68Ga, 64Cu labelling and affinity study of NODAGANOC, a NODAGA conjugated somatostatin analogue (#5)
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 sst1,2,3,5.[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 nmoles of peptide and 800µL of 1M ammonium acetate buffer (pH 4.4) without further purification of the final product. 64Cu-NODAGANOC was prepared after incubation 15 minutes at RT of 10 nmoles of conjugate with 50µL of 64CuCl2 (67MBq) in ammonium acetate buffer (0.1M, 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 2h.
Results:The competition curve was analyzed with GraphPad Prism Software, the IC50 of NODAGANOC is 1.2±0.5nM. 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 2h.
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.
- [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.