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Abstract: Radioimmunotherapy has proven clinically effective in patients with non-Hodgkin''s lymphoma. Radioimmunotherapy trials have so far been performed with β-emitting isotopes. In contrast to β-emitters, the shorter range and high linear energy transfer (LET) of α particles allow for more efficient and selective killing of individually targeted tumor cells. However, there are several obstacles to the use of α-particle immunotherapy, including problems with chelation chemistry and nontarget tissue toxicity. The α-emitting radioimmunoconjugate 227Th-DOTA-p-benzyl-rituximab is a new potential anti-lymphoma agent that might overcome some of these difficulties. The present study explores the immunoreactivity, in vivo stability and biodistribution, as well as the effect on in vitro cell growth, of this novel radioimmunoconjugate. To evaluate in vivo stability, uptake in balb/c mice of the α-particle-emitting nuclide 227Th alone, the chelated form, 227Th-p-nitrobenzyl-DOTA and the radioimmunoconjugate 227Th-DOTA-p-benzyl-rituximab was compared in a range of organs at increasing time points after injection. The immunoreactive fraction of 227Th-DOTA-p-benzyl-rituximab was 56–65%. During the 28 days after injection of radioimmunoconjugate only, very modest amounts of the 227Th had detached from DOTA-p-benzyl-rituximab, indicating a relevant stability in vivo. The half-life of 227Th-DOTA-p-benzyl-rituximab in blood was 7.4 days. Incubation of lymphoma cells with 227Th-DOTA-p-benzyl-rituximab resulted in a significant antigen-dependent inhibition of cell growth. The data presented here warrant further studies of 227Th-DOTA-p-benzyl-rituximab. [Copyright &y& Elsevier]

Purpose: The main goals were to study the safety and tolerability of the alpha-emitter radium-223 (223Ra) in breast and prostate cancer patients with skeletal metastases. In addition, pain palliation was evaluated., Experimental Design: Fifteen prostate and 10 breast cancer patients enrolled in a phase I trial received a single i.v. injection of 223Ra. Five patients were included at each of the dosages: 46, 93, 163, 213, or 250 kBq/kg and followed for 8 weeks. Palliative response was evaluated according to the pain scale of the European Organization for Research and Treatment of Cancer QLQ C30 questionnaire at baseline and at 1, 4, and 8 weeks after injection., Results: Weekly blood sampling during follow-up revealed mild and reversible myelosuppression with nadir 2 to 4 weeks after the injection. Importantly, for thrombocytes only grade 1 toxicity was reported. Grade 3 neutropenia and leucopenia occurred in two and three patients, respectively. Mild, transient diarrhea was observed in 10 of the 25 patients. Nausea and vomiting was more frequently observed in the highest dosage group. Serum alkaline phosphatase decreased with nadir averages of 29.5% in females and 52.1% in males. Pain relief was reported by 52%, 60%, and 56% of the patients after 7 days, 4, and 8 weeks, respectively. 223Ra cleared rapidly from blood and was below 1% of initial level at 24 hours. Gamma camera images indicated, in accordance with pretreatment (99m)Tc-MDP scans, accumulation of 223Ra in skeletal lesions. Elimination was mainly intestinal. Median survival exceeded 20 months., Conclusions: 223Ra was well tolerated at therapeutically relevant dosages. Phase II studies have therefore been initiated.