In vitro affinity of Tc-99(m)-labelled N2S2 conjugates of chrysamine G foramyloid deposits of systemic amyloidosis

To date, systemic amyloidosis is diagnosed histologically in vitro using Co ngo red staining or in vivo using iodine-123 serum amyloid P component (I-1 23-SAP) scintigraphy. Tc-99(m)-labelled derivatives of chrysamine G (CG), a Lipophilic analogue of Congo red, were synthesized as potential tracer age nts for direct and quantitative scintigraphic evaluation of amyloid deposit s. To determine the affinity of Tc-99(m)-MAMA-CG, Tc-99(m)-Me(4)MAMA-CG and Tc-99(m)-MAMA-CG diethyl ester for amyloid, in vitro autoradiography was p erformed on sections of human kidney biopsy cylinders from kidneys with amy loid deposits (types AA, A lambda and A kappa) or control kidney tissue aft er incubation with the respective tracer agents. The binding of Tc-99(m)-MA MA-CG and its tetramethyl derivative was higher to kidney biopsy material w ith amyloid deposits of the AA, A lambda, or A kappa type compared with con trol kidney tissue. This higher binding was prevented by the presence of 10 muM Congo red in the incubation medium. The diethyl ester of Tc-99(m)-MAMA -CG did not demonstrate increased binding to Congo red-positive kidney tiss ue. In conclusion, Tc-99(m)-MAMA-CG and Tc-99(m)-Me(4)MAMA-CG localize spec ifically to amyloid deposits in human kidney tissue, suggesting that these tracer agents may be applicable as specific targeting agents for diagnostic purposes in clinical amyloidosis. ((C) 2001 Lippincott Williams & Wilkins) .