Importance of receptor density in alpha radioimmunotherapy in B cell malignancies: an in-vitro study.
BACKGROUND
External beam 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.


OBJECTIVE
To assess the binding of rituximab to samples of B cell chronic lymphocytic leukaemia (B-CLL) and splenic lymphoma with villous lymphocytes (SLVL), and to evaluate the induction of apoptosis by conventional therapies as well as with Bi conjugated to rituximab.


METHODS
213Bi was eluted from a 225Ac generator and conjugated to CD20 antibody (rituximab) with CHX-A''-DTPA as chelator. Binding assays with 213Bi-rituximab were correlated to antibody binding capacity obtained by flow cytometry. Apoptosis was scored by flow cytometric analyses of the cells stained with annexin V-FITC and 7-amino-actinomycin D.


RESULTS
Binding of 213Bi-rituximab was significantly lower for B-CLL compared to SLVL samples (12+/-3 and 42+/-10 213Bi atoms per cell, respectively, at 370 kBq.ml(-1)). The induction of apoptosis did not differ significantly between the two groups (B-CLL and SLVL) after external gamma irradiation or treatment with methylprednisolone and fludarabine (17+/-12% and 18+/-11%; 23+/-14% and 21+/-12%; 9+/-9% and 11+/-8%, respectively; all results expressed as percentages of all cells). Rituximab conjugated or not to 213Bi induced significantly more apoptosis in SLVL (42+/-19% and 42+/-17%) compared to B-CLL samples (27+/-12% and 6+/-8%).


CONCLUSIONS
Binding assays confirm that SLVL samples present more CD20 antigens compared to B-CLL samples. Conventional therapies such as fludarabine, methylprednisolone or external gamma irradiation induce similar responses in the two populations but SLVL samples present higher sensitivity towards 213Bi-rituximab. These data are in favour of alpha-RIT in SLVL patients.
Vandenbulcke
Katia
K
Department of Radiopharmacy, Ghent University, Belgium.
Thierens
Hubert
H
Offner
Fritz
F
Janssens
Ann
A
de Gelder
Virginie
V
Bacher
Klaus
K
Philippé
Jan
J
De Vos
Filip
F
Dierckx
Rudi
R
Apostolidis
Christos
C
Morgenstern
Alfred
A
Slegers
Guido
G
D000512:Alpha Particles / Q000627:therapeutic use; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000378:metabolism*; D017209:Apoptosis / Q000528:radiation effects*; D001729:Bismuth / Q000493:pharmacokinetics / Q000627:therapeutic use*; D006801:Humans; D016393:Lymphoma, B-Cell / Q000378:metabolism* / Q000532:radiotherapy*; D016499:Radioimmunotherapy / Q000379:methods; D011868:Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000627:therapeutic use; D018121:Receptors, Cytokine / Q000378:metabolism*; D000069283:Rituximab; D016896:Treatment Outcome; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D018121:Receptors, Cytokine; D000069283:Rituximab; D001729:Bismuth