Aim: Alemtuzumab is a monoclonal antibody targeting the CD52 antigen expressed on (malignant) B and T cells, and is indicated for haematological malignancies. Not all patients benefit equally from therapy with alemtuzumab, underlining the need for a better selection of patients before start of therapy. Radiolabeled alemtuzumab may prove useful as a non invasive technique for patient selection. Therefore, alemtuzumab labeled with the PET isotope 89-Zirconium was developed and tested in mice bearing a human non-Hodgkin's B cell lymphoma xenograft. Material & Methods: Irradiated male NOD/SCID mice were injected subcutaneously with 107 DoHH2 (CD52 positive) cells. 89Zr-alemtuzumab for PET-imaging was developed and tested in vitro and in vivo. Biodistribution and tissue/organ including tumour uptake was compared to 111-Indium labeled non specific human immunoglobulin G (111In-IgG). Small-animal PET imaging and ex vivo biodistribution was performed at 144h after co-injection of 89Zr-alemtuzumab and 111In-IgG. Furthermore, uptake of both tracers was compared in both tumour and non-tumour bearing mice. Results: Subcutanous injection of DoHH2 cells in resulted in a palpable tumour 5 weeks after inoculation in 50% of the mice. 89Zr-alemtuzumab was stable in saline at 4°C and in serum at 37°C for seven days. Radiochemical purity was 97,6 ± 1,8%. PET showed intense uptake of 89Zr-alemtuzumab in tumour and spleen at 144h. Uptake in tumour of 89Zr-alemtuzumab was 14.9 ± 16.6 % injected dose per g tissue (%ID/g) vs 4.5 ± 7.7 %ID/g 111In-IgG (n=6, p=0.06). The tumour to blood ratio of 89Zr-alemtuzumab was 63 ± 51 vs 2 ± 3 of 111In-IgG (p<0.05). Furthermore, significant uptake of 89Zr-alemtuzumab was seen in spleen, liver, and bone (p<0.05). Spleen uptake of 89Zr-alemtuzumab in tumour positive mice was 101.3 ± 67.2 %ID/g (n=6) vs 25.0 ± 9.9 %ID/g in tumour negative mice (n=10, p<0.05). 111In-IgG uptake did not differ substantially in both groups. Conclusion: Radiochemical purity, stability and binding properties of 89Zr-alemtuzumab were good. PET imaging correlated well with ex vivo biodistribution data of 89Zr-alemtuzumab. However, quantification of images was difficult. Specific tumour uptake of 89Zr-alemtuzumab in tumour xenograft and spleen was observed. Therefore, radiolabeled alemtuzumab is a new tracer suitable for noninvasive in vivo imaging of CD52 expressing tumours. Table: Ex vivo biodistribution of 89Zr-alemtuzumab and 111In-IgG. (Table Presented).
|Status||Published - 1-okt-2010|