RADIOLABELING OF ANTI-CD20 WITH Re-188 FOR TREATMENT OF NON-HODGKIN’S LYMPHOMA: RADIOCHEMICAL CONTROL

The development of tumor-selective radiopharmaceuticals is clinically desirable as a means of detecting or confirming the presence and location of primary and metastatic lesions and monitoring tumor response to (chemo)therapy. In addition, the application of targeted radiotherapeutics provides a unique and effective modality for direct tumor treatment. In this manner the radioimmunotherapy (RIT) uses the targeting features of monoclonal antibody to deliver radiation from an attached radionuclide. Antibody therapy directed against the CD20 antigen on the surface of B-cells is considered one of the first successful target-specific therapies in oncology. The radionuclide rhenium-188 (Re) is currently produced from the father nuclide tungsten-188 (W) through a transportable generator system. Because of its easy availability and suitable nuclear properties (EβMAX = 2.1 MeV, t1/2 = 16.9 h, Eγ = 155 keV), this radionuclide is considered an attractive candidate for application as therapeutic agent and could be conveniently utilized for imaging and dosimetric purposes. The purpose of this work is to show the radiochemical control of the optimized formulation (solution) and lyophilized formulation (kit) of labeled rituximab (anti-CD20) with Re. Rituximab was reduced by incubation with 2-mercaptoethanol at room temperature. The number of resulting free sulfhydryl groups was assayed with Ellman’s reagent. Radiochemical purity of Re-rituximab was evaluated using instant thin layer chromatography-silica gel (ITLC-SG). Quality control methods for evaluation of radiochemical purity showed good labeling yield of the antibody.