Pyridine complexing agents and targeting immunoreagents useful in therapeutic and diagnostic compositions

A targeting radioactive immunoreagent comprising

• a metal radionuclide ion,
• a complexing agent, and
• an immunoreactive group covalently bonded to said complexing agent,
• said complexing agent having the structure ##STR39## wherein R is selected from hydrogen, alkyl, alkoxy, alkylthio, alkylamino, alkylformamido, aryl, aryloxy, heterocyclyl and a protein reactive group;
• each R.sup.1 is independently selected from hydrogen, alkyl, alkoxy, alkylthio, alkylamino, alkylformamido, aryl, aryloxy, heterocyclyl and a protein reactive group, wherein each alkyl and alkylene moiety contains 1 to 20 carbon atoms, each aryl or arylene moiety contains 6-20 carbon atoms, and each heterocyclyl group contains at least 1, 5 or 6 membered ring and a heteroatom selected from the group consisting of N, S, P and O;
• each R.sup.2 is independently selected from hydroxy, carboxy, hydroxyalkyl, carbonyliminodiacetic acid, methyleneiminodiacetic acid, methylenethioethyleneiminodiacetic acid, hydrazinylidenediacetic acid, and a salt of such acids, or the two R.sup.2 groups, taken together, represent the atoms necessary to complete a macrocyclic ring structure containing at least one heteroatom coordinating site and at least one alkylene group forming part of the ring structure;
• each R.sup.3 is independently selected from hydrogen, alkyl, alkoxy, alkylthio, alkylamino, alkylformamido, aryl, aryloxy, heterocyclyl and a protein reactive group;
• each R.sup.4 is independently selected from hydrogen and a protein reactive group;
• n is 0, 1, 2, 3, or 4;
• o is 0 or 1;
• m is 0 or 1;
• provided that at least one of n and m is 0 and at least one of R, R.sup.1, R.sup.3 and R.sup.4 is a protein reactive group.