Kumaresan Pappanaicken R, Natarajan Arutselvan, Song Aimin, Wang Xiaobing, Liu Ruiwu, DeNardo Gerald, DeNardo Sally, Lam Kit S
Division of Hematology and Oncology, and Radiodiagnosis and Therapy, Department of Internal Medicine, UC Davis Cancer Center, University of California Davis, School of Medicine, Sacramento, California 95817.
Bioconjug Chem. 2007 Jan-Feb;18(1):175-82. doi: 10.1021/bc0602681.
New strategies are needed to protect normal organs from radiation in cancer radioimmunotherapy (RIT). This can be achieved by rapid clearance of radiometal in the circulation after accumulation of radioimmunoconjugates (RIC) in the tumor. Our strategy is to place highly efficient and specific cleavable linkers between radiometal chelates and the tumor targeting agents. Such linkers must be resistant to cleavage by enzymes present in the plasma and the tumor. After radiotargeting agents have accumulated in the tumor, a cleaving agent can be administered "on demand" to cleave a specific linker, resulting in the release of radiometal from the circulating RIC in a form that will have rapid renal clearance. We have selected TNKase, a thrombolytic agent approved for patient use, as our model on-demand cleaving agent. To identify TNKase-specific linkers, we screened fluorescent-quenched random "one-bead-one-compound" (OBOC) combinatorial peptide libraries. d-Amino acid containing peptides that were specific for TNKase but were resistant to cleavage by plasma and tumor-associated proteases were identified. One of these peptide substrates (rqYKYkf) was used to link the DOTA chelate to ChL6, a monoclonal antibody known to target breast cancer. This antibody conjugate was stable in plasma for 7 days while preserving the immunoreactivity to intact tumor cells. The addition of TNKase at clinical achievable plasma level (10 mug/mL) resulted in the release of 28% of the radiometal from the radioimmunoconjugate within 72 h. This lead linker, after further optimization to increase its response to TNKase, may be useful in the development of more effective radioimmunotherapeutic and radioimaging agents.
在癌症放射免疫疗法（RIT）中，需要新的策略来保护正常器官免受辐射。这可以通过在肿瘤中积累放射免疫缀合物（RIC）后迅速清除循环中的放射性金属来实现。我们的策略是在放射性金属螯合物与肿瘤靶向剂之间放置高效且特异的可裂解连接子。此类连接子必须抵抗血浆和肿瘤中存在的酶的裂解作用。在放射性靶向剂在肿瘤中积累后，可以“按需”给予裂解剂以裂解特定的连接子，从而使放射性金属以可快速经肾脏清除的形式从循环的RIC中释放出来。我们选择了已被批准用于患者的溶栓剂TNKase作为我们的按需裂解剂模型。为了鉴定TNKase特异性连接子，我们筛选了荧光猝灭的随机“一珠一化合物”（OBOC）组合肽库。鉴定出了对TNKase特异但对血浆和肿瘤相关蛋白酶的裂解具有抗性的含d-氨基酸的肽。其中一种肽底物（rqYKYkf）被用于将DOTA螯合物与ChL6（一种已知靶向乳腺癌的单克隆抗体）连接。该抗体缀合物在血浆中7天保持稳定，同时保留了对完整肿瘤细胞的免疫反应性。在临床可达到的血浆水平（10μg/mL）添加TNKase导致72小时内28%的放射性金属从放射免疫缀合物中释放出来。这种先导连接子在进一步优化以增强其对TNKase的反应后，可能有助于开发更有效的放射免疫治疗剂和放射成像剂。
