Humanized M195 monoclonal antibody conjugated to recombinant gelonin: an anti-CD33 immunotoxin with antileukemic activity.
The recently characterized immunotoxin HuM195-gelonin consists of a humanized anti-CD33 monoclonal antibody conjugated to the single-chain plant toxin gelonin. Binding of the immunotoxin to hematopoietic cells that express the CD33 differentiation antigen has been demonstrated and results in cytotoxicity due to ribosomal inactivation by gelonin. Blast cells from most patients with acute myelogenous leukemia express CD33, whereas normal stem cells necessary for maintenance of hematopoiesis do not. We asked whether an immunoconjugate using recombinant gelonin rather than plant gelonin is toxic to acute myelogenous leukemia (AML) cell lines and primary AML blasts obtained from patients and exposed to the immunotoxin in vitro. The CD33pos cell lines HL60, OCI/AML2, and OCI/ AML5 showed decreased proliferation when exposed to immunotoxin for 24-72 h. The CD33neg cell line OCI/AML3 was relatively resistant to HuM195, and all cell lines were resistant to equimolar concentrations of unconjugated antibody and gelonin. Primary blast cultures from seven patients with AML had CD33 detectable on 75.7-99.8% of cells by flow cytometry, and all showed dose-dependent decreases in clonogenic cell survival during 24-h incubation with the immunotoxin. Cells selected for low CD33 expression by cell sorting or by prolonged incubation with immunotoxin could reexpress CD33 at baseline levels and remained sensitive to immunotoxin. We conclude that humanized M195 conjugated to recombinant gelonin has antileukemic activity and should be considered for clinical testing in Phase I trials.
Division of Medicine, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
L C
LC
Pagliaro
B
B
Liu
R
R
Munker
M
M
Andreeff
E J
EJ
Freireich
D A
DA
Scheinberg
M G
MG
Rosenblum
D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology*; D015703:Antigens, CD / Q000276:immunology*; D015214:Antigens, Differentiation, Myelomonocytic / Q000276:immunology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D016026:Bone Marrow Transplantation; D015925:Cryopreservation; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology*; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000473:pathology; D010940:Plant Proteins / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000494:pharmacology; D054789:Ribosome Inactivating Proteins, Type 1; D012680:Sensitivity and Specificity; D063268:Sialic Acid Binding Ig-like Lectin 3; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D000972:Antineoplastic Agents, Phytogenic; C571163:CD33 protein, human; D000922:Immunotoxins; D010940:Plant Proteins; D011994:Recombinant Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D063268:Sialic Acid Binding Ig-like Lectin 3; C025674:GEL protein, Gelonium multiflorum