Endothelial angiotensin-converting enzyme and neutral endopeptidase in isolated human umbilical vein: An effective bradykinin inactivation pathway

In Vivo Enzyme Inhibition Improves the Targeting of [177Lu]DOTA-GRP(13–27) in GRPR-Positive Tumors in Mice

“…In vivo stability of [ 177 Lu]DOTA-GRP (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27) For metabolic evaluation assays, 40-60 MBq of 177 LuCl 3 was added to 3 nmol total peptide in the labeling solution (specific activity [SA]: 13-20 MBq/nmol), and the test radiotracer was injected as bolus (100 lL, in saline, vehicle) together with vehicle (100 lL, control A) or PA (100 lL of vehicle containing 300 lg PA, PA treated B) in the tail vein of male Swiss albino mice (30 -5 g, from NCSR Demokritos Animal House Facility). After 5 minutes, blood was collected from the heart of the animals under anesthesia and immediately transferred into prechilled polypropylene tubes, containing EDTA, and placed on ice.…”

“…Internalization of [ 177 Lu]DOTA-GRP (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27) in PC-3 cells PC-3 cells were seeded in six-well plates ( & 1-1.5 · 10 6 cells/well) before the day of the experiment and reached confluence after 24 hours of incubation. Internalization studies were performed, as described previously, 19 by using & 40,000 cpm of 177 Lu-radioconjugate corresponding to 250 fmol total peptide in 150 lL of 0.5% bovine serum albumin/phosphate-buffered saline (PBS).…”

“…37,38 Since [ 177 Lu]DOTA-GRP (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27) contains two basic amino acid residues, Lys 13 and Arg 19 , coinjection of the Lys solution was expected to reduce the renal accumulation of this radiolabeled compound as well. In the current study, the GRP analog [ 177 Lu]DOTA-GRP (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27) was preclinically evaluated for future application in targeted radionuclide therapy of GRPRexpressing human tumors in receptor-positive, tumor-bearing mice. Aiming at a biodistribution with a favorable tumor-tokidney ratio, the authors implemented the innovative strategy of coinjecting the NEP inhibitor (PA) as well as Lys with the radiotracer to increase GRPR targeting in combination with renal uptake inhibition.…”

“…Moreover, in vivo stability studies in Swiss albino mice revealed rapid degradation of the radiopeptide ( & 20% intact peptide at 5 minutes p.i.). 18 This radiotracer, once exposed to proteolytic enzymes within the body, was rapidly degraded due to the higher number of possible cleavage sites in the natural peptide motif compared to the GRP (18)(19)(20)(21)(22)(23)(24)(25)(26)(27) peptide analog ([ 99m Tc]Demomedin C). 19 Increased resistance to such proteolytic activity might translate into prolonged circulation of radiolabeled peptide analogs preferably leading to higher receptor targeting as well as higher tumor uptake of radioactivity in tumor lesions.…”

“…Its water-solubility, potency, commercial availability, and low costs, render PA an excellent candidate for these purposes. [23][24][25][26] The authors were interested in exploring the effects of PA against in vivo degradation of radiopeptide analogs originating from a variety of peptide families. This innovative method showed promise regarding improved in vivo stability of peptide analogs from different peptide families, including a GRP analog targeting GRPR in pilot studies, as recently published by these groups.…”