GROWTH PLATE CELLULAR FUNCTION FOLLOWING RADIOTHERAPY

放射治疗经常被用作儿童骨和软组织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导致肢体长度差异或角畸形。关于生长板在单独放射治疗中的功能知之甚少，关于放射防护策略的作用就更少了。我们对大鼠的初步研究表明，通过分离和放射性保护剂氨磷汀（WR-2721），生长板功能得以保留。我们研究小组成员已经将正常大鼠生长板的差异生长定义为软骨细胞动力学多个参数的函数，但这种分析尚未用于辐照生长板的研究。我们最初在动物模型中进行的组织形态计量学研究表明，生长板的辐照会导致以下几个事件：短暂的生长和增殖减少，早期软骨细胞凋亡，通过增加基质生产来维持一些骨生长，以及随后积极增殖的细胞克隆的回归——所有这些都可以通过放射保护剂治疗得到改善。第一个具体目的是利用我们建立的生长大鼠单侧后肢x射线照射模型，通过测量生长板中软骨细胞动力学和关键免疫组织化学标志物来验证上述机制假设。第二个特定的目的，使用相同的研究设计，是测试假设自由基清除剂氨磷汀在照射前立即给予时维持增殖并减少细胞凋亡，并且它以剂量分离的方式以加性方式起作用。第三个具体目标是测试米索前列醇（一种已知能改善DNA修复的放射保护剂）和IL-1（一种已知能诱导原始祖细胞循环的放射保护剂）将各自导致生长板免受辐射的保护的假设，其机制与分离和氨磷汀的机制不同，并且是附加的。该项目的长期目标是确定通过不同和互补机制作用于生长板的放射保护剂，对这些放射保护剂与分离相结合进行测试，从而制定策略，最终允许对生长中的儿童的恶性肿瘤进行更安全、更有效的放射治疗。

Radiotherapy is frequently employed as adjunctive treatment for childhood bone and soft-tissue malignancies, but its use in a growing limb frequently results in crippling limb length discrepancy or angular deformity. Little is known regarding growth plate function in the face of radiotherapy alone and even less regarding the effects of radioprotectant strategies. Our preliminary work in rats documented sparing of growth plate function by fractionation and additional sparing by the radioprotectant amifostine (WR-2721). Members of our research team have defined the differential growth of the normal rat growth plate as a function of multiple parameters of chondrocyte kinetics, but this analysis has not been used in the study of the irradiated growth plate. Our initial histomorphometric studies in an animal model suggest the hypothesis that irradiation of the growth plate results in several events: transiently decreased growth and proliferation, early chondrocyte apoptosis, maintenance of some bone growth by increased matrix production, and subsequent return of actively proliferating cellular clones --all of which can be improved by radioprotectant treatment. The first specific aim is to test the above mechanistic hypothesis by measuring chondrocyte kinetics and key immunohistochemical markers in the growth plate using our established unilateral hind limb x-irradiation model in the growing rat. The second specific aim, using the same research design, is to test the hypothesis that the free radical scavenger amifostine maintains proliferation and decreases apoptosis when given immediately preceding irradiation, and that it acts in an additive fashion with dose fractionation. The third specific aim is to test the hypotheses that misoprostol (a radioprotectant known to improve DNA repair) and IL-1 (a radioprotectant known to induce cycling of primitive progenitor cells) will each result in growth plate protection from irradiation by a mechanism unique from and additive to that of fractionation and amifostine. The long-term objectives of this project are to identify radioprotectants, which act by different and complementary mechanisms upon the growth plate, to test these radioprotectants in combination with fractionation and thereby develop strategies that will ultimately permit safer and more effective radiotherapy for malignancies in the growing child.