and 186/188Re-CTMP: Novel Agents for Bone Pain Palliation and Their Comparison with 153Sm-EDTMP

A b s t r a c t Designing ideal radiopharmaceuticals for use as bone pain palliatives require the use of a moderate energy β- emitter with a stable carrier molecule. Cyclic polyaminophosphonate ligands are known to form complexes with higher thermodynamic stability and kinetic inertness. The present study therefore envisages the use of a few moderate energy β- emitters, viz. 177Lu (T1/2 = 6.71 d, Eβmax = 497 keV), 153Sm (T1/2 = 46.27 h, Eβmax = 810 keV), 175Yb (T1/2 = 4.2 d, Eβmax = 480 keV) and 186Re (T1/2 = 90 h, Eβmax = 1.07 MeV) as the radioisotopes and cyclic polyazamacrocyclic tetramethyl phosphonates namely, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylene phosphonic acid (DOTMP) and 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetramethylene phosphonic acid (CTMP), apart from the widely used ethylenediaminetetramethylene phosphonic acid (EDTMP) for the development of potential bone pain palliation agents. All the radionuclides under investigation can be produced with adequate specific activity using moderate flux reactors. The comparatively longer half-lives of 177Lu, 175Yb and 186Re will provide much needed logistic advantages in countries with limited reactor facilities. In the present study, 177Lu-DOTMP, 153Sm-DOTMP, 175Yb-EDTMP and 186/188Re-CTMP complexes were prepared with high radiochemical purities (>98%) under optimized reaction conditions. All the radiolabeled complexe