Monoclonal antibody internalization by tumor cells: an experimental model for potential radioimmunotherapy applications.
The monoclonal IgM 3G5, which reacts with the surface membranes of rat insulinoma cells RINm5F, was purified by HPLC and labeled with 125I using Protag-125; bovine IgG (bIgG) was similarly radiolabeled, and used as a control. 125I-3G5 was incubated with RINm5F cells either at 4 degrees C or at 37 degrees C. 125I-3G5 bound onto RINm5F cells growing in Petri dishes remained approx. constant over 44 h when incubated at 4 degrees C, whereas at 37 degrees C radioactivity was released back in the medium starting at 3 h (plateau at approx. 20 h). At the end of incubation at 37 degrees C, activity in the medium included a high percentage of free 125I (15.69 vs 2.62% for bIgG, and 1% for 3G5 at 4 degrees C). In a cell suspension experiment, cell-bound 125I-3G5 also remained constant over a 24 h incubation at 4 degrees C, whereas at 37 degrees C it decreased to 37.5% of its initial value (64.1% at 4 h). Concomitant microautoradiography showed diffuse radioactive deposits within the RINm5F cells following incubation with 125I-3G5 (but not 125I-bIgG) at 37 degrees C. These results indicate that 3G5-IgM reacts with a surface antigen on the RINm5F cells, but is rapidly internalized by the cells: within the cells, this antibody undergoes some metabolic processing which results in the release of free 125I outside the cells.
Mariani
G
G
Harvard Medical School, Boston, Massachusetts.
Abbeele
A D
AD
Venkateshan
C N
CN
Kaldany
A
A
Ito
S
S
Adelstein
S J
SJ
Kassis
A I
AI
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000954:Antigens, Surface / Q000276:immunology*; D002460:Cell Line; D006801:Humans; D066298:In Vitro Techniques; D007340:Insulinoma / Q000276:immunology / Q000378:metabolism; D009374:Neoplasms, Experimental / Q000276:immunology* / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000276:immunology / Q000378:metabolism; D051381:Rats
D000911:Antibodies, Monoclonal; D000954:Antigens, Surface