188Re-labeled bisphosphonates as potential bifunctional agents for therapy in patients with bone metastases

Two new bisphosphonates have been examined for their ability to bind 188Re and deliver it selectively to bone. The bisphosphonates are prototype compounds with potential to deliver rhenium radionuclides and a second therapy modality to bone metastases. A conjugate between diethylenetriaminepentaacetic acid and bisphosphonate (DTPA/BP) and a conjugate between 5-fluorouracil and bisphosphonate (5-FU/BP) were prepared and labeled at high radiochemical purity with 188Re and biodistribution studies were carried out in normal Balb/C mice. The compounds showed rapid blood clearance and elimination from soft tissues with substantial retention of activity in the bone comparable to 188Re-hydroxyethylidine diphosphonate used as a control. At 8 h bone activity was 3.51% of injected dose for 188Re-DTPA/BP and 6.38% of injected dose for 188Re-5-FU/BP representing 69.6% and 80.6% of total body radioactivity, respectively. The two compounds show the potential for combination therapy of painful bone metastases.