Improvement in radiolabelling proteins with the ^99mTc‐tricarbonyl‐core [^99mTc(CO)₃]⁺, by thiol‐derivatization with iminothiolane: application to γ‐globulins and annexin V

Abstract

Abstract The aim of this study was to improve the radiolabelling of proteins with the 99m Tc‐tricarbonyl‐[Tc(I)(CO) 3 ] + core by introducing thiol groups to their structure. To achieve this goal, γ‐globulins and annexin V were derivatized with mercaptobutyrimidyl groups (MBG) after reaction with 2‐iminothiolane. The optimal conditions permitted attachment of an average of 3.3 thiol groups on γ‐globulins and 1.0 to annexin V. The radiolabelling assays were carried out by incubating 3.2 nmol of either γ‐globulin‐SH or unmodified γ‐globulin with 60 MBq 99m Tc‐tricarbonyl produced from an Isolink ® kit (Mallinckrodt) under different reaction conditions. Results clearly showed that the introduction of three MBG could double the radiolabelling yields to more than 90% in a short time (30 mn, 37°C). Such results would never have been reached with unmodified γ‐globulins alone. Under the same conditions when using 1–2 nmol derivatized annexin V, the average radiolabelling yield was 55% against 19% with the unmodified protein. The 99m Tc‐tricarbonyl‐conjugates were challenged with cysteine or histidine and showed good stability. Copyright © 2005 John Wiley & Sons, Ltd.