In vitro and in vivo evaluation of direct rhenium-188-labeled anti-CD52 monoclonal antibody alemtuzumab for radioimmunotherapy of B-cell chronic lymphocytic leukemia

De Decker, Mario; Bacher, Klaus; Thierens, Hubert; Slegers, Guido; Dierckx, Rudi A.; De Vos, Filip

doi:10.1016/j.nucmedbio.2008.03.001

« Previous Next »Nuclear Medicine and Biology
Volume 35, Issue 5 , Pages 599-604, July 2008

In vitro and in vivo evaluation of direct rhenium-188-labeled anti-CD52 monoclonal antibody alemtuzumab for radioimmunotherapy of B-cell chronic lymphocytic leukemia

Mario De Decker
- Department of Radiopharmacy, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium
- Department of Nuclear Medicine and Molecular Imaging, University Medical Centre Groningen, Groningen, Netherlands
- Corresponding author. Department of Radiopharmacy, University Ghent, 9000 Ghent, Belgium. Tel.: +32 09 332 30 28; fax: +32 09 332 38 07.
Klaus Bacher
- Department of Medical Physics and Radiation Protection, Ghent University, Ghent, Belgium
Hubert Thierens
- Department of Medical Physics and Radiation Protection, Ghent University, Ghent, Belgium
Guido Slegers
- Department of Medical Imaging of Domestic Animals, Ghent University, Ghent, Belgium
Rudi A. Dierckx
- Department of Nuclear Medicine and Molecular Imaging, University Medical Centre Groningen, Groningen, Netherlands
Filip De Vos
- Department of Radiopharmacy, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium

Received 5 October 2007; received in revised form 26 February 2008; accepted 4 March 2008.

Abstract

Alemtuzumab (Campath, Berlex) is a humanized IgG1 rat monoclonal antibody directed against the cell surface CD52 antigen, found on lymphocytes and monocytes. It is being developed for the treatment of chronic lymphocytic leukemia (CLL), autoimmune disease and for the prevention of transplant rejection. This study focused on synthesis, quality control, in vitro evaluation and biodistrubution of ¹⁸⁸Re-labeled alemtuzumab for radioimmunotherapy of B-cell CLL.

¹⁸⁸Re-alemtuzumab was synthesized using a direct radiolabeling method. Reduction of the intramolecular disulfide bonds of the antibody was performed with tris-(carboxyethyl)-phosphine (Pierce), using a 1:60 molar excess. Reaction took place at room temperature for 20 min. A PD-10 desalting column was used to purify the reduced antibody from excess phospine.

Complexation and transchelation of ¹⁸⁸ReO₄⁻ was achieved using sodium gluconate as weak chelator and SnCl₂ as reducing agent. Quality control was done using instant thin-layer chromatography. Binding assays were performed on a CD52-positive cell line (HuT-78). Female NMRI mice were injected intravenously with 20 μg radiolabeled alemtuzumab and killed at preset time intervals for biodistribution studies. Tissues were dissected, weighed and counted for determination of radioactivity. Data were expressed as percentage injected activity per gram of tissue (% IA/g tissue) or as percentage injected activity (% IA).

¹⁸⁸Re-alemtuzumab was prepared achieving high radiochemical yields. Labeling efficiency of more than 95% can be obtained using optimal reaction conditions. ¹⁸⁸Re-alemtuzumab showed good in vitro stability, remaining intact at 24 h after radiolabeling.

In mice, ¹⁸⁸Re-alemtuzumab showed high uptake in the blood (25.10±1.36% IA at 1 h p.i.), followed by a biexponential clearance (t_1/2α=4.790 h and t_1/2β=55.45 h). Increased uptake was observed in kidneys and heart (9.29±0.46% IA/g in kidneys and 6.10±1.82% IA/g in heart at 1 p.i.). The highest absorbed radiation dose was received by the kidneys (0.159–3.26 mGy/MBq) and heart wall (0.0705–0.132 mGy/MBq). The predicted radiation dose for the total body was in the range of 0.0459–0.0529 mGy/MBq. The effective dose for the human reference adult was estimated to be approximately 0.0486–0.195 mSv/MBq.

¹⁸⁸Re-alemtuzumab can be prepared with high radiochemical yield and purity and showed good in vitro behavior and favorable biodistribution. Therefore, ¹⁸⁸Re-alemtuzumab would be an ideal candidate for radioimmunotherapy of chronic lymphocytic leukemia.

Keywords: Alemtuzumab, Chronic lymphocytic leukemia, Rhenium-188