Influence of the Molar Activity of ^203/212Pb-PSC-PEG₂-TOC on Somatostatin Receptor Type 2-Binding and Cell Uptake

• Main Authors: Marc Pretze (Author), Enrico Michler (Author), Roswitha Runge (Author), Kerstin Wetzig (Author), Katja Tietze (Author), Florian Brandt (Author), Michael K. Schultz (Author), Jörg Kotzerke (Author)
• Format: Book
• Published: MDPI AG, 2023-11-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.

Summary

(1) Background: In neuroendocrine tumors (NETs), somatostatin receptor subtype 2 is highly expressed, which can be targeted by a radioactive ligand such as [¹⁷⁷Lu]Lu-1,4,7,10-tetraazacyclododecane-<i>N</i>,<i>N</i>',<i>N</i>",<i>N</i>‴,-tetraacetic acid-[Tyr³,Thr⁸]-octreotide (¹⁷⁷Lu-DOTA-TOC) and, more recently, by a lead specific chelator (PSC) containing ^203/212Pb-PSC-PEG₂-TOC (PSC-TOC). The molar activity (A_M) can play a crucial role in tumor uptake, especially in receptor-mediated uptake, such as in NETs. Therefore, an investigation of the influence of different molar activities of ^203/212Pb-PSC-TOC on cell uptake was investigated. (2) Methods: Optimized radiolabeling of ^203/212Pb-PSC-TOC was performed with 50 µg of precursor in a NaAc/AcOH buffer at pH 5.3-5.5 within 15-45 min at 95° C. Cell uptake was studied in AR42 J, HEK293 sst2, and ZR75-1 cells. (3) Results: ^203/212Pb-PSC-TOC was radiolabeled with high radiochemical purity >95% and high radiochemical yield >95%, with A_M ranging from 0.2 to 61.6 MBq/nmol. The cell uptake of ²⁰³Pb-PSC-TOC (A_M = 38 MBq/nmol) was highest in AR42 J (17.9%), moderate in HEK293 sstr (9.1%) and lowest in ZR75-1 (0.6%). Cell uptake increased with the level of A_M. (4) Conclusions: A moderate A_M of 15-40 MBq/nmol showed the highest cell uptake. No uptake limitation was found in the first 24-48 h. Further escalation experiments with even higher A_M should be performed in the future. It was shown that A_M plays an important role because of its direct dependence on the cellular uptake levels, possibly due to less receptor saturation with non-radioactive ligands at higher A_M.

Item Description

10.3390/ph16111605
1424-8247