title: Reduction of the nonspecific animal toxicity of anti-Tac(Fv)-PE38 by mutations in the framework regions of the Fv which lower the isoelectric point.
abstract: Anti-Tac(Fv)-PE38, also called LMB-2, is a very active recombinant immunotoxin that has produced eight responses, including a durable clinical complete remission in a recently completed phase I trial of leukemias and lymphomas. Dose escalation was limited by liver toxicity. We have noted that the Fv of anti-Tac has an isoelectric point (pI) of 10.2. We hypothesize that the overall positive charge on the Fv portion of anti-Tac(Fv)-PE38 contributes to nonspecific binding to liver cells and results in dose-limiting liver toxicity. We have used a mouse model to investigate the basis of this toxicity and found that lowering the pI of the Fv of anti-Tac from 10.2 to 6. 82 by selective mutation of surface residues causes a 3-fold decrease in animal toxicity and hepatic necrosis. This change in pI did not significantly alter the CD25 binding affinity, the cytotoxic activity toward target cells, or antitumor activity, resulting in a 3-fold improvement in the therapeutic index. If this decreased toxicity occurs in humans, it should greatly increase the clinical utility of this immunotoxin.
authors.affiliation: Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: M
authors.initials: M
authors.lastname: Onda
authors.forename: R J
authors.initials: RJ
authors.lastname: Kreitman
authors.forename: G
authors.initials: G
authors.lastname: Vasmatzis
authors.forename: B
authors.initials: B
authors.lastname: Lee
authors.forename: I
authors.initials: I
authors.lastname: Pastan
mesh_terms: D036002:ADP Ribose Transferases; D000818:Animals; D000911:Antibodies, Monoclonal; D000912:Antibodies, Neoplasm / Q000235:genetics / Q000633:toxicity*; D000970:Antineoplastic Agents / Q000633:toxicity; D001427:Bacterial Toxins; D004305:Dose-Response Relationship, Drug; D005098:Exotoxins / Q000235:genetics / Q000633:toxicity*; D005260:Female; D007128:Immunoglobulin Fragments / Q000235:genetics / Q000633:toxicity*; D000922:Immunotoxins / Q000235:genetics / Q000633:toxicity*; D007526:Isoelectric Point; D008099:Liver / Q000187:drug effects; D051379:Mice; D008819:Mice, Nude; D009154:Mutation; D009374:Neoplasms, Experimental / Q000188:drug therapy; D011994:Recombinant Proteins / Q000633:toxicity; D013329:Structure-Activity Relationship; D018675:Toxicity Tests; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D000911:Antibodies, Monoclonal; D000912:Antibodies, Neoplasm; D000970:Antineoplastic Agents; D001427:Bacterial Toxins; D005098:Exotoxins; D007128:Immunoglobulin Fragments; D000922:Immunotoxins; D011994:Recombinant Proteins; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C077707:B3(Fv)-PE38KDEL recombinant immunotoxin; C055966:immunoglobulin Fv