Experimental data for administration of insulin-like growth factor 1 (IGF-1) and basic fibroblast growth factor (bFGF) for prevention of radiation myelopathy

Abstract

Current models of radiation myelopathy provide a rationale for growth factor-based prevention strategies. Thus, we tested whether insulin-like growth factor-1 (IGF-1) and basic fibroblast growth factor (bFGF) alone or in combination modulate radiation tolerance of the rat cervical spinal cord. The cervical spinal cord of 68 adult Fisher F344 rats received a total dose of 30-36 Gy, given as a single fraction of 16 Gy followed by a second radiation dose of 14-20 Gy. Continuous intrathecal infusion of bFGF (44 rats) or saline (24 rats) into the cisterna magna was given concomitantly. A further experiment included 14 additional rats which were treated with subcutaneous injection of IGF-1 parallel to irradiation with a total dose of 34 Gy or 36 Gy. 20 rats received combined treatment, i.e. intrathecal infusion of bFGF plus subcutaneous injection of IGF-1, starting 24 hours before irradiation (total dose 33 Gy or 36 Gy) for a total of 4 days. Animals were followed until myelopathy developed or for a maximum of 12 months. Histopathologic examinations were performed post mortem. Treatment with bFGF alone or IGF-1 alone increased the median time to myelopathy significantly. In the 36-Gy group, after combination treatment a comparable prolongation of latency was seen. Moreover, rats treated with 33 Gy and combined bFGF plus IGF-1 showed a significantly reduced risk of myelopathy, too (p = 0.0015, Figures 1 and 2). Combination of IGF-1 and bFGF was more potent than single agent treatment. We observed a significantly reduced myelopathy rate at an intermediate radiation dose level and a longer time to myelopathy at a high-dose level. This finding strengthens the evidence that brief therapeutic intervention can decrease radiation-induced neurotoxicity. Further studies will be undertaken to optimize this strategy.