Engineering Cell Type Specific Toxins

单克隆抗体在体外和体内选择性结合肿瘤细胞分化抗原。我们已经设计出一些方法，将毒性极强的蛋白质与抗体连接起来，通过克隆毒素并使其突变来减少非靶细胞的毒性，从而选择性地杀死肿瘤细胞。一些使用白喉毒素点突变的设计允许靶向肿瘤细胞的毒性比非靶向细胞高20万倍。转铁蛋白受体作为脑肿瘤的靶标尤其有吸引力，因为它在神经元和神经胶质细胞中含量很低或不存在，而且它在许多不同类型的脑肿瘤中都有高表达。在转铁蛋白与突变白喉毒素相关的I期和II期临床试验中，许多患者在治疗后脑肿瘤大小显着减小。患者的剂量限制性毒性表现为血管损伤。在动物模型中，我们探索了一种新的策略，通过全身递送氯喹来保护脑血管系统，而不是保护脑肿瘤细胞免受免疫毒素的侵害。我们还开发了针对肌肉细胞的蓖麻毒素，用于治疗肌张力障碍和其他肌肉痉挛疾病的免疫毒素。这些方法用于全身治疗，或许也用于脑癌的一个局限性是，患者可能对毒素产生免疫反应。因此，我们已经探索了使用可能是非免疫原性的人类蛋白质来启动肿瘤细胞死亡的方法。人类细胞毒性蛋白，如嗜酸性粒细胞衍生的神经毒素，已经被设计并与抗体联系在一起，并被发现能特异性杀死肿瘤细胞。Bcl-2家族中的有毒蛋白Bax和Bad，诱导细胞凋亡，也被设计成结合细胞并特异性杀死它们。由于Bax和Bad是Bcl-2蛋白家族的成员，也包括抗凋亡成员，我们试图开发一种新的策略，通过靶向Bcl-xl细胞来防止神经元损失。最近的研究结果表明，Bcl-xl可以在体外和体内传递给细胞，以防止神经元凋亡，并可能具有抑制脊髓损伤和中风期间神经元损失的潜力。

Monoclonal antibodies selectively bind tumor cell differentiation antigens in vitro and in vivo. We have devised methods of linking extremely toxic proteins to the antibodies to selectively kill tumor cells by cloning the toxins and mutating them to decrease non-target cell toxicity. Some designs using a point mutant of diphtheria toxin allow 200,000 times more toxicity to target tumor cells than nontarget cells. The transferrin receptor is particularly attractive as a target on brain tumors because it is very low or absent on neurons and glial cells and because it is highly expressed on many different types of brain tumor. In phase I and phase II clinical trials of transferrin linked to a mutant diphtheria toxin many patients showed a significant decrease in brain tumor size in response to the treatment. The dose limiting toxicity in patients appeared to be vascular damage. In animal models we have explored a new strategy to prevent this vascular toxicity by systemic delivery of chloroquine to protect the brain vasculature but not protect the brain tumor cells for the immunotoxin. We have also developed immunotoxins for treatment of dystonia and other muscle spasm diseases by targeting ricin to muscle cells. One limitation of these approaches for systemic therapy and perhaps also for brain cancer is that patients can develop an immune response to the toxin. Therefore we have explored ways to use human proteins that may be nonimmunogenic to initiate tumor cell death. Human cytotoxic proteins such as the eosinophil derived neurotoxin have been engineered and linked to antibodies and found to specifically kill tumor cells. Toxic proteins in the Bcl-2 family, Bax and Bad, that induce apoptosis, have also been engineered to bind cells and specifically kill them. As Bax and Bad are members of the Bcl-2 family of proteins that also includes anti-apoptotic members we sought to develop a new strategy to prevent neuron loss by targeting Bcl-xl to cells. Recent results show that Bcl-xl can be delivered to cells in vitro and in vivo to prevent neuron apoptosis and may have potential for inhibiting neuron loss during spinal cord injury and stroke.