Bisphosphonates as radionuclide carriers for imaging or systemic therapy

Bisphosphonates (BP's), biologically stable analogs of naturally occurring pyrophosphates, became the treatment of choice for pathologic conditions characterized by increased osteoclast-mediated bone resorption, namely Paget's disease, osteoporosis and tumor bone disease. Moreover, the clinical success of BP's is also associated with their use in 99(m)Tc-based radiopharmaceuticals for bone imaging. In addition to the successful delivery of 99(m)Tc (gamma-emitter) to bone, BP's have also been used to deliver beta(-)-particle emitting radiometals (e.g. Sm-153, Re-186/188) for bone-pain palliation. The main goal of this Review is to update the most recent research efforts toward the synthesis, characterization and biological evaluation of novel BP-containing radiometal complexes and radiohalogenated compounds for diagnostic or therapeutic purposes. The structure and in vivo properties of those compounds will be discussed and compared to the clinically available ones, namely in terms of image quality and therapeutic effect. We will also mention briefly the use of BP's as carriers of multimodal nuclear and optical imaging probes.