Design optimization of a new 64Cu/NOTA truncated NPY analog with improved stability and Y1 affinity, the first step toward successful breast cancer PET Imaging.

Objectives NPY-Y1 receptor (NPY-Y1R) is a promising target for breast cancer imaging.. Our group had already tested a series of truncated NPY analogs derived from BVD-15 ( ; [Pro30, Tyr32, Leu34]NPY(28-36)-NH2) for 64Cu-labelling. Unfortunately the biological half-live of the most potent tracer, [Lys(64Cu/DOTA)4]BVD15, when injected in mouse plasma was shorter than 15 minutes. In this study, we improved the design of this tracer to increase its stability in vitro and in vivo and to maintain its targeting capability.

Methods To improve the peptide tracer stability, modifications of the peptide backbone, the chelator and the use of D- and non-natural amino acids were proposed. The peptides were synthesized on solid phase and conjugated to NOTA chelator. Binding studies on MCF-7 human breast cancer cells were performed after each structural modification to make sure that the potency and the selectivity of the new NOTA-peptide conjugates to NPY-Y1R were maintained (Table 1). Once identified, active compounds were radiolabeled with 64Cu. Plasma stability, cellular uptake, internalization, and blocking studies on MCF-7 cells were performed in order to rapidly identify the promising candidates for in vivo studies.

Results A promising candidate presenting a very low Ki (9 nM) and showing a very high stability in plasma up to 20 h and in vivo for 45 minutes has been identified. Cell assays showed a constant uptake and internalization over the whole experiment. The internalized fraction after 2h was ~20%. The radiopeptide uptake was blocked in presence of an excess of unlabeled peptide.

Conclusions A new 64Cu-labeled peptide presenting a good stability and an excellent affinity to NPY-Y1R has been found. On the basis of the cellular results, the 64Cu/NOTA-BVD15 derivative appears to have a potential for the targeting of NPY-Y1R positive tumors. 1) Balasubramaniam A, Dhawan VC, Mullins DE, Chance WT, Sheriff S, Guzzi M, Prabhakaran M, Parker EM, [2001], J Med Chem 44: 1479-1482.

• Download figure
• Open in new tab
• Download powerpoint