Design and synthesis of 225Ac radioimmunopharmaceuticals

McDevitt, Michael R.; Ma, Dangshe; Simón, Jaime; Frank, R.T.; Scheinberg, David A.

doi:10.1016/s0969-8043(02)00167-7

Cited by 188 publications

(203 citation statements)

References 13 publications

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“…To ensure identical radiolabeling levels (radioactivity-to-lipid ratio) across all liposome types, the levels of radioactivity introduced to the liposome suspension for encapsulation were adjusted in advance based on the loading efficacy measured for each liposome composition. Antibodies were radiolabeled following a published protocol described in detail in the supplemental data (21).…”

Section: Liposome Preparation and Radiolabeling With 225 Acmentioning

confidence: 99%

Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with²²⁵Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

et al. 2013

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This study evaluates targeted liposomes loaded with the a-particle generator 225 Ac to selectively kill prostate-specific membrane antigen (PSMA)-expressing cells with the aim to assess their potential for targeted antivascular radiotherapy. Methods: In this study, PEGylated liposomes were loaded with 225 Ac and labeled with the mouse antihuman PSMA J591 antibody or with the A10 PSMA aptamer. The targeting selectivity, extent of internalization, and killing efficacy of liposomes were evaluated on monolayers of prostate cancer cells intrinsically expressing PSMA (human LNCaP and rat Mat-Lu cells) and on monolayers of HUVEC induced to express PSMA (induced HUVEC). Results: The loading efficiency of 225 Ac into preformed liposomes ranged from 58.0% 6 4.6% to 85.6% 6 11.7% of introduced radioactivity. The conjugation reactions resulted in approximately 17 6 2 J591 antibodies and 9 6 2 A10 aptamers per liposome. The average size of liposomes, 107 6 2 nm in diameter, was not affected by conjugation or loading. LNCaP cells exhibit 2:1:0.5 relative PSMA expression, compared with MatLu and induced HUVEC, respectively, based on flow cytometry detecting association of the J591 antibody. J591-labeled liposomes display higher levels of total specific binding to all cell lines than A10 aptamer-labeled liposomes. Specific cell association of targeted liposomes increases with incubation time. Cytotoxicity studies demonstrate that radiolabeled J591-labeled liposomes are most cytotoxic, with median lethal dose values, after 24 h of incubation, equal to 1.96 (5.3 · 10 25 ), 2.92 · 10 2 (7.9 · 10 23 ), and 2.33 · 10 1 Bq/mL (6.3 · 10 24 mCi/mL) for LNCaP, Mat-Lu, and induced HUVEC, respectively, which are comparable to the values for the radiolabeled J591 antibody. For A10 aptamer-labeled liposomes, the corresponding values are 3.70 · 10 1 (1.0 · 10 23 ), 1.85 · 10 3 (5.0 · 10 22 ), and 4.07 · 10 3 Bq/mL (1.1 · 10 21 mCi/mL), respectively. Conclusion: Our studies demonstrate that anti-PSMA-targeted liposomes loaded with 225 Ac selectively bind, become internalized, and kill PSMA-expressing cells including endothelial cells induced to express PSMA. These findings-combined with the unique ability of liposomes to be easily tuned, in terms of size and surface modification, for optimizing biodistributions-suggest the potential of PSMA-targeting liposomes encapsulating a-particle emitters for selective antivascular a radiotherapy.

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Section: Liposome Preparation and Radiolabeling With 225 Acmentioning

confidence: 99%

Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with²²⁵Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

et al. 2013

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“…The low yield in the second step results from the competing hydrolysis reaction of the isothiocyanate moiety. The mass amounts of DOTA and IgG as well as the activity amount of 225 Ac were optimized (19) and adding more or less of any of these components will not significantly improve the overall yield. The reported specific activity 1.406 kBq/microgram (0.038 Ci/g) was on the same order as the specific activities used clinically with the 225 Ac-DOTA-HuM195 therapeutic drug (24) and these 'small' doses have demonstrated antileukemic effects.…”

Section: Liposome and Antibody Radiolabeling And Quality Controlmentioning

confidence: 99%

Enhanced Retention of the α-Particle-Emitting Daughters of Actinium-225 by Liposome Carriers

et al. 2007

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Targeted α-particle emitters hold great promise as therapeutics for micrometastatic disease. Because of their high energy deposition and short range, tumor targeted α-particles can result in high cancercell killing with minimal normal-tissue irradiation. Actinium-225 is a potential generator for α-particle therapy: it decays with a 10-day half-life and generates three α-particle emitting daughters. Retention of 225 Ac daughters at the target increases efficacy; escape and distribution throughout the body increases toxicity. During circulation, molecular carriers conjugated to 225 Ac cannot retain any of the daughters. We previously proposed liposomal encapsulation of 225 Ac to retain the daughters, whose retention was shown to be liposome-size dependent. However, daughter retention was lower than expected: 22% of theoretical maximum decreasing to 14%, partially due to binding of 225 Ac to the phospholipid membrane. In this study, MUltiVEsicular Liposomes (MUVELs) composed of different phospholipids were developed to increase daughter retention. MUVELs are large liposomes with entrapped smaller lipid-vesicles containing 225 Ac. PEGylated MUVELs stably retained over time 98% of encapsulated 225 Ac. Retention of 213 Bi, the last daughter, was 31% of the theoretical maximum retention of 213 Bi for the liposome sizes studied. MUVELs were conjugated to an anti-HER2/neu antibody (immunolabeled MUVELs), and were evaluated in vitro with SKOV3-NMP2 ovarian cancer cells, exhibiting significant cellular internalization (83%). This work demonstrates that immunolabeled MUVELs could be able to deliver higher fractions of generated α-particles per targeted 225 Ac compared to the relative fractions of α-particles delivered by 225 Ac-labeled molecular carriers.

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“…Its radiochemical purity was typically 90% or greater. Previous studies have shown that an average of 5.4 DOTA per antibody are attached (19).…”

Section: Preparation Of the Radioimmunoconjugatesmentioning

confidence: 99%

“…A first limitation to the use of targeted 225 Ac isotope generators is the poor yield of labeled antibody (19). Chelation of Ac-225 stably under physiological conditions requires the use the macrocyclic chelator DOTA with all four carboxylic groups available (Antczak et al, unpublished data).…”

Section: Introductionmentioning

confidence: 99%

Influence of the Linker on the Biodistribution and Catabolism of Actinium-225 Self-Immolative Tumor-Targeted Isotope Generators

et al. 2006

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Current limitations to applications of monoclonal antibody (mAb) targeted isotope generators in radioimmunotherapy include the low mAb labeling yields and the non-specific radiation of normal tissues by non-targeted radioimmunoconjugates (RIC). Radiotoxicity occurs in normal organs that metabolize radiolabeled proteins and peptides, primarily liver and kidneys, or in radiosensitive organs with prolonged exposure to the isotope from the blood, such as the bone marrow. Actinium-225 nanogenerators also have the problem of released alpha emitting daughters. 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 to 8 fold. In addition, one bifunctional chelating agent incorporated a cleavable linker to alter the catabolism of the alpha particle emitting mAb conjugate. This linker was designed to be sensitive to cathepsins to allow release and clearance of the chelated radiometal after internalization of the radioimmunoconjugate into the cell. We compared the properties of the cleavable conjugate (mAb-DOTA-G3FC) to non-cleavable constructs (mAb-DOTA-NCS and mAb-DOTA-SH). The cleavable RIC was able to release 80% of its radioactive payload when incubated with purified cathepsin B. The catabolism of the constructs mAb-DOTA-G3FC and mAb-DOTA-NCS was investigated in vitro and in vivo. RIC integrity was retained at 85% over a period of 136 hours in mouse serum in vivo. Both conjugates were degraded over time inside HL-60 cells after internalization and in mouse liver in vivo. While we found that the rates of degradation of the two RICs in those conditions were similar, the amounts of the radiolabeled product residues were different. The cleavable mAb-DOTA-G3FC conjugate yielded a larger proportion of fragments below 6kDa in size in mouse liver in vivo after 12 hours than the DOTA-NCS conjugate. Biodistribution studies in mice showed that the mAb-DOTA-G3FC construct yielded a higher liver dose and prolonged liver retention of radioactivity compared to the mAb-DOTA-NCS conjugate. The accumulation in the liver seemed to be in part caused by the maleimide functionalization of the antibody, since the non-cleavable mAb-DOTA-SH maleimide-functionalized control conjugate displayed the same biodistribution pattern. These results provide an insight into the catabolism of RICs, by demonstrating that the release of the radioisotope from a RIC is not a sufficient condition to allow the radioactive moiety to clear from the body. The excretion mechanisms of radiolabeled fragments seem to constitute a major limiting step in the chain of events leading to their clearance.

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Design and synthesis of 225Ac radioimmunopharmaceuticals

Cited by 188 publications

References 13 publications

Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with²²⁵Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with²²⁵Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

Enhanced Retention of the α-Particle-Emitting Daughters of Actinium-225 by Liposome Carriers

Influence of the Linker on the Biodistribution and Catabolism of Actinium-225 Self-Immolative Tumor-Targeted Isotope Generators

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Design and synthesis of 225Ac radioimmunopharmaceuticals

Cited by 188 publications

References 13 publications

Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with225Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with225Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

Enhanced Retention of the α-Particle-Emitting Daughters of Actinium-225 by Liposome Carriers

Influence of the Linker on the Biodistribution and Catabolism of Actinium-225 Self-Immolative Tumor-Targeted Isotope Generators

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Product

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Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with²²⁵Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer

Anti–Prostate-Specific Membrane Antigen Liposomes Loaded with²²⁵Ac for Potential Targeted Antivascular α-Particle Therapy of Cancer