title: Targeted actinium-225 in vivo generators for therapy of ovarian cancer.
abstract: Advanced ovarian cancer is largely incurable, but initially it is frequently confined to the i.p. space. We explored i.p. radioimmunotherapy in a mouse model of human ovarian cancer. Use of a targeted actinium-225 ((225)Ac) in vivo generator of alpha particles exploits the extreme, selective cytotoxicity of alpha particles, while providing a feasible half-life to enable delivery to tumor. (225)Ac chelated with 2-(p-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10 tetraacetic acid was conjugated to trastuzumab, an anti-HER-2/neu antibody. The radioimmunoconjugate was tested for immunoreactivity, internalization, and cytotoxicity using a human ovarian carcinoma cell line, SKOV3. (225)Ac-labeled trastuzumab retained immunoreactivity (50-90%), rapidly internalized into cells (50% at 2 h), and had an ED(50) of 1.3 nCi/ml after 4 days of incubation in vitro. i.p. administered (225)Ac- or (111)In-labeled trastuzumab behaved similarly with high tumor uptake [56-60% injected dose per gram (% ID/g) at 4 h, which increased to 65-70% ID/g at 24 h]. Tumor uptake was 3-5-fold higher than liver and spleen, the normal organs with the highest uptake. i.v. administration of (111)In-labeled trastuzumab produced slightly higher normal organ uptake compared with i.p.-administered (111)In-labeled trastuzumab. However, tumor uptake was low, 5%-26% ID/g. Therapy was examined with native trastuzumab and 220, 330, and 450 nCi of (225)Ac-labeled trastuzumab or (225)Ac-labeled control antibody at different dosing schedules. Therapy was initiated 9 days after tumor seeding. Groups of control mice and those administered native trastuzumab had median survivals of 33 and 37 or 44 days, respectively. Median survival was 52-126 days with (225)Ac-labeled trastuzumab at various doses and schedules, and 48-64 days for (225)Ac-labeled control the same schedules. Deaths from toxicity occurred with the highest activity levels. In conclusion, i.p. administration with a (225)Ac-labeled internalizing anti-HER-2/neu antibody can extend survival significantly in a nude mouse model of human ovarian cancer at levels that produce no apparent gross toxicity.
authors.affiliation: Department of Molecular Pharmacology and Chemistry, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Borchardt
authors.forename: Rui R
authors.initials: RR
authors.lastname: Yuan
authors.forename: Matthias
authors.initials: M
authors.lastname: Miederer
authors.forename: Michael R
authors.initials: MR
authors.lastname: McDevitt
authors.forename: David A
authors.initials: DA
authors.lastname: Scheinberg
mesh_terms: D000186:Actinium / Q000627:therapeutic use*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D019281:Dimerization; D005260:Female; D006801:Humans; D007205:Indium Radioisotopes; D051379:Mice; D009368:Neoplasm Transplantation; D010051:Ovarian Neoplasms / Q000532:radiotherapy*; D016499:Radioimmunotherapy / Q000379:methods*; D014018:Tissue Distribution; D014183:Transplantation, Heterologous; D000068878:Trastuzumab; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D007205:Indium Radioisotopes; D000186:Actinium; D000068878:Trastuzumab