conclusion: For the first time to our knowledge, we have established and quantified the effect of AMF prophylactic therapy on angiogenesis in the setting of radiotherapy. This important finding may further be optimized for an effective translation into the clinical arena of pathologic fracture treatment in HNC reconstruction. Our results set the stage for exploration of this targeted therapy alone and in combination with other therapies to mitigate radiation effects in the clinical setting.