PRETARGETING RADIOIMMUNOTHERAPY OF CD20+ LYMPHOMAS

描述(申请人提供)：初步临床试验表明，放射性标记的抗CD2O单抗可以在65%-90%的化疗失败的淋巴瘤患者中实现缓解。然而，大多数接受常规放射性标记抗体(RAB)治疗的患者随后复发并死于复发的淋巴瘤。本研究方案的目的是优化B细胞淋巴瘤的放射免疫治疗(RIT)，采用两步预靶向扩增策略，以提高传统RIT的疗效并降低毒性。将研究两种不同的预靶向方法，一种是使用链霉亲和素(SA)和放射性生物素，另一种是使用分子工程的双特异性抗CD20 x抗配体抗体，这些抗体与放射性标记的配体共价结合。首先，我们将比较抗CD2O、抗CD22和抗DR抗体-SA结合物在裸鼠模型中的生物分布、毒性和有效性。其次，我们将研究两种分子工程重组四价单链抗体-SA融合蛋白([scFv]4-SA)的药代动力学、生物分布、毒性和有效性，并将其与标准的合成抗体-SA化学结合物进行比较。第三，我们将比较4个基因工程SA突变体分子与天然SA结合生物素或合成的二价双生物素靶向分子的预靶向方案的相对优点。这些链霉亲和素突变体将提供一个独特的机会来测试SA亲和力对肿瘤穿透的影响，正如“结合部位障碍”假说中所描绘的那样。第四，我们将评估新型分子设计的双特异性抗CD2Ox反配体Abs的药代动力学、生物分布、毒性和有效性，该Abs具有分子工程结合口袋，能够与合成的放射性标记亲电配体共价结合。这些双特异性抗CD2O x抗配体抗体将在淋巴瘤异种移植模型中直接与SA-生物素预靶向方法进行比较。我们假设，与传统的RIT相比，本方案中定义的预靶向策略将改善吸收辐射的肿瘤与正常器官的比率，从而以比目前可行的更低的毒性提高应答率和反应持续时间。我们假设，前靶向治疗将不再需要给予清髓性剂量的131I-抗CD20抗体和造血干细胞挽救，以获得最大的应答率和存活率。我们预计这些临床前实验的结果将迅速转化为我们针对人类非霍奇金淋巴瘤的临床RIT计划。

DESCRIPTION (provided by the applicant): Preliminary clinical trials have demonstrated that radiolabeled anti-CD2O monoclonal antibodies can achieve remissions in 65-90 percent of lymphoma patients failing chemotherapy. However, most patients treated with conventional radiolabeled antibodies (RAb) subsequently relapse and die of recurrent lymphoma. The objective of this research proposal is to optimize radioimmunotherapy (RIT) of B cell lymphomas utilizing two-step pretargeting amplification strategies to improve the efficacy and decrease the toxicity of conventional RIT. Two separate pretargeting approaches will be investigated, one using streptavidin (SA) and radioactive biotin and the second employing molecularly engineered bispecific anti-CD20 x anti-ligand antibodies which bind covalently to radiolabeled ligands. First, we will compare the biodistributions, toxicities and efficacies of anti-CD2O, anti-CD22, and anti-DR antibody-SA conjugates pretargeted to lymphoma xenografts in an athymic mouse model, followed by radiobiotin administration. Second, we will investigate the pharmacokinetics, biodistributions, toxicities, and efficacies of 2 molecularly engineered recombinant tetravalent single chain antibody-SA fusion proteins ([scFv]4-SA) and compare them to standard synthetic antibody-SA chemical conjugates. Third, we will compare the relative merits of 4 genetically engineered SA mutant molecules with native SA for pretargeting protocols in combination with either biotin or a synthetic divalent bis-biotin targeting molecule. These streptavidin mutants will afford a unique opportunity to test the effect of SA avidity on tumor penetration as delineated in the "binding site barrier" hypothesis. Fourth, we will evaluate the pharmacokinetics, biodistributions, toxicities, and efficacies of novel molecularly designed bispecific anti-CD2O x anti-ligand Abs which possesses a molecularly engineered binding pocket capable of binding covalently to synthetic radiolabeled electrophilic ligands. These bispecific anti-CD2O x anti-ligand Abs will be compared directly to the SA-biotin pretargeting approach in lymphoma xenograft models. We hypothesize that the pretargeting strategies defined in this proposal will improve the tumor-to-normal organ ratios of absorbed radiation compared with conventional RIT, allowing improvement in response rates and response durations with less toxicity than is currently feasible. We hypothesize that pretargeting will eliminate the necessity of administering myeloablative doses of 131I-anti-CD20 Ab with hematopoietic stem cell rescue to achieve maximal response rates and survival rates. We anticipate rapid translation of the results of these preclinical experiments into our clinical RIT program for human Non-Hodgkin's lymphomas.