Radiolabeled fusion toxins for cancer therapy

DETAILED DESCRIPTION The present invention describes the synthesis and purification of a new class of compounds known as radiolabeled fusion toxins (RFT), in which both toxin and radionuclide tags are contained on the same growth factor (murine granulocyte macrophage colony stimulating factor (mGM-CSF) or murine interleukin-4 (mIL-4)), that are tested for binding reactivity, protein synthesis inhibition and cytotoxicity in in vitro studies with mouse and human colon cancer cell lines and for in vivo binding and therapy in a syngeneic colon cancer model and in athymic nude mice bearing human colon cancer xenografts.
The killing of cells by radiolabeled antibodies occurs at a distance from the antibody binding site, and is a function of the energy and type of emission of the radionuclide.
The cytotoxic activity of recombinant fusion toxins occurs after internalization of toxin into the cell, enzymatic inactivation of cellular ribosomes, and termination of protein synthesis.
Radiolabeling the entire recombinant fusion toxin molecule produces a radiolabeled fusion toxin through the synthesis of a hybrid molecule that retains the cytotoxic advantages of both the radionuclide and the fusion toxin.
RFT are capable of killing tumor cells by two different mechanisms, inhibition of protein synthesis and DNA damage.
The addition of the radionuclide to the fusion toxin allows for the killing of cells to which the fusion toxin does not bind or internalize.
Despite the efficacy of IT, genetically engineered recombinant fusion toxins have several advantages over IT which include: 1) large amounts of recombinant fusion toxins can be produced easily and at a lower cost by E.
coli expression systems and purified to near homogeneity by standard column chromatography in comparison to most IT which are heterogeneous products; 2) the protein product and its binding characteristics are uniform and are not affected by chemical derivatization; 3) recombinant fusion toxins are more easily modified by mutating the genes that encode them to increase chemical stability; 4) recombinant fusion toxins appear to be more effective in producing tumor regressions in animal models; and 5) they have a lower molecular weight leading to a shorter plasma half-life and better tumor penetration