The long range objectives of this proposal are to prepare radiolabeled antibodies that are tumor specific and organ non-specific for cancer diagnosis and therapy. To achieve these objectives an indirect approach will be used to radiolabel antibodies with 111-In, 99mTc, and 90-Y. The indirect approach consists of three steps. Bifunctional chelating agents are first synthesized. These chelators are then conjugated to antibodies. The chelators are radiolabeled with the metallic radionuclides either prior to or after the conjugation to antibodies. DTPA analogues will be used as bifunctional chelators because DTPA was reported to make stable complexes with various metallic ions. Once antibodies are radiolabeled through the above steps, the chemical stability of the radiolabeled antibodies will be tested by incubating the serum in vitro. The immunoreactivity will be determined by affinity binding assays. The labeled antibody will then be injected into mice or rats with tumor xenografts or pharmacokinetic studies and imaging. A successful radioimmunoimaging or therapy is mainly determined by a relative term, a tumor to background ratio. The maximum tumor uptake was reported to take place within 1 or 2 days postinjection of 111-In or 131I labeled antibodies and 6 hrs postinjection of the radiolabeled Fab fragments. However, successful radioimmunoimaging of tumor was achieved 2 to 7 days postinjection even though the time of maximum tumor concentration has passed and background activity persists. The limiting factor for 111-In and 99mTc labeled antibodies as successful tumor imaging agents was reported to be high activities in liver. spleen and kidney (especially for F(ab')2 and Fab fragments). The major aim of this proposal is to minimize the background activities. To achieve this goal, 1) we propose to develop reliable chemical methods to conjugate DTPA analogues to antibodies which result in minimum deactivation of immunoreactivity and optimum clearance from, blood, liver and kidney. We will place a spacer with a chemical bond, less stable than a peptide bond, between DTPA and antibody. 2) We will optimize conditions for radiolabeling the antibody DTPA conjugates with 111-In, 99mTc and 90-Y. 3) We will develop analytical methods to separate immunoreactive antibody from irrelevant or deactivated antibody. 4) We will investigate a system to amplify a tumor to background ratio. 5) We will investigate the effects of pharmacokinetic parameters such as antibody concentration, antigen concentration (or tumor size) and circulating antigen on the tumor to background ratio.
