Influence of the Linker on the Biodistribution and Catabolism of Actinium-225 Self-Immolative Tumor-Targeted Isotope Generators
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- 作者：Christophe Antczak ; Jaspreet S. Jaggi ; Clare V. LeFave ; Michael J. Curcio ; Michael R. McDevitt ; David A. Scheinberg
- 刊名：Bioconjugate Chemistry
- 出版年：2006
- 出版时间：November 2006
- 年：2006
- 卷：17
- 期：6
- 页码：1551 - 1560
- 全文大小：134K
- 年卷期：v.17,no.6(November 2006)
- ISSN：1520-4812
文摘
Current limitations to applications of monoclonal antibody (mAb) targeted isotope generators in radioimmunotherapyinclude the low mAb labeling yields and the nonspecific radiation of normal tissues by nontargetedradioimmunoconjugates (RIC). Radiotoxicity occurs in normal organs that metabolize radiolabeled proteins andpeptides, primarily liver and kidneys, or in radiosensitive organs with prolonged exposure to the isotope from theblood, such as the bone marrow. Actinium-225 nanogenerators also have the problem of released 
-emittingdaughters. We developed two new bifunctional chelating agents (BCA) in order to address these issues. Thiol-maleimide conjugation chemistry was employed to increase the efficiency of the mAb radiolabelings by up to8-fold. In addition, one bifunctional chelating agent incorporated a cleavable linker to alter the catabolism of the-particle-emitting mAb conjugate. This linker was designed to be sensitive to cathepsins to allow release andclearance of the chelated radiometal after internalization of the radioimmunoconjugate into the cell. We comparedthe properties of the cleavable conjugate (mAb-DOTA-G3FC) to noncleavable constructs (mAb-DOTA-NCS and mAb-DOTA-SH). The cleavable RIC was able to release 80% of its radioactive payload when incubatedwith purified cathepsin B. The catabolism of the constructs mAb-DOTA-G3FC and mAb-DOTA-NCS wasinvestigated in vitro and in vivo. RIC integrity was retained at 85% over a period of 136 h in mouse serum invivo. Both conjugates were degraded over time inside HL-60 cells after internalization and in mouse liver invivo. While we found that the rates of degradation of the two RICs in those conditions were similar, the amountsof the radiolabeled product residues were different. The cleavable mAb-DOTA-G3FC conjugate yielded a largerproportion of fragments below 6kDa in size in mouse liver in vivo after 12 h than the DOTA-NCS conjugate.Biodistribution studies in mice showed that the mAb-DOTA-G3FC construct yielded a higher liver dose andprolonged liver retention of radioactivity compared to the mAb-DOTA-NCS conjugate. The accumulation inthe liver seemed to be in part caused by the maleimide functionalization of the antibody, since the noncleavablemAb-DOTA-SH maleimide-functionalized control conjugate displayed the same biodistribution pattern. Theseresults provide an insight into the catabolism of RICs, by demonstrating that the release of the radioisotope froma RIC is not a sufficient condition to allow the radioactive moiety to clear from the body. The excretion mechanismsof radiolabeled fragments seem to constitute a major limiting step in the chain of events leading to their clearance.
-emittingdaughters. We developed two new bifunctional chelating agents (BCA) in order to address these issues. Thiol-maleimide conjugation chemistry was employed to increase the efficiency of the mAb radiolabelings by up to8-fold. In addition, one bifunctional chelating agent incorporated a cleavable linker to alter the catabolism of the-particle-emitting mAb conjugate. This linker was designed to be sensitive to cathepsins to allow release andclearance of the chelated radiometal after internalization of the radioimmunoconjugate into the cell. We comparedthe properties of the cleavable conjugate (mAb-DOTA-G3FC) to noncleavable constructs (mAb-DOTA-NCS and mAb-DOTA-SH). The cleavable RIC was able to release 80% of its radioactive payload when incubatedwith purified cathepsin B. The catabolism of the constructs mAb-DOTA-G3FC and mAb-DOTA-NCS wasinvestigated in vitro and in vivo. RIC integrity was retained at 85% over a period of 136 h in mouse serum invivo. Both conjugates were degraded over time inside HL-60 cells after internalization and in mouse liver invivo. While we found that the rates of degradation of the two RICs in those conditions were similar, the amountsof the radiolabeled product residues were different. The cleavable mAb-DOTA-G3FC conjugate yielded a largerproportion of fragments below 6kDa in size in mouse liver in vivo after 12 h than the DOTA-NCS conjugate.Biodistribution studies in mice showed that the mAb-DOTA-G3FC construct yielded a higher liver dose andprolonged liver retention of radioactivity compared to the mAb-DOTA-NCS conjugate. The accumulation inthe liver seemed to be in part caused by the maleimide functionalization of the antibody, since the noncleavablemAb-DOTA-SH maleimide-functionalized control conjugate displayed the same biodistribution pattern. Theseresults provide an insight into the catabolism of RICs, by demonstrating that the release of the radioisotope froma RIC is not a sufficient condition to allow the radioactive moiety to clear from the body. The excretion mechanismsof radiolabeled fragments seem to constitute a major limiting step in the chain of events leading to their clearance.