Development of NOTA/DOTA cyclo-RGD dimers labelled with Ga-68 for cancer diagnosis and therapy follow-up

Full text of publication follows. The ανβ3 integrin receptor, expressed on tumor cell membranes can be preferentially targeted by peptides containing the RGD sequence, resulting in a versatile cell recognition system. DOTA-E- [c(RGDfK)2] and NOTA-SCN-Bn-E-[c(RGDyK)2] were labelled with Ga-68 and tested for radiolabelling yield, purity, stability, in vitro binding and ex vivo biodistribution. The radiolabelling was performed using an automated system with in-line quality control and Ga-68 eluate from a tin oxide based Ge-68/Ga-68 generator, purified and concentrated to 400 MBq in 0.1 ml water on an anionic exchanger resin. DOTA/NOTA-derivatized peptides were labeled by heating at 95 C. degrees. Elution, concentration, labeling and purification procedures took 20 min. The ex-vivo biodistribution of ⁶⁸Ga-DOTA-E-[c(RGDfK)2] and ⁶⁸Ga-NOTA-SCN-Bn-E-[c(RGDyK)2] was tested in tumor bearing animal models. Real-time quantification of bio-molecular interactions was determined: on- and off-rates, affinity of DOTA/NOTA cyclo-RGD dimers to tumor cell-surface receptors. Nanomoles of peptides were labeled and purified, RCP>98%. The biodistribution pattern of ⁶⁸Ga- NOTA-SCN-Bn-E-[c(RGDyK)2] in melanoma rats shows high and stable tumor uptake up to 11.6% ID/g. The blood clearance is fast, the renal elimination is more rapid than in the case of ⁶⁸Ga-DOTA-E-[c(RGDfK)2]. Higher tumor to background ratios was observed. Binding to receptors is achieved in the first 3 min of incubation and remains stable for 30 min. The radiolabelling with Ga-68 of very promising candidates for imaging targets of interest in cancer diagnosis and therapy follow-up such as ανβ3 receptors, were successfully adapted on the automated module, reducing reaction time and operator exposure. The biological evaluations of ⁶⁸Ga-DOTA-E-[c(RGDfK)2] and ⁶⁸Ga-NOTA-SCN-Bn-E-[c(RGDyK)2] show a high and stable tumor uptake of both compounds. (authors)