First preclinical evaluation of [225Ac]Ac-DOTA-JR11 and comparison with [177Lu]Lu-DOTA-JR11, alpha versus beta radionuclide therapy of NETs

BACKGROUND

The [¹⁷⁷Lu]Lu-DOTA-TATE mediated peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs) is sometimes leading to treatment resistance and disease recurrence. An interesting alternative could be the somatostatin antagonist, [¹⁷⁷Lu]Lu-DOTA-JR11, that demonstrated better biodistribution profile and higher tumor uptake than [¹⁷⁷Lu]Lu-DOTA-TATE. Furthermore, treatment with alpha emitters showed improvement of the therapeutic index of PRRT due to the high LET offered by the alpha particles compared to beta emitters. Therefore, [²²⁵Ac]Ac-DOTA-JR11 can be a potential candidate to improve the treatment of NETs (Graphical abstract). DOTA-JR11 was radiolabeled with [²²⁵Ac]Ac(NO₃)₃ and [¹⁷⁷Lu]LuCl₃. Stability studies were performed in phosphate buffered saline (PBS) and mouse serum. In vitro competitive binding assay has been carried out in U2OS-SSTR2 + cells for ^natLa-DOTA-JR11, ^natLu-DOTA-JR11 and DOTA-JR11. Ex vivo biodistribution studies were performed in mice inoculated with H69 cells at 4, 24, 48 and 72 h after injection of [²²⁵Ac]Ac-DOTA-JR11. A blocking group was included to verify uptake specificity. Dosimetry of selected organs was determined for [²²⁵Ac]Ac-DOTA-JR11 and [¹⁷⁷Lu]Lu-DOTA-JR11.

RESULTS

[²²⁵Ac]Ac-DOTA-JR11 has been successfully prepared and obtained in high radiochemical yield (RCY; 95%) and radiochemical purity (RCP; 94%). [²²⁵Ac]Ac-DOTA-JR11 showed reasonably good stability in PBS (77% intact radiopeptide at 24 h after incubation) and in mouse serum (~ 81% intact radiopeptide 24 h after incubation). [¹⁷⁷Lu]Lu-DOTA-JR11 demonstrated excellent stability in both media (> 93%) up to 24 h post incubation. Competitive binding assay revealed that complexation of DOTA-JR11 with ^natLa and ^natLu did not affect its binding affinity to SSTR2. Similar biodistribution profiles were observed for both radiopeptides, however, higher uptake was noticed in the kidneys, liver and bone for [²²⁵Ac]Ac-DOTA-JR11 than [¹⁷⁷Lu]Lu-DOTA-JR11.

CONCLUSION

[²²⁵Ac]Ac-DOTA-JR11 showed a higher absorbed dose in the kidneys compared to [¹⁷⁷Lu]Lu-DOTA-JR11, which may limit further studies with this radiopeptide. However, several strategies can be explored to reduce nephrotoxicity and offer opportunities for future clinical investigations with [²²⁵Ac]Ac-DOTA-JR11.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board

BACKGROUND

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biannual highlight commentary to update the readership on trends in the field of radiopharmaceutical development.

MAIN BODY

This commentary of highlights has resulted in 21 different topics selected by each coauthoring Editorial Board member addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals.

CONCLUSION

Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field in various topics including new PET-labelling methods, FAPI-tracers and imaging, and radionuclide therapy being the scope of EJNMMI Radiopharmacy and Chemistry.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board

BACKGROUND

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to update the readership on trends in the field of radiopharmaceutical development.

RESULTS

This commentary of highlights has resulted in 21 different topics selected by each member of the Editorial Board addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals. Also the first contribution in relation to MRI-agents is included.

CONCLUSIONS

Trends in (radio)chemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

Hydroxyapatite chemisorption of N,N',N'-trimethylenephosphonate-poly(ethyleneimine) (PEI-MP) combined with Sn2+ or Sn4+

To study the mechanism by which proposed bone-seeking radiopharmaceuticals consisting of tin (as l17mSn) and N,N',N'-trimethylenephosphonate-poly(ethyleneimine) (PEI-MP) are taken up and accumulated in bone tissue, the adsorption of Sn2+, Sn4+, and phosphonate polymer PEI-MP on hydroxyapatite was measured in vitro. Hydroxyapatite is the main mineral phase of bone; therefore, by determining the affinity of the metal ions and the ligand-and hence their complexes-for hydroxyapatite, the extent to which the radiopharmaceutical will be adsorbed can be predicted. The adsorption of the tin-phosphonate complexes and the two individual components to the solid phase was measured by inductively coupled plasma optical emission spectroscopy at physiological pH, at room temperature, and for a period of 48 h. The tin complexes and free ligand exhibited unique binding affinities. By varying the oxidation state of the metal ion (Sn2+, and Sn4+) and the size of the polyphosphonate ligand (using 10-30 and 30-50 kDa fractions), the adsorption characteristics of the individual components could be adapted. The tin-PEI-MP combination that showed the most favorable adsorption behavior was that of Sn2+ and PEI-MP(10-30 kDa), which had a maximum adsorption capacity of 2.21 +/- 0.14 micromol m(-2) and an affinity of 9.8 +/- 4.0 dm3 mmol(-1) with respect to the ligand and 2.30 +/- 0.07 micromol m(-2) and 26.6 +/- 6.1 dm3 mmol(-1) for the metal ion-as derived from the Langmuir adsorption model. The ligand showed enhanced adsorption when complexed with tin. This research provided a preliminary indication that the tin-PEI-MP combination could be favorable to other bone-seeking radiopharmaceuticals since the maximum adsorption capacities are comparable while PEI-MP offers the opportunity of using the enhanced permeability and retention effect for enhanced tumor accumulation.