phosphoramidon and Neoplasms

Cholecystokinin subtype 2 receptors (CCK2R) are overexpressed in several human cancers, including medullary thyroid carcinoma. Gastrin and cholecystokinin (CCK) peptides that bind with high affinity and specificity to CCK2R can be used as carriers of radioactivity to CCK2R-expressing tumor sites. Several gastrin and CCK related peptides have been proposed for diagnostic imaging and radionuclide therapy of primary and metastatic CCK2R-positive human tumors. Their clinical application has been restricted to a great extent by their fast in vivo degradation that eventually compromises tumor uptake. This problem has been addressed by structural modifications of gastrin and CCK motifs, which, however, often lead to suboptimal pharmacokinetic profiles. A major enzyme implicated in the catabolism of gastrin and CCK based peptides is neutral endopeptidase (NEP), which is widely distributed in the body. Coinjection of the NEP inhibitor phosphoramidon (PA) with radiolabeled gastrin and other peptide analogs has been recently proposed as a new promising strategy to increase bioavailability and tumor-localization of radiopeptides in tumor sites. Specifically, co-administration of PA with the truncated gastrin analog [(111)In-DOTA]MG11 ([((111)In-DOTA)DGlu(10)]gastrin(10-17)) impressively enhanced the levels of intact radiopeptide in mouse circulation and has led to an 8-fold increase of CCK2R-positive tumor uptake in SCID mice. This increased tumor uptake, visualized also by SPECT/CT imaging, is expected to eventually translate into higher diagnostic sensitivity and improved therapeutic efficacy of radiolabeled gastrin analogs in CCK2R-expressing cancer patients.

Topics: Animals; Carcinoma, Neuroendocrine; Cholecystokinin; Gastrins; Gene Expression Regulation, Neoplastic; Glycopeptides; Humans; Kidney; Kidney Neoplasms; Ligands; Mice; Mice, SCID; Models, Chemical; Neoplasm Transplantation; Neoplasms; Neprilysin; Peptides; Radiopharmaceuticals; Receptor, Cholecystokinin B; Thyroid Neoplasms; Tomography, Emission-Computed, Single-Photon; Tomography, X-Ray Computed

Radiolabeled octreotide analogs are most successfully being applied today in clinical cancer imaging and treatment. Propagation of this paradigm to other radiopeptide families has been greatly hampered by the inherent poor metabolic stability of systemically administered peptide analogs. We hypothesized that the in vivo coadministration of specific enzyme inhibitors would improve peptide bioavailability and hence tumor uptake. Through single coinjection of the neutral endopeptidase inhibitor phosphoramidon (PA), we were able to provoke remarkable rises in the percentages of circulating intact somatostatin, gastrin, and bombesin radiopeptides in mouse models, resulting in a remarkable increase in uptake in tumor xenografts in mice.. The peptide conjugates [DOTA-Ala(1)]SS14 (DOTA-Ala-Gly-c[Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys]-OH), PanSB1 (DOTA-PEG2-dTyr-Gln-Trp-Ala-Val-βAla-His-Phe-Nle-NH2), and DOTA-MG11 (DOTA-dGlu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2) were labeled with (111)In by 20 min of heating at an acidic pH. Metabolic stability was studied with high-performance liquid chromatography analysis of blood samples collected 5 min after the injection of the test radiopeptide alone or with PA into mice. Biodistribution was studied after injection of each (111)In-labeled radiopeptide alone or after coinjection of PA in tumor-bearing severe combined immunodeficient (SCID) mice.. The amount of intact [(111)In-DOTA-Ala(1)]SS14 detected in the mouse circulation at 5 min after the injection of PA increased impressively-from less than 2% to 86%-whereas the uptake in AR4-2J xenografts rose from less than 1 percentage injected dose per gram of tissue (%ID/g) to 14 %ID/g at 4 h after injection. Likewise, the coadministration of PA resulted in a marked increase in the amount of circulating intact (111)In-PanSB1-from 12% to 80%-at 5 min after injection, and radioligand uptake in human PC-3 xenografts in SCID mice escalated from less than 4 %ID/g to greater than 21 %ID/g at 4 h after injection. In a similar manner, the coadministration of PA resulted in an equally impressive increase in intact [(111)In-DOTA]MG11 levels in the mouse bloodstream-from less than 5% to 70%-at 5 min after injection, leading to a remarkable increase in radiotracer uptake-from 2 %ID/g to greater than 15 %ID/g-in both AR4-2J tumors and A431(CCKR+) tumors (i.e., tumors induced by A431 cells transfected to stably express the human cholecystokinin subtype 2 receptor) in mice at 4 h after injection. This effect was well visualized by SPECT/CT imaging of AR4-2J tumor-bearing mice at 4 h after injection.. The results of this study clearly demonstrate that the coadministration of key enzyme inhibitors can effectively prolong the survival of radiolabeled peptides in the circulation, securing their safe transit to the target. This strategy clearly provoked an unprecedented increase in radiolabel accumulation in tumor xenografts in mice; this increase might translate into higher diagnostic sensitivity or improved therapeutic efficacy of radiopeptide drugs in cancer patients. Hence, our findings provide exciting new opportunities for the application of biodegradable (radio)peptide drugs of either natural or synthetic origin as well as for the rationale design of analogs that are stable in vivo.

Topics: Animals; Bombesin; Chromatography, High Pressure Liquid; Enzyme Inhibitors; Female; Gastrins; Glycopeptides; Humans; Indium Radioisotopes; Male; Mice; Mice, SCID; Neoplasm Transplantation; Neoplasms; Peptides; Protein Binding; Radiopharmaceuticals; Somatostatin; Tomography, Emission-Computed, Single-Photon; Tomography, X-Ray Computed

Serum succinyl (Ala)3-p-nitroanilide hydrolyzing elastase-like activity which elevates in patients with obstructive jaundice, is due to the joint action of two enzymes: first, succinyl (Ala)3-p-nitroanilide is cleaved to succinyl (Ala)2 and Ala-p-nitroanilide by metalloendopeptidase, and then Ala-p-nitroanilide is cleaved to Ala and p-nitroaniline by aminopeptidase. We adopt a new assay method for serum endopeptidase activity using HPLC.

Topics: Adult; Aminopeptidases; Anti-Bacterial Agents; Cholestasis; Chromatography, High Pressure Liquid; Diabetes Mellitus; Endopeptidases; Female; Glycopeptides; Humans; Immunodiffusion; Kidney; Leucine; Male; Metalloendopeptidases; Neoplasms; Oligopeptides; Peptides; Protease Inhibitors