Research Project
3180609
The overall objective of the proposed research is to develop methodology for radiolabeling proteins with metal radionuclides, specifically Technetium-99m for diagnostic purposes and Re-186 for radiotherapy. Meeting this general goal would result in the use of radiolabeled antibodies for detection, staging and treatment of tumors, radiolabeled fibrinogen or related proteins such as E1-fragment for non-invasive detection of clots, and many other potential applications where proteins or peptides localize in organs in a manner reflecting disease. We plan to begin with derivatives of the diamide dimercaptide (N2S2) chelating agents that form very stable complexes with technetium and rhenium, -SCH2CONHCH2-(R)NHCOCH2S(R=-CO2-,CH2CO2-), derivatize the carboxylate group which is not bound to the metal, separate the derivatized complex from reactants, and react the activated carboxylate group with the protein. The processing will eliminate excess ligand and reagents so that only tracer level quantities of the metal complex react with the proteins. Thus, the radiolabeling will result from well defined chemistry under very mild conditions with protein in molar excess of labeling complex. We will evaluate carboxyl activating groups such as substituted phenyl and hydroxyl amine esters to optimize protein reactivity and minimize hydrolytic instability. These studies will be initially carried out with glycine and Epsilon-aminocaproic acid as model amines. In order to adjust ionic charge modifications to the proteins, we will evaluate derivatives that result in amidinate connecting groups and alkylation as well. After optimizing conditions with model amino acids, incorporation of the activated esters into IgG as a model protein will be evaluated. Antibodies such as that to p97 melanoma antigen and its fragments will be labeled and biological parameters including tumor cell binding and uptake in tumor bearing mice evaluated. Following demonstration of biological efficacy, we will attach the ligand to the proteins using similar methods and develop technology to exchange Tc-99m/Re-188 from labile complexes into the protein attached ligand. This approach would provide greater potential convenience in utilization.
