Tumour targeting with indium and silver labelled macrocycles

Abstract

Monoclonal antibodies which recognise tumour associated antigens provide a means of targeting radionuclides selectively to tumour cells. Work has been directed towards the synthesis of functionalised macrocyclic ligands to bind indium(III) [(^111)In:- γ-emitter] and gallium(III) [(^67)Ga:- γ-emitter] for use in radioimmunoscintigraphy and silver(I) [(^111)Ag:- β-emitter] for use in radioimmunotherapy. Macrocyclic ligands have been selected to bind the respective radionuclides rapidly, under mild conditions, to form complexes which are kinetically inert in vivo. Four tribasic hexadentate macrocyclic ligands (9, 10, 11 and 12-membered rings) have been synthesised to bind indium and gallium. Comparison of the rate of (^111)In uptake under mild conditions at low concentration (10-100 µM) revealed that the nine-membered triaza-triacid was the most effective. The X-ray crystal structures of the indium and gallium complexes of the [9]-N(_3)-triacid have been determined. A C-functionalised derivative of the [9]-N(_3)-triacid has been synthesised by two routes, both starting from (2S)-Lysine. The syntheses of two N-functionalised derivatives of the [9]-N(_3)-triacid are also described. Antibody linkage has been effected (in collaborative work with Celltech Ltd.) by reacting the functionalised macrocycle with a heterobifunctional linker molecule (maleimide ester) followed by incubation with the antibody (previously treated with 2-iminothiolane).Three new nitrogen and sulphur donor macrocyclic ligands have been synthesised to bind silver(I) and the 1:1 silver complexes have been isolated as crystalline solids and characterised by FAB mass spectrometry and (^1)H nmr. Silver(I) complexes of two of the ligands have been characterised by X-ray crystallographic analysis. The stability constants (log K(_s), MeOH) for the silver(1) complexes of the[18]-membered N(_4)S(_2) and N(_4)S(_2)Me(_4) macrocyclic ligands (14.1 and 14.6respectively) are the highest recorded for monocyclic ligands.