MONOCLONAL ANTIBODY-TOXIN CONJUGATES FOR TUMOR THERAPY IN VIVO

单抗选择性结合肿瘤细胞分化 体外和体内的抗原。自然效应器机构通常 不会介导对单抗结合细胞的杀伤，所以我们 已经设计出了将剧毒蛋白质与 选择性杀伤肿瘤细胞的抗体。 两种方法将有毒蛋白质，如蓖麻毒素与抗体偶联， 已经被用来在体外杀死抗原阳性细胞。蓖麻毒素 两个亚基，A亚基阻止蛋白质合成 胞浆和B亚基结合所有细胞上的半乳糖基团 而且还有助于将蓖麻毒素A链运输到 胞浆。1)蓖麻毒素A链与抗体的连接产生 低非靶毒性但也有靶细胞毒性的试剂 体内应用缓慢；2)完整的蓖麻毒素与 抗体可导致非常强的靶细胞毒性，但非 靶细胞杀伤必须被阻止的配体阻止 与细胞结合的蓖麻毒素B链。这限制了它的应用范围 在体外100 mM乳糖可以阻断蓖麻毒素结合的情况下。 我们已经成功地开发了几种新的方法来应用 体内的免疫毒素。1)克隆毒素，然后改变其 在基因水平上构建，以降低非靶细胞毒性；2) 化学修饰蓖麻毒素以确定其位置 并可能提高蓖麻毒素半乳糖结合部位的疗效 蓖麻毒素与抗体相连；3)开发新的方法来阻断非 蓖麻毒素体内靶细胞毒性的研究。我们发现了一个 阻断蓖麻毒素半乳糖结合部位的单抗 类似于乳糖；4)鞘内给药 抗体为脑肿瘤提供了一种新的成像方法；5)鞘内 应用免疫毒素治疗脑肿瘤 在动物模型中杀死2~5个对数的肿瘤细胞；6)制备 用于人脑肿瘤患者的临床试验。

Monoclonal antibodies selectively bind tumor cell differentiating antigens in vitro and in vivo. Natural effector mechanisms often do not mediate killing of monoclonal antibody bound cells so we have devised methods of linking extremely toxic proteins to the antibodies to selectively kill tumor cells. Two methods of coupling toxic proteins, like ricin to antibodies, have been used to kill antigen positive cells in vitro. Ricin has two subunits, the A subunit blocks protein synthesis when in the cytosol and the B subunit binds galactose groups on all cell surfaces but also facilitates the transport of ricin A chain to the cytosol. 1) Linkage of the ricin A chain to antibodies yields reagents with low non-target toxicity but target cell toxicity too slow for in vivo applications; 2) Linkage of intact ricin to antibodies results in very potent target cell toxicity but the non- target cell killing must be prevented by a ligand which blocks ricin B chain binding to cells. This has limited its application to in vitro situations where 100 mM lactose can block ricin binding. We have succeeded in developing several new approaches to apply immunotoxins in vivo. 1) Cloning of toxins then altering their structure at the gene level to decrease non-target cell toxicity; 2) Chemical modification of ricin to determine the location of the ricin galactose binding site and to possibly improve efficacy of ricin linked to antibodies; 3) Develop new ways to block the non- target cell toxicity of ricin in vivo. We have discovered a monoclonal antibody which blocks the ricin galactose binding site similar to lactose; 4) Intrathecal administration of monoclonal antibodies allows a new way to image brain tumors; 5) Intrathecal administration of immunotoxins for therapy of brain tumors that kill 2 to 5-logs of tumor cells in animal models; and 6) Preparation for clinical trials of human brain tumor patients.