Lymphoma imaging: Radiolabelling rituximab with technetium 99 metastable in three steps procedure

Objectives Lymphomas are the most frequent haematological malignancy. In non-Hodgkin lymphomas (NHL), more than 90% of tumour cells express the CD 20 antigen. At the end of supportive care, the evaluation of remission is based on computed tomography and positron emission tomography coupled with computer tomography with [18F]-fluorodeoxyglucose. Unfortunately, these techniques are not specific and cannot distinguish residual active tumour from inflammation common in this disease. The aim of this study was to develop a specific radiotracer of NHL CD 20+ cells with technetium 99 m using rituximab an anti-CD 20 antibody. Materials and methods Rituximab was radiolabelled with technetium 99 m using Isolink ® (tricarbonyl compound) in a three steps procedure without any specific antibody reducer. We evaluated the effectiveness of the radiolabelling by testing the radioligand in vitro (binding and immunoreactivty assays) and in vivo in mice xenografted with lymphoma. Results Radiolabelling yield was greater than 97%. The integrity of the protein was preserved with a Kd = 4.57 nM and an immunoreactivity of 96%. In vivo study showed that the tumour was detectable 5 h post injection but the best ratio was observed 24 h after injection. Conclusions We described a rituximab radiolabelling method in three steps. In a 1 h, a solution of [99mTc(CO)3]rituximab was prepared, without purification step. This method respects GMP standards. This procedure might be clinically can be used for diagnosis, evaluation of extension, response to treatment, follow-up and evaluation of residual disease in patients with NHLs, with higher specificity.