Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0406810 (NAME)
 13,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A blocked immunotoxin, consisting of ricin and AR-3 monoclonal antibody joined by a short thioether bond, was previously synthesized. This conjugate had lost the ability to bind the galactosidic residues of Sepharose 6B, probably because of the steric restraint of the antibody molecule on the ricin B chain. In in vitro assays immunotoxin was active only on cells expressing the corresponding AR-3 epitope. The in vivo activity of our blocked immunotoxin was assessed by injecting it directly into the peritoneal cavity of tumour-bearing nude mice. The animals were i.p. grafted with the HT-29 cell line, which was derived from a human colorectal adenocarcinoma expressing the antigen CAR-3, against which the AR-3 monoclonal antibody is directed. The best protocol tested, to arrive at the optimal regimen for the i.p. blocked immunotoxin therapy, required the administration of the immunotoxin (2 micrograms) on days 4 and 6 after the graft. The mice were killed on different subsequent days to determine the therapeutic effects. Histological sections of the different organs were prepared and stained with haematoxylin/eosin and were also examined by an immunocytochemical method with AR-3 monoclonal antibody to confirm the presence of the relating antigen on the tumour cell surface. The blocked immunotoxin substantially suppressed tumour growth of the grafted HT-29 cells, without showing any undesirable ricin toxicity. Most importantly, established transplanted HT-29 tumour cells treated with blocked immunotoxin almost completely regressed, while under the same conditions the not blocked immunotoxin, an irrelevant immunotoxin, ricin, and the AR-3 alone failed to inhibit tumour growth.
 ...
PMID:Blocked and not blocked whole-ricin-antibody immunotoxins: intraperitoneal therapy of human tumour xenografted in nude mice. 265 70

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.
 ...
PMID:Comparison of blocked and non-blocked ricin-antibody immunotoxins against human gastric carcinoma and colorectal adenocarcinoma cell lines. 326 8

Immunotoxins have been extensively studied for the treatment of neoplasias; their intracavitary administration could be useful for the therapy of tumors confined to the pleural or peritoneum spaces. To study the feasibility of this "locoregional" treatment, a pharmacokinetic study of immunotoxins delivery is necessary. Ricin, a plant toxin extracted from the seeds of Ricinus communis, has often been used in immunoconjugates for its high activity; nevertheless, appropriate strategies have been necessary to limit the aspecific toxicity. We previously prepared a AR-3-ricin immunotoxin lacking the ability to bind galactosidic cell surface residues, a so-called sterically blocked immunotoxin. The monoclonal antibody AR-3, an IgG1 specific to the CAR-3 antigen, was able to recognize human colorectal adenocarcinomas. Preclinical trials in nude mice, intraperitoneally grafted with the target neoplasia, showed that this immunotoxin suppressed tumor growth without showing any undesirable ricin toxicity. In the present work we report the pharmacokinetic properties of this immunotoxin, showing the in vivo stability and a relatively long blood survival. With a biodistribution study in tumor-bearing mice, we demonstrate that in tumor-invaded tissues, the concentration of the specific AR-3-ricin immunotoxin was higher and progressively increased in a multiple-dose regimen. In contrast, an irrelevant immunotoxin behaved differently because it did not show specific tumor uptake. Moreover the pharmacokinetic data reported in this work improve the potential for "locoregional" treatment of malignancy with blocked immunotoxins.
 ...
PMID:Pharmacokinetics of an antibody-ricin conjugate administered intraperitoneally to mice. 804 6