title: In vitro evaluation of 213Bi-rituximab versus external gamma irradiation for the treatment of B-CLL patients: relative biological efficacy with respect to apoptosis induction and chromosomal damage.
abstract: 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).
authors.affiliation: Department of Radiopharmacy, Faculty of Pharmaceutical Sciences, Ghent University, Gent, Belgium. katia.vandenbulcke@rug.ac.be
authors.forename: Katia
authors.initials: K
authors.lastname: Vandenbulcke
authors.forename: Filip
authors.initials: F
authors.lastname: De Vos
authors.forename: Fritz
authors.initials: F
authors.lastname: Offner
authors.forename: Jan
authors.initials: J
authors.lastname: Philippé
authors.forename: Christos
authors.initials: C
authors.lastname: Apostolidis
authors.forename: Roger
authors.initials: R
authors.lastname: Molinet
authors.forename: Tuomo K
authors.initials: TK
authors.lastname: Nikula
authors.forename: Klaus
authors.initials: K
authors.lastname: Bacher
authors.forename: Virginie
authors.initials: V
authors.lastname: de Gelder
authors.forename: Anne
authors.initials: A
authors.lastname: Vral
authors.forename: Christophe
authors.initials: C
authors.lastname: Lahorte
authors.forename: Hubert
authors.initials: H
authors.lastname: Thierens
authors.forename: Rudi A
authors.initials: RA
authors.lastname: Dierckx
authors.forename: Guido
authors.initials: G
authors.lastname: Slegers
mesh_terms: D000368:Aged; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D058846:Antibodies, Monoclonal, Murine-Derived; D017209:Apoptosis / Q000528:radiation effects; D001729:Bismuth / Q000627:therapeutic use*; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005720:Gamma Rays / Q000627:therapeutic use*; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood* / Q000532:radiotherapy*; D008214:Lymphocytes / Q000528:radiation effects*; D008297:Male; D015162:Micronucleus Tests; D008875:Middle Aged; D008954:Models, Biological; D011829:Radiation Dosage; D011868:Radioisotopes / Q000627:therapeutic use*; D012016:Reference Values; D012062:Relative Biological Effectiveness; D000069283:Rituximab; D016896:Treatment Outcome
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D011868:Radioisotopes; D000069283:Rituximab; D001729:Bismuth