Couto J R, Blank E W, Peterson J A, Ceriani R L
Cancer Research Fund of Contra Costa, Walnut Creek, California 94596, USA.
Cancer Res. 1995 Apr 15;55(8):1717-22.
Mc3 is a murine mAb that is highly effective in treating breast tumors in experimental radioimmunotherapy. Mc3 binds to BA46, a 46-kDa glycoprotein of the human milk fat globule membrane that is also expressed in breast carcinoma cells. We cloned and sequenced cDNAs encoding the variable regions of Mc3 and constructed an IgG1, kappa human/mouse chimeric antibody. We then humanized the variable regions of Mc3 using a positional consensus method and retaining residues that might either contact the complementarity-determining regions or the opposite chain. This positional consensus is novel in that it does not include residues with buried side chains. Humanized Mc3 retained full binding affinity, and fully competes with murine Mc3 for antigen binding. Humanized and murine 131I-labeled Mc3 behaved identically in athymic nu/nu mice biodistribution studies. The tumor uptake levels for both antibodies increased over a period of 4 days within a range of 13-20% of the injected dose per g with extremely favorable tumor:normal ratios. Also, a single therapeutic dose of 131I-labeled humanized Mc3 in the same animal model reduced the average tumor size and produced one of five cures while in the uninjected control tumor growth continued unabated. We believe that these results justify the implementation of Phase I human clinical trials for imaging and radioimmunotherapy of breast cancer.
Mc3是一种鼠单克隆抗体，在实验性放射免疫治疗中对治疗乳腺肿瘤非常有效。Mc3与BA46结合，BA46是一种人乳脂肪球膜的46 kDa糖蛋白，也在乳腺癌细胞中表达。我们克隆并测序了编码Mc3可变区的cDNA，并构建了一种IgG1、κ人/鼠嵌合抗体。然后，我们使用位置一致法对Mc3的可变区进行人源化，并保留可能与互补决定区或相反链接触的残基。这种位置一致法的新颖之处在于它不包括侧链被掩埋的残基。人源化的Mc3保留了完全的结合亲和力，并且在抗原结合方面与鼠Mc3完全竞争。在无胸腺裸鼠生物分布研究中，人源化和鼠源的131I标记的Mc3表现相同。两种抗体的肿瘤摄取水平在4天内均有所增加，范围为每克注射剂量的13%-20%，肿瘤与正常组织的比率非常有利。此外，在同一动物模型中，单次治疗剂量的131I标记的人源化Mc3降低了平均肿瘤大小，并产生了五分之一的治愈效果，而未注射的对照肿瘤则持续无节制地生长。我们认为，这些结果证明了开展乳腺癌成像和放射免疫治疗的I期人体临床试验是合理的。
