Conclusion
Based on these in vitro data, the agonist (64)Cu-CB-TE2A-Y3-TATE demonstrates the most promise as an agent for targeted radiotherapy in p53 positive, SSTr2-positive tumors.
Methods
Receptor binding, internalization, cyclic adenosine monophosphate (cAMP) and nuclear localization studies were performed with the somatostatin receptor subtype 2 (SSTr2) agonists, (64)Cu-CB-TE2A-Y3-TATE and (64)Cu-DOTA-Y3-TATE vs. antagonist, (64)Cu-CB-TE2A-sst2-ANT, in SSTr2-transfected p53 +/+ and -/- HCT116 colorectal carcinoma cells.
Results
The antagonist, (64)Cu-CB-TE2A-sst2-ANT, bound 8-9-fold more SSTr2 binding sites than did the (64)Cu-labeled agonists. (64)Cu-CB-TE2A-Y3-TATE was more efficiently internalized than (64)Cu-DOTA-Y3-TATE, while (64)Cu-CB-TE2A-sst2-ANT showed lower yet significant levels of internalization. CB-TE2A-Y3-TATE acted as a full agonist, inhibiting cAMP production, whereas CB-TE2A-sst2-ANT showed no inhibition of cAMP production. The (64)Cu from agonists (64)Cu-DOTA-Y3-TATE and (64)Cu-CB-TE2A-Y3-TATE showed greater nuclear localization at 24 h in p53 +/+ vs. -/- cells; however, there was no difference in the levels of (64)Cu from the antagonist based on p53 status. Surprisingly, the DOTA and CB-TE2A-conjugated agonists showed similar nuclear localization in the p53 +/+ and -/- cells, suggesting no difference in (64)Cu release from these chelators in the HCT116 cell lines.