MONOCLONAL ANTIBODY-TOXIN CONJUGATES FOR TUMOR THERAPY IN VIVO

单抗选择性结合肿瘤细胞分化抗原 在体外和体内。自然效应器机制通常不会起到中介作用 杀死单抗结合的细胞，所以我们设计了 将剧毒蛋白与抗体联系起来，选择性地杀死 肿瘤细胞。 已经有两种方法将有毒蛋白质，如蓖麻毒素与抗体偶联 用于体外杀伤抗原阳性细胞。蓖麻毒素有两个亚基，即 A亚基在胞浆中阻止蛋白质合成，而B亚基则阻止蛋白质合成 结合所有细胞表面的半乳糖基团，但也有助于 将蓖麻毒素A链运输到细胞质。1)蓖麻毒素A链的连接 TO抗体产生非靶标毒性低但靶向细胞的试剂 毒性太慢，不能在体内应用；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 必须通过一种阻断蓖麻毒素B链的配体来防止细胞杀伤 绑定到细胞。这限制了它在体外的应用。 其中100 mM的乳糖可以阻止蓖麻毒素的结合。 我们正在测试几种在体内应用免疫毒素的新方法。1) 克隆毒素，然后在基因水平上改变其结构以 降低非靶细胞毒性；2)将蓖麻毒素化学修饰为 确定蓖麻毒素半乳糖结合部位的位置，并可能 提高与抗体相连的蓖麻毒素的有效性；3)开发新的方法 体内阻断蓖麻毒素的非靶细胞毒性。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 到乳糖。在豚鼠身上的初步体内试验显示， 无毒性的完整蓖麻毒素免疫毒素延长存活时间 对动物来说。4)鞘内注射单抗允许 一种新的脑肿瘤成像方法。我们现在正在测试鞘内 应用免疫毒素治疗脑肿瘤。

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 are testing 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. Preliminary in vivo trials in guinea pigs show over a 2 fold extension of survival time with intact ricin immunotoxins with no toxicity to animals. 4) Intrathecal administration of monoclonal antibodies allows a new way to image brain tumors. We are now testing intrathecal administration of immunotoxins for therapy of brain tumors.