Vandenbulcke Katia, De Vos Filip, Offner Fritz, Philippé Jan, Apostolidis Christos, Molinet Roger, Nikula Tuomo K, Bacher Klaus, de Gelder Virginie, Vral Anne, Lahorte Christophe, Thierens Hubert, Dierckx Rudi A, Slegers Guido
Department of Radiopharmacy, Faculty of Pharmaceutical Sciences, Ghent University, Gent, Belgium.
Eur J Nucl Med Mol Imaging. 2003 Oct;30(10):1357-64. doi: 10.1007/s00259-003-1228-8. Epub 2003 Jul 3.
External source radiotherapy and beta radioimmunotherapy (RIT) are effective treatments for lymphoid malignancies. The development of RIT with alpha emitters is attractive because of the high linear energy transfer (LET) and short path length, allowing higher tumour cell kill and lower toxicity to healthy tissues. We assessed the relative biological efficacy (RBE) of alpha RIT (in vitro) compared to external gamma irradiation with respect to induction of apoptosis in B chronic lymphocytic leukaemia (B-CLL) and induction of chromosomal damage in healthy donor B and T lymphocytes. The latter was measured by a micronucleus assay. 213Bi was eluted from a 225Ac generator and conjugated to CD20 antibody (rituximab) with CHX-A"-DTPA as a chelator. B-CLL cells from five patients were cultured for 24 h in RPMI/10% FCS while exposed to 213Bi conjugated to CD20 antibody or after external 60Co gamma irradiation. Binding assays were performed in samples of all patients to calculate the total absorbed dose. Apoptosis was scored by flow cytometric analyses of the cells stained with annexin V-FITC and 7-AAD. Apoptosis was expressed as % excess over spontaneous apoptosis in control. Full dose range experiments demonstrated 213Bi-conjugated CD20 antibody to be more effective than equivalent doses of external gamma irradiation, but showed that similar plateau values were reached at 10 Gy. The RBE for induction of apoptosis in B-CLL was 2 between 1.5 and 7 Gy. The micronucleus yield in lymphocytes of healthy volunteers was measured to assess the late toxicity caused by induction of chromosomal instability. While gamma radiation induced a steady increase in micronucleus yields in B and T cells, the damage induced by 213Bi was more dramatic, with RBE ranging from 5 to 2 between 0.1 Gy and 2 Gy respectively. In contrast to gamma irradiation, 213Bi inhibited mitogen-stimulated mitosis almost completely at 2 Gy. In conclusion, high-LET targeted alpha particle exposure killed B-CLL cells more effectively than did external gamma irradiation at a low dose (RBE=2), while a plateau was reached at a high dose. Long-term toxicity on healthy B and T lymphocytes was systematically higher for the alpha emitter (RBE=5 to 2).
外照射放疗和β放射免疫疗法（RIT）是治疗淋巴系统恶性肿瘤的有效方法。由于α发射体具有高线性能量传递（LET）和短程长度，因此开发α发射体的RIT具有吸引力，它能更有效地杀死肿瘤细胞，对健康组织的毒性更低。我们评估了α RIT（体外）与外照射γ射线相比，在诱导B慢性淋巴细胞白血病（B-CLL）细胞凋亡以及在健康供体的B淋巴细胞和T淋巴细胞中诱导染色体损伤方面的相对生物学效应（RBE）。后者通过微核试验进行测量。从225Ac发生器中洗脱213Bi，并以CHX-A”-DTPA作为螯合剂将其与CD20抗体（利妥昔单抗）偶联。来自5名患者的B-CLL细胞在RPMI/10%胎牛血清中培养24小时，同时暴露于与CD20抗体偶联的213Bi或接受外照射60Co γ射线。对所有患者的样本进行结合试验以计算总吸收剂量。通过对用膜联蛋白V-FITC和7-AAD染色的细胞进行流式细胞术分析来对凋亡进行评分。凋亡以相对于对照中自发凋亡的过量百分比表示。全剂量范围实验表明，与CD20抗体偶联的213Bi比同等剂量的外照射γ射线更有效，但显示在10 Gy时达到相似的平台值。在1.5至7 Gy之间，B-CLL细胞凋亡诱导的RBE为2。测量健康志愿者淋巴细胞中的微核产率，以评估由染色体不稳定性诱导所导致的晚期毒性。虽然γ射线辐射导致B细胞和T细胞中的微核产率稳步增加，但213Bi诱导的损伤更为显著，在0.1 Gy至2 Gy之间，RBE分别为5至2。与γ射线辐射不同，213Bi在2 Gy时几乎完全抑制了有丝分裂原刺激的有丝分裂。总之，高LET靶向α粒子照射在低剂量时（RBE = 2）比外照射γ射线更有效地杀死B-CLL细胞，而在高剂量时达到平台期。α发射体对健康B淋巴细胞和T淋巴细胞的长期毒性系统性更高（RBE = 5至2）。
