PURPOSE: We have developed a (186)Re-mercaptoacetylglycylglycylglycine complex-conjugated bisphosphonate ((186)Re-MAG3-HBP) for the treatment of painful bone metastases. We assumed competitive inhibitors of protein binding to be useful for procuring a favorable biodistribution of (186)Re-MAG3-HBP for the palliation of bone pain because it has been reported that the concurrent administration of (99m)Tc-MAG3 and drugs with high affinity for serum protein produced competitive displacement at specific binding sites and enhanced total clearance and tissue distribution. METHODS: The displacement effects of several protein-binding inhibitors on the protein binding of (186)Re-MAG3-HBP were investigated. Biodistribution experiments were performed by intravenously administering (186)Re-MAG3-HBP into rats with ceftriaxone as a competitive protein-binding inhibitor or saline. RESULTS: The protein binding of (186)Re-MAG3-HBP in rat serum, human serum, and a human serum albumin solution was significantly decreased by the addition of ceftriaxone, which has high affinity for binding site I on serum albumin. In the biodistribution experiments, pretreatment with ceftriaxone enhanced the clearance of the radioactivity of (186)Re-MAG3-HBP in blood and nontarget tissues but had no effect on accumulation in bone. CONCLUSIONS: The findings suggested that the use of protein-binding competitive inhibitors would be effective in improving the pharmacokinetics of radiopharmaceuticals with high affinity for serum protein.
PURPOSE: We have developed a (186)Re-mercaptoacetylglycylglycylglycine complex-conjugated bisphosphonate ((186)Re-MAG3-HBP) for the treatment of painful bone metastases. We assumed competitive inhibitors of protein binding to be useful for procuring a favorable biodistribution of (186)Re-MAG3-HBP for the palliation of bone pain because it has been reported that the concurrent administration of (99m)Tc-MAG3 and drugs with high affinity for serum protein produced competitive displacement at specific binding sites and enhanced total clearance and tissue distribution. METHODS: The displacement effects of several protein-binding inhibitors on the protein binding of (186)Re-MAG3-HBP were investigated. Biodistribution experiments were performed by intravenously administering (186)Re-MAG3-HBP into rats with ceftriaxone as a competitive protein-binding inhibitor or saline. RESULTS: The protein binding of (186)Re-MAG3-HBP in rat serum, human serum, and a human serum albumin solution was significantly decreased by the addition of ceftriaxone, which has high affinity for binding site I on serum albumin. In the biodistribution experiments, pretreatment with ceftriaxone enhanced the clearance of the radioactivity of (186)Re-MAG3-HBP in blood and nontarget tissues but had no effect on accumulation in bone. CONCLUSIONS: The findings suggested that the use of protein-binding competitive inhibitors would be effective in improving the pharmacokinetics of radiopharmaceuticals with high affinity for serum protein.
Authors: J M O'Sullivan; A R Norman; V R McCready; G Flux; F M Buffa; B Johnson; J Coffey; G Cook; J Treleaven; A Horwich; R A Huddart; C C Parker; D P Dearnaley Journal: Eur J Nucl Med Mol Imaging Date: 2006-03-30 Impact factor: 9.236