Interleukin 2 receptor-targeted cytotoxicity. Interleukin 2 receptor-mediated action of a diphtheria toxin-related interleukin 2 fusion protein.

Abstract

Over the past decade there has been considerable interest in the assembly of conjugate toxin molecules whose action is directed toward specific target cells. A wide variety of cell surface-directed ligands (e.g., mAbs, lectins, polypeptide hormones, growth factors) have been coupled through disulfide linkage to nontoxic fragments of plant and/or microbial toxins (reviewed in 1, 2) . In particular, mAbs have been used to direct the cytotoxic action of ricin, both the A chain and intact toxin, and fragments of diphtheria toxin to specific antigenbearing cells . This class of conjugate toxins are widely known as immunotoxins, and have been the subject of several recent reviews (3-6).In contrast to chemical cross-linking to form conjugate toxins, our approach to the development of targeted toxins has involved genetic assembly of chimeric toxin genes that are expressed from recombinant strains of Escherichia coli K12 (6, 7). We have selected targeting ligands whose cell surface receptors are known to undergo obligatory receptor-mediated endocytosis in the design of chimeric toxins that are composed of portions of diphtheria toxin linked to peptide hormones and/or growth factors. We have used rDNA methodologies to construct fusion genes in which that portion of the diphtheria tox gene which encodes the receptor-binding domain has been genetically replaced with the cDNA encoding the ligand of choice . Murphy et al. (6) and Williams et al. (7) have described the genetic construction of fusion toxins in which a-melanocytestimulating hormone (a-MSH)' and IL-2 have served as the receptor-binding component of the hybrid . Since both peptides have been shown to bind to surface receptors and are internalized by receptor-mediated endocytosis (8-10), we reasoned that both a-MSH toxin and IL-2 toxin should be selectively toxic for a-MSH and high affinity IL-2-R-bearing cells, respectively . Indeed, the action

Immunomodulatory effects of RXR rexinoids: modulation of high-affinity IL-2R expression enhances susceptibility to denileukin diftitox

“…22,23 The susceptibility of both normal and neoplastic cells to denileukin diftitox-induced cytotoxicity is dependent on the expression of the high-affinity IL-2R, consisting of the p55 (␣), p75 (␤), and p64 (␥) subunits. [24][25][26] The inhibitory concentration of 50% (IC 50 ) of high-affinity IL-2R-expressing cells is 10 Ϫ12 M, whereas cells expressing intermediate-affinity receptors (p75, p64) are intoxicated at an IC 50 of 10 Ϫ10 M. 27 Cells expressing only p55 are relatively resistant (IC 50 of 10 Ϫ8 M). Expression of high-affinity IL-2R is restricted to activated T lymphocytes, activated B lymphocytes, and activated macrophages, whereas intermediate-affinity receptors are found on natural killer cells and resting T cells.…”

Dendritic Cell Vaccination in Combination with Anti-CD25 Monoclonal Antibody Treatment: A Phase I/II Study in Metastatic Melanoma Patients

“…Denileukin diftitox (Ontak) is a recombinant IL-2/diphtheria toxin conjugate that is designed to direct the cytotoxic action of diphtheria toxin to cells that express the IL-2R (26). Thus far, clinical studies in which Ontak was administered to melanoma patients showed that it may reduce the number of circulating Tregs and cause regression of melanoma metastases (27)(28)(29).…”

Inability of a Fusion Protein of IL-2 and Diphtheria Toxin (Denileukin Diftitox, DAB389IL-2, ONTAK) to Eliminate Regulatory T Lymphocytes in Patients With Melanoma

“…It encoded a 68-kDa protein containing the first 486 amino acids of DT and the full-length sequence for IL-2. 18,19 It was extensively studied in the late 1980s and early 1990s and had modest success in phase I and II clinical trials against various lymphoid malignancies (intermediate-and low-grade non-Hodgkin lymphoma, Hodgkin disease, cutaneous T cell leukemia (CTCL)). 20 However, an exceptionally short in vivo half-life (related in large part to its hydrophobicity and tendency to aggregate in solution) prompted efforts to improve on the original design.…”