Endocrine Abstracts

Introduction: DOTANOC is a largely used somatostatin analogue in NETs investigations. In NODAGANOC, the DOTA is replaced by NODAGA, a chelator derivative from NOTA which is the ‘gold standard’ for Ga³⁺ and Cu²⁺ chelation because it forms more stable complexes than DOTA.[1] The aim of our study is to evaluate the affinity of NODAGANOC for somatostatin receptors (sst) and to develop a ⁶⁸Ga and ⁶⁴Cu labelled NODAGANOC for a future use in PET imaging.

Material and methods: The affinity of NODAGANOC was evaluated (n=3) in AR4-2J rat pancreatic cell line which express mRNA of sst_1,2,3,5.[2] IC₅₀ values for the binding to living AR4-2J cells were determined from competition experiments between NODAGANOC (Concentrations from 1.7×10⁻¹² to 10⁻⁶M) and 15.10⁻⁹M ⁶⁸Ga-DOTANOC.

Radiolabelling: ⁶⁸Ga-NODAGANOC was prepared instantly at RT by mixing the fraction of eluate containing >90% (613±54MBq) of the available generator activity with 35 nmol of peptide and 800 μl of 1M ammonium acetate buffer (pH 4.4) without further purification of the final product. ⁶⁴Cu-NODAGANOC was prepared after incubation 15 min at RT of 10 nmol of conjugate with 50 μl of ⁶⁴CuCl₂ (67MBq) in ammonium acetate buffer (0.1 M, pH 8.54)[3]. The radiochemical purities (RCP) were determined by RP-HPLC. The stabilities of the labelled compounds were evaluated by HPLC at RT and in human plasma for 2 h.

Results: The competition curve was analyzed with GraphPad Prism Software, the IC50 of NODAGANOC is 1.2±0.5 nM. The labelled products were obtained with high radiochemical purities (>95% for ⁶⁸Ga-NODAGANOC and 100% for ⁶⁴Cu-NODAGANOC) without purification of the final product. In all cases, RCP remains >90% for 2 h.

Conclusion: The nanomolar affinity for living cells AR4-2J makes NODAGANOC a potential interesting vector for targeting of pathologies overexpressing the sst. The radiolabelling described methods can be performed without costly equipment and allows to ⁶⁸Ga and ⁶⁴Cu-NODAGANOC with high radiochemical purities without further purification.

References

[1] E. W. Price and C. Orvig, “Matching chelators to radiometals for radiopharmaceuticals,” Chem. Soc. Rev., vol. 43, no. 1, pp. 260–290, Dec. 2013.

[2] E. Hofsli, L. Thommesen, K. Nørsett, S. Falkmer, U. Syversen, A. Sandvik, and A. Laegreid, “Expression of chromogranin A and somatostatin receptors in pancreatic AR42J cells,” Mol. Cell. Endocrinol., vol. 194, no. 1–2, pp. 165–173, Aug. 2002.

[3] J. Oxboel, M. Brandt-Larsen, C. Schjoeth-Eskesen, R. Myschetzky, H. H. El-Ali, J. Madsen, and A. Kjaer, “Comparison of two new angiogenesis PET tracers 68Ga-NODAGA-E[c(RGDyK)]2 and 64Cu-NODAGA-E[c(RGDyK)]2; in vivo imaging studies in human xenograft tumors,” Nucl. Med. Biol., vol. 41, no. 3, pp. 259–267, Mar. 2014.