GROWTH PLATE CELLULAR FUNCTION FOLLOWING RADIOTHERAPY

放射治疗经常被用作儿童骨骼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往往会导致肢体长度不一致或角度畸形。单纯面对放射治疗时生长板的功能知之甚少，对于放射防护策略的影响更是知之甚少。我们在大鼠身上的初步工作记录了通过分级和放射保护剂氨磷汀(WR-2721)额外的保留生长板功能。我们的研究小组成员将正常大鼠生长板的差异生长定义为软骨细胞动力学的多个参数的函数，但这种分析尚未用于辐射生长板的研究。我们最初在动物模型中进行的组织形态计量学研究表明，生长板的照射会导致几个事件：短暂的生长和增殖减少，早期软骨细胞凋亡，通过增加基质生产维持一些骨生长，以及随后活跃的增殖细胞克隆的恢复--所有这些都可以通过放射防护治疗得到改善。第一个具体目的是利用我们建立的生长期大鼠单侧后肢X射线照射模型，通过测量生长板中软骨细胞的动力学和关键免疫组织化学标志物来验证上述机制假说。第二个特定的目标，使用相同的研究设计，是为了检验这样一个假设，即自由基清除剂氨磷汀在照射前立即给予时，维持增殖和减少凋亡，并且它的作用方式与剂量分级相加。第三个具体目的是验证这样的假设，即米索前列醇(已知的一种促进DNA修复的辐射防护剂)和IL-1(已知的诱导原始祖细胞循环的辐射防护剂)将通过一种不同于分级和氨磷汀的独特机制和附加机制来保护生长板免受辐射。该项目的长期目标是确定在生长板上以不同和互补的机制起作用的辐射防护剂，并结合分割来测试这些辐射防护剂，从而开发最终允许对成长中的儿童的恶性肿瘤进行更安全和更有效的放射治疗的策略。

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.