The detection of early micrometastasis or disseminated single tumor cells poses a problem for conventional diagnosis procedures. Using a panel of monoclonal antibodies against cytokeratin and the 17-lA epithelial antigen we identified immunocytochemically tumor cells in bone marrow of patients with breast cancer (n = 155) and colorectal cancer (n = 57) at the time of surgery of the primary tumor. Monoclonal antibody CK2, recognizing the human cytokeratin component 18 in simple epithelia, appeared to be the most suitable reagent because of its negative reaction with bone marrow samples of the noncarcinoma patients (n = 75). Its specificity was further demonstrated in a double-marker staining procedure using an anti-leukocyte common antigen monoclonal antibody (T200) as counterstain. A comparative analysis showed that immunocytology was clearly superior to conventional cytology (n = 212) and histology (n = 39). In 9.5-20.5% of patients without distant metastasis, tumor cells could be detected in bone marrow. We found a significant correlation between tumor cells in bone marrow and conventional risk factors, such as distant metastasis or lymph node involvement. In a first approach toward immunotherapy we demonstrated in 3 patients that infused monoclonal antibody 17-lA can label single tumor cells in bone marrow in vivo. We then used this approach to follow up 7 patients undergoing 17-4A therapy in an adjuvant clinical trial.

No abstract

72 As, 74 As, 77 As / Radioactive arsenic / Germanium target / Radiochemical separation / Labelled antibodies Summary. Radioarsenic labelled radiopharmaceuticals could add special features to molecular imaging with positron emission tomography (PET). For example the long physical half-lives of 72 As (T 1/2 = 26 h) and 74 As (T 1/2 = 17.8 d) in conjunction with their high positron branching rates of 88% and 29%, respectively, allow the investigation of slow physiological or metabolical processes, like the enrichment and biodistribution of monoclonal antibodies in tumour tissue or the characterization of stem cell trafficking. A method for separation and purification of no-carrier-added (nca) arsenic from irradiated metallic germanium targets based on distillation and anion exchange is developed. It finally converts the arsenic into an * As(III) synthon in PBS buffer and pH 7 suitable for labelling of proteins via As−S bond formations. The method delivers radioarsenic in high purity with separation factors of 10 6 from germanium and an overall yield from target to labelling synthon of > 40%. In a proof-ofprinciple experiment, the monoclonal antibody Bevacizumab, directed against the human VEGF receptor, was labelled with a radiochemical yield > 90% within 1 h at room temperature with nca 72/74/77 As.

Fast progressing immuno-PET gives reasons to develop new potential medium-long and long-lived radioisotopes. One of the promising candidates is 90 Nb. It has a half-life of 14.6 h, which allows visualizing and quantifying processes with medium and slow kinetics, such as tumor accumulation of antibodies and antibodies fragments or polymers and other nanoparticles. 90 Nb exhibits a high positron branching of 53% and an optimal energy of β + emission of E mean = 0.35 MeV only. Consequently, efficient radionuclide production routes and Nb V labeling techniques are required. 90 Nb was produced by the 90 Zr(p,n) 90 Nb nuclear reaction on natural zirconium targets. No-carrier-added (n.c.a.) 90 Nb was separated from the zirconium target via a multi-step separation procedure including extraction steps and ion-exchange chromatography. Protein labeling was exemplified using the bifunctional chelator desferrioxamine attached to the monoclonal antibody rituximab. Desferrioxamine was coupled to rituximab via two different routes, by the use of N-succinyldesferrioxamine (N-suc-Df) and by means of the bifunctional derivative p-isothiocyanatobenzyl-desferrioxamine B (Df-Bz-NCS), respectively. Following antibody modification, labeling with 90 Nb was performed in HEPES buffer at pH 7 at room temperature. In vitro stability of the radiolabeled conjugates was tested in saline buffer at room temperature and in fetal calf serum (FCS) at 37 • C.The selected production route led to a high yield of 145 ± 10 MBq/μA h of 90 Nb with high radioisotopic purity of > 97%. This yield may allow for large scale production of about 10 GBq 90 Nb. The separation procedure resulted in 76-81% yield. The Zr/ 90 Nb decontamination factor reaches 10 7 . Subsequent radiolabeling of the two different conjugates with 90 Nb gave high yields; after one hour incubation at room temperature, more than 90% of 90 Nb-Df-mAb was formed in both cases. At room temperature in aqueous solution, both 90 Nb-Df-mAb constructs were more than 99% stable over a period of 18 d.The developed production and separation strategy provided 90 Nb with purity appropriate for radiolabeling applications.