Comparison of blocked and non-blocked ricin-antibody immunotoxins against human gastric carcinoma and colorectal adenocarcinoma cell lines.
To avoid non-specific binding of intact ricin-antibody conjugates, we prepared a new blocked thioether-linked ricin-antibody IT, in which the galactose binding site of ricin had lost the ability to bind to galactosidic residues of Sepharose 6B gel. As carrier agent, the monoclonal antibody AR-3, which defines the CAR-3 tumour-associated antigenic determinant expressed selectively on different human carcinoma cell lines, was used. Purification of the new conjugate was performed in three sequential steps: (1) by HPLC gel filtration on TSK G3000SW to remove the unconjugated ricin: (2) by affinity chromatography on Affi-Gel Blue to separate the free antibody from the conjugate and (3) by affinity chromatography on Sepharose 6B to separate the galactose-binding IT from the non-binding moiety. The cytotoxicity of the blocked and non-blocked thioether-linked IT was compared with that of classical ricin-antibody IT conjugated via SPDP and that of ricin A chain IT. The comparison was made on two different target cell lines (KATO III human gastric carcinoma and HT-29 human colorectal carcinoma) versus two control cell lines (HL-60 promyelocytic pre-leukaemic and COLO38 melanoma). The results showed that the blocked thioether IT displayed a more selective toxicity to target cells than the non-blocked IT and was much more potent than the ricin A chain conjugate.
Cattel
L
L
Applied Medicinal Chemistry Institute, University of Turin, Italy.
Delprino
L
L
Brusa
P
P
Dosio
F
F
Comoglio
P M
PM
Prat
M
M
D000230:Adenocarcinoma / Q000628:therapy*; D002460:Cell Line; D015179:Colorectal Neoplasms / Q000628:therapy*; D006801:Humans; D000922:Immunotoxins / Q000627:therapeutic use*; D012276:Ricin / Q000627:therapeutic use*; D013274:Stomach Neoplasms / Q000628:therapy*; D013440:Sulfides / Q000494:pharmacology*
D000922:Immunotoxins; D013440:Sulfides; D012276:Ricin