An efficient, reproducible and fast preparation of 188Re-anti-CD20 for the treatment of non-Hodgkin's lymphoma

Background Therapies using Y-90-anti-CD20 or I-131-anti-CD20 have demonstrated their efficacy in patients with B-cell non-Hodgkin's lymphoma. Re-188 is a radionuclide useful for radioimmunotherapy. Aim To develop a procedure for efficient labelling of anti-CD20 with Re-188 from lyophilized formulations to achieve high radiochemical yield, high specific activity and preservation of the molecular recognition after a simple kit reconstitution without further purification. Methods Re-188-anti-CD20 was prepared by a direct labelling method using sodium tartrate as a weak competing ligand. Different lyophilized formulations were prepared to optimize tartrate and stannous chloride concentration, pH and reaction time. To evaluate the biological recognition a comparative study of the in-vitro binding of Re-188-anti-CD20, 1251 -anti-CD20 (positive control) and Re-188-anti-CEA (negative control) to normal B lymphocytes was performed. Biodistribution studies in normal mice were accomplished to assess the in-vivo Re-188-anti-CD20 complex stability. Results 188Re labelled anti-CD20 was obtained with high radiochemical purities (> 97 %) and high specific activity (0.5-0.7 GBq(.)mg(-1)) 1-1.5 h after addition of sodium perrhenate solution to a kit containing 4.4 mu M anti-CD20, 4 mM anhydrous stannous chloride, and 140 mM dihydrate sodium tartrate at pH 4. The binding of Re-188-anti-CD20 to cells was in the same range as I-125-anti-CD20 (> 80 %) and was significantly different to cell binding of Re-188-anti-CEA (< 10 %). No evidence of free Re-188 release was found at 2, 4 and 24 h after Re-188-anti-CD20 administration in mice. Lyophilized kits showed high stability during the storage at 4 degrees C for 6 months. Conclusions Optimal reaction conditions were defined enabling high radiochemical purities of Re-188-anti-CD20 to be obtained routinely and therefore potentially useful in the treatment of non-Hodgkin's lymphoma.