Zr-89-N-sucDf-Amc-2NaI -KuE (Zr-89 PSMA Df) offers a prolonged time frame for prostate cancer imaging with potentially improved tumor detection

Ziel/Aim Today, the detection of prostate carcinoma lesions by means of PSMA-PET is usually realized in within few hours after injections with the available radiotracers such as e.g. Ga-68 PSMA 11 or F-18-JK-PSMA 7. It cannot be expected that the optimum contrast is achieved within such short time of biodistribution. Therefore, in order to overcome this limitation, we have proposed a new PSMA-binding compound that exploits the longer physical half-life (78 h) of Zr-89: Zr-89 PSMA Df.

Methodik/Methods The precursor was provided by ABX GmbH (Radeberg). The N-sucDF-Fe moiety functionalizes the molecule for labeling with Zr-89. The Zr-89 PSMA Df was characterized in vitro by the calculation of the corresponding K_d value, the cellular uptake and the internalization in LNCaP cells. Its biodistribution in vivo was studied with LNCaP prostate tumor xenograft in mice and PET-imaging experiments were conducted on a Focus 220 micro PET scanner. For reasons of comparison, analogue experiments and compound characterization were carried out with Ga-68 PSMA 11 and F-18 JK-PSMA 7.

Ergebnisse/Results The labelling of Zr-89 PSMA Df was performed in a radiochemical purity ≥ 99.9  %. It showed very high stability in PBS and human serum until 7 d at 37 ^oC. At 2 h, all radiotracers showed a comparable tumor uptake of approximately 20  % ID/g. Zr-89-PSMA Df allowed the acquisition of small animal PET-images with demarcated tumor after 24 h and 52 h p.i., showing that over time the compound remains in the tumor with very low activity in background except for the kidneys. The analysis of the PET-images also revealed that tumor-to-background ratios are increasing over time.

Schlussfolgerungen/Conclusions This study demonstrates that the tumor uptake and the biodistribution in normal tissues of Zr-89 PSMA Df is comparable to Ga-68 PSMA-11 and F-18 JK-PSMA 7. The small animal PET data suggest that Zr-89 PSMA Df remains in the tumor up to 52 h p.i. with increasing tumor/background ratio. Together with the long half-life of the Zr-89-label, this novel tracer may therefore allow late PET-acquisition with improved lesion detection.