Impact of interleukin‐2‐receptor‐targeted cytotoxins on a unique model of murine interleukin‐2‐receptor‐expressing malignancy

Abstract

DAB486IL-2 is a genetically engineered fusion protein consisting of a portion of diphtheria toxin fused to human IL-2. It is specifically cytotoxic for tumor cells which bear high-affinity IL-2 receptors (IL-2R). DAB389IL-2 is a similarly constructed hybrid protein which is smaller than DAB486IL-2 and is slightly more potent in vitro. We have developed a murine model of IL-2R-expressing malignancy to study the in vivo efficacy of these genetically engineered cytotoxins. Following intravenous administration of CP3 cells, C57BL/6 mice develop tumors which are lymphatic in distribution. When mice are injected i.v. with 10(6) CP3 cells, 90% of the animals show signs of observable tumor by day 10 to 20; death occurs in 50% of untreated animals by day 30. Intravenous treatment of mice with DAB486IL-2 (10 micrograms daily for 10 days), beginning 24 hr after administration of CP3 cells, increases mean survival time by approximately 50%. In comparative studies, DAB389IL-2 is more potent in vivo than DAB486IL-2, with approximately 90% of treated animals with no evidence of tumor at 60 days. The mechanism of action of tumor inhibition by DAB486IL-2 is specific, since treatment of animals which have IL-2R-negative EL4 tumors has not resulted in increased survival time. In addition, treatment of such tumors with DAglu53B486IL-2, a fusion protein which can bind to the IL-2R but is incapable of inhibiting protein synthesis, is ineffective.

Targeted Diphtheria Toxin-Based Therapy: A Review Article

“…To improve the short half-life of DT486IL-2, which is on the order of 5 min (Bacha et al, 1990), and to reduce the immunogenicity of the molecule, shorter DT fragments were investigated by removing the remaining hydrophobic sequences of its binding domain (Chaudhary et al, 1991; Kuzel et al, 1993). DAB389IL-2, which is a 58 kDa variant containing 97 fewer amino acids than its parent molecule, DAB486IL-2, showed a fivefold improvement in affinity for the IL-2R and an approximately 10-fold increase in cytotoxicity toward IL-2R-positive cancer cells (Bacha et al, 1991; Kiyokawa et al, 1991). Cell lines of hematopoietic malignancies expressing the high-affinity IL-2R displayed IC 50 s of 10 –12 to 10 –11 M. Cells exhibiting an intermediate-affinity receptor had IC 50 s on the order of 10 –10 to 10 –9 M, and cells with low-affinity IL-2R had IC 50 values greater than 10 –7 M (Bacha et al, 1991; Re et al, 1996).…”

“…DAB389IL-2, which is a 58 kDa variant containing 97 fewer amino acids than its parent molecule, DAB486IL-2, showed a fivefold improvement in affinity for the IL-2R and an approximately 10-fold increase in cytotoxicity toward IL-2R-positive cancer cells (Bacha et al, 1991; Kiyokawa et al, 1991). Cell lines of hematopoietic malignancies expressing the high-affinity IL-2R displayed IC 50 s of 10 –12 to 10 –11 M. Cells exhibiting an intermediate-affinity receptor had IC 50 s on the order of 10 –10 to 10 –9 M, and cells with low-affinity IL-2R had IC 50 values greater than 10 –7 M (Bacha et al, 1991; Re et al, 1996). DAB389IL-2 has also shown an improved half-life of 72 min (LeMaistre et al, 1998).…”

Novel Monoclonal Antibodies for the Treatment of Chronic Lymphocytic Leukemia

“…This agent targets malignancies expressing the medium and high affinity IL-2 receptors, composed of -subunit (CD25), -subunit (CD122) and -subunit (CD-132). Denileukin diftitox is toxic to IL-2R expressing cells in tissue culture and in murine model [126,127].…”

DAB389IL2 (ONTAK®) fusion protein therapy of chronic lymphocytic leukaemia

“…Cell extracts were purified on an anti-DT affinity column, denatured, reduced, separated by size exclusion high pressure liquid chromatography and refolded by dialysis. DAB 389 IL2 was selectively cytotoxic to IL-2R bearing cells in vitro and in animal models [42,43].…”