Cell death triggered by alpha-emitting 213Bi-immunoconjugates in HSC45-M2 gastric cancer cells is different from apoptotic cell death.
OBJECTIVE
Radioimmunotherapy with alpha-particle-emitting nuclides, such as 213Bi, is a promising concept for the elimination of small tumour nodules or single disseminated tumour cells. The aim of this study was to investigate cellular damage and the mode of cell death triggered by 213Bi-immunoconjugates.


METHODS
Human gastric cancer cells (HSC45-M2) expressing d9-E-cadherin were incubated with different levels of activity of 213Bi-d9MAb targeting d9-E-cadherin and 213Bi-d8MAb, which does not bind to d9-E-cadherin. Micronucleated (M) cells, abnormal (A) cells and apoptotic (A) [(MAA)] cells were scored microscopically in the MAA assay following fluorescent staining of nuclei and cytoplasm. Chromosomal aberrations were analysed microscopically following Giemsa staining. The effect of z-VAD-fmk, known to inhibit apoptosis, on the prevention of cell death was investigated following treatment of HSC45-M2 cells with sorbitol as well as 213Bi-d9MAb. Activation of caspase 3 after incubation of HSC45-M2 cells with both sorbitol and 213Bi-d9MAb was analysed via Western blotting.


RESULTS
Following incubation of HSC45-M2 human gastric cancer cells expressing d9-E-cadherin with 213Bi-d9MAb the number of cells killed increased proportional to the applied activity concentration. Microscopically visible effects of alpha-irradiation of HSC45-M2 cells were formation of micronuclei and severe chromosomal aberrations. Preferential induction of these lesions with specific 213Bi-d9MAb compared with unspecific 213Bi-d8MAb (not targeting d9-E-cadherin) was not observed if the number of floating, i.e. unbound 213Bi-immunoconjugates per cell exceeded 2 x 10(4), most likely due to intense crossfire. In contrast to sorbitol-induced cell death, cell death triggered by 213Bi-immunoconjugates was independent of caspase 3 activation and could not be inhibited by z-VAD-fmk, known to suppress the apoptotic pathway.


CONCLUSIONS
213Bi-immunoconjugates seem to induce a mode of cell death different from apoptosis in HSC45-M2 cells.
Seidl
Christof
C
Department of Nuclear Medicine, Technische Universität München, Ismaninger Strasse 22, 81675, Munich, Germany. christof.seidl@lrz.tum.de
Schröck
Hedwig
H
Seidenschwang
Sabine
S
Beck
Roswitha
R
Schmid
Ernst
E
Abend
Michael
M
Becker
Karl-Friedrich
KF
Apostolidis
Christos
C
Nikula
Tuomo K
TK
Kremmer
Elisabeth
E
Schwaiger
Markus
M
Senekowitsch-Schmidtke
Reingard
R
D000512:Alpha Particles; D000911:Antibodies, Monoclonal / Q000008:administration & dosage*; D017209:Apoptosis / Q000528:radiation effects*; D001729:Bismuth / Q000008:administration & dosage*; D045744:Cell Line, Tumor; D002869:Chromosome Aberrations / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D048629:Micronuclei, Chromosome-Defective / Q000528:radiation effects; D011829:Radiation Dosage; D016499:Radioimmunotherapy / Q000379:methods; D011868:Radioisotopes / Q000008:administration & dosage*; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D013274:Stomach Neoplasms / Q000235:genetics / Q000473:pathology* / Q000532:radiotherapy*; D016896:Treatment Outcome
D000911:Antibodies, Monoclonal; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D001729:Bismuth