Cytotoxicity of IL6-PE40 and derivatives on tumor cells expressing a range of interleukin 6 receptor levels

In vitro and in vivo antitumor effects of the recombinant immunotoxin IL6(T23)-PE38KDEL in multiple myeloma

IL6(T23)-PE38KDEL is a chimeric molecule composed of interleukin 6 (IL6), missing the N-terminal 23 amino acids, and fused to a truncated mutant form of Pseudomonas exotoxin (PE38KDEL). The aim of this study was to evaluate this recombinant immunotoxin in terms of its specific cytotoxicity to IL6R-overexpressing multiple myeloma (MM) cells in vitro, as well as its antitumor effects and side effects in vivo. IL6(T23)-PE38KDEL was expressed in Escherichia coli, refolded and purified from inclusion bodies. The purified IL6(T23)-PE38KDEL was found to be selectively cytotoxic to IL6 receptor-positive tumor cells in vitro. IC(50) values of IL6(T23)-PE38KDEL were evaluated by MTS assay. Toxicity and maximum-tolerated dose of IL6(T23)-PE38KDEL were determined in mice. The antitumor activity of IL6(T23)-PE38KDEL was evaluated in mice with MM through intravenous injection and interventional therapy. Intravenous administration of IL6(T23)-PE38KDEL caused a significantly increased survival time in treated mice, and exhibited dose- and time-dependent antitumor effects against MM mice. Moreover, complete tumor regression was observed in 30 and 80% of mice treated intravenously and intraperitoneally, respectively, with 0.4 mg/kg/day for 10 days. These results demonstrated that the recombinant immunotoxin IL6(T23)-PE38KDEL kills IL6R-overexpressing cancer cells, and causes significant tumor regression.

Preparation of a Claudin-Targeting Molecule Using a C-Terminal Fragment ofClostridium perfringensEnterotoxin

Although most malignant tumors are epithelia-derived carcinomas, methods for specific and effective delivery of antitumor agents to carcinomas have not been developed. Recent reports indicate that epithelia overexpress claudin-3 and -4, which are integral membrane proteins of epithelial tight junctions. This suggests that claudins can be targeted for tumor therapy, but there is not currently a method for delivering drugs to claudin-expressing cells. In the present study, we evaluated whether a potent claudin-4-binding C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE) would allow targeting to claudin-4-expressing cells. We fused C-CPE to the protein synthesis inhibitory factor (PSIF), which lacks the cell binding domain of Pseudomonas exotoxin. This fusion protein, C-CPE-PSIF, was cytotoxic to MCF-7 human breast cancer cells, which express endogenous claudin-4, but it was not toxic to mouse fibroblast L cells, which lack endogenous claudin-4. The cytotoxicity of C-CPE-PSIF was attenuated by pretreating the MCF-7 cells with C-CPE but not bovine serum albumin. Also, deletion of the claudin-4-binding region of C-CPE reduced the cytotoxicity of C-CPE-PSIF. Finally, we found that C-CPE-PSIF is toxic to L cells expressing claudin-4 but not to normal L cells or cells expressing claudin-1, -2, or -5. These results indicate that use of the C-CPE peptide may provide a novel way to target drugs to claudin-expressing cells.

Interleukin-6 and new strategies for the treatment of cancer, hyperproliferative diseases and paraneoplastic syndromes

Interleukin-6 (IL-6) is a pleiomorphic cytokine whose growth factor properties play an important role in the development and progression of many types of cancer. IL-6 is produced in response to a variety of stimuli, and is required for the development of T and B lymphocytes to effector cells. In certain neoplasias, such as multiple myeloma, IL-6 is both produced and required for survival by the cancer cell itself. In other neoplasias, IL-6 may come from tissue surrounding the tumour. Thus, therapeutic strategies aimed at inhibiting the production, expression or action of IL-6 would be quite beneficial in the treatment of cancer. Moreover, IL-6 is a pathophysiological factor in several hyperproliferative diseases and the paraneoplastic syndromes that often accompany cancer, such as cachexia and osteoporosis; thus, anti-IL-6 therapy would be useful in treating these entities as well. This expert opinion acquaints the reader with IL-6, its physiological responses, the cancer types with which it is associated, and discusses the current state of therapy aimed at inhibiting it.

Recombinant toxins in haematologic malignancies and solid tumours

Recombinant toxins constitute a new modality for the treatment of cancer, since they target cells displaying specific surface-receptors or antigens. They are fusion proteins, which contain toxin and ligand regions, and are produced in Escherichia coli. The ligand may be a growth factor or a fragment of an antibody, and the toxin is usually one of the two bacterial toxins: Pseudomonas exotoxin and diphtheria toxin. Compared to the earlier generation chemical conjugates of ligands and toxins, recombinant toxins have many advantages, including homogeneity with respect to the connection between the ligand and toxin, ease and yield of production and small size. A variety of chemotherapy-resistant haematologic and solid tumours have been targeted with recombinant toxins, and clinical trials with many of them have recently demonstrated their effectiveness. Moreover, their unwanted toxic effects are different from those of most chemotherapeutic agents, supporting the expectation that they can be combined with existing modalities to improve the clinical resources available to treat cancer in humans.

Riboflavin-mediated delivery of a macromolecule into cultured human cells

Cell surface receptors for the vitamins folic acid and biotin have been previously reported to mediate the endocytosis of vitamin-conjugated macromolecules into cultured cells. To evaluate whether a similar uptake pathway for riboflavin-conjugated macromolecules might exist, riboflavin was covalently linked to bovine serum albumin (BSA) via the vitamin's ribityl side chain, and uptake of the protein by cultured human cells was examined. Whereas unconjugated BSA was not internalized by KB, A549, SK-LU-1 or SK-OV cells, riboflavin-conjugated BSA was readily internalized (>106 molecules/cell). Analysis of the uptake pathway revealed that the riboflavin-BSA conjugate likely docks on cells at a carrier/transport protein that is distinct from the uptake pathway for free riboflavin and then enters via normal membrane cycling. Evidence for this contention is: (i) the internalized conjugate accumulates in endosomal compartments, (ii) uptake into cells is halted at temperatures near 0 degreesC where membrane trafficking is abrogated, (iii) cell association is inhibited by unlabeled riboflavin-BSA, but not by free riboflavin, and (iv) cellular uptake of [3H]riboflavin is only partially inhibited by riboflavin-BSA. Regardless of the pathway of internalization, these data demonstrate that riboflavin conjugation can facilitate protein entry into human cells in culture.

Immunotoxins for targeted cancer therapy

Immunotoxins constitute a new modality for the treatment of cancer, since they target cells displaying specific surface-receptors or antigens. Immunotoxins contain a ligand such as a growth factor, monoclonal antibody, or fragment of an antibody which is connected to a protein toxin. After the ligand subunit binds to the surface of the target cell, the molecule internalizes and the toxin kills the cell. Bacterial toxins which have been targeted to cancer cells include Pseudomonas exotoxin and diphtheria toxin, which are well suited to forming recombinant single-chain or double-chain fusion toxins. Plant toxins include ricin, abrin, pokeweed antiviral protein, saporin and gelonin, and have generally been connected to ligands by disulfide-bond chemistry. Immunotoxins have been produced to target hematologic malignancies and solid tumors via a wide variety of growth factor receptors and antigens. Challenges facing the clinical application of immunotoxins are discussed.

Pseudomonas exotoxin and recombinant immunotoxins derived from it

Pseudomonas exotoxin (PE) is a bacterial toxin that kills mammalian cells by gaining entry to the cytosol and inactivating protein synthesis. The toxin binds and enters cells via the alpha 2-macroglobulin receptors. Within cells, the toxin is processed in several steps to produce an enzymatically active 37-kDa C-terminal fragment which translocates to the cytosol and ADP-ribosylates elongation factor 2. Because PE is a very potent toxin, derivatives of it have been produced which, when joined to various binding ligands, are capable of killing specific target cells. It is hoped that this strategy will lead to the development of effective therapeutic agents for the treatment of human diseases such as cancer, AIDS, and various immunologic disorders.

Targeting growth factor receptors with fusion toxins

Recombinant toxins which bind to growth factor receptors have been prepared and used to kill cells responsible for malignant or autoimmune disease. Our strategy has been to genetically fuse ligands to different forms of Pseudomonas exotoxin which due to mutations or deletions do not bind to normal cells. The resulting recombinant chimeric toxins, in concentrations often less than 1 ng/ml, selectively kill cells expressing the appropriate growth factor receptor. The ligand may be a growth factor, such as transforming growth factor alpha (TGF alpha), interleukin 6 (IL6) or interleukin 2 (IL2), or single chain antigen binding proteins, such as the variable heavy and light regions of the monoclonal antibody anti-Tac. These chimeric toxins kill not only established cell lines but also fresh tumor cells from patients and display anti-tumor activity toward human malignant tumors in nude mice. While clinical trials are beginning with some of these agents, work continues to improve the effectiveness of recombinant chimeric toxins, and to widen the scope of disorders which might be treated by this approach.

Recombinant toxins for cancer treatment

Recombinant toxins target cell surface receptors and antigens on tumor cells. They kill by mechanisms different from conventional chemotherapy, so that cross resistance to conventional chemotherapeutic agents should not be a problem. Furthermore, they are not mutagens and should not induce secondary malignancies or accelerate progression of benign malignancies. They can be mass-produced cheaply in bacteria as homogeneous proteins. Either growth factor-toxin fusions or antibody-toxin fusions can be chosen, depending on the cellular target.