188Rhenium-EDTMP: A potential therapeutic bone agent

Bone seeking radiopharmaceuticals such as ethylenediaminetetramethylene phosphonate (EDTMP) complexes of ¹⁵³Sm and ¹⁶⁶Ho are receiving considerable attention for therapeutic treatment of bone metastases. Rhenium-188 has both beta-particle emissions for a therapeutic effect and gamma-emissions for imaging and it is available from an in-house generator system similar to the current ^99mTc generator, which makes it convenient for clinical use. The preparation of ¹⁸⁸Re-EDTMP is described using ¹⁸⁸Re, which was obtained from the alumina-based ¹⁸⁸W/¹⁸⁸Re generator. Dependence of the radiolabeling yield of ¹⁸⁸Re-EDTMP on reducing agent concentration, EDTMP concentration, incubation time, pH and addition of carrier was examined. In the case of optimum conditions, the radiolabeling yields of ¹⁸⁸Re-EDTMP were ~98% for carrier-free as well as carrier-added ¹⁸⁸Re. The addition of ascorbic acid plays an important role in the stability of carrier-free as well as carrier-added ¹⁸⁸Re-EDTMP preparations. The biodistribution of carrier-free and carrier-added ¹⁸⁸Re-EDTMP compounds in rats was also studied. The results show that ¹⁸⁸Re (carrier-added)-EDTMP is a potential bone pain palliation radiopharmaceutical due to its high skeletal uptake, rapid blood clearance and relatively low soft tissue absorption.