The objectives of this proposal are to develop chemical methods to label antibodies with Tc-99m that produce a high tumor to background activity ratio for the scintigraphic detection of tumors at an early time interval after injection.
The specific aims are to synthesize bifunctional dismide dithiol derivatives that make stable complexes with Tc-99m. The carbon backbone of the bifunctional chelators is derivatized with a carboxy group so that the total charge of their Tc-99m complexes is -2 at pH 7.4 which is ideal for the chelators to clear fast from the liver and to excrete through the kidneys. The carboxy group of the chelators is activated to the corresponding N-hydroxysuccinimide ester to conjugate the chelators to the amino groups of antibody or further derivatized to introduce chemical linkages containing one or three ester bonds which are quite stable in serum but readily cleavable in vivo by liver enzymes. The cleavage of the ester bond is expected to produce metabolites which clear fast from the liver and excrete through the kidneys. The other end of the chemical linkages contains an activated ester or an amino group. The activated ester is later reacted with antibody. The amino group is reacted with some of activated esters of polyglutamic acid and the remaining activated esters are later reacted with antibody to conjugate a large number of the chelators to antibody. The activated esters of polyglutamic acid are also used to conjugate peripheral vasodilators to antibody to increase the blood flow to tumors. The diamide dithiol derivatives are labeled with Tc-99m before and after the conjugation to antibody. The chemical parameters such as reducing agents, the pH values of the medium, buffer systems, the concentrations of the reactants and transchelating agents will be investigated to find an optimum condition to label the diamide dithiol moiety exclusively without labeling the low affinity site of antibody. The immunoreactivity of the labeled antibodies will be determined by affinity chromatography and cell-binding assays. The chemical stability of the label will be determined by HPLC, electrophoresis and TLC analyses of the serum incubates, urine samples and liver extracts. Analytical methods such as affinity chromatography and HPCL will be developed to purify immunoreactive antibodies from deactivated or irrelevant antibodies in order to improve the tumor targeting. The biodistribution of the labeled antibodies and the tumor imaging will be investigated using rats with affinity beads localized in the lungs and nude mice implanted with human tumor xenografts.
| John, C S; Schlemper, E O; Hosain, P et al. (1992) Synthesis, characterization and biodistribution of a new hexadentate aminethiol ligand labeled with Tc-99m. Int J Rad Appl Instrum B 19:269-74 |
