In vivo targeting of dead tumor cells in a murine tumor model using a monoclonal antibody specific for the La autoantigen.
OBJECTIVE
To investigate the potential of the La-specific monoclonal antibody (mAb) 3B9 as an in vivo tumor-targeting agent.


METHODS
The murine EL4 lymphoma cell line was used for in vitro studies and the EL4 model in which apoptosis was induced with cyclophosphamide and etoposide was used for in vivo studies. In vitro studies compared 3B9 binding in the EL4 cell with that in its counterpart primary cell type of the thymocyte. For in vivo studies, 3B9 was intrinsically or extrinsically labeled with carbon-14 or 1,4,7,10-tetra-azacylododecane-N,N',N'',N''''-tetraacetic acid-indium-111, respectively, and biodistribution of the radiotracers was investigated in EL4 tumor-bearing mice, which were treated or not with chemotherapy.


RESULTS
La-specific 3B9 mAb bound EL4 cells rather than thymocytes, and binding was detergent resistant. 3B9 binding to dead EL4 cells in vitro was specific, rapid, and saturable. Significantly, more 3B9 bound dead EL4 tumor explant cells after host mice were treated with chemotherapy, which suggested that DNA damage induced 3B9 binding. Tumor binding of 3B9 in vivo was antigen specific and increased significantly after chemotherapy. Tumor accumulation of 3B9 peaked at approximately 50% of the injected dose per gram of tumor 72 h after chemotherapy and correlated with increased tumor cell death. Tumor/organ ratios of 3B9 biodistribution, which included the tumor/blood ratio, exceeded unity 48 or more hours after chemotherapy.


CONCLUSIONS
La-specific mAb selectively targeted dead tumor cells in vivo, and targeting was augmented by cytotoxic chemotherapy. This novel cell death radioligand may be useful both for radioimmunoscintigraphy and radioimmunotherapy.
Al-Ejeh
Fares
F
Experimental Therapeutics Laboratory, Hanson Institute, School of Pharmacy and Medical Sciences, University of South Australia, and Department of Medical Oncology, Royal Adelaide Hospital, Australia.
Darby
Jocelyn M
JM
Pensa
Katherine
K
Diener
Kerrilyn R
KR
Hayball
John D
JD
Brown
Michael P
MP
D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001324:Autoantigens / Q000276:immunology*; D003131:Combined Modality Therapy; D003520:Cyclophosphamide / Q000494:pharmacology; D004249:DNA Damage / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D015151:Immunoblotting; D018796:Immunoconjugates; D007205:Indium Radioisotopes / Q000493:pharmacokinetics; D016399:Lymphoma, T-Cell / Q000276:immunology / Q000473:pathology / Q000628:therapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000276:immunology / Q000473:pathology / Q000628:therapy; D016499:Radioimmunotherapy; D012261:Ribonucleoproteins / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays; D000097585:SS-B Antigen
D000911:Antibodies, Monoclonal; D018906:Antineoplastic Agents, Alkylating; D000972:Antineoplastic Agents, Phytogenic; D001324:Autoantigens; D003520:Cyclophosphamide; D005047:Etoposide; D018796:Immunoconjugates; D007205:Indium Radioisotopes; D012261:Ribonucleoproteins; D000097585:SS-B Antigen