Growth Plate Cellular Function Following Radiotherapy

描述(申请人提供)：放射治疗被用作儿童恶性肿瘤的辅助治疗，但在生长中的肢体中使用放射治疗经常会导致肢体长度不一致或角度畸形。我们的初步工作已经建立了生长板辐射效应的体内模型，并记录了通过分级和放射防护剂氨磷汀[WR-2721]、己酮可可碱、米索前列醇、硒和IL-1a来保护生长板功能。即使联合使用，这些辐射前治疗也不能完全逆转辐射的损害效应。我们利用体内免疫组织化学、组织形态计量学和体视学技术进行的研究表明，生长板损伤后的恢复潜力主要由PTHrP驱动，其次是FGF2和TGF-b。这最初的结果是基质的积累，紧随其后的是再生的增殖性克隆的出现，这些克隆的恢复似乎与减少肢体长度差异直接相关。然而，生长板辐射恢复的进一步改进的潜力似乎在于结合放射防护剂和辐射恢复方法，而后者尚未在生长板中进行研究。 我们的第一个具体目标是使用激光显微解剖和分子生物学技术来检验这样的假设，即生长板放射恢复最初是由PTHrP及其下游信号级联驱动的，以及随后的再生克隆由来自保留区软骨细胞的正常功能软骨细胞组成。我们的第二个具体目标是在体外和体内测试这一假设，即在放射治疗后刺激抑制的PTHrP轴将促进生长板的恢复。第三个具体目标是验证这样一种假设，即使用放射防护和辐射恢复策略的联合治疗将比单独使用任何一种策略提供明显更好的生长板功能。 该项目的长期目标是确定一种放射防护和放射恢复的组合策略，该策略将通过对生长板的补充机制作用于生长板，以在所需的放射治疗期间尽可能保持接近正常的生长板功能。

DESCRIPTION (provided by applicant): Radiotherapy is employed as adjunctive treatment for childhood malignancies, but its use in a growing limb frequently results in crippling limb length discrepancy or angular deformity. Our initial work has established an in vivo model for radiation effects on the growth plate and documented sparing of growth plate function by fractionation and the radioprotectants amifostine [WR-2721], pentoxifylline, misoprostol, selenium, and IL-1a. Even used in combination, these pre-radiation treatments have provided incomplete reversal of the damaging effects of irradiation. Our studies using in vivo immunohistochemical, histomorphometric, and stereologic techniques have suggested that the potential for recovery following growth plate injury is driven by PTHrP primarily, and by FGF2 and TGF-b secondarily. This results initially in accumulation of matrix followed closely by appearance of regenerative proliferative clones, the restoration of which appears to be directly related to reduction of limb length discrepancy. However, the potential for further improvements in growth plate radiation recovery appears to lie in combining radioprotectant with radiorecovery approaches, and the latter has not been investigated in the growth plate. Our first specific aim is to use laser microdissection and molecular biology techniques to test the hypotheses that growth plate radiorecovery is driven initially by PTHrP with its downstream signaling cascade and that the consequent regenerative clones are comprised of normally functioning chondrocytes derived from reserve zone chondrocytes. Our second specific aim is to test both in vitro and in vivo the hypothesis that stimulating the depressed PTHrP axis after radiotherapy will improve growth plate recovery. The third specific aim is to test the hypothesis that combination therapy using radioprotection and radiorecovery strategies will provide significantly better growth plate function than either strategy alone. The long term objectives of this project are to identify a combination strategy of radioprotection and radiorecovery that will act by complementary mechanisms upon the growth plate to maintain as close to normal growth plate function as possible during needed radiotherapy treatment.