VAPC-1 Targeted ⁶⁴Cu-TP3805 kit preparation and its evaluation

Introduction Previously, our laboratory has shown that ⁶⁴Cu-TP3805 can specifically target VPAC-1 receptors and be used for positron emission tomography (PET) imaging of breast (BC) and prostate cancer (PC) in humans. Present work is aimed at the formulation of a freeze-dried diaminedithiol-peptide (N₂S₂-TP3805) kit and it's evaluation for the preparation of ⁶⁴Cu labeled TP3805. Parameters such as pH, temperature and incubation time were examined that influenced the radiolabeling efficiency and stability of the product. Methods Kits were prepared under different conditions and radiolabeling efficiency of TP3805 kit was evaluated for a range of pH 3.5–8.5, after addition of ⁶⁴Cu in 30 μl, 0.1 M HCl. Incubation temperature (37-90 °C) and time (30-120 min.) were also investigated. Kits were stored at −10 °C and their long term stability was determined as a function of their radiolabeling efficiency. Further, stability of ⁶⁴Cu-TP3805 complex was evaluated in presence of fetal bovine serum and bovine serum albumin by using SDS polyacrylamide gel electrophoresis. Kits were then used for PET imaging of BC and PC following eIND (101550) and institutional approvals. Specificity of ⁶⁴Cu-TP3805 for VPAC-1 was examined with digital autoradiography (DAR) of prostate tissues obtained after prostatectomy, benign prostatic hyperplasia (BPH) tissue, and benign and malignant lymph nodes. Results were compared with corresponding tissue histology. Results Radiolabeling efficiency was ≥95% at final pH ~7.2 when incubated at 50 °C for 90 min. Kits were stable up to 18 months when stored at −10 °C, and ⁶⁴Cu-TP3805 complex exhibited excellent stability for up to 4 h at room temperature. ⁶⁴Cu-TP3805 complex did not show any transchelation even after 2 h incubation at 37 °C in 10% FBS as well as in BSA as determined by SDS PAGE analysis. DAR identified ≥95% of malignant lesions 11 new PC lesions, 20 high grade prostatic intraepithelial neoplasia, 2/2 ejaculatory ducts and 5/5 urethra verumontanum not previously identified The malignant lymph nodes were correctly identified by DAR and for 3/3 BPH patients, and 5/5 cysts, DAR was negative. In human BC (n = 19) and PC (n = 26) were imaged with 100% sensitivity. Conclusion Availability of ready to use N₂S₂-peptide kits for ⁶⁴Cu labeling is convenient and eliminates possible day to day variation during its routine preparation for clinical use.