Immunotoxins ITs

Limitations to IT therapy include their immunogenicity and toxicity. Dose-limiting side-effects of IT therapy include hepatotoxicity and vascular leak syndrome. 

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The development of monoclonal antibodies (mAbs) has revolutionized cancer treatment, and several mAbs are today approved for clinical use. Treatment resistance is often a problem in mAbs-treatment where multiple treatment series are necessary [100]. Dmg response can be increased by binding mAbs to cytotoxic compounds, such as protein toxins, forming immunotoxins (ITs) [101]. The historical problems with first and second generation ITs are largely solved by the use of recombinant DNA technology where chimeric proteins consisting of the Fv-ffagment of an antibody and... 

Faguet, G.B. and Agee, J.F. (1997) The chronic lymphocytic leukemia antigen (cCLLa) as immunotherapy target assessment of LD50 and MTD of four ricin-based anti-cCLLa immunotoxins (ITs) in Balb/c mice. Leuk Lymphoma, 25, 531. 

Immunotoxins (ITs) are chimeric proteins consisting of an antibody linked to a toxin. The antibody confers specificity (ability to recognize and react with the target), whereas the toxin confers cytotoxicity (ability to kill the target) (1-3). ITs have been used in both mice and humans to eliminate tumor cells, autoimmune cells, and virus-infected cells (4-6). 

SMPT, succinimidyloxycarbonyl-a-methyl-a-(2-pyridyldithio)toluene, contains an NHS ester end and a pyridyl disulfide end similar to SPDP, but its hindered disulfide makes conjugates formed with this reagent more stable (Thorpe et al., 1987) (Chapter 5, Section 1.2). The reagent is especially useful in forming immunotoxin conjugates for in vivo administration (Chapter 21, Section 2.1). A water-soluble analog of this crosslinker containing an extended spacer arm is also commercially available as sulfo-LC-SMPT (Thermo Fisher). 

PDPH has been used in the preparation of immunotoxin conjugates (Zara et al., 1991). It has also been used to create a unique conjugate of nerve growth factor (NGF) with an... 

It has become apparent that the method of crosslinking can dramatically affect the activity of an immunotoxin in vivo. This is true not only with regard to possible direct blocking by the crosslinker of the enzymatic active site which is responsible for inactivation of ribosomes, but the chemistry of conjugation also is an important factor in proper binding and entry of the... 

A-chain immunotoxins, however, may not be quite as cytotoxic as conjugates formed from intact toxin molecules (Manske et al., 1989). In an alternative approach to A chain use, the intact toxin of two-subunit proteins is directly conjugated to a monoclonal without isolation of the A chain. Conjugation of an antibody with intact A-B chain toxins can be done without a cleavable linker, as long as the A chain can still separate from the B chain once it is internalized. Therefore, it is important to avoid intramolecular crosslinking during the conjugation process which can prevent release of the A-B complex. In addition, since the B chain... 

LC-SPDP (Chapter 5, Section 1.1) is an analog of SPDP containing a hexanoate spacer arm within its internal cross-bridge. The increased length of the extended crosslinker is important in some conjugations to avoid steric problems associated with closely linked macromolecules. However, for the preparation of immunotoxins, no advantages were observed for LC-SPDP over SPDP (Singh et al., 1993). 

However, since SMCC forms nonreversible thioether linkages with sulfhydryl groups, it only can be used in the preparation of immunotoxins if intact A-B toxins are employed in the conjugate. In such conjugates, the A chain still have the potential for reductive release from the B-chain subunit after cellular docking and internalization. Immunotoxins prepared with A-chain or single-subunit toxins will not display cytotoxicity if crosslinked with SMCC, since the crosslinker does not create cleavable disulfide bonds upon conjugation. 

It is widely accepted that cigarette smoking is linked to community acquired pneumonia and is one of the major risk factors for respiratory infections.39,40 Cigarette smoke is composed of two components, the vapor and particulate phase. The immunosuppressive effect of tobacco smoke is partly due to nicotine, which occurs in the particulate portion. Nicotine, as well as other immunotoxins in tobacco smoke, are thought to be respon-... 

The approval of fhese immunotoxin conjugates demonstrates rather remarkably how this truly targeted technological approach has already shown it can work in at least two clinical situations. 

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