ABSTRACT
PURPOSE: Rituximab was the first chimeric monoclonal antibody to be approved for treatment of indolent B-cell non-Hodgkin's lymphoma (NHL). It is directed against the CD20 antigen, which is expressed by 95% of B-cell NHLs. The aim of this study was to explore the possibility of radiolabelling rituximab with (99m)Tc for use as an imaging agent in NHL for early detection, staging, remission assessment, monitoring for metastatic spread and tumour recurrence, and assessment of CD20 expression prior to (radio)immunotherapy. METHODS: Rituximab was purified from Mabthera solution (Roche), photo-activated at 302 nm by UV irradiation and radiolabelled with (99m)Tc. The effectiveness of the labelling method was evaluated by determination of the number of free thiol groups per photoreduced antibody, radiochemical purity and in vitro stability of (99m)Tc-rituximab. RESULTS: On average, 4.4 free thiol groups per photoreduced antibody were determined. Radiolabelling yields greater than 95% were routinely observed after storage of the photo-activated antibody at -80 degrees C for 195 days. The direct binding assay showed preserved ability of (99m)Tc-rituximab to bind to CD20, with an average immunoreactive fraction of 93.3%. The internalisation rate was proven to be low, with only 5.3% of bound (99m)Tc-rituximab being internalised over 4 h at 37 degrees C. CONCLUSION: Our results demonstrate that (99m)Tc-rituximab of high radiochemical purity and with preserved binding affinity for the antigen can be prepared by photoreduction and that the method shows good reproducibility. (99m)Tc-rituximab will be further explored as an imaging agent applicable in NHL for the purposes mentioned above.
Subject(s)
Antibodies, Monoclonal/metabolism , Lymphoma, B-Cell/diagnostic imaging , Lymphoma, B-Cell/metabolism , Organotechnetium Compounds/metabolism , Antibodies, Monoclonal/chemistry , Antibodies, Monoclonal/radiation effects , Antibodies, Monoclonal, Murine-Derived , Cell Line, Tumor , Drug Stability , Feasibility Studies , Humans , Organotechnetium Compounds/chemistry , Organotechnetium Compounds/radiation effects , Photochemistry/methods , Radionuclide Imaging , Radiopharmaceuticals/chemical synthesis , Radiopharmaceuticals/radiation effects , Reproducibility of Results , Rituximab , Sensitivity and Specificity , Staining and Labeling/methods , Ultraviolet RaysSubject(s)
Annexin A5/chemistry , Antineoplastic Agents/therapeutic use , Apoptosis , Isotope Labeling/methods , Melanoma/diagnostic imaging , Melanoma/drug therapy , Organotechnetium Compounds/chemistry , Photochemotherapy/methods , Animals , Annexin A5/pharmacokinetics , Annexin A5/radiation effects , Hot Temperature , Mice , Organotechnetium Compounds/pharmacokinetics , Organotechnetium Compounds/radiation effects , Phosphatidylserines/metabolism , Radionuclide Imaging , Radiopharmaceuticals/chemical synthesis , Radiopharmaceuticals/pharmacokinetics , Radiopharmaceuticals/radiation effects , Treatment OutcomeABSTRACT
The sensitivity of technetium-99m- (99mTc) d,l-HMPAO to radiolytically induced dissociation in aqueous solutions was investigated. It was found that cobalt-60 (60Co) gamma irradiation of solutions containing 99mTc-d,l-HMPAO with only 1600 cGy reduced the lipophilic chelates' radiochemical purity (RCP) to 50%-60%. The radiolytic sensitivity of 99mTc-meso-HMPAO is significantly lower. The results indicate that radiolytically produced intermediates limit the in vitro stability of 99mTc-d,l-HMPAO.
