IMMUNOTOXINS: A MAGIC BULLET IN CANCER THERAPY

Immunotoxins are composed of a protein toxin connected to a binding ligand such as an antibody or growth factor. These molecules bind to surface antigens and kill cells by catalytic inhibition of protein synthesis within the cell cytosol. Immunotoxins have evolved with time and technology and recently, third generation immunotoxins are made by recombinant DNA techniques. The majority of these immunotoxins targeted antigens selectively expressed on cancer cells. It has been hoped that these agents could cause regression of malignant disease in patients. The studies carried over the plasma clearance of antibody-ricin-A-chain immunotoxins have been shown that after intravenous injection in animals of different species, immunotoxins are rapidly eliminated from the bloodstream. It is due to the mannose residues on the rich A-chain moiety which are specifically recognized by liver cells. The coadministration of yeast mannan with immunotoxin enhances the level of active immunotoxin in circulation by inhibition of liver uptake, which drastically improves the anti-cancer efficacy of immunotoxin in vivo. Immunotoxins can be given in combination with other anticancer therapies to manage tumour penetration. Immunotoxins also firmly increase the viral mortality when used along with effective anti-retroviral drugs. Besides many advantages, the development of many immunotoxins for cancer therapy has still many challenges like immunogenicity, unwanted toxicity, and difficulty in production, limited half-life, and resistance. Key words: Immunotoxins, antitumor, rDNA technique, ricin-A-chain immunotoxins, antiretroviral