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Introduction to Chemical Construction of Immunotoxins and Their Immunopathol Persa. 2016;2(1):e02 Mini-Review Immunopathologia Persa http www.immunopathol.comm Introduction to chemical construction of immunotoxins and their applications in the treatment of diseases Seyed Seifollah Beladi-Mousavi1, Khadije Hajibabaei2, Azam Hamledari3, Mohammad-Reza Tamadon4, Mohammad-Reza Ardalan5* 1Chronic Renal Failure Research Center, Ahvaz Junishapur University of Medical Sciences, Ahvaz, Iran 2Department of Chemistry, Faculty of Sciences, Najafabad Branch, Islamic Azad University, Najafabad, Iran 3Hourtash Food Laboratory, Najafabad, Isfahan, Iran 4Department of Nephrology, Semnan University of Medical Sciences, Semnan, Iran 5Chronic Kidney Disease Research Center, Tabriz University of Medical Sciences, Tabriz, Iran Correspondence to Abstract Prof. Mohammad-Reza Ardalan; Email: [email protected] Immunotoxins are mostly contain a monoclonal antibody part linked to a toxin, generally of bacterial or plant origin. The antibody gives specificity (ability to identify and react with the Received 28 November 2015 target), while the toxin gives cytotoxicity (ability to kill the target). In this paper, we will explain Accepted 26 December 2015 about the different parts of immunotoxins, linkage methods of the antibody to the toxin and Published online 13 January 2016 their application in treatment of cancer and other diseases. This review will help physicians better inform patients about the potential benefits of these experimental treatments. Keywords: Immunotoxins, Monoclonal antibody, Toxin, Chemical cross linkers, Cancer Introduction Key point Citation: Beladi- Immunotoxins are mostly contain a mono- Mousavi SS, Hajibabaei clonal antibody part linked to a toxin, gener- Immunotoxins are mostly contain a K, Hamledari A, monoclonal antibody part linked to a ally of bacterial or plant origin. The antibody Tamadon MR, Ardalan toxin, generally of bacterial or plant origin. MR. Introduction to gives specificity (ability to identify and react They are made by chemically conjugating chemical construction with the target), while the toxin gives cyto- an antibody to a toxin and mostly of immunotoxins and toxicity (ability to kill the target) (1-3). It has their applications in the immunotoxins are produced to kill cancer treatment of diseases. been used in both mice and humans to root cells and cancer treatment. Immunopathol Persa. out autoimmune cells, tumor cells, and virus 2016;2(1):e02. infected cells (4). (6,7). Growth factors and cytokines that Materials and Methods are immunologic proteins and smaller than For this mini-review, we used a diversity MoAbs, have also been genetically fused and of sources by searching through PubMed/ chemically conjugated to protein toxins (8). Medline, Scopus, EMBASE, EBSCO and di- Mechanism of action of immunotoxin is rectory of open access journals (DOAJ). The shown in Figure 1. The MoAb-moiety first search was conducted, using combination of binds specifically to its antigen expressed on the following key words and or their equiva- target cells, following which the entire anti- lents; immunotoxins, monoclonal antibody, gen-IT complex is internalized. Once inside toxin, chemical cross linkers and cancers. the cell, the bond between the MoAb and toxin is broken, thereby releasing free toxin Immunotoxins and their mechanism of into the cytoplasm. The toxin kill cells by action preventing protein synthesis, a distinctive The first immunotoxins were prepared in mechanism of action that is toxic to both the initial 1980s when monoclonal antibod- dividing and non-dividing cells. While, the ies (MoAbs) reacting with cancer cells be- toxin-moiety is unable to enter the cell au- came widely available (5). tonomously, and while, it is inactive outside Immunotoxins are made by chemically the cell, hence, it is only hazardous for cells, conjugating an antibody to a protein tox- which are capable to bind and internalizing in, devoid of its natural binding domain the MoAb. The action mechanism of im- Copyright © 2016 The Author(s); Published by Nickan Research Institute. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Beladi-Mousavi SS et al same epitope (the part of an antigen that is identified by the antibody) (11). The Moab’s binding specificity is the major property determining its suitability as atoxin transporter. Ideally, the MoAb binds an antigen that is expressed solely on thosecells that are to be eliminated. Mechanism of action as is that moAb recognize and bind to specific proteins created by cells that is epitope. Each monoclonal antibody recognizes one specific protein. Some moAb have attached to drugs, toxin or radiation. The MoAb capable finds the cancer cells and sends the drug, toxin or radiation directly to them. These are named Figure 1. Mechanism of action. conjugated MoAb. They work in diverse ways depending on the protein they are targeting. Thus different moAb have to be prepared to target different types of cancer. Various kinds of moAb are now available to treat cancer. Some are licensed to treat specific types of cancer. Some newer types are in clinical trials yet. Various kinds of moAb lead to different side effects. It can take a long time to progress this type of treatment because design moAb can be very complicated (12) Figure 2. Covalent bonds cross-linking antibody to toxin. Toxins munotoxin depends on the type of toxin. Pseudomonas The toxins most commonly applied for the construction of exotoxin (PE) and diphtheria toxin (DT) deactivate elon- immunotoxins are derived from either bacteria or plants gation factor-2 (EF-2), whereas plant toxins for example and have in common that they catalytically and irrevers- ricin toxin A (RTA) and ribosome-inactivating protein ibly disrupt protein synthesis, typically at picomolar con- (RIP) deactivate 28S RNA. In either case, the intoxicated centration. The bacterial toxins most extensively studied cell is unable to synthesize proteins which results in cell so far are PE and DT. The plant toxins, also referred to death (9). as ribosome inhibitory proteins (RIP), can be divided As mentioned, cells instead of MoAbs, or its fragments can into holotoxins (type II RIP), including abrin, mistletoe also be under attack by cytokines which receptor is over lectin, modeccin, and ricin, and hemitoxins (type I RIP), expressed on the target cell. As an alternative to chemical such as gelonin, pokeweed antiviral protein (PAP), and linkage, MoAb-fragments or cytokines can also be genet- saporin (13). ically spliced to a toxin, generating a recombinant immu- notoxin. The linkage of the antibody to the toxin Conventional immunotoxins are produced by linking Monoclonal antibody part a toxin and cell binding ligand using one of two gener- Antibodies are proteins constructed by the B lymphocytes al methods, chemical or genetic. Two types of chemical of the immune system in response to antigens as foreign bonds can be used to production of immunotoxins; thio- factor. According to their chemical and physical proper- ether bonds (14) and disulfide bonds (15) (Figure 2). Di- ties, antibodies can be divided in IgM, IgG, IgA, IgE, an sulfide bonds are sensitive to reduction in the target cells IgD classes, each having its own function in the host de- cytoplasm there with releasing the toxin so that it can keep fense system. IgG is the antibody class most widely ex- its inhibitory activity only in the cells binding the antibody ploited for clinical use. Antibodies can be considered as moiety (16). Disulfide bonds has been used to make im- bifunctional molecules. Bifunctional antibodies have a munotoxins containing single-chain plant toxins (poke- variety of potential uses. For example, they have also been weed antiviral protein [PAP], ricin A chain (RTA), saporin, used to deliver immunotoxins. In this case, one arm of the gelonin, and so forth). Because mammalian enzymes can- bifunctional antibody is connected to the cell-surface an- not break thioether bonds, thioether-linked conjugates of tigen on the target cell, while the other is connected to a toxins and antibodies are not cytotoxic to target cells (17). toxin. The cell are first exposed to bifunctional antibody But there are two exceptions. The first exception is an im- and then toxin. This work leads to immunotoxin did not munotoxin with the intact ricin toxin (RT). RT is formed lose toxic activity and keeps by internalized antibody toxin of two polypeptide chains linked by a disulfide bond. If complex (10). the antibody is bound to the toxin through the RTB, in MoAbs are a type of monospecific and bifunctional anti- the target cell cytosol the toxic chain can be released by re- bodies which are made of identical immune cells that are duction of the interchain disulfide bond (18). The second all clones of a unique parent cell, the antibodies of mono- exception is an immunotoxin produced with PE. it can be clonal have monovalent affinity, in that, they attach to the joined to antibody by a thioether link, since this toxin has 2 Immunopathologia Persa Volume 2, Issue 1, January 2016 Immunotoxins for treatment of diseases a protease-sensitive peptide bond that is cleaved intracel- efits of these experimental treatments. lularly to prepare a toxic type bound to the remains of the molecule by a disulfide bond (Figure 2). Authors’ contribution KH and AH prepared primary draft. SSBM, MRA and MRT edited the manuscript. All authors read and signed the final manuscript. Used of immunotoxins in treatment of diseases Mostly, immunotoxins are produced to kill cancer cells Conflicts of interest and cancer treatment. Other applications for immunotox- The authors declared no competing interests. ins is immune regulation and the treatment of parasitic or Ethical considerations viral diseases. Ethical issues (including plagiarism, data fabrication, double publi- cation) have been completely observed by the authors. Used in the treatment of hairy cell leukemia Hairy cell leukemia (HCL) is a seldom seen cancer of cells Funding/Support identified as B-lymphocytes.
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