The therapeutic agent, 153Sm - 1,4,7,10 - tetraazacyclododecanetetramethylenephosphonic acid (153Sm-DOTMP) is a promising new radiopharmaceutical for the potential treatment of osteogenic tumors. To aid in the determination of a patient’s eligibility status and/or monitor treatment efficacy, having a diagnostic agent with similar in vivo characteristics would be advantageous. Thus, the new bone-seeking PET-agent 55Co-DOTMP (t1/2 = 17.5 h, β+avg = 0.57 keV, 76%) was developed and pre-clinically evaluated. The 55Co-DOTMP complex was made in quantitative radiochemical yield, determined via radioTLC of the crude product. The labeling conditions were rapid (10 min, 37 ○C, pH = 7 - 8), requiring as little as 0.42 mM DOTMP (final concentration). Specific activities of up to 6.13 μCi/nmol for the final product were achieved. Stability tests in PBS and mouse serum were performed, showing that 97.6 ± 0.2% and 98 ± 2% of the complex remained intact after 24 h, respectively. In vivo biodistribution in healthy Sprague Dawley rats (n = 3) and female CD1 mice (n = 5) showed a profile very similar to that of 153Sm-DOTMP. Renal excretion was the primary mode of clearance, and no significant uptake in non-target areas was observed. Bone uptake at 24 h post-injection was 3.5 ± 0.5 %ID/g in rats and 4 ± 1 %ID/g in mice (Figure 1A). Small animal PET/CT images taken at 4 and 24 h in mice showed excellent contrast, with uptake concentrated at areas of more rapid bone turnover (Figure 1B). The excellent pharmacokinetic profile of 55Co-DOTMP, which closely mimics that of 153Sm-DOTMP, warrants its further development.

New 55Co PET-agent as a diagnostic analog for 153Sm-DOTMP

255th National Meeting (2018)

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