Abstract
DOTA-functionalized bisphosphonates are useful tools for positron emission tomography (PET) imaging of bone metastases when radiolabeled with gallium-68.1 Moreover, the versatility of DOTA also allows the complexation of radiometals with therapeutic applications (e.g. 177Lu), positioning these bisphosphonates as attractive theranostic agents. Among these molecules, BPAMD is a compound whose radiolabeling with 68Ga has already been described, but only through manual methods.2,3 Thus, 2 fully-automated protocols for 68Ga radiolabeling of BPAMD on the GAIA® ± LUNA® synthesis module(s) were designed, and a thorough study of the radiolabeling conditions was undertaken. Specifically, different reaction buffers (5 tested), anti-radiolysis compounds (2 tested), vector quantities (2 tested) and reaction vessel types (3 tested) were investigated. Each reaction condition was studied in triplicate. In addition, a reverse-phase radio-HPLC control method based on an ion-pairing approach was implemented to measure radiochemical purity (RCP). [68Ga]Ga-BPAMD was produced in high RCP (>93% in both radio-TLC and radio-HPLC) and high radiochemical yield (>91%) using 0.3 M HEPES buffer. The nature of the reaction vessel showed no significant effect on the radiolabeling outcome. Similarly, addition of an anti-radiolysis compound to the reaction medium did not improve the already excellent stability of [68Ga]Ga-BPAMD over time (RCP >92% over 4h). An efficient and reliable terminal purification method, based on a "bind and elute" approach using solid phase extraction cartridges, has yet to be identified in order to achieve excellent RCP levels. The radiolabeled product obtained by automated synthesis was evaluated in vivo on healthy mice. Micro-PET imaging showed rapid, intense accumulation in the joints (shoulders and along the backbone), demonstrating its bone tropism.